Lower jaw-to-forepaw rapid and delayed reorganization in the rat forepaw barrel subfield in primary somatosensory cortex

We used the forepaw barrel subfield (FBS), that normally receives input from the forepaw skin surface, in rat primary somatosensory cortex as a model system to study rapid and delayed lower jaw-to-forepaw cortical reorganization. Single and multi-unit recording from FBS neurons was used to examine the FBS for the presence of "new" lower jaw input following deafferentations that include forelimb amputation, brachial plexus nerve cut, and brachial plexus anesthesia. The major findings are as follows: (1) immediately following forelimb deafferentations, new input from the lower jaw becomes expressed in the anterior FBS; (2) 7-27 weeks after forelimb amputation, new input from the lower jaw is expressed in both anterior and posterior FBS; (3) evoked response latencies recorded in the deafferented FBS following electrical stimulation of the lower jaw skin surface are significantly longer in both rapid and delayed deafferents compared to control latencies for input from the forepaw to reach the FBS or for input from lower jaw to reach the LJBSF; (4) the longer latencies suggest that an additional relay site is imposed along the somatosensory pathway for lower jaw input to access the deafferented FBS. We conclude that different sources of input and different mechanisms underlie rapid and delayed reorganization in the FBS and suggest that these findings are relevant, as an initial step, for developing a rodent animal model to investigate phantom limb phenomena.

Perspectives into the possible effects of the B.1.1.7 variant of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on spermatogenesis

B.1.1.7 is a recently discovered variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) associated with increased transmissibility. Recent findings indicate that this variant has a propensity to infect adolescents and children at higher rates than adults. The virus gains entry into various body cells utilizing angiotensin-converting enzyme 2 (ACE-2) and basigin (CD147) as receptors. The virus mainly affects type II pneumocytes of lungs, endothelial cells, enterocytes, and renal tubular cells. It is reported to affect testes, causing testicular pain, and producing histopathological changes, as observed in some autopsies. The B.1.1.7 variant can also affect various cells in the testes. This raises a major concern regarding the long-term effects of the viral infection on spermatogenesis and highlights the pressing need for a robust database of serum samples from infected male children.

Focality of the Induced E-Field Is a Contributing Factor in the Choice of TMS Parameters: Evidence from a 3D Computational Model of the Human Brain

Transcranial magnetic stimulation (TMS) is a promising, non-invasive approach in the diagnosis and treatment of several neurological conditions. However, the specific results in the cortex of the magnitude and spatial distribution of the secondary electrical field (E-field) resulting from TMS at different stimulation sites/orientations and varied TMS parameters are not clearly understood. The objective of this study is to identify the impact of TMS stimulation site and coil orientation on the induced E-field, including spatial distribution and the volume of activation in the cortex across brain areas, and hence demonstrate the need for customized optimization, using a three-dimensional finite element model (FEM). A considerable difference was noted in E-field values and distribution at different brain areas. We observed that the volume of activated cortex varied from 3000 to 7000 mm3 between the selected nine clinically relevant coil locations. Coil orientation also changed the induced E-field by a maximum of 10%, and we noted the least optimal values at the standard coil orientation pointing to the nose. The volume of gray matter activated varied by 10% on average between stimulation sites in homologous brain areas in the two hemispheres of the brain. This FEM simulation model clearly demonstrates the importance of TMS parameters for optimal results in clinically relevant brain areas. The results show that TMS parameters cannot be interchangeably used between individuals, hemispheres, and brain areas. The focality of the TMS induced E-field along with its optimal magnitude should be considered as critical TMS parameters that should be individually optimized.

Structural and functional organization of the lower jaw barrel subfield in rat primary somatosensory cortex

Barrel subfields in rodent primary somatosensory cortex (SI) are important model systems for studying cortical organization and reorganization. During cortical reorganization that follows limb deafferentation, neurons in deafferented forelimb SI become responsive to previously unexpressed inputs from the lower jaw. Although the lower jaw barrel subfield (LJBSF) is a likely source of the input, this subfield has received little attention. Our aim was to describe the structural and functional organization of the normal LJBSF. To investigate LJBSF organization, a nomenclature for lower jaw skin surface was developed, cytochrome oxidase (CO) was used to label flattened-cut LJBSF sections, microelectrodes were used to map the lower jaw skin surface representation in SI, and electrolytic lesions, recovered from electrode penetrations, were used to align the physiological map to the underlying barrel map. LJBSF is a tear-shaped subfield containing approximately 24 barrels, arranged in eight mediolateral rows and a barrel-free zone capping the anterior border. The representation of the lower jaw skin consisting of chin vibrissae and microvibrissae embedded in common fur is somatotopically organized in a single map in the contralateral SI. This physiological map shows that the activity from the vibrissae aligns with the CO-staining of the underlying LJBSF. LJBSF barrels receive topographically ordered barrel-specific input from individual vibrissa and microvibrissae in the lower jaw but not from trident whiskers. The barrel-free zone receives topographically ordered input from the lower lip. These data demonstrating that the LJBSF is a highly organized subfield are essential for understanding its possible role in cortical reorganization.

Repetitive microstimulation in rat primary somatosensory cortex (SI) strengthens the connection between homotopic sites in the opposite SI and leads to expression of previously ineffective input from the ipsilateral forelimb

The primary somatosensory cortex (SI) receives input from the contralateral forelimb and projects to homotopic sites in the opposite SI. Since homotopic sites in SI are linked by a callosal pathway, we proposed that repetitive intracortical microstimulation (ICMSr) of neurons in layer V of SI forelimb cortex would increase spike firing in the opposite SI cortex thereby strengthening the callosal pathway sufficiently to allow normally ineffective stimuli from the ipsilateral forelimb to excite cells in the ipsilateral SI. The forelimb representation in SI in one hemisphere was mapped using mechanical and electrical stimulation of the contralateral forelimb, a homotopic site was similarly identified in the opposite SI, the presence of ipsilateral peripheral input was tested in both homotopic sites, and ICMS was used to establish an interhemispheric connection between the two homotopic recording sites. The major findings are: (1) each homotopic forelimb site in SI initially received short latency input only from the contralateral forelimb; (2) homotopic sites in layer V in each SI were interconnected by a callosal pathway; (3) ICMSr delivered to layer V of the homotopic SI in one hemisphere generally increased evoked response spike firing in layer V in the opposite homotopic site; (4) increased spike firing was often followed by the expression of a longer latency normally ineffective input from the ipsilateral forelimb; (5) these longer latency ipsilateral responses are consistent with a delay time sufficient to account for travel across the callosal pathway; (6) increased spike firing and the resulting ipsilateral peripheral input were also corroborated using in-vivo intracellular recording; and (7) inactivation of the stimulating site in SI by lidocaine injection or local surface cooling abolished the ipsilateral response, suggesting that the ipsilateral response was very likely relayed across the callosal pathway. These results suggest that repetitive microstimulation can do more than expand receptive fields in the territory adjacent to the stimulating electrode but in addition can also alter receptive fields in homotopic sites in the opposite SI to bring about the expression of previously ineffective input from the ipsilateral forelimb.

A newly identified nociresponsive region in the transitional zone (TZ) in rat sensorimotor cortex

The primary somatosensory cortex (S1) comprises a number of functionally distinct regions, reflecting the diversity of somatosensory receptor submodalities innervating the body. In particular, two spatially and functionally distinct nociceptive regions have been described in primate S1 (Vierck et al., 2013; Whitsel et al., 2019). One region is located mostly in Brodmann cytoarchitectonic area 1, where a subset of neurons exhibit functional characteristics associated with myelinated Aδ nociceptors and perception of 1st/sharp, discriminative pain. The second region is located at the transition between S1 and primary motor cortex (M1) in area 3a, where neurons exhibit functional characteristics associated with unmyelinated C nociceptors and perception of 2nd/slow, burning pain. To test the hypothesis that in rats the transitional zone (TZ) - which is a dysgranular region at the transition between M1 and S1 - is the functional equivalent of the nociresponsive region of area 3a in primates, extracellular spike discharge activity was recorded from TZ neurons in rats under general isoflurane anesthesia. Thermonoxious stimuli were applied by lowering the contralateral forepaw or hindpaw into a 48-51 °C heated water bath for 5-10 s. Neurons in TZ were found to be minimally affected by non-noxious somatosensory stimuli, but highly responsive to thermonoxious skin stimuli in a slow temporal summation manner closely resembling that of nociresponsive neurons in primate area 3a. Selective inactivation of TZ by topical lidocaine application suppressed or delayed the nociceptive withdrawal reflex, suggesting that TZ exerts a tonic facilitatory influence over spinal cord neurons producing this reflex. In conclusion, TZ appears to be a rat homolog of the nociresponsive part of monkey area 3a. A possibility is considered that this region might be primarily engaged in autonomic aspects of nociception.

Contributions of Nociresponsive Area 3a to Normal and Abnormal Somatosensory Perception

Traditionally, cytoarchitectonic area 3a of primary somatosensory cortex (SI) has been regarded as a proprioceptive relay to motor cortex. However, neuronal spike-train recordings and optical intrinsic signal imaging, obtained from nonhuman sensorimotor cortex, show that neuronal activity in some of the cortical columns in area 3a can be readily triggered by a C-nociceptor afferent drive. These findings indicate that area 3a is a critical link in cerebral cortical encoding of secondary/slow pain. Also, area 3a contributes to abnormal pain processing in the presence of activity-dependent reversal of gamma-aminobutyric acid A receptor-mediated inhibition. Accordingly, abnormal processing within area 3a may contribute mechanistically to generation of clinical pain conditions. PERSPECTIVE: Optical imaging and neurophysiological mapping of area 3a of SI has revealed substantial driving from unmyelinated cutaneous nociceptors, complementing input to areas 3b and 1 of SI from myelinated nociceptors and non-nociceptors. These and related findings force a reconsideration of mechanisms for SI processing of pain.

A review of current theories and treatments for phantom limb pain

Following amputation, most amputees still report feeling the missing limb and often describe these feelings as excruciatingly painful. Phantom limb sensations (PLS) are useful while controlling a prosthesis; however, phantom limb pain (PLP) is a debilitating condition that drastically hinders quality of life. Although such experiences have been reported since the early 16th century, the etiology remains unknown. Debate continues regarding the roles of the central and peripheral nervous systems. Currently, the most posited mechanistic theories rely on neuronal network reorganization; however, greater consideration should be given to the role of the dorsal root ganglion within the peripheral nervous system. This Review provides an overview of the proposed mechanistic theories as well as an overview of various treatments for PLP.

Hand-to-Face Remapping But No Differences in Temporal Discrimination Observed on the Intact Hand Following Unilateral Upper Limb Amputation

Unilateral major limb amputation causes changes in sensory perception. Changes may occur within not only the residual limb but also the intact limb as well as the brain. We tested the hypothesis that limb amputation may result in the detection of hand sensation during stimulation of a non-limb-related body region. We further investigated the responses of unilateral upper limb amputees and individuals with all limbs intact to temporally based sensory tactile testing of the fingertips to test the hypothesis that changes in sensory perception also have an effect on the intact limb. Upper extremity amputees were assessed for the presence of referred sensations (RSs)—experiencing feelings in the missing limb when a different body region is stimulated, to determine changes within the brain that occur due to an amputation. Eight of 19 amputees (42.1%) experienced RS in the phantom limb with manual tactile mapping on various regions of the face. There was no correlation between whether someone had phantom sensations or phantom limb pain and where RS was found. Six of the amputees had either phantom sensation or pain in addition to RS induced by facial stimulation. Results from the tactile testing showed that there were no significant differences in the accuracy of participants in the temporal order judgment tasks (p = 0.702), whereby participants selected the digit that was tapped first by a tracking paradigm that resulted in correct answers leading to shorter interstimulus intervals (ISIs) and incorrect answers increasing the ISI. There were also no significant differences in timing perception, i.e., the threshold accuracy of the duration discrimination task (p = 0.727), in which participants tracked which of the two digits received a longer stimulus. We conclude that many, but not all, unilateral upper limb amputees experience phantom hand sensation and/or pain with stimulation of the face, suggesting that there could be postamputation changes in neuronal circuitry in somatosensory cortex. However, major unilateral limb amputation does not lead to changes in temporal order judgment or timing perception tasks administered via the tactile modality of the intact hand in upper limb amputees.

Wireless simultaneous stimulation-and-recording device to train cortical circuits in somatosensory cortex

We describe for the first time the design, implementation, and testing of a telemetry controlled simultaneous stimulation and recording device (SRD) to deliver chronic intercortical microstimulation (ICMS) to physiologically identified sites in rat somatosensory cortex (SI) and test hypotheses that chronic ICMS strengthens interhemispheric pathways and leads to functional reorganization in the enhanced cortex. The SRD is a custom embedded device that uses the Cypress Semiconductor's programmable system on a chip (PSoC) that is remotely controlled via Bluetooth. The SRC can record single or multiunit responses from any two of 12 available inputs at 1-15 ksps per channel and simultaneously deliver stimulus pulses (0-255 μA; 10 V compliance) to two user selectable electrodes using monophasic, biphasic, or pseudophasic stimulation waveforms (duration: 0-5 ms, inter-phase interval: 0-5 ms, frequency: 0.1-5 s, delay: 0-10 ms). The SRD was bench tested and validated in vivo in a rat animal model.

Differential Pattern of Interhemispheric Connections Between Homotopic Layer V Regions in the Forelimb Representation in Rat Barrel Field Cortex

Layer V neurons in forelimb and shoulder representations in rat first somatosensory cortex (SI) project to the contralateral SI. However, few studies have addressed whether projections from specific subregions of the forelimb representation, namely forepaw, wrist, or forearm, terminate at homotopic sites in the contralateral SI. Neuroanatomical retrograde (cholera toxin B subunit [CT-B]) or anterograde (biodextran amine [BDA]) tracers were injected into physiologically identified sites in layer V in specific forelimb and/or shoulder representations in SI to examine the projection to contralateral SI in young adult rats (N = 17). Injection and target sites were flattened and cut in a tangential plane to relate labeling to the body map or cut along a coronal plane to relate labeling to cortical layers. Results indicate that layer V neurons project to cortical laminae II-VI in contralateral SI, with the densest labeling in layer V followed by layer III. In contrast, layer V neurons send sparse projections to layer IV. Furthermore, layer V neurons in wrist, forearm, and shoulder project to homotopic sites in contralateral layer V, while neurons in the forepaw representation project largely to sites in perigranular and dysgranular cortex adjacent to their homotopic territory. Our results provide evidence for a differential pattern of interhemispheric projections from forelimb and shoulder representations to the opposite SI and a detailed description of areal and laminar projection patterns of layer V neurons in the SI forelimb and shoulder cortices.

Forelimb amputation-induced reorganization in the ventral posterior lateral nucleus (VPL) provides a substrate for large-scale cortical reorganization in rat forepaw barrel subfield (FBS)

In this study, we examined the role of the ventral posterior lateral nucleus (VPL) as a possible substrate for large-scale cortical reorganization in the forepaw barrel subfield (FBS) of primary somatosensory cortex (SI) that follows forelimb amputation. Previously, we reported that, 6 weeks after forelimb amputation in young adult rats, new input from the shoulder becomes expressed throughout the FBS that quite likely has a subcortical origin. Subsequent examination of the cuneate nucleus (CN) 1 to 30 weeks following forelimb amputation showed that CN played an insignificant role in cortical reorganization and led to the present investigation of VPL. As a first step, we used electrophysiological recordings in forelimb intact adult rats (n=8) to map the body representation in VPL with particular emphasis on the forepaw and shoulder representations and showed that VPL was somatotopically organized. We next used stimulation and recording techniques in forelimb intact rats (n=5) and examined the pattern of projection (a) from the forelimb and shoulder to SI, (b) from the forepaw and shoulder to VPL, and (c) from sites in the forepaw and shoulder representation in VPL to forelimb and shoulder sites in SI. The results showed that the projections were narrowly focused and homotopic. Electrophysiological recordings were then used to map the former forepaw representation in forelimb amputated young adult rats (n=5) at 7 to 24 weeks after amputation. At each time period, new input from the shoulder was observed in the deafferented forepaw region in VPL. To determine whether the new shoulder input in the deafferented forepaw VPL projected to a new shoulder site in the deafferented FBS, we examined the thalamocortical pathway in 2 forelimb-amputated rats. Stimulation of a new shoulder site in deafferented FBS antidromically-activated a cell in the former forepaw territory in VPL; however, similar stimulation from a site in the original shoulder representation, outside the deafferented region, in SI did not activate cells in the former forepaw VPL. These results suggest that the new shoulder input in deafferented FBS is relayed from cells in the former forepaw region in VPL. In the last step, we used anatomical tracing and stimulation and recording techniques in forelimb intact rats (n=9) to examine the cuneothalamic pathway from shoulder and forepaw receptive field zones in CN to determine whether projections from the shoulder zone might provide a possible source of shoulder input to forepaw VPL. Injection of biotinylated dextran amine (BDA) into physiologically identified shoulder responsive sites in CN densely labeled axon terminals in the shoulder representation in VPL, but also gave off small collateral branches into forepaw VPL. In addition, microstimulation delivered to forepaw VPL antidromically-activated cells in shoulder receptive field sites in CN. These results suggest that forepaw VPL also receives input from shoulder receptive sites in CN that are latent or subthreshold in forelimb intact rats. However, we speculate that following amputation these latent shoulder inputs become expressed, possibly as a down-regulation of GABA inhibition from the reticular nucleus (RTN). These results, taken together, suggest that VPL provides a substrate for large-scale cortical reorganization that follows forelimb amputation.

Forelimb amputation-induced reorganization in the cuneate nucleus (CN) is not reflected in large-scale reorganization in rat forepaw barrel subfield cortex (FBS)

We examined reorganization in cuneate nucleus (CN) in juvenile rat following forelimb amputation (n=34) and in intact controls (n=5) to determine whether CN forms a substrate for large-scale reorganization in forepaw barrel subfield (FBS) cortex. New input from the shoulder first appears in the FBS 4 weeks after amputation, and by 6 weeks, the new shoulder input comes to occupy most of the FBS. Electrophysiological recording was used to map CN in controls and in forelimb amputees during the first 12 weeks following deafferentation and at 26 and 30 weeks post-amputation. Mapping was confined to a location 300 μm anterior to the obex where a medial-to-lateral row of electrode penetrations traversed through a complete complement of cytochrome-oxidase stained clusters (called barrelettes) that are associated with the representation of the glabrous forepaw digits and pads and adjacent non-cluster zones that are associated with the representation of the wrist, arm, and shoulder. Following amputation, non-cluster zones became occupied with new input from the body/chest and head/neck, while the cluster zone remained largely devoid of new input except at the border. A regression analysis comparing controls and amputees over the first 12 weeks post-amputation found significant differences for the total area of new input from the body/chest and head/neck in the non-cluster zones, while no significant differences were found for any new input into the cluster zone. When the averaged areas of a body-part representation were re-examined as a percentage of the averaged zonal area, a non-significant increase in new input from the body was observed within the cluster zone during post-amputation weeks 2-3 that returned to baseline in the subsequent weeks. In contrast, significant differences in averaged area of body-part representations for body/chest and head/neck were found in non-cluster zones over the first 12 weeks post-amputation. The present findings suggest that reorganization occurs only within the non-cluster zones whereby new input from the body/chest and head/neck moves in and occupies the deafferented territory immediately after amputation. Additionally, the lack of significant differences in new shoulder input in either cluster or non-cluster zones over the first 12 weeks after amputation suggests that CN provides an unlikely substrate for large-scale reorganization in the FBS.

Functional and structural organization of the forelimb representation in cuneate nucleus in rat

We examined the physiological representation of the forelimb in the cuneate nucleus (CN) of forelimb-intact young adult rats (n=38) as the first part in a series of studies aimed at understanding the possible role that CN plays in delayed cortical reorganization that follows forelimb amputation. Metabolic labeling with cytochrome oxidase (CO) and electrophysiological mapping were used to examine the relationship between the structural and functional organization of CN. CN is a cylinder-shaped structure that lies bilaterally in the brainstem and extends nearly 4mm in the rostrocaudal direction. The forelimb is represented along the rostrocaudal extent. CN contains three zones; the rostral and caudal zones receive input largely from deep muscle and joint receptors and a middle zone, in the vicinity of the obex, receives input primarily from cutaneous receptors in the skin. The middle zone is somatotopically organized with the glabrous digits represented centrally, bordered on the medial side by ulnar wrist, ulnar forearm, and posterior upper arm representations; on the lateral side by radial wrist, radial forearm, and anterior upper arm representations; and on dorsal side by the dorsal digits and dorsal hand. The middle zone also contains well-defined CO-filled glomerular structures, called barrelettes, which are located within a homogenously stained field. The barrelettes are associated with the representation of the glabrous digits, with D5 represented most dorsal followed sequentially in a ventral-to-lateral direction by the representation of D4, D3, D2, and D1. The digit representations are topographically organized with the distal digit surface represented laterally with respect to the more medially lying proximal digit surface. The digit and palmar pads are also represented by barrelettes located on the medial side of CN. In contrast, the dorsal digit surfaces are represented dorsally and the dorsal hand is represented directly beneath the cuneate fasciculus, in a region devoid of barrelettes. The representations of the ulnar and radial wrist, forearm, and upper arm also lie within the homogeneously stained field in CN. The forelimb representation is bordered on the medial side by representation of trunk and hindlimb, and on the lateral side by representation of shoulder, ear, and head. While the present findings support and extend previous electrophysiological and anatomical studies of CN in the rat, they also provide a detailed physiological description of the functional organization of CN that is necessary for subsequent understanding of the functional reorganization of CN that may result following forelimb amputation.

Prenatal alcohol exposure reduces the size of the forelimb representation in motor cortex in rat: an intracortical microstimulation (ICMS) mapping study

Children with fetal alcohol spectrum disorder (FASD) often exhibit sensorimotor dysfunctions that include deficits in motor coordination and fine motor control. Although the underlying causes for these motor abnormalities are unknown, they likely involve interactions between sensory and motor systems. Rodent animal models have been used to study the effects of prenatal alcohol exposure (PAE) on skilled reaching and on the development and organization of somatosensory barrel field cortex. To this end, PAE delayed the development of somatosensory cortex, reduced the size of whisker and forelimb representations in somatosensory barrel field cortex, and delayed acquisition time to learn a skilled reaching task. However, whether PAE also affects the motor cortex (MI) remains to be determined. In the present study, we investigated the effect of PAE on the size of the forelimb representation in rat MI, thresholds for activation, and the overlap between motor and sensory cortical forelimb maps in sensorimotor cortex. Pregnant Sprague-Dawley rats were assigned to alcohol (Alc), pair-fed (PF), and chow-fed (CF) groups on gestation day 1 (GD1). Rats in the Alc group (n=4) were chronically intubated daily with binge doses of alcohol (6g/kg body weight) from GD1 to GD20 that resulted in averaged blood alcohol levels measured on GD10 (mean=191.5+/-41.9mg/dL) and on GD17 (mean=247.0+/-72.4mg/dL). PF (n=2) and CF (n=3) groups of pregnant rats served as controls. The effect of PAE on the various dependent measures was obtained from multiple male offspring from each dam within treatment groups, and litter means were compared between the groups from alcohol-treated and control (Ct: CF and PF) dams. At approximately 8 weeks of age, rats were anesthetized with ketamine/xylazine and the skull opened over sensorimotor cortex. A tungsten microelectrode was then inserted into the depths of layer V and intracortical microstimulation was used to deliver trains of pulses to evoke muscle contractions and/or movements; maximum stimulating < or =100microA. When a motor response was observed, the threshold for movement was measured and the motor receptive field projected to the cortical surface to serve as representative point for that location. A motor map for the forelimb representation was generated by systematically stimulating at adjacent sites until current thresholds reached the maximum and/or motor responses were no longer evoked. The major findings in this study were as follows: (1) PAE significantly reduced the area of the forelimb representation in the Alc offspring (6.01mm(2), standard error of the mean=+/-0.278) compared with the Ct offspring (8.03mm(2)+/-0.586), (2) PAE did not significantly reduce the averaged threshold for activation of movements between groups, (3) PAE significantly reduced the percent overlap (Alc=31.1%, Ct=55.4%) between the forelimb representation in sensory and motor cortices, and (4) no significant differences were observed in averaged body weight, hemisphere weight, or age of animal between treatment groups. These findings suggest that the effects of PAE are not restricted to somatosensory barrel field cortex but also involve the MI and may underlie deficits in motor control and sensorimotor integration observed among children with FASD.

EDTA chelation therapy, without added vitamin C, decreases oxidative DNA damage and lipid peroxidation

Chelation therapy is thought to not only remove contaminating metals but also to decrease free radical production. However, in standard ethylene diamine tetracetic acid (EDTA) chelation therapy, high doses of vitamin C with potential pro-oxidant effects are often added to the chelation solution. The authors demonstrated previously that the intravenous administration of the standard chelation cocktail, containing high amounts of vitamin C, resulted in an acute transitory pro-oxidant burst that should be avoided in the treatment of pathologies at risk of increased oxidative stress such as diabetes and cardiovascular disease. The current study was designed to determine the acute and chronic biochemical effects of chelation therapy on accepted clinical, antioxidant variables. An EDTA chelation cocktail not containing ascorbic acid was administered to six adult patients for five weeks (10 sessions of chelation therapy); antioxidant indicators were monitored. Immediately after the initial chelation session, in contrast with the data previously reported with the standard cocktail containing high doses of vitamin C, none of the oxidative stress markers were adversely modified. After five weeks, plasma peroxide levels, monitored by malondialdehyde, decreased by 20 percent, and DNA damage, monitored by formamidopyrimidine-DNA glycosylase (Fpg) sensitive sites, decreased by 22 percent. Remaining antioxidant-related variables did not change. In summary, this study demonstrates that multiple sessions of EDTA chelation therapy in combination with vitamins and minerals, but without added ascorbic acid, decreases oxidative stress. These results should be beneficial in the treatment of diseases associated with increased oxidative stress such as diabetes and cardiovascular diseases.

Intravenous magnesium sulfate with and without EDTA as a magnesium load test-is magnesium deficiency widespread?

Serum/plasma measurements do not reflect magnesium deficits in clinical situations, and magnesium load tests are used as a more accurate method to identify magnesium deficiency in a variety of disease states as well as in subclinical conditions. The objective of this study was to determine if people are indeed magnesium deficient or if the apparent magnesium deficiency is due to the composition of the infusate used in the load test. Magnesium load tests were performed on seven patients using three different Mg solution infusions-a Mg-EDTA (ethylene diamine tetraacetic acid)-nutrient cocktail used in EDTA chelation therapy containing several components including vitamins and minerals, and the same cocktail without EDTA and an infusion of an identical amount of magnesium in normal saline solution. There was no significant difference in the amount of magnesium retained in the 24 h after infusion among the three infusates. All infusates resulted in very high magnesium retention compared to previous published magnesium load studies. Magnesium deficiency may be widespread, and the relationship of Mg deficiency to related diseases requires further study.

Genetic analysis of tongue size and taste papillae number and size in recombinant inbred strains of mice

Quantitative trait loci (QTLs) analysis has been used to examine natural variation of phenotypes in the mouse somatosensory cortex, hippocampus, cerebellum, and amygdala. QTL analysis has also been utilized to map and identify genes underlying anatomical features such as muscle, organ, and body weights. However, this methodology has not been previously applied to identification of anatomical structures related to gustatory phenotypes. In this study, we used QTL analysis to map and characterize genes underlying tongue size, papillae number, and papillae area. In a set of 43 BXD recombinant inbred (RI) mice (n = 111) and 2 parental strains (C57BL/6J and DBA/2J; n = 7), we measured tongue length, width, and weight. In a subset of 23 BXD RI mice and the parental mice, we measured filiform and fungiform papillae number and fungiform papillae area. Using QTL linkage analysis (through WebQTL), we detected 2 significant and noninteracting QTLs influencing tongue length on chromosomes 5 and 7. We also found a significant QTL on chromosome 19 underlying fungiform papillae area and a suggestive QTL on chromosome 2 linked to fungiform papillae number. From these QTLs, we identified a number of candidate genes within the QTL intervals that include SRY-box containing gene, nebulin-related anchoring protein, and actin-binding LIM protein 1. This study is an important first step in identifying genetic factors underlying tongue size, papillae size, and papillae number using QTL analysis.

Genetic analysis of posterior medial barrel subfield (PMBSF) size in somatosensory cortex (SI) in recombinant inbred strains of mice

BACKGROUND

Quantitative trait locus (QTL) mapping is an important tool for identifying potential candidate genes linked to complex traits. QTL mapping has been used to identify genes associated with cytoarchitecture, cell number, brain size, and brain volume. Previously, QTL mapping was utilized to examine variation of barrel field size in the somatosensory cortex in a limited number of recombinant inbred (RI) strains of mice. In order to further elucidate the underlying natural variation in mouse primary somatosensory cortex, we measured the size of the posterior medial barrel subfield (PMBSF), associated with the representation of the large mystacial vibrissae, in an expanded sample set that included 42 BXD RI strains, two parental strains (C57BL/6J and DBA/2J), and one F1 strain (B6D2F1). Cytochrome oxidase labeling was used to visualize barrels within the PMBSF.

RESULTS

We observed a 33% difference between the largest and smallest BXD RI strains with continuous variation in-between. Using QTL linkage analysis from WebQTL, we generated linkage maps of raw total PMBSF and brain weight adjusted total PMBSF areas. After removing the effects of brain weight, we detected a suggestive QTL (likelihood ratio statistic [LRS]: 14.20) on the proximal arm of chromosome 4. Candidate genes under the suggestive QTL peak for PMBSF area were selected based on the number of single nucleotide polymorphisms (SNPs) present and the biological relevance of each gene. Among the candidate genes are Car8 and Rab2. More importantly, mRNA expression profiles obtained using GeneNetwork indicated a strong correlation between total PMBSF area and two genes (Adcy1 and Gap43) known to be important in mouse cortex development. GAP43 has been shown to be critical during neurodevelopment of the somatosensory cortex, while knockout Adcy1 mice have disrupted barrel field patterns.

CONCLUSION

We detected a novel suggestive QTL on chromosome 4 that is linked to PMBSF size. The present study is an important step towards identifying genes underlying the size and possible development of cortical structures.

Early postnatal alcohol exposure reduced the size of vibrissal barrel field in rat somatosensory cortex (SI) but did not disrupt barrel field organization

Prenatal alcohol exposure (PAE) has been shown to alter the somatosensory cortex in both human and animal studies. In rodents, PAE reduced the size, but not the pattern of the posteromedial barrel subfield (PMBSF) associated with the representation of the whiskers, in newborn, juvenile, and adult rats. However, the PMBSF is not present at birth, but rather first appears in the middle of the first postnatal week during the brain-growth spurt period. These findings raise questions whether early postnatal alcohol exposure might disrupt both barrel field pattern and size, questions that were investigated in the present study. Newborn Sprague-Dawley rats were assigned into alcohol (Alc), nutritional gastric control (GC), and suckle control (SC) groups on postnatal day 4 (P4). Rat pups in Alc and GC were artificially fed with alcohol and maltose-dextrin dissolved in milk, respectively, via an implant gastrostomy tube, from P4 to P9. Pups in the Alc group received alcohol (6.0 g/kg) in milk, while the GC controls received isocaloric equivalent maltose-dextrin dissolved in milk. Pups in the SC group remained with their mothers and breast fed throughout the experimental period. On P10, pups in each group were weighed, sacrificed, and their brains removed and weighed. Cortical hemispheres were separated, weighed, flattened, sectioned tangentially, stained with cytochrome oxidase, and PMBSF measured. The sizes of barrels and the interbarrel septal region within PMBSF, as well as body and brain weights were compared between the three groups. The sizes of PMSBF barrel and septal areas were significantly smaller (P<.01) in Alc group compared to controls, while the PMBSF barrel pattern remained unaltered. Body, whole-brain, forebrain, and hemisphere weights were significantly reduced (P<.01) in Alc pups compared to control groups. GC and SC groups did not differ significantly in all dependent variables, except body weight at P9 and P10 (P<.01). These results suggest that postnatal alcohol exposure, like prenatal exposure, significantly influenced the size of the barrel field, but not barrel field pattern formation, indicating that barrel field pattern formation consolidated prior to P4. These results are important for understanding sensorimotor deficits reported in children suffering from fetal alcohol spectrum disorder (FASD).

Long-term effects of prenatal alcohol exposure on the size of the whisker representation in juvenile and adult rat barrel cortex

Children of mothers who abused alcohol during pregnancy are often reported to suffer from growth retardation and central nervous system (CNS) abnormalities. The use of prenatal alcohol exposed (PAE) animal models has revealed reductions in body and brain weights as well as regional specific brain deficits in neonatal pups. Recently, we and others reported reductions in the size of the posteromedial barrel subfield (PMBSF) in first somatosensory cortex (SI) associated with the representation of the large mystacial vibrissae in neonatal rats and mice that were exposed to alcohol at various times during gestation. While these reductions in barrel field size were reported in neonates, it was unclear whether similar reductions persisted later in life or whether some catch-up might take place in older animals. In the present study, we examined the effect of PAE on measures of barrel field size in juvenile (6 weeks of age) and adult (7 months of age) rats; body and brain weights were also measured. Pregnant rats (Sprague-Dawley) were intragastrically gavaged during gestational days 1-20 with alcohol (6 g/kg) to simulate a binge-like pattern of alcohol consumption (Alc); 6 g/kg alcohol produced blood alcohol levels ranging between 207.4 and 478.6 mg/dl. Chow-fed (CF), pair-fed (PF), and cross-foster (XF) groups served as normal, nutritional/stress, and maternal controls, respectively, for juvenile rats; an XF group was not included for adult rats. The major findings in the present study are (i) PAE significantly reduced the size of the total barrel field in Alc juvenile rats (13%) and adult rats (9%) compared to CF controls, (ii) PAE significantly reduced the total averaged sizes of individual PMBSF barrels in juvenile (14%) and adult (13%) rats, (iii) PAE did not significantly alter the septal area between barrels or the barrel pattern, (iv) PAE significantly reduced body weight of juvenile rats but only in comparison to PF controls (18%), (v) PAE significantly reduced whole brain (8%) and forebrain (7%) weights of juvenile rats but not adult rats, (vi) no differences were observed in forebrain/PMBSF body ratios nor was forebrain weight correlated with PMBSF area, and (vii) PAE resulted in a greater reduction in anterior barrels compared to posterior barrels. These results suggest that the effects of PAE previously reported in neonate PMBSF areas persist into adulthood.

Prenatal alcohol exposure delays the development of the cortical barrel field in neonatal rats

In-utero alcohol exposure produces sensorimotor developmental abnormalities that often persist into adulthood. The rodent cortical barrel field associated with the representation of the body surface was used as our model system to examine the effect of prenatal alcohol exposure (PAE) on early somatosensory cortical development. In this study, pregnant female rats were intragastrically gavaged daily with high doses of alcohol (6 gm/kg body weight) throughout the first 20 days of pregnancy. Blood alcohol levels were measured in the pregnant dams on gestational days 13 (G13) and G20. The ethanol treated group (EtOH) was compared to the normal control chowfed (CF) group, nutritionally matched pairfed (PF) group, and cross-foster (XF) group. Cortical barrel development was examined in pups across all treatment groups from G25, corresponding to postnatal day 2 (P2), to G32 corresponding to P9. The EtOH and control group pups were weighed, anesthetized, and perfused. Brains were removed and weighed with, and without cerebellum and olfactory bulbs, and neocortex was removed and weighed. Cortices were then flattened, sectioned tangentially, and stained with a metabolic marker, cytochrome oxidase (CO) to reveal the barrel field. Progression of barrel development was distinguished into three categories: (a) absent, (b) cloudy barrel-like pattern, and (c) well-formed barrels with intervening septae. The major findings are: (1) PAE delayed barrel field development by one or more days, (2) the barrel field first appeared as a cloudy pattern that gave way on subsequent days to an adult-like pattern with clearly demarcated intervening septal regions, (3) the barrel field developed differentially in a lateral-to-medial gradient in both alcohol and control groups, (4) PAE delayed birth by one or more days in 53% of the pups, (5) regardless of whether pups were born on G23 (normal expected birth date for non-alcohol controls) or as in the case for the alcohol-delayed pups born as late as G27, the barrel field was never present at birth suggesting the importance of postnatal experience on barrel field development, and (6) PAE did not disrupt the normal barrel field pattern, although both total body and brain weights were compromised. These findings suggest that PAE delays the development of the somatosensory cortex (SI); such delays may interfere with timing and formation of cortical circuits. It is unknown whether other nuclei along the somatosensory pathway undergo similar delays in development or if PAE selectively disrupts cortical circuitry.

Genetic analysis of barrel field size in the first somatosensory area (SI) in inbred and recombinant inbred strains of mice

We measured the combined area of posterior medial barrel subfield (PMBSF) and anterior lateral barrel subfield (ALBSF) areas in four common inbred strains (C3H/HeJ, A /J, C57BL /6J, DBA/2J), B6D2F1, and ten recombinant inbred (RI) strains generated from C57BL/6J and DBA/2J progenitors (BXD) as an initial attempt to examine the genetic influences underlying natural variation in barrel field size in adult mice. These two subfields are associated with the representation of the whisker pad and sinus hairs on the contralateral face. Using cytochrome oxidase labeling to visualize the barrel field, we measured the size of the combined subfields in each mouse strain. We also measured body weight and brain weight in each strain. We report that DBA/2J mice have a larger combined PMBSF/ALBSF area (6.15 +/- 0.10 mm(2), n = 7) than C57BL /6J (5.48 +/- 0.13 mm(2), n = 10), C3H/HeJ (5.37 +/- 0.16 mm(2), n = 10), and A/J mice (5.04 +/- 0.09 mm(2), n = 15), despite the fact that DBA/2J mice have smaller average brain and body sizes. This finding may reflect dissociation between systems that control brain size with those that regulate barrel field area. In addition, BXD strains (average n = 4) and parental strains showed considerable and continuous variation in PMBSF/ALBSF area, suggesting that this trait is polygenic. Furthermore, brain, body, and cortex weights have heritable differences between inbred strains and among BXD strains. PMBSF/ALBSF pattern appears similar among inbred and BXD strains, suggesting that somatosensory patterning reflects a common plan of organization. This data is an important first step in the quantitative genetic analysis of the parcellation of neocortex into diverse cytoarchitectonic zones that vary widely within and between species, and in identifying the genetic factors underlying barrel field size using quantitative trait locus (QTL) analyses.

Prenatal alcohol exposure (PAE) reduces the size of the forepaw representation in forepaw barrel subfield (FBS) cortex in neonatal rats: relationship between periphery and central representation

Prenatal alcohol exposure (PAE) alters limb development that may lead to structural and functional abnormalities of the limb reported in children diagnosed with Fetal Alcohol Spectrum Disorder. To determine whether PAE alters the central representation of the forelimb we used the rodent barrel cortex as our model system where it was possible to visualize and quantitatively measure the size of the forepaw representation in the forepaw barrel subfield (FBS) in first somatosensory cortex. In the present study, we examined the effects of PAE on pattern and size of the forepaw and forepaw representation in FBS in neonatal rats at gestational day 32 that corresponds to postnatal day 9. Pregnant Sprague-Dawley rats were chronically intubated with binge doses of ethanol (6 g/kg) from gestational day 1 through gestational day 20. The offspring of the ethanol treated dams comprised the ethanol (EtOH) group. The effect of PAE on the EtOH group was compared with a nutritional-controlled pairfed (PF) group and a normal chowfed (CF) group. The ventral (glabrous) surface area of the forepaw digits, length of digit 2 through digit 5, and the corresponding glabrous forepaw digit representations in the FBS were measured and compared between treatment groups. In rats exposed to in utero alcohol, the sizes of the overall glabrous forepaw and forepaw digits were significantly reduced in EtOH pups compared to CF and PF pups; overall glabrous forepaw area was 11% smaller than CF controls. Glabrous digit lengths were also smaller in EtOH rats compared to CF controls and significantly smaller in digit 2 through digit 4. The glabrous digit representation in FBS was 18% smaller in the EtOH group when compared to the CF treatment. However, PAE did not produce malformations in the forepaw or alter the pattern of the forepaw representation in FBS; instead, PAE significantly reduced both body and brain weights compared to controls. Unexpectedly, little or no correlation was observed between the size of the glabrous forepaw compared to the size of the glabrous forepaw representation in the FBS for any of the treatment groups. The present findings of PAE-related alterations in sensory periphery and the central cortical representation may underlie deficits in sensorimotor integration reported among children with Fetal Alcohol Spectrum Disorder.

Prenatal alcohol exposure alters the size, but not the pattern, of the whisker representation in neonatal rat barrel cortex

Maternal alcohol exposure results in a variety of neurodevelopmental abnormalities that include cognitive and sensorimotor dysfunctions that often persist into adulthood. Many reports of central nervous system disturbances associated within a clinical diagnosis of fetal alcohol syndrome point toward disturbances in central information processing. In this study, we used the rat barrel field cortex as a model system to examine the effects of prenatal alcohol exposure (PAE) on the organization and size of the large whisker representation in layer IV of the posteromedial barrel subfield (PMBSF) in somatosensory cortex. Pregnant rats (Sprague-Dawley) were intragastrically gavaged daily with alcohol doses (6 gm/kg body weight) from gestational day 1 to day 20 in a chronic binge pattern which produced blood alcohol levels ranging between 260 mg/dl and 324 mg/dl. Chow-fed (CF), pair-fed (PF), and cross-foster (XF) groups served as normal, nutritionally matched, and maternal controls, respectively, for the ethanol-exposed (EtOH) treatment group. All pups were examined on gestational day 32 corresponding approximately to postnatal day 9. EtOH and control group pups were weighed, anesthetized, and perfused. Brains were removed and weighed, with and without cerebellum and olfactory bulbs, and the neocortex was removed and weighed. Cortices were then flattened, sectioned tangentially, and stained with a metabolic marker-cytochrome oxidase-to reveal the barrel field. A subset of 27 cortical barrels, associated with the representation of the large whisker pad, was selected to examine in detail. The major results were: (i) the total barrel field area comprising the PMBSF was significantly reduced in EtOH (by 17%) and XF (by 16%) pups compared with CF pups, (ii) the sizes of individual barrels within the PMBSF were also significantly reduced in EtOH (16%) and XF (18%) pups, (iii) the septal region between barrels was also significantly reduced in EtOH (18%) and XF (12%) pups, (iv) anteriorly located barrels underwent greater reduction in size relative to the posteriorly located barrels, (v) body weights were also significantly reduced in EtOH (21%) and XF (27%) pups, (vi) total brain weight [with and without (forebrain) cerebellum/olfactory bulbs] and cortical weights were also significantly reduced in EtOH (total brain weight 15%, forebrain weight 16%, cortical weight 15%) and XF (18%, 19%, 20%) pups, and in contrast (vi) neither the overall barrel field pattern nor the pattern of individual barrels in the PMBSF was altered. These findings suggest that PAE reduces body and brain weight as well as the central cortical representation of the whisker pad, while leaving the overall barrel field pattern unperturbed. While these results might appear to support a miniaturization hypothesis (smaller PMBSF, smaller brain, smaller body weight), PAE also shows regional vulnerability within the PMBSF whereby anteriorly located barrels are most affected.

Delayed reorganization of the shoulder representation in forepaw barrel subfield (FBS) in first somatosensory cortex (SI) following forelimb deafferentation in adult rats

We previously reported that 6-16 weeks after forelimb amputation in adult rats, neurons in layer IV of rat first somatosensory cortex (SI) in the forepaw barrel subfield (FBS) associated with the representation of the forepaw became responsive to new input from the shoulder (Pearson et al. 1999). These new shoulder-responsive sites in deafferented FBS had longer evoked response latencies than did sites in the shoulder representation located in the posterior part of the trunk subfield, hereafter referred to as the original shoulder representation. Furthermore, projection neurons in the original shoulder representation in both intact and deafferented adults did not extend their axons into the FBS, and ablation of the original shoulder representation cortex and/or the second somatosensory cortex (SII) failed to eliminate new shoulder input in the deafferented FBS (Pearson et al. 2001). These results led us to conclude that large-scale reorganization in FBS quite likely involved a subcortical substrate. In addition, the time course for large-scale cortical reorganization following forelimb amputation was unknown, and this information could shed light on potential mechanisms for large-scale cortical reorganization. In the present study, we extended our previous findings of large-scale cortical reorganization in the FBS by investigating the time course for reorganization following forelimb amputation. The major findings are: a) deafferented forelimb cortex remained unresponsive to shoulder stimulation during the 1st week following forelimb amputation; b) new responses to shoulder stimulation were first observed in deafferented forelimb cortex 2-3 weeks after forelimb amputation; however, the new shoulder input was restricted to locations in the former forearm cortex; c) islet(s) of new shoulder representation were first observed in deafferented FBS 4 weeks after amputation; these islets occupied a larger percentage of FBS in subsequent weeks; d) portions of FBS remained unresponsive as many as 4 months after deafferentation (maximum time examined between amputation and recording); and e) the increase in total size of the shoulder representation appeared to result from the establishment of new shoulder representations that were often discontinuous from the original shoulder representation. These findings provide evidence that forelimb amputation results in delayed reorganization of the FBS and we describe possible mechanisms and substrates underlying the reorganization.

Removal of GABAergic inhibition alters subthreshold input in neurons in forepaw barrel subfield (FBS) in rat first somatosensory cortex (SI) after digit stimulation

Our objective was to test the hypothesis that suppression of GABAergic inhibition results in an enhancement of responses to stimulation of the surround receptive field. Neurons in the forepaw barrel subfield (FBS) in rat first somatosensory cortex (SI) receive short latency suprathreshold input from a principal location on the forepaw and longer latency subthreshold input from surrounding forepaw skin regions. Input from principal and surround receptive field sites was examined before, during, and after administration of the GABA(A) receptor blocker bicuculline methiodide (BMI) (in 165 mM NaCl at pH 3.3-3.5). In vivo extracellular recording was used to first identify the location of the glabrous forepaw digit representation within the FBS. In vivo intracellular recording and labeling techniques were then used to impale single FBS neurons in layer IV as well as neurons in layers III and V, determine the receptive field of the cell, and fill the cell with biocytin for subsequent morphological identification. The intracellular recording electrode was fastened with dental wax to a double-barrel pipette for BMI iontophoresis and current balance. A stimulating probe, placed on the glabrous forepaw skin surface, was used to identify principal and surround components of the receptive field. Once a cell was impaled and a stable recording was obtained, a stimulating probe was placed at a selected site within the surround receptive field. Single-pulse stimulation (1 Hz) was then delivered through the skin probe and the percentage of spikes occurring in 1-min intervals before BMI onset was used as a baseline measure. BMI was then iontophoresed while the periphery was simultaneously stimulated, and spike percentage measured during and after BMI ejection was compared with the pre-BMI baseline. The major findings are: (1) suppression of GABAergic inhibition enhanced evoked responses to firing level from sites in surround receptive fields in 65% of the cells ( n=17); (2) evoked responses were rapidly elevated (within 1 min) to suprathreshold firing in the presence of BMI in 31% of the cells; (3) GABAergic inhibition was reversible [suprathreshold spiking gradually reversed to subthreshold excitatory postsynaptic potentials (EPSPs) in 45% of the cells tested]; (4) BMI altered the stimulus-evoked and non-stimulus-evoked firing pattern in SI neurons from single spikes to burst patterns in all tested cells; and (5) iontophoresis of NaCl (165 mM) without BMI was ineffective in altering evoked responses in control cells ( n=4). The present findings support the notion that subthreshold input from surround receptive fields is one possible mechanism for rapid cortical reorganization in barrel cortex and that GABAergic inhibition may regulate its expression. Possible corticocortical and thalamocortical substrates for subthreshold input to reach barrel neurons are discussed.

EDTA chelation effects on urinary losses of cadmium, calcium, chromium, cobalt, copper, lead, magnesium, and zinc

The efficacy of a chelating agent in binding a given metal in a biological system depends on the binding constants of the chelator for the particular metals in the system, the concentration of the metals, and the presence and concentrations of other ligands competing for the metals in question. In this study, we make a comparison of the in vitro binding constants for the chelator, ethylenediaminetetraacetic acid, with the quantitative urinary excretion of the metals measured before and after EDTA infusion in 16 patients. There were significant increases in lead, zinc, cadmium, and calcium, and these increases roughly corresponded to the expected relative increases predicted by the EDTA-metal-binding constants as measured in vitro. There were no significant increases in urinary cobalt, chromium, or copper as a result of EDTA infusion. The actual increase in cobalt could be entirely attributed to the cobalt content of the cyanocobalamin that was added to the infusion. Although copper did increase in the post-EDTA specimens, the increase was not statistically significant. In the case of magnesium, there was a net retention of approximately 85% following chelation. These data demonstrate that EDTA chelation therapy results in significantly increased urinary losses of lead, zinc, cadmium, and calcium following EDTA chelation therapy. There were no significant changes in cobalt, chromium, or copper and a retention of magnesium. These effects are likely to have significant effects on nutrient concentrations and interactions and partially explain the clinical improvements seen in patients undergoing EDTA chelation therapy.

Large-scale cortical reorganization following forelimb deafferentation in rat does not involve plasticity of intracortical connections

Physiological mapping of the body representation 1 month or longer after forelimb removal in adult rats revealed new pockets of shoulder representation in the forepaw barrel subfield (FBS) in the first somatosensory cortex (SI). These "new" shoulder representations have longer evoked response latencies than sites in the shoulder representation within the trunk subfield, hereafter referred to as the "original" shoulder representation. We postulated that the "new" shoulder representations in the FBS were relayed from the "original" shoulder representation. We investigated this hypothesis by studying anatomical connectivity between the "original" shoulder representation and the FBS in intact control and forelimb deafferented adult rats using Phaseolus vulgaris leucoagglutinin (PHA-L), biocytin, and biotin dextran-amine (BDA) as anterograde tracers. The retrograde tracer cholera toxin beta subunit (CT-B) injected into the FBS was also used to study connectivity between the "original" shoulder representation and the FBS. Using these anatomical tracing techniques, we were unable to show the existence of a direct corticocortical connection between the "original" shoulder representation in the trunk subfield and the FBS in either intact or deafferented rats. Functional connectivity between the two cortical regions was studied by ablating the "original" shoulder representation alone or in combination with the shoulder representation in the second somatosensory cortex (SII) while recording evoked responses in the FBS following electrical stimulation of the shoulder. Both ablations failed to eliminate the evoked responses at the "new" shoulder sites in the FBS, suggesting that SI and SII are not necessary for "new" shoulder input in the FBS. It is suggested that subcortical sites may play a major role in large-scale cortical reorganization. Results of projections from the "original" shoulder representation to parietal medial (PM), parietal lateral (PL), SII, parietal ventral (PV), and parietal rhinal (PR) sensory fields and agranular lateral (AgL) and agranular medial (AgM) motor fields are also described.

Location and distribution of Fos protein expression in rat hippocampus following acute moderate aerobic exercise

Hippocampal neurons are activated during endurance exercise; however, little attention has been given to the location and spatial distribution of these neurons. We have, therefore, used Fos protein expression to identify the location and distribution of hippocampal neurons that become activated during acute moderate aerobic exercise. Adult rats were assigned into trained running (TR), trained nonrunning (TNR), untrained nonrunning (UNR), and cage-bound (CB) groups. Rats in the TR and TNR groups were trained to run, for three 20-min running periods separated by 3 min rest, on a treadmill. Rats in the UNR group spent identical time on a nonactivated treadmill, while rats in the CB group remained in their home cages throughout the training and experimentation. After training to criterion performance for both TR and TNR groups, both groups were rested for 1 day. Rats in the TR were then run on the treadmill to criterion level, while those in TNR and UNR groups spent equivalent time on the nonactivated treadmill. Animals in all groups were then killed and their brains removed, sectioned, and processed for Fos protein immunocytochemistry. Fos-like immunoreactive (FLI) neurons were counted in the dentate and CA1-3 fields of the hippocampus. The total numbers of hippocampal FLI neurons, as well as FLI neurons in each hippocampal region, were compared among groups. The total numbers of FLI neurons in the hippocampus, as well as in individual regions, were significantly greater in the TR group compared with the other three groups. Similarly, significant differences were found between the TNR group when compared with UNR and CB groups. Conversely, a significant difference existed between UNR and CB only in the CA1 field, which may account for the significant difference in the total number of hippocampal FLI neurons between these two groups. These results show that Fos induction occurs in the hippocampus during moderate physical exercise. Furthermore, the importance of the incorporation of adequate controls to account for possible differences in expression of immediate early gene expression due to trained performing, trained nonperforming, and untrained groups is discussed. The results indicate that adequate control for nonexercise stimuli is necessary for studies of the effect of exercise on the brain when expression of immediate early genes such as c-fos is used as an outcome measure.

Thalamocortical arbors extend beyond single cortical barrels: an in vivo intracellular tracing study in rat

Neurons in layer IV of rat somatosensory (SI) barrel cortex receive punctate somatic input from well-defined regions of the periphery. Following peripheral deafferentation, SI neurons in deafferented cortex respond to new input from neighboring regions of the skin surface. The precise mechanism(s) through which this occurs is unknown, although corticocortical and barreloid to barrel connections have been suggested as possible substrates. Because layer-IV barrels receive a strong afferent input from ventroposterior (VP) thalamic projection neurons, any divergence in the thalamocortical (TC) projection to multiple cortical barrels could also provide an anatomical substrate for rapid cortical reorganization. We used in-vivo intracellular recording methods to record and physiologically identify neurons in rat VP and to label those neurons with an intracellular tracer. Thalamic neurons (n=117) were impaled with sharp intracellular electrodes, and the receptive field(s) and firing pattern were measured. Cells were then injected with biocytin or biotinylated dextran amine (BDA). A total of 38 labeled TC neurons were quantitatively analyzed for soma size and dendritic arborization size; quantitative analysis of TC-axon arborizations in layer IV of barrel cortex was carried out in a total of 13 TC neurons. Two different axon-arborization patterns were identified in SI cortex: direct-projecting axons (n=6) were observed to project to and arborize within a single cortical barrel as well as extend their fibers into adjacent barrels; bifurcating-type axons (n=7) were seen to bifurcate in the subcortical white matter or in layer VI and then project to multiple barrel columns, where they arborized in layer IV. Axon fibers were always observed in three or more cortical barrels (mean=5, range=3-7). The mean mediolateral extent of arborizations in layer IV for the direct-projecting and bifurcating type axons were 458 microm and 1,302 microm, respectively, and these were significantly different (t=3.78, P<0.01). Axon-fiber length within cortical laminae was measured for each arborization pattern in relationship to the total fiber length within a cortical column. Direct-projecting axons always had greater than 50% of their fiber length within layer IV. Bifurcating-type axons were differentially distributed within multiple columns and always had less than 50% of their total column fiber length in layer IV. Morphological analysis of TC somata and dendrites revealed no correlation between local neuron morphology and axonal-arborization patterns. All intracellularly recorded TC neurons had similar adapting firing patterns when injected with a long-duration pulse. Our results showed that TC neurons project to multiple cortical barrels with one barrel receiving the principal input. This divergent TC projection pattern in SI cortex may provide an anatomical substrate for cortical plasticity and must be considered in any mechanism of rapid cortical reorganization.

Effects of large-scale limb deafferentation on the morphological and physiological organization of the forepaw barrel subfield (FBS) in somatosensory cortex (SI) in adult and neonatal rats

The physiological representation of the shoulder and surrounding body was examined in layer IV of somatosensory cortex (SI) in rats that had underground removal of the forelimb, either as newborns on postnatal day three (PND-3) or as adults (at least 8 weeks of age). Electrophysiological recordings were used to map the shoulder and body representations (physiological map), and the mitochondria marker, cytochrome oxidase (CO), was used to visualize recording sites in barrel and barrel-like structures (morphological map) in layer IV of deafferents and intact controls. The SI shoulder representation lies in a nebulously stained region that lies posterior to the forearm, wrist, and forepaw representations; the latter region is associated with the well-defined forepaw barrel subfield (FBS). The major findings are: (1) the shoulder is represented as a single zone located at the posterior extent of the SI body map in intact rats; (2) limb deafferentation in adult or neonatal rats that were physiologically mapped 6-16 weeks post-amputation resulted in two or more islets of "new" representation of the shoulder in the FBS in addition to the representation of the "original" shoulder in the posterior part of the body map; (3) deafferentations made in neonatal rats, physiologically mapped as adults, had a significantly greater (Mann-Whitney U) amount of "new" cortical representation within the FBS than did rats deafferented as adults; (4) fewer unresponsive sites in the FBS were found for neonate deafferents than for adult deafferents; (5) evoked response latencies following electrical stimulation of the shoulder were shortest for cortical sites within the "original" shoulder representation in intact controls, and latencies recorded at the "original" shoulder representation in deafferents were also shorter than latencies recorded in "new" shoulder representations in both groups of deafferents; and (6) morphological maps of the FBS were altered in neonate deafferents to the extent that the barrel structure was poorly formed, as exemplified by the absence of the four mediolateral running bands; however, the overall ovoid shape of the FBS was still apparent, but not as sharply defined as for intact controls or adult deafferents. Possible mechanisms for reorganization following large-scale deafferentation are discussed.

Specificity in the interaction of HVA Ca2+ channel types with Ca2+-dependent AHPs and firing behavior in neocortical pyramidal neurons

Intracellular recordings and organic and inorganic Ca2+ channel blockers were used in a neocortical brain slice preparation to test whether high-voltage-activated (HVA) Ca2+ channels are differentially coupled to Ca2+-dependent afterhyperpolarizations (AHPs) in sensorimotor neocortical pyramidal neurons. For the most part, spike repolarization was not Ca2+ dependent in these cells, although the final phase of repolarization (after the fast AHP) was sensitive to block of N-type current. Between 30 and 60% of the medium afterhyperpolarization (mAHP) and between approximately 80 and 90% of the slow AHP (sAHP) were Ca2+ dependent. Based on the effects of specific organic Ca2+ channel blockers (dihydropyridines, omega-conotoxin GVIA, omega-agatoxin IVA, and omega-conotoxin MVIIC), the sAHP is coupled to N-, P-, and Q-type currents. P-type currents were coupled to the mAHP. L-type current was not involved in the generation of either AHP but (with other HVA currents) contributes to the inward currents that regulate interspike intervals during repetitive firing. These data suggest different functional consequences for modulation of Ca2+ current subtypes.

In vivo intracellular recording and labeling of neurons in the forepaw barrel subfield (FBS) of rat somatosensory cortex: possible physiological and morphological substrates for reorganization

We examined the physiological properties and morphology of neurons in the forepaw barrel subfield (FBS) in somatosensory cortex (SI) of adult rats using in vivo intracellular recording and biocytin labeling techniques. Our results show that both pyramidal and non-pyramidal type spiny neurons can be activated with short latency by peripheral stimulation. FBS neurons within individual barrels receive both suprathreshold and subthreshold convergent input from one or more forepaw digits and pads. We hypothesize that some of these subthreshold inputs may be elevated to firing level by some, as yet unknown, mechanism(s) following peripheral deafferentation. Examination of the relationship between the dendritic pattern of labeled neurons and individual barrels within the FBS suggests that neurons with dendrites extending into neighboring barrel bands may serve as a possible morphological substrate for immediate reorganization.

Electrical stimulation of a forepaw digit increases the physiological representation of that digit in layer IV of SI cortex in rat

We studied the physiological representation of digit three (D3) in rat somatosensory cortex (SI) before and immediately after electrical stimulation (1.5x threshold for 2 h) of the glabrous tip of D3 in anesthetized animals (n = 6). Measurements of D3 representation were also made in anesthetized non-stimulated control animals (n = 2). The post-stimulation areal measurements of D3 representation in experimental animals were statistically significantly larger than both pre-stimulation measurements in experimental animals and post-stimulation measurements in control animals. Our results suggest that short-term electrical stimulation is sufficient to expand the D3 representation in each of the experimental animals, while the maps in non-stimulated controls showed little variation. The fact that these studies were carried out in anesthetized animals suggests that the results are independent of the state of the animal. The present findings emphasize the importance of afferent input in modulating cortical organization.

Relationship between representation of hindpaw and hindpaw barrel subfield (HBS) in layer IV of rat somatosensory cortex

We describe the organization of the hindpaw barrel subfield (HBS) in layer IV of rat somatosensory cortex (SI) and relate this organization to the representation of the hindpaw. The ovoid-shaped, HBS is oriented anterior to posterior and comprises barrels and barrel-like structures, the most prominent of which consist of at least five anteriorly-located elongated barrel bands. Posterior to these elongated bands is a cluster of four barrels. Two additional barrels are found, one lateral, the other medial. The lateral border is formed by a nearly continuous band that overlaps portions of the anterior elongated bands and posterior barrels. The HBS shows considerable variability in size and shape; nevertheless, the overall pattern reflects a common plan of organization. Electrophysiological mapping confirmed that hindpaw representation is somatotopically organized. The glabrous toes are represented anteriorly, the pads posteriorly, and the dorsal hairy skin of the toes and hindpaw laterally. By aligning physiological and morphological (HBS) maps according to lesion sites, our data suggest that the elongated anteriorly-located barrel bands represent the hindpaw toes, the four toe pads are represented immediately posterior followed by barrels representing the plantar pads. The representations of dorsal hairy skin of toe and dorsal hindpaw form the lateral border; the heel and ankle are represented most posterior. We interpret our findings as support that individual barrels in the HBS are associated with discrete regions of the hindpaw; however, the precise relationship of structure and function reported between the vibrissae and posteromedial barrel subfield (PMBSF) and between the forepaw and the forepaw barrel subfield (FBS) were not observed.

Digit removal leads to discrepancies between the structural and functional organization of the forepaw barrel subfield in layer IV of rat primary somatosensory cortex

The physiological representation of the forepaw in rat primary somatosensory cortex (SI) is topographically organized. This representation is associated with the unique arrangement of barrels in layer IV of the forepaw barrel subfield (FBS) in SI and provides an example of a relationship between cortical structure and function. It has been reported that removal of peripheral afferent input to the FBS prior to postnatal day 5 or 6 results in a disorganized FBS, while deafferentation at later times produces little or no alteration of the FBS. Therefore, restricted deafferentations of individual digits in adult rats should result in little, if any, disruption of the FBS, while at the same time eliminating afferent input to the FBS from a localized region of the periphery. This manipulation is likely to create a mismatch between structure and function and offer insight into what barrels actually represent in the adult deafferent. In the present study, we amputated digit three (D3) in eight adult rats, allowed a 1-month survival time, physiologically mapped the representation of D2, D4, and the stump, and compared this physiological map to the underlying barrels in the FBS. Our results showed that FBS barrels formerly associated with the representation of D3 were now associated with the representation of surrounding digits D2 and D4, as well as the remaining stump. By superimposing the morphological and physiological map upon one another, it was clear that the D2 and D4 representations expanded into the former D3 barrel territory and septae between the barrels. The reorganized physiological map was somatotopically organized, even though the general configuration of the morphological map remained unaltered, as visualized with cytochrome oxidase staining. These results suggest that in the deafferent, neurons within FBS barrels previously associated with the representation of punctate regions of skin become associated with neighboring regions of skin. A morphological substrate to account for this cortical reorganization is described.

Relationship between the organization of the forepaw barrel subfield and the representation of the forepaw in layer IV of rat somatosensory cortex

We studied the organization of the forepaw barrel subfield (FBS) in layer IV of adult rat somatosensory cortex using the mitochondrial marker cytochrome oxidase and related this organization to the representation of the forepaw. The FBS is an ovoid structure consisting of barrels and barrel-like structures, the most conspicuous of which form four centrally located medio lateral running bands. Each band contains three to four barrels. These centrally located bands are bordered along their entire lateral side by a nebulous zone of undifferentiated labeling. At the anterior border, two small barrels are located laterally and one or two larger barrels are located medially. Medial to the central zone are three well-defined barrels. The posterior border consists of a nebulous field of labeling and occasional barrel-like structures. The results from our electrophysiological recording and mapping revealed that the forepaw representation was topographically organized into a single map and that the forepaw map matches almost precisely with individual barrels and barrel-like structures in the FBS. Each of the four central bands is associated with the representation of a single glabrous digit. Digit two (D2) is represented anteriorly and followed posteriorly by D3 through D5. Within each digit band the digit is somatotopically organized, with the skin over the distal phalanx represented in the two lateral barrels and the middle and proximal phalanges represented in the medial barrel(s). The dorsal hairy digit skin and dorsal hand are represented in the lateral zone. D1 is represented by two small anteriorly located barrels. Medial to the representation of the glabrous digits is the representation of the palmar pads. The representation of these pads, in turn, lies between the representations of the thenar (located anteriorly) and hypothenar (located posteriorly) pads. Posterior to the hypothenar pad representation lie the representations of the wrist and forearm. While the present results support the conclusion that individual barrels are associated with discrete locations on the forepaw, examples were found where the recording site was not precisely located within the predicted barrel. Some of these errors may be accounted for by limitations in the mapping techniques; nevertheless, the FBS offers an excellent model system to study relationships between cortical structure and function.

Large unresponsive zones appear in cat somatosensory cortex immediately after ulnar nerve cut

The organization of the primary somatosensory cortex innervated by the ulnar nerve was studied before and immediately after ulnar nerve transection in 11 cats electrophysiologically mapped under Nembutal or Ketamine anesthesia. The cortex was reexamined a second time beginning 42 hr after nerve transection in four cats anesthetized with Nembutal. One additional sham-operated control was also mapped. The region of cortex formerly served by the ulnar nerve remained largely unresponsive to somatic stimulation independent of the type of anesthetic used during recording. Nonetheless, animals anesthetized with Ketamine had more new responsive sites in deafferented cortex following nerve cut than cats anesthetized with Nembutal. New responses, when observed, were evoked by stimulation of a region of skin adjacent to the region served by the ulnar nerve. These findings suggest that the immediate response to deafferentation of somatosensory cortex is a limited acquisition of novel responses restricted to a region immediately adjacent to cortex containing normal afferent input.

Reevaluation of area 3b in the cat based on architectonic and electrophysiological studies: regional variability with functional and anatomical consistencies

Most anatomical and electrophysiological studies of the cat primary somatosensory cortex rely on Hassler and Muhs-Clement's (J. Hirnforsch. 6:377-420, 1964) cyto- and myeloarchitectonic description distinguishing area 3a from area 3b; however, discrepancies in the delineation of these areas in published studies suggest that many workers have found it difficult to apply those criteria systematically. We examined the cytoarchitecture of area 3b in Nissl stained sagittal sections from which electrophysiological data had been obtained prior to sacrifice. Rostrocaudal rows of electrode penetrations placed at different mediolateral positions in the gyrus located regions responsive to stimulation of either cutaneous or deep structures. Small electrolytic lesions allowed these data to be related to the cytoarchitecture. A systematic study throughout the trunk and limb representations found cutaneous responses in cortical regions characterized by a thick and cell-dense granular layer IV, however these same regions had a variable population of medium-sized and/or large pyramidal cells in layer V. Pyramidal cells were practically absent from the forelimb representation, but were present to varying degrees in the trunk and hindlimb representations. Moreover, the relative thickness and cell-density in layer IV were greater in the forelimb than in the hindlimb representations. Deep responses were found in cortex characterized by a thinner layer IV. Since the characteristics of layer V in area 3a were variable, it was less useful for identification of the border between areas 3a and 3b. Clear changes in the intensity and laminar distribution of acetylcholinesterase staining occurred between areas 3a and 3b, making this a useful adjunct to the Nissl stain.

Early development of the SI cortical barrel field representation in neonatal rats follows a lateral-to-medial gradient: an electrophysiological study

Development of the barrel field in layer IV of SI cortex of neonatal rats was studied in vivo using electrophysiological recording techniques. This study was designed to determine (a) the earliest time SI cortex is responsive to peripheral mechanical and/or electrical stimulation and (b) whether the development of the SI cortical barrel field map of the body surface follows a differential pattern of development similar to the pattern previously demonstrated using peanut agglutinin (PNA) binding (McCandlish et al. 1989). Carbon fiber microelectrodes were used to record evoked responses from within the depth of the cortex in neonatal rats between postnatal day 1. (PND-1), defined as the day of birth, and PND-14. Evoked responses were first recorded approximately 12 h after birth. These responses in the youngest animals were of low amplitude, monophasic waveshape, and long latency, with long interstimulus intervals necessary to drive the cortex. Increases in amplitude and complexity of waveshape and decreases in latency were observed over subsequent postnatal days. The earliest responses recorded on middle PND-1 were evoked by stimulation of the face and/or mystacial vibrissae. The next responses were evoked approximately 24 h after birth (late PND-1) by stimulation of the forelimb. The last responses were evoked approximately 36 h after birth (middle PND-2), by stimulation of the hindlimb. The physiological map of the representation of the body surface follows a developmental gradient similar to the gradient observed using PNA histochemistry; however, the lectin-generated morphological map lagged approximately 48 h behind the physiological map.(ABSTRACT TRUNCATED AT 250 WORDS)

Contributions of low-threshold calcium current and anomalous rectifier (Ih) to slow depolarizations underlying burst firing in human neocortical neurons in vitro

The slow depolarization that underlies the voltage-dependent burst-firing behavior of human neocortical neurons is mediated by a low-threshold calcium conductance in concert with the anomalous rectifier current, Ih. The slow depolarization could be elicited by depolarization from negative membrane potentials or as a rebound following hyperpolarization. The rebound depolarization was time- and voltage-dependent. Most of the slow depolarization was blocked by inorganic calcium blockers. The remainder of the depolarization and the 'sag' in the hyperpolarizing voltage responses were blocked by extracellular Cs+.

Organization of the mouse motor cortex studied by retrograde tracing and intracortical microstimulation (ICMS) mapping

The motor representation of the body musculature was studied in 11 adult mice by using ICMS. The motor responses elicited from both granular and agranular cortical fields showed that the mouse motor cortex is topographically organized; however, within the representation of individual body-parts the movements are multiply represented. In addition, several sites were encountered where more than one movement was elicited at the same stimulus threshold. The locations of pyramidal cells contributing axons to the pyramidal tract were examined by means of retrograde tracing with HRP injected into the cervical enlargement. This procedure labeled neurons only in lamina V in granular and agranular cortical fields. The similarities between the organization of motor cortex demonstrated in this study and the organization in the rat suggest that the rat and mouse share a common plan of rodent motor cortical organization.

Ulnar nerve innervation of paw and SI cortex of cat: substrate for reorganization

We studied the distribution of the peripheral nerves innervating the distal forepaw by recording receptive fields from fascicles of the ulnar, radial, and median nerves and compared this result with the peripheral nerve representation in primary somatosensory (SI) cortex of cat. Our findings suggest that SI cortex receives input, in large part, from multiple peripheral nerves even when those nerves do not show a strong overlapping pattern in the periphery. This overlap pattern observed in SI cortex may be responsible, in part, for the immediate reorganization which is known to follow peripheral nerve deafferentation.

Early development of SI cortical barrel subfield representation of forelimb in normal and deafferented neonatal rat as delineated by peroxidase conjugated lectin, peanut agglutinin (PNA)

Development of the barrel field representation of the forelimb in the primary somatosensory cortex (SI) was studied in normal and deafferented neonatal rat pups by means of the peroxidase conjugated lectin peanut agglutinin (PNA), which most likely binds to radial glial cells within barrel boundaries. 1. Alterations in lectin binding were seen in animals sacrificed on postnatal day 8 (PND-8) if deafferentation took place on PND-1 (day of birth) through PND-6. 2. Deafferentation on PND-5 or on PND-6 had the least effect on lectin binding. In these animals, lectin binding was reduced, although the prospective representation was intact. 3. Deafferentation on PND-2, 3, and 4 had the greatest effect on lectin binding. In these animals, lectin binding was reduced and the prospective cortical representation was disrupted. 4. Deafferentation on PND-1 resulted in reduced lectin binding, however the prospective cortical representation was only slightly impaired compared to that in animals deafferented on PND-2, 3, and 4. 5. These results suggest that SI barrel field boundaries are important to plasticity and that a sensitive period for predevelopment of the forelimb barrels consists of postnatal days 1 through 6. Furthermore, the formation of normal SI barrel field boundaries requires an ongoing interaction between incoming afferents and radial glial cells.

Absence of responses to microstimulation at the hand-face border in baboon primary motor cortex

Intracortical microstimulation (ICMS) was used to map the primary motor cortex of four adult female baboons, anesthetized with a mixture of halothane and nitrous oxide and supplemented with sodium pentobarbital. The sequence of observed muscle contractions in response to ICMS provided evidence of an orderly mototopic representation of the tongue, face, hand, forearm and upper body. A zone of cortex unresponsive to microstimulation was consistently observed at the border between the face and hand representation of the mototopic map. This zone was observed in all four animals and was consistent over time. Repeated confirmations of the unresponsive nature of these regions were obtained both early and late in the same experiment. No motor-unit responses or muscle contractions were detected by electromyographic (EMG) recording during stimulation of the unresponsive zones. The absence of both visually observed and EMG-recorded contractions and the fact that muscle contractions could be elicited from adjacent regions of cortex with ICMS as low as 1-5 microA provide compelling evidence that the finding reflects a true physiological condition rather than an experimental artifact.