Common fur and mystacial vibrissae parallel sensory pathways: 14 C 2-deoxyglucose and WGA-HRP studies in the rat

Trigeminal Sensory Supply Is Essential for Motor Recovery after Facial Nerve Injury

Recovery of mimic function after facial nerve transection is poor. The successful regrowth of regenerating motor nerve fibers to reinnervate their targets is compromised by (i) poor axonal navigation and excessive collateral branching, (ii) abnormal exchange of nerve impulses between adjacent regrowing axons, namely axonal crosstalk, and (iii) insufficient synaptic input to the axotomized facial motoneurons. As a result, axotomized motoneurons become hyperexcitable but unable to discharge. We review our findings, which have addressed the poor return of mimic function after facial nerve injuries, by testing the hypothesized detrimental component, and we propose that intensifying the trigeminal sensory input to axotomized and electrophysiologically silent facial motoneurons improves the specificity of the reinnervation of appropriate targets. We compared behavioral, functional, and morphological parameters after single reconstructive surgery of the facial nerve (or its buccal branch) with those obtained after identical facial nerve surgery, but combined with direct or indirect stimulation of the ipsilateral infraorbital nerve. We found that both methods of trigeminal sensory stimulation, i.e., stimulation of the vibrissal hairs and manual stimulation of the whisker pad, were beneficial for the outcome through improvement of the quality of target reinnervation and recovery of vibrissal motor performance.

Bilateral plasticity of Vibrissae SII representation induced by classical conditioning in mice

The somatosensory cortex in mice contains primary (SI) and secondary (SII) areas, differing in somatotopic precision, topographic organization, and function. The role of SII in somatosensory processing is still poorly understood. SII is activated bilaterally during attentional tasks and is considered to play a role in tactile memory and sensorimotor integration. We measured the plasticity of SII activation after associative learning based on classical conditioning, in which unilateral stimulation of one row of vibrissae was paired with a tail shock. The training consisted of three daily 10 min sessions, during which 40 pairings were delivered. Cortical activation driven by stimulation of vibrissae was mapped with 2-[(14)C]deoxyglucose (2DG) autoradiography 1 d after the end of conditioning. We reported previously that the conditioning procedure resulted in unilateral enlargement of 2DG-labeled cortical representation of the "trained" row of vibrissae in SI. Here, we measured the width and intensity of the labeled region in SII. We found that both measured parameters in SII increased bilaterally. The increase was observed in cortical layers II/III and IV. Apparently, plasticity in SII is not a simple reflection of changes in SI. It may be attributable to bilateral integrative role of SII, its lesser topographical specificity, and strong involvement in attentional processing.

Passive vs. active touch-induced activity in the developing whisker pathway

The mouse trigeminal (V) system undergoes significant postnatal structural and functional developmental changes. Histological modules (barrelettes, barreloids and barrels) in the brainstem, thalamus and cortex related to actively moved (whisking) tactile hairs (vibrissae) on the face allow detailed studies of development. High-resolution [(3) H]2-deoxyglucose (2DG) emulsion autoradiography with cytochrome oxidase histochemistry was used to analyze neuronal activity changes related to specific whisker modules in the developing and mature mouse V system provoked by passive (experimenter-induced) and active (animal-induced) displacements of a single whisker (D4). We tested the hypothesis that neuronal activity patterns change in relation to the onset of active touch (whisking) on postnatal day (P)14. Quantitative image analyses revealed: (i) on P7, when whisker-like patterns of modules are clear, heightened 2DG activity in all appropriate modules in the brainstem, thalamus and cortex; (ii) on P14, a transitory activity pattern coincident with the emergence of whisking behavior that presages (iii) strong labeling of the spinal V subnucleus interpolaris and barrel cortex produced by single-whisker-mediated active touch in adults and (iv) at all above-listed ages and structures, significant suppression of baseline activity in some modules surrounding those representing the stimulated whisker. Differences in activity patterns before and after the onset of whisking behavior may be caused by neuronal activity induced by whisking, and by strengthening of modulatory projections that alter the activity of subcortical inputs produced by whisking behavior during active touch.

Bone marrow-derived mesenchymal stem cell transplantation does not improve quality of muscle reinnervation or recovery of motor function after facial nerve transection in rats

Recently, we devised and validated a novel strategy in rats to improve the outcome of facial nerve reconstruction by daily manual stimulation of the target muscles. The treatment resulted in full recovery of facial movements (whisking), which was achieved by reducing the proportion of pathologically polyinnervated motor endplates. Here, we posed whether manual stimulation could also be beneficial after a surgical procedure potentially useful for treatment of large peripheral nerve defects, i.e., entubulation of the transected facial nerve in a conduit filled with suspension of isogeneic bone marrow-derived mesenchymal stem cells (BM-MSCs) in collagen. Compared to control treatment with collagen only, entubulation with BM-MSCs failed to decrease the extent of collateral axonal branching at the lesion site and did not improve functional recovery. Post-operative manual stimulation of vibrissal muscles also failed to promote a better recovery following entubulation with BM-MSCs. We suggest that BM-MSCs promote excessive trophic support for regenerating axons which, in turn, results in excessive collateral branching at the lesion site and extensive polyinnervation of the motor endplates. Furthermore, such deleterious effects cannot be overridden by manual stimulation. We conclude that entubulation with BM-MSCs is not beneficial for facial nerve repair.

