Differential susceptibility to ageing of rat preganglionic neurones projecting to the major pelvic ganglion and of their afferent inputs

We have analysed age-related changes in the morphology of preganglionic neurones in the lumbosacral spinal cord, labelled following injection of retrograde tracers into the major pelvic ganglion of young adult and aged male rats. We have also examined changes in neurotransmitter-characterised spinal afferent inputs to these neurones, or to the nuclei in which they lie, using light and electron microscope immunohistochemistry. In previous investigations of the major pelvic ganglion, the sympathetic, but not parasympathetic, postganglionic neurones were seen to exhibit age-related changes and the same pattern is seen in the preganglionic neurones. This included an apparent reduction in the numbers of sympathetic preganglionic neurones, and a reduction in the length of their dendrites and the complexity of their branches. Ultrastructural immunohistochemical studies described here reveal significant reductions in the area of synaptic contact made by glutamate-immunoreactive boutons onto the dendrites of sympathetic (but not parasympathetic) preganglionic neurones, while contacts from boutons immunoreactive for glycine or gamma-aminobutyric acid (GABA) were unchanged. There is also a reduction in synaptic contacts received by sympathetic somata from boutons immunoreactive for none of these amino acids. Serotonin-immunoreactive terminals are closely associated with preganglionic autonomic neurones, and these are reduced in number in sympathetic, but not parasympathetic, spinal nuclei of aged rats. However, serial section electron microscopy has so far failed to demonstrate conventional synaptic contacts between serotonergic terminals and the dendrites or somata of the preganglionic autonomic neurones. In young animals, axon terminals immunoreactive for thyrotropin-releasing hormone (TRH) are abundant in all spinal laminae including area X, but in aged animals, such terminals are significantly reduced in number in regions containing preganglionic sympathetic, but not parasympathetic, neurones. These results indicate that the sympathetic preganglionic neuron populations that project to the major pelvic ganglion, and the spinal inputs they receive, show a number of degenerative changes in aged rats which are not seen parasympathetic preganglionic neuronal populations.

Deafferentation-induced abnormal neurofilament phosphorylation in red nucleus neurones

Hippocampal deafferentation has been proposed as a pathogenetic mechanism for neurofibrillary tangle (NFT) formation in human mesolimbocortical dementia. We previously developed a rodent model of hippocampal deafferentation involving bilateral destructive lesions of the ventrotegmental area (VTA), septum of the medial forebrain and entorhinal cortex combined with pharmacological inhibition of serotonin 5-HT2 and dopamine D1 receptors. Unexpectedly, we observed an alteration in phosphorylated neurofilament protein immunoreactivity and argyrophilia in magnocellular neurones of the red nucleus. Here, we determined the neuroanatomical, pharmacological and temporal requirements for this effect on red nucleus neurones. We found that abnormal phosphorylation and argyrophilia were critically dependent on bilateral destruction of the VTA and antagonism of 5-HT2 receptors. Although extensive neurofilament hyperphosphorylation and argyrophilia were observed in red nucleus magnocellular neurones within nine days of treatment, no NFTs were formed and these effects were transitory. Resolution of these cytoskeletal abnormalities was accompanied by increased expression of the calcium binding protein, parvalbumin, suggesting that alterations in intraneuronal calcium levels may modify the deafferentation response.

Neurotrophin-4 deficient mice have a loss of vagal intraganglionic mechanoreceptors from the small intestine and a disruption of short-term satiety

Intraganglionic laminar endings (IGLEs) and intramuscular arrays (IMAs) are the two putative mechanoreceptors that the vagus nerve supplies to gastrointestinal smooth muscle. To examine whether neurotrophin-4 (NT-4)-deficient mice, which have only 45% of the normal number of nodose ganglion neurons, exhibit selective losses of these endings and potentially provide a model for assessing their functional roles, we inventoried IGLEs and IMAs in the gut wall. Vagal afferents were labeled by nodose ganglion injections of wheat germ agglutinin-horseradish peroxidase, and a standardized sampling protocol was used to map the terminals in the stomach, duodenum, and ileum. NT-4 mutants had a substantial organ-specific reduction of IGLEs; whereas the morphologies and densities of both IGLEs and IMAs in the stomach were similar to wild-type patterns, IGLEs were largely absent in the small intestine (90 and 81% losses in duodenum and ileum, respectively). Meal pattern analyses revealed that NT-4 mutants had increased meal durations with solid food and increased meal sizes with liquid food. However, daily total food intake and body weight remained normal because of compensatory changes in other meal parameters. These findings indicate that NT-4 knock-out mice have a selective vagal afferent loss and suggest that intestinal IGLEs (1) may participate in short-term satiety, probably by conveying feedback about intestinal distension or transit to the brain, (2) are not essential for long-term control of feeding and body weight, and (3) play different roles in regulation of solid and liquid diet intake.