Manually-stimulated recovery of motor function after facial nerve injury requires intact sensory input

We have recently shown in rat that daily manual stimulation (MS) of vibrissal muscles promotes recovery of whisking and reduces polyinnervation of muscle fibers following repair of the facial nerve (facial-facial anastomosis, FFA). Here, we examined whether these positive effects were: (1) correlated with alterations of the afferent connections of regenerated facial motoneurons, and (2) whether they were achieved by enhanced sensory input through the intact trigeminal nerve. First, we quantified the extent of total synaptic input to motoneurons in the facial nucleus using synaptophysin immunocytochemistry following FFA with and without subsequent MS. We found that, without MS, this input was reduced compared to intact animals. The number of synaptophysin-positive terminals returned to normal values following MS. Thus, MS appears to counteract the deafferentation of regenerated facial motoneurons. Second, we performed FFA and, in addition, eliminated the trigeminal sensory input to facial motoneurons by extirpation of the ipsilateral infraorbital nerve (IONex). In this paradigm, without MS, vibrissal motor performance and pattern of end-plate reinnervation were as aberrant as after FFA without MS. MS did not influence the reinnervation pattern after IONex and functional recovery was even worse than after IONex without MS. Thus, when the sensory system is intact, MS restores normal vibrissal function and reduces the degree of polyinnervation. When afferent inputs are abolished, these effects are eliminated or even reversed. We conclude that rehabilitation strategies must be carefully designed to take into account the extent of motor and/or sensory damage.

Early-phase of learning enhances communication between brain hemispheres

In the somatosensory system, inputs from one side of the body are only transmitted to the contralateral primary somatosensory cortex, but both sides of the body representation can interact via interhemispheric connections. These interactions depend on the behavioural requirements of the animal and its level of arousal. During the process of learning, alertness and attention may modify the responsiveness of neuronal pathways. We functionally mapped the brains of mice by using [14C]2-deoxyglucose (2DG) autoradiography during the first and the third session of a classical conditioning paradigm, involving whiskers stimulation on one side of the muzzle paired with an aversive or appetitive unconditioned stimulus. During the first pairing session, an increased 2DG uptake was seen in the barrel cortex of both hemispheres, independently of the type of applied unconditioned stimulus. In the third session of the sensory pairing, activation of the barrel cortex was solely contralateral, as expected after unilateral whisker stimulation. Thus, sensory stimulation directed to one cerebral hemisphere during the initial stages of Pavlovian conditioning activates the primary sensory area in both hemispheres. These results suggest that during the early phase of conditioning, when alertness is presumably strongest, the interhemispheric interactions are enhanced.

Voltage-sensitive dye imaging of intervibrissal fur-evoked activity in the rat somatosensory cortex

The intervibrissal fur-evoked activity in the rat somatosensory cortex was investigated using high-resolution optical imaging with a voltage-sensitive dye. The optical imaging revealed that the intervibrissal fur representation forms a U-shaped band around the borders of the posteromedial barrel subfield (PMBSF), and that this representation is characterized by a rostral-to-caudal somatotopic organization. When GABA(A)-mediated inhibition was partially suppressed by treatment with bicuculline, stimulation of the intervibrissal fur elicited spreading of an excitation wave in an area outside the PMBSF. The spreading wave propagated in both directions along the aforementioned U-shaped band of cortex, but barely invaded the center of the PMBSF. These imaging results suggest a distinct subdivision of cortex adjacent to, but outside, the PMBSF in the rat somatosensory cortex; this region receives input from intervibrissal fur, and seems to process its sensory information through well-developed local horizontal connections.

Normotopic and heterotopic cortical representations of mystacial vibrissae in rats with subcortical band heterotopia

The tish rat is a neurological mutant exhibiting bilateral cortical heterotopia similar to those found in certain epileptic patients. Previous work has shown that thalamocortical fibers originating in the ventroposteromedial nucleus, which in normal animals segregate as 'barrel' representations for individual whiskers, terminate in both normotopic and heterotopic areas of the tish cortex (Schottler et al., 1998). Thalamocortical innervation terminates as barrels in layer IV and diffusely in layer VI of the normotopic area. Discrete patches of terminals are also observed in the underlying heterotopic area suggesting that representations of individual vibrissa may be present in the heterotopic somatosensory areas. The present study examines this issue by investigating the organization of the vibrissal somatosensory system in the tish cortex. Staining for cytochrome oxidase or Nissl substance reveals a normal complement of vibrissal barrels in the normotopic area of the tish cortex. Dense patches of cytochrome oxidase staining are also found in the underlying lateral portions of the heterotopic area (i.e. the same area that is innervated by the ventroposteromedial nucleus). Injections of retrograde tracers into vibrissal areas of either the normotopic or heterotopic area produce topographically organized labeling of neurons restricted to one or a small number of barreloids within the ventroposteromedial nucleus of the thalamus. Physical stimulation of a single whisker (D3 or E3) elicits enhanced uptake of [(14)C]2-deoxyglucose in restricted zones of both the normotopic and heterotopic areas, demonstrating that single whisker stimulation can increase functional activity in both normotopic and heterotopic neurons. These findings indicate that the barrels are intact in the normotopic area and are most consistent with the hypothesis that at least some of the individual vibrissae are 'dually' represented in normotopic and heterotopic positions in the primary somatosensory areas of the tish cortex.

Identification of a developmental gradient of estrogen receptor expression and cellular localization in the developing and adult female rat primary somatosensory cortex

Immunohistochemistry was used to investigate the spatiotemporal distribution of estrogen receptor alpha and beta (ER alpha, ER beta) in the posteromedial barrel subfield (PMBS) of the cerebral cortex in developing and adult female rats. Counting of immunopositive cells in predefined areas from each layer of the PMBS showed that at PN3, ER alpha immunoreactivity (IR) was present in every cell, whereas ER beta-IR was not detected. At PN6, about 59% of the cells were ER alpha immunopositive and low levels of ER beta-IR were observed in scattered cells. At PN18 the proportion of ER alpha-IR cells decreased to 49%; however, ER beta-IR became widespread and was detected in 39% of cells. By PN25 only faint ER alpha-IR was observed and in the adults ER alpha-IR was not detected. In contrast, at PN25 and in adults, ER beta-IR was detected in about half the cells of the PMBS. Regarding the cellular localization of ER-IR, at PN3 an outside-in gradient of cytoplasmic to nuclear localization of ER alpha-IR was observed. At PN18 and in adults ER beta-IR was preferentially localized to the nucleus of principal neurons, and to the cytoplasm of small, stellate-shaped interneurons. Together, these observations reveal a developmental transition of ER expression in the PMBS; ER alpha is expressed during early development, ER alpha and ER beta are co-expressed at later developmental times, and only ER beta is expressed in adults. These changes in ER expression and localization suggest that ER alpha and ER beta may play important, but different roles in the formation and function of the PMBS region of the primary somatosensory cortex.

Corticothalamic projections from layer 5 of the vibrissal barrel cortex in the rat

This study bears on the projections of layer 5 cells of the vibrissal sensory cortex to the somatosensory thalamus in rats. Small groups of cells were labeled with biotinylated dextran amine (BDA), and their axonal arborizations were individually reconstructed from horizontal sections counterstained for cytochrome oxidase. Results show that the vast majority ( approximately 95%) of layer 5 axons that innervate the somatosensory thalamus are collaterals of corticofugal fibers that project to the brainstem. The anterior pretectal nucleus, the deep layers of the superior colliculus, and the pontine nuclei are among the structures most often coinnervated. In the thalamus, layer 5 axons terminate exclusively in the dorsal part of the posterior group (Po), where they form clusters of large terminations. Because dorsal Po projects to multiple cortical areas, we sought to determine whether all recipient areas return a layer 5 projection to this part of the thalamus. Additional experiments using fluoro-gold and BDA injections provided evidence that the primary somatosensory area is the sole source of layer 5 projections to dorsal Po but that this thalamic region receives convergent layer 6 projections from the primary and second somatosensory areas and from the motor and insular cortices. These results show that layer 5 projections do not overlap in associative thalamic nuclei, thus defining area-related subdivisions. Furthermore, the coinnervation of brainstem nuclei by layer 5 CT axons suggests that this pathway conveys to the thalamus a copy of the cortical output aimed at brainstem structures.

Corticofugal axons from adjacent 'barrel' columns of rat somatosensory cortex: cortical and thalamic terminal patterns

The cortical representations of the vibrissae of the rat form a matrix in which each whisker has its own area of cortex, called a 'barrel'. The afferent pathways from the periphery travel first to the trigeminal nuclei and thence via the ventroposteromedial thalamus (VPM) to the cortical barrels have been described in detail. We have studied the output from barrels by filling adjacent areas of the primary somatosensory cortex (SI) with either Phaseolus vulgaris leucoagglutinin (PHA-L) or biotinylated dextran amine (BDA) and demonstrating the course and terminations of the axons that arise within the barrel fields. The method not only dramatically illustrates the previously described corticothalamic pathway to VPM but also demonstrates a strict topography in the cortical afferents to the thalamic reticular nucleus (RT). Cells supplying the RT projection are found below the barrels in layer IV. Connections to the posterior thalamus, on the other hand, have no discernible topography and are derived from cortical areas surrounding the barrels. Thus the outputs of these 'septal' areas return to the region from which they receive thalamic input. The corticocortical connections are also visible in the same material. Contralateral cortical connections arise from the cells of the septa between barrels. The projections to secondary somatosensory area (SII) are mirror images of the barrel pattern in SI with rather more overlap but nonetheless a recognisable topography.

Cerebellar Golgi cells in the rat: receptive fields and timing of responses to facial stimulation

Golgi cells are the only elements within the cerebellar cortex that inhibit granule cells. Despite their unique position there is little information on how Golgi cells respond to afferent input. We studied responses of Golgi cells to mechanical stimulation of the face, in Crus I-II of ketamine-xylazine anaesthetized rats. In 41 rats, 87 putative Golgi cells were identified, based on spike characteristics and on location of electrolytic lesions in the granular layer. They displayed a slow firing rhythm at rest (8.4 spikes/s). Most Golgi cells (84%) showed excitatory responses to tactile input. Their receptive fields (RFs) included, in 78%, the entire ipsilateral infraorbital nerve territory, and extended, in 14%, to other trigeminal nerve branches and, in 48%, to the contralateral face. Excitatory responses consisted of multiple, precisely timed (+/- 1 ms) spikes. Most peristimulus time histograms (PSTHs) (69%) showed an early (5-10 ms) and a late (13-26 ms) excitatory component, with each component consisting of a single PSTH peak. In some PSTHs the early component was a double peak (< 4 ms interval). In others, only one, early or late, PSTH peak was observed. The excitatory components were followed by a silent period (28-69 ms latency), the duration of which (13-200 ms) varied with response amplitude. In single cells, response profiles changed with stimulus location. In simultaneously recorded cells, evoked profiles differed for identical stimuli. Differences in RF size between early 'double' and 'single' peaks suggested that they resulted from direct mossy fibre and parallel fibre input, respectively. Late PSTH peaks were assumed to reflect corticopontine activation.

Partial denervation of the whiskerpad in adult mice: altered patterns of metabolic activity in barrel cortex

One hundred days after unilateral C-row nerve transection in the adult mouse whiskerpad, the caudal follicles of row C are reinnervated with approximately 80 % of the original number of axons [Corthésy, M.-E., Bronchti, G. & Welker, E. (1999) Eur. J. Neurosci. , 11, 2835-2846]. To what extent is this reinnervation functional, and how does it interact with the enlargement of the functional representation of neighbouring rows subsequent to the denervation? Using the autoradiographic deoxyglucose method, we studied the whisker representation at the level of the barrel cortex 100 days post lesionem. We stimulated whiskers belonging to the denervated row C, the neighbouring rows B and D, or to all five rows A-E. The deoxyglucose uptake was measured in tangential sections through layer IV. The results indicate that, 100 days post lesionem, whiskers of row C reactivate their cortical barrels. However, (i) the magnitude of this cortical response was reduced; (ii) row C barrels were equivalently activated by the stimulation of the neighbouring rows; and (iii) when all whiskers were stimulated, we observed a significantly reduced deoxyglucose uptake over the representation of nonlesioned whiskers of rows D and E. Therefore, 100 days after the peripheral nerve lesion the reinnervation of the whiskerpad had not restored a normal pattern of activation at the level of the barrel cortex. We propose that this is due to a modified interaction between the representations of the various rows of follicles at the cortical level that does not return to normal.

Differential expression of Fos protein after transection of the rat infraorbital nerve in the trigeminal nucleus caudalis

To determine the effects of nerve injury on Fos expression, temporal and spatial distributions of Fos-positive neurons in the trigeminal nucleus caudalis were examined after tissue injury for isolation of the infraorbital nerve as controls and transection of this nerve as well as noxious chemical stimulation by formalin injection in adult rats. Fos immunoreactivity was markedly elevated in laminae I and II of the only ipsilateral nucleus caudalis 2 h after these surgical procedures and noxious chemical stimulation. The distributions of Fos-positive neurons were restricted rostro-caudally following formalin injection and tissue injury compared to transection of the infraorbital nerve. One day after tissue injury and nerve transection, however, Fos-positive neurons were distributed bilaterally in laminae III and IV extending rostro-caudally and medio-laterally in this nucleus, and this persisted over the 2-week study period. The number of Fos-positive neurons in the side ipsilateral to nerve transection was markedly less than that in the contralateral side whereas positive neurons in the tissue injured rats were distributed symmetrically along the rostro-caudal axis. There was no difference in the contralateral sides between nerve transection and tissue injury groups. The rostro-caudal level showing reduction in Fos expression corresponded roughly to the sites of central termination of the injured nerve in this nucleus, suggesting a role for the primary afferents in the reduction of Fos expression in laminae III and IV neurons of the ipsilateral nucleus caudalis.

Functional development of the vibrissae somatosensory system of the rat: (14C) 2-deoxyglucose metabolic mapping study

Functional development of the rat whisker somatosensory system was studied by using the (14C) 2-deoxyglucose (2DG) metabolic mapping technique. Restrained rat pups had their left mystacial vibrissae stroked for 30 minutes and their brains harvested, sectioned, and autoradiographed from the level of the lower medulla to the frontal cortex. Subjects were tested at postnatal days (PNDs) 0-9 and 21. At birth, all subjects exhibited a significant increase of 2DG uptake in the left spinal trigeminal nuclei, the principal trigeminal sensory nucleus, and a portion of the right ventral posteromedial thalamic nucleus. The primary somatosensory cortex exhibited significant 2DG uptake contralateral to stimulation by PND 6, followed by the secondary somatosensory cortex at PND 7. The pattern of 2DG uptake in the somatosensory cortices became more intense and well defined by PND 9. Given that the somatosensory system develops in an orderly fashion from the periphery to higher brain structures, the present results show that brain structures mediating whisker sensory input are not metabolically active until projections from lower somatosensory centers are established. Neurons become responsive to whisker stimulation in the subcortical structures at birth and in the somatosensory cortex a few days later. This cortical activity follows the organization of the upper tier of thalamocortical fibers into a "barrelfield." Moreover, there is a gradual enhancement in functional activity of the vibrissa neurons at different somatosensory nuclei as rats mature. The present study elucidates the time course of functional development in the rat somatosensory system.

LCBF changes in rat somatosensory cortex during whisker stimulation monitored by dynamic H2 clearance

We evaluated increases in local cerebral blood flow (LCBF) localized to single activated cortical columns by H2 clearance methods. The rat whisker-barrel cortex is a model for cortical function and neural processing in active explorative behaviors. Up to four 30-40 microns Pt wire electrodes were inserted in or near the rat whisker-barrel cortex. Electrode positions were mapped by postmortem histology. H2 was generated electrochemically by constant current from one electrode and detected by one or more other electrodes 300-500 microns away. Changes in LCBF produced inverse changes in PH2. Shifts during steady H2 generation were calibrated against standard H2 inhalation clearance curves at rest and during inhalation of 7.5% CO2 for 1 min for quantitative estimates of LCBF. Contralateral whisker stimulation at 3 Hz, 1 min duration and delivered every 2 min produced the largest increases in LCBF. LCBF responses were detected in approximately 1 s. Stimulation of single whiskers produced the largest responses when an electrode was in the corresponding barrel. These results indicate that increased neural activity in a single cortical column produces blood flow responses primarily in that column.

Trigeminal structure-function relationships: a reevaluation based on long-range staining of a large sample of brainstem a beta fibers

Prior studies suggest that some classes of thickly myelinated (A beta) afferents have distinct morphologies in the trigeminal (V) brainstem complex, and that single fibers have collaterals with different shapes in the four V subnuclei. However, these conclusions are based upon relatively few and incompletely stained fibers and limited statistical rigor. In the present study, 104 fibers were stained more completely with neurobiotin in rats to provide within-fiber intersubnucleus comparisons, and between-fiber intrasubnucleus comparisons, of collaterals associated with a vibrissa, guard hairs, hairy skin, glabrous skin, or oral structures. Collaterals from all functional categories had similar qualitative features and were distributed somatotopically in the transverse plane according to known maps. Fiber categories were not disproportionately represented at particular sites along the brainstem's rostrocaudal axis, although most fibers adhered to an onion-leaf topography in caudalis. Surprisingly few structure-function relationships were revealed by multivariate analysis of variance and post hoc group comparisons, as follows: Arbors were larger in caudalis than in any other subnucleus; collaterals were most numerous in interpolaris; vibrissa afferents had more collaterals than oral and guard hair afferents; and oral fibers had larger arbors than vibrissa or guard hair afferents in subnucleus oralis. Peripheral receptor association and response adaptation rate failed to predict arbor shapes and terminal bouton numbers in any V subnucleus. These data confirm that the locations of V primary afferent arbors are predicted by their receptive fields. However, collateral number and morphology are predicted only to a very limited extent by the V subnucleus and peripheral receptor affiliation--a conclusion that contrasts with those of most prior studies of somatosensory primary afferents.

Whisker stimulation metabolically activates thalamus following cortical transplantation but not following cortical ablation

Local cerebral glucose utilization was assessed during whisker stimulation by 2-deoxyglucose autoradiography. Whisker stimulation increased local cerebral glucose utilization in brainstem, thalamus and whisker sensory cortex in normal rats. Whereas whisker stimulation increased glucose metabolism in brainstem, whisker stimulation failed to increase glucose metabolism in thalamus of rats that had whisker sensory cortex ablated 5 h to five weeks previously. The failure of whisker stimulation to activate thalamus after cortical ablations was probably not due to decreased cortical input to thalamus because whisker stimulation activated thalamus after large cortical tetrodotoxin injections. Failure of whisker stimulation to activate thalamus at early times (5 h and one day) after cortical ablations was not due to thalamic neuronal death, since it takes days to weeks for axotomized thalamic neurons to die. The failure of whisker stimulation to activate thalamus at early times after cortical ablations was likely due to the failure of trigeminal brainstem neurons that project to thalamus to activate axotomized thalamic neurons. This might occur because of synaptic retraction, glial stripping or inhibition of trigeminal brainstem synapses onto thalamic neurons. The thalamic neuronal death that occurs over the days and weeks following cortical ablations was associated with thalamic hypometabolism. This is consistent with the idea that the thalamic neurons die because of the absence of a cortically derived trophic factor, since the excitotoxic thalamic cell death that occurs following cortical kainate injections is associated with thalamic hypermetabolism. The glucose metabolism of parts of the host thalamus was higher and the glucose metabolism in surrounding nuclei lower than the normal side of thalamus in rats that sat quietly and had fetal cortex transplants placed into cavities in whisker sensory cortex five to 16 weeks previously. Whisker stimulation in these subjects activated the contralateral host thalamus and fetal cortical transplants. This was accomplished using a double-label 2-deoxyglucose method to assess brain glucose metabolism in the same rat while it was resting and during whisker stimulation. The high glucose metabolism of parts of host thalamus ipsilateral to the fetal cortical transplants is consistent with prolonged survival of some axotomized thalamic neurons. The finding that whisker stimulation activates portions of host thalamus further suggests that the cortical transplants maintained survival of the host thalamic neurons and that synaptic connections between whisker brainstem and thalamic neurons were functional.

2-DG uptake patterns related to single vibrissae during exploratory behaviors in the hamster trigeminal system

Stimulation of one or several whiskers activates discrete foci throughout the trigeminal (V) neuraxis. These foci contribute to patterns, corresponding to the patterns of vibrissae, that have been directly related to aggregates of cells and axon terminals in the "barrel" cortex. Here, we combine high-resolution, 2-deoxyglucose (2DG) mapping and cytochrome oxidase (CO) staining to determine whether the known pattern of V primary afferent projections is sufficient to deduce the functional activation of their targets during exploratory behavior. Four adult hamsters had all of their large mystacial vibrissae trimmed acutely, except for C3 on the left, and B2 and D4 on the right; in two others, the left C3 and right A1 and E4 whiskers were spared. After fasting overnight, 2DG was injected and the animals behaved freely in the dark for 45 minutes. The brainstem, thalamus, and cortices were sectioned, then processed for both CO staining and 2DG autoradiography. Image-processing microscopy was used to separate the autoradiographic silver grains from the histochemical staining. CO patches were patterned in a whisker-like fashion in the full rostrocaudal extent of V nucleus principalis and in caudal portions of spinal V subnuclei interpolaris and caudalis, but absent in subnucleus oralis. 2DG silver grains were densest above those CO patches in the pattern corresponding to the active whiskers. There were no consistent 2DG foci in subnuclei oralis or rostral caudalis. In these same cases, prominent 2DG labeling was restricted to the appropriate barrels in the contralateral cortex. Only one case, however, displayed a clear and appropriate region of heightened 2DG uptake in contralateral ventroposteromedial thalamus (VPM) and the adjacent part of the reticular thalamic nucleus. Patterns of increased glucose utilization with single whisker stimulation are well matched to the CO patterns that mirror distributions of neurons associated with a vibrissa in the V brainstem complex, thalamus, and cortex. Single whiskers are represented by relatively homogeneous longitudinal columns of 2DG labeling in the V brainstem nuclei. The columns are not continuous through the axial extent of the V brainstem complex; rather, they occur separately within principalis, interpolaris, and caudalis. While whisker columns were consistently labeled in interpolaris and caudalis in all animals, the labeling was increasingly variable in principalis, barrel cortex, and VPM, respectively. This suggests that the behaving animal can and does significantly modulate activity in this major, synaptically secure pathway.

Sensory stimulation induces local cerebral glycogenolysis: demonstration by autoradiography

Brain glycogen stores are localized primarily to glia and undergo continuous utilization and resynthesis. To study the function of glycogen under normal conditions in brain, we developed an autoradiographic method of demonstrating local-glycogen utilization in the awake rat. The method employs labeling of brain glycogen with 14C(3,4)glucose, in situ microwave fixation of brain metabolism, and anhydrous tissue preparation. With this technique, tactile stimulation of the rat face and vibrissae was found to accelerate the utilization of labeled glycogen in brain regions known to receive sensory input from face and vibrissae: the contralateral somatosensory cortex and the ipsilateral trigeminal, sensory and motor nuclei. These findings demonstrate a link between neuronal activity and local glycogen utilization in mammalian brain and suggest that, like other tissues, brain may respond to sudden increases in energy demand in part by rapid glycolytic metabolism of glycogen. As cerebral glycogen is restricted primarily to glia, these observations also support a close coupling of glial energy metabolism with neuronal activity.

Maturation of cerebral oxidative metabolism in the cat: a cytochrome oxidase histochemistry study

The maturation of brain oxidative capacity was studied in kittens, using cytochrome oxidase histochemistry, at different ages throughout development. Optical densitometry values of reacted tissue were obtained for 50 different structures of the brain. In general, most structures reached adult levels of oxidative capacity by 30 days of age with some motor areas (e.g., cerebellum, red nucleus) exhibiting adult values as early as 7 days of age. Thereafter, some structures (e.g., basal ganglia, thalamus) exhibited levels of cytochrome oxidase activity that exceeded adult values for varying periods of time. These findings indicate regional heterogeneity in the maturation of cerebral oxidative capacity. Furthermore, these maturational patterns appear to correlate well with previous observations from anatomical, physiological and neurobehavioral studies.

The rat's postero-orbital sinus hair: II. Normal morphology and the increase in peripheral innervation with adjacent nerve section

The morphology and innervation of the postero-orbital (PO) sinus hair has been studied in normal rats and in adult animals in which an adjacent nerve, the infraorbital nerve, was sectioned on postnatal day 0 or day 7. The normal morphology of the follicle was similar to that of mystacial sinus hairs. However, the normal innervation differed from mystacial follicles in three respects: (1) instead of a separate innervation, the deep vibrissal nerve (DVN) and dermal plexus were supplied by a common follicle and skin nerve, named here the postero-orbital cutaneous nerve, a branch of the zygomaticofacial nerve; (2) the entry of the DVN through the capsule was highly variable; in some cases fascicles entered in close proximity, but in others they were widely distributed around the capsule; and (3) two or three small nerves, called here anastomosing nerves, were found to leave the PO follicle. These arose from the DVN after it had passed through the capsule to the cavernous sinus. The anastomosing nerves passed back through the capsule and ascended on the outer surface of the follicle to join the dermal plexus. Each nerve contained 1-4 myelinated fibres and 11-35 unmyelinated fibres. Infraorbital (IO) nerve section on day 0 caused a 19% (P less than 0.001, n = 8) increase in numbers of fibers to the DVN on the lesioned side. Most of the increase was due to unmyelinated fibres with no significant change in myelinated axons. No change in axon numbers in the DVN occurred after day 7 lesions. Labelling of the mystacial pad and the PO follicle did not result in any double labelling of cells in the trigeminal ganglion, in either normal or lesioned animals, making it improbable that the increased numbers of unmyelinated axons arose from rerouting of infraorbital fibres. It is suggested that the increased innervation of the PO follicle may arise by the rescue of ganglion cells from developmentally programmed cell death.

The rat's postero-orbital sinus hair: I. Brainstem projections and the effect of infraorbital nerve section at different ages

The central terminations, in the trigeminal nucleus, of afferents from the rat's postero-orbital (PO) sinus hair have been investigated with transganglionic transport of horseradish peroxidase (HRP) and succinic dehydrogenase (SDH) histochemistry. The normal pattern of terminations has been compared with that found after section of an adjacent nerve, the infraorbital (IO) nerve, at three ages: neonatal, 1 week old, and adult. The PO afferent fibres have three separate representations in the brainstem--in trigeminal sensory nucleus principalis (Vp) and rostral subnucleus oralis (Vo), in trigeminal subnucleus interpolaris (Vi), and in caudal trigeminal subnucleus caudalis (Vc) and C1 dorsal horn. In coronal sections the areas of terminations were seen as oval patches lying ventrolaterally in Vp, Vo, and Vi and ventromedially in Vc and C1. Following neonatal IO nerve section the terminal areas were approximately doubled in Vp, Vo, and Vi but were unchanged in Vc and C1. IO nerve section at day 7 also caused a significant, though smaller (1.4x compared with 2.0x), increase in the terminal areas in the rostral three nuclei, without changing Vc and C1. However, no significant change in area occurred after adult IO nerve section. SDH histochemistry at 3 to 4 weeks of age showed patches of terminals on both normal and lesioned sides consistent with those seen after HRP. Previous studies have reported increased functional representation of surrounding intact skin regions, including the PO sinus hairs, after neonatal but not adult, IO nerve section. The present results show that there are concomitant anatomical changes. Like the functional results, the extent of the anatomical changes are dependent on the maturity of the rat when lesioned.

Central projections of primary sensory neurons innervating different parts of the vibrissae follicles and intervibrissal skin on the mystacial pad of the rat

The cell bodies and central projections of neurons innervating the vibrissae follicles and adjacent skin in the rat were investigated by retrograde and transganglionic transport of HRP. The cell bodies of neurons innervating the vibrissa follicle via the deep vibrissa nerve (DVN) were the largest, followed by those innervating the follicle via the superficial vibrissa nerve (SVN). The smallest cell bodies were those innervating the intervibrissal skin. The DVN neurons terminated centrally as an almost uninterrupted column through the trigeminal sensory nuclear complex. The DVN projections to nucleus caudalis and C1 dorsal horn were entirely restricted to laminae III, IV, and V. Besides the projections to lamina V, the DVN projections were strictly localized somatotopically at all levels replicating the peripheral organization of the vibrissae. The SVNs projected sparsely to midlevels of the main sensory nucleus but not to nuclei oralis and interpolaris. The main SVN projections appeared in laminae I-III of nucleus caudalis. In addition, a small projection to lamina V was observed. The projections to laminae II and III were organized mediolaterally in a similar way as the DVN projections; those to laminae I and V were less restricted. The intervibrissal skin neurons projected sparsely to the caudal main sensory nucleus and to the border between nuclei oralis and interpolaris. The projections to nucleus caudalis were restricted to laminae I-III and V and were organized in a similar way as the SVN projections.

Development of whisker representation in the cortex of the tammar wallaby Macropus eugenii

The somatosensory cortex associated with the whiskers has been studied in adult tammar wallabies (Macropus eugenii) and in pouch young from 60-120 days of pouch life. The time course of anatomical changes examined with succinic dehydrogenase (SDH) histochemistry and Nissl staining has been correlated with the maturation of electrically evoked cortical responses to stimulation of the whisker follicles. The earliest signs of aggregates of SDH reaction product in layer IV of the cortex were seen at 85 days, coincident with the first recordings of an immature cortical evoked potential. Aggregates, in a pattern corresponding to that of the facial whiskers, were most clearly seen from 90-140 days. At later stages, and in the adult, they were present but their arrangement was less clearly seen. By 186 days the electrical activity resembled the mature pattern. Patches of SDH activity in layer IV were not associated with changes in soma density characteristic of true barrels.

Areal distributions of cortical neurons projecting to different levels of the caudal brain stem and spinal cord in rats

Distributions of corticospinal and corticobulbar neurons were revealed by tetramethylbenzidine (TMB) processing after injections of wheatgerm agglutinin conjugated to horseradish peroxidase (WGA:HRP) into the cervical or lumbar enlargements of the spinal cord, or medullary or pontine levels of the brain stem. Sections reacted for cytochrome oxidase (CO) allowed patterns of labeled neurons to be related to the details of the body surface map in the first somatosensory cortical area (SI). The results indicate that a number of cortical areas project to these subcortical levels: (1) Projection neurons in granular SI formed a clear somatotopic pattern. The hindpaw region projected to the lumbar enlargement, the forepaw region to the cervical enlargement, the whisker pad field to the lower medulla, and the more rostral face region to more rostral brain stem levels. (2) Each zone of labeled neurons in SI extended into adjacent dysgranular somatosensory cortex, forming a second somatotopic pattern of projection neurons. (3) A somatotopic pattern of projection neurons in primary motor cortex (MI) paralleled SI in mediolateral sequence corresponding to the hindlimb, forelimb, and face. (4) A weak somatotopic pattern of projection neurons was suggested in medial agranular cortex (Agm), indicating a premotor field with a rostromedial-to-caudolateral representation of hindlimb, forelimb, and face. (5) A somatotopic pattern of projection neurons representing the foot to face in a mediolateral sequence was observed in medial parietal cortex (PM) located between SI and area 17. (6) In the second somatosensory cortical area (SII), neurons projecting to the brain stem were immediately adjacent caudolaterally to the barrel field of SI, whereas neurons projecting to the upper spinal cord were more lateral. No projection neurons in this region were labeled by the injections in the lower spinal cord. (7) Other foci of projection neurons for the face and forelimb were located rostral to SII, providing evidence for a parietal ventral area (PV) in perirhinal cortex (PR) lateral to SI, and in cortex between SII and PM. None of these regions, which may be higher-order somatosensory areas, contained labeled neurons after injections in the lower spinal cord. Thus, more cortical fields directly influence brain stem and spinal cord levels related to sensory and motor functions of the face and forepaw than the hindlimb. The termination patterns of corticospinal and corticobulbar projections were studied in other rats with injections of WGA:HRP in SI.(ABSTRACT TRUNCATED AT 400 WORDS)

Evidence for a cholinergic mechanism of "learned" changes in the responses of barrel field neurons of the awake and undrugged rat

Due to its functional importance and its large and highly differentiated central projections, the vibrissal system of rodents is a prime object for the study of sensory plasticity, especially at the cortical level: the representation of vibrissae in the "barrel field", a part of the somatic cortex, is exceptionally precise and is susceptible to experience-induced changes. In a previous series of experiments, we found that a sensory-sensory conditioning procedure, pairing two vibrissal stimulations, produces significant changes in responses of single neurons of the barrel field in the chronic awake and undrugged rat: (1) the appearance of an excitatory response to a stimulus that was ineffective before pairing ("conditioned response"); (2) the modifications of pre-existing responses consisting of the suppression of afferent inhibition and the appearance of long-latency excitatory components. We report here that the micro-iontophoretic application of atropine abolishes "conditioned responses" and restores afferent inhibition. Acetylcholine facilitates an enlargement of the receptive field and induces a sustained mode of discharge to stimuli. These data provide a new and direct support to the hypothesis that cholinergic mechanisms are involved in the sensory cortex plasticity.

Trigeminal nerve section induces Fos-like immunoreactivity (FLI) in brainstem and decreases FLI in sensory cortex

Transecting the infraorbital nerve to the rat whiskers induced Fos-like immunoreactivity (FLI) in lamina I and II neuronal nuclei of the spinal trigeminal nucleus pars caudalis (Sp5c). The Fos-like immunostaining persisted for several weeks. The prolonged expression of FLI in Sp5c could be related to persistent activity in the sectioned nerve, or to trophic effects of injured ganglion neurons on brainstem cells. We postulate that Fos and related proteins may be involved in mediating alterations in gene expression associated with relatively long-term CNS adaptations to peripheral nerve injuries. Surprisingly, FLI decreased in contralateral sensory cortex, mainly in layers 2, 3 and 6, up to several days after the lesion. These decreases of cortical FLI may be due to decreased sensory neuronal activity, and/or to reducing the trophic influence of thalamic inputs on cortical neurons.