Contralateral treatment with lidocaine reduces spinal neuronal activity in mononeuropathic rats

In anaesthetised and paralysed rats with chronic constriction of the sciatic nerve, the effects of subcutaneous contralateral lidocaine (100 microl) on the activity of lumbar (L(4)-L(5)) wide dynamic range neurons ipsilateral to the constriction have been investigated. The results show reduction of the spontaneous hyperactivity for 60 min; suppression or reduction of the responses to contralateral noxious stimulation for 60 min; lack of effect on the responses to ipsilateral noxious stimulation, except for the afterdischarge duration, reduced for 60 min. The finding that the altered neuronal activity following peripheral nerve injury associated to behavioural signs of neuropathic pain, can be reduced by contralateral treatment, may provide further suggestions to neuropathic pain mechanisms and management.

Plasticity of the human motor cortex and recovery from stroke

By a variety of mechanisms, the human brain is constantly undergoing plastic changes. Plasticity can be studied with phenomena such as peripheral deafferentation and motor learning. Spontaneous recovery from stroke in the chronic stage likely comes about because of plasticity, and the best recovery seems to result from reorganization in the damaged hemisphere. Knowledge about the physiology of brain plasticity has led to the development of new techniques for rehabilitation.

Somatotopic reorganization in the brainstem and thalamus following peripheral nerve injury in adult primates

Injury-induced reorganization of central somatotopic maps is a phenomenon that has proven to be useful for elucidating the mechanisms and time course of neural plasticity. To date, the overwhelming majority of this line of research has focused on such plastic events in cortical areas, at the expense of subcortical structures. In this study, we used multi-unit electrophysiological recording techniques to assess the somatotopic organization of brainstem and thalamic areas following chronic survival from paired median and ulnar nerve section in adult squirrel monkeys. We report that the extent of cutaneously-driven reorganization in both the cuneate nucleus of the brainstem and the ventroposterior lateral nucleus of the thalamus is comparable to that previously documented for area 3b of cortex. These observations are consistent with those previously reported in thalamus, and are unique for brainstem.

A-fibres sprouting from lamina I into lamina II of spinal dorsal horn after peripheral nerve injury in rats

We have examined the labeling pattern in the spinal dorsal horn by an intra-sciatic nerve injection of cholera toxin B subunit conjugated horseradish peroxidase (HRP) after transection of the posterior cutaneous nerve and inferior gluteal nerve, and found that the cholera toxin B subunit conjugated HRP labeling in lamina I was expanding into lamina II and there was a shrinking gap between lamina I and lamina III. This result suggests that A-fibre sprouting arise after peripheral nerve injury, but mainly from small calibre Adelta-fibres which terminate in lamina I.

Topographic architecture of stress-related pathways targeting the noradrenergic locus coeruleus

Peripheral sympathetic nerves and brainstem noradrenergic neurons of the locus coeruleus (LC) respond in parallel to a variety of stress-related stimuli which results in norepinephrine release both peripherally and centrally. Elucidation of central pathways subserving modulation of LC neurons point to extranuclear noradrenergic dendrites of LC somata that extend into peri-coerulear areas as a major target of afferents that participate in behavioral and physiological responses to stress. Anterograde tract tracing combined with immunoelectron microscopic detection of the catecholamine synthesizing enzyme tyrosine hydroxylase (TH) has demonstrated that the nucleus of the solitary tract (NTS) and the ventrolateral aspect of the periaqueductal gray (PAG), regions that participate in coordinating autonomic and motor behavior in response to stress, preferentially target the rostral ventromedial aspect of the peri-LC. In contrast, limbic forebrain afferents including the central nucleus of the amygdala (CNA) and the bed nucleus of the stria terminalis (BNST), regions that coordinate emotional responses to external stressors, provide direct synaptic input to noradrenergic dendrites that extend into rostral dorsolateral peri-coerulear areas. Neurochemical identification of transmitter systems impinging on LC indicate that the CNA provides corticotropin-releasing factor (CRF), a peptide essential for integrated physiological responses to stress, to the dorsolateral LC. Endogenous opioid peptides that originate from medullary sources, however, target primarily the "core" of the LC. Our physiological data suggest that stress engages CRF and opioid afferents to the LC, which have opposing influences on this noradrenergic system. The balance between opioid and CRF influences acting in the LC may, in part, maintain the balance of active and passive coping behaviors in response to stress. Understanding the afferent and neurochemical organization of the LC may help elucidate adaptations in neural circuits associated with stress which impact on central noradrenergic function.

Functional recovery after brain lesion--contralateral neuromodulation: an fMRI study

Behavioral recovery takes place even after permanent damage to the entire brain region normally controlling sensorimotor hind limb function in the rat. In our study, 2 weeks after full behavioral recovery from an experimental unilateral permanent brain damage, the topographic representation of the previous paretic hindlimb was investigated by fMRI. The analysis showed that during electrical stimulation of the previously paretic hindlimb, two normally inactive brain regions were now being activated. One region was the non-damaged contralateral sensori-motor cortex and the other region was located lateral to the lesion. These results suggest that behavioral recovery can be explained by functional reorganization and neuromodulation of the brain.

Susceptibility to kindling and neuronal connections of the anterior claustrum

The claustrum has been implicated in the kindling of generalized seizures from limbic sites. We examined the susceptibility of the anterior claustrum itself to kindling and correlated this with an anatomical investigation of its afferent and efferent connections. Electrical stimulation of the anterior claustrum resulted in a pattern of rapid kindling with two distinct phases. Early kindling involved extremely rapid progression to bilaterally generalized seizures of short duration. With repeated daily kindling stimulations, early-phase generalized seizures abruptly became more elaborate and prolonged, resembling limbic-type seizures as triggered from the amygdala. We suggest that the rapid rate of kindling from the anterior claustrum is an indication that the claustrum is functionally close to the mechanisms of seizure generalization. In support of our hypothesis, we found significant afferent, efferent, and often reciprocal connections between the anterior claustrum and areas that have been implicated in the generation of generalized seizures, including frontal and motor cortex, limbic cortex, amygdala, and endopiriform nucleus. Additional connections were found with various other structures, including olfactory areas, nucleus accumbens, midline thalamus, and brainstem nuclei including the substantia nigra and the dorsal raphe nucleus. The anatomical connections of the anterior claustrum are consistent with its very high susceptibility to kindling and support the view that the claustrum is part of a forebrain network of structures participating in the generalization of seizures.

Gastroprotective and vasodilatory effects of epidermal growth factor: the role of sensory afferent neurons

Epidermal growth factor (EGF) has been shown to exert gastric hyperemic and gastroprotective effects via capsaicin-sensitive afferent neurons, including the release of calcitonin gene-related peptide (CGRP). We examined the protective and vasodilatory effects of EGF on the gastric mucosa and its interaction with sensory nerves, CGRP, and nitric oxide (NO) in anesthetized rats. Intragastric EGF (10 or 30 microg) significantly reduced gastric mucosal lesions induced by intragastric 60% ethanol (50.6% by 10 microg EGF and 70.0% by 30 microg EGF). The protective effect of EGF was significantly inhibited by pretreatment with capsaicin desensitization, human CGRP1 antagonist hCGRP-(8-37), or N(omega)-nitro-L-arginine methyl ester (L-NAME). Intravital microscopy showed that topically applied EGF (10-1,000 microg/ml) dilated the gastric mucosal arterioles dose dependently and that this vasodilatory effect was significantly inhibited by equivalent pretreatments. These findings suggest that EGF plays a protective role against ethanol-induced gastric mucosal injury, possibly by dilating the gastric mucosal arterioles via capsaicin-sensitive afferent neurons involving CGRP and NO mechanisms.

Reduction in inflammation-induced sensitization of dorsal horn neurons by transcutaneous electrical nerve stimulation in anesthetized rats

Transcutaneous electrical nerve stimulation (TENS) is utilized to treat a variety of painful conditions. Inflamed animals present with an increased response to noxious stimuli, i.e., hyperalgesia, at the site of injury (primary hyperalgesia) and outside the site of injury (secondary hyperalgesia). Further, following acute inflammation, dorsal horn neurons show an increased responsiveness to peripherally applied stimuli, which has been termed sensitization. Previous studies demonstrate a reduction in dorsal horn neuron activity following TENS treatment in normal animals and a reduction in primary and secondary hyperalgesia in acutely inflamed animals. The purpose of this study was to examine the effects of TENS on dorsal horn neurons sensitized by acute inflammation. Extracellular recordings from wide dynamic range (WDR), high threshold (HT) and low threshold (LT) dorsal horn neurons in anesthetized rats were assessed for spontaneous activity, responses to innocuous and noxious mechanical stimulation and receptive field size. Responses were measured before and 3 h after induction of inflammation, and immediately and 1 h after application of either high (100 Hz) or low (4 Hz) frequency TENS (motor intensity, pulse duration = 100 microseconds). TENS was applied to the inflamed paw to encompass the receptive field of the neuron for 20 min. WDR and HT dorsal horn neurons sensitized to mechanical stimulation after induction of inflammation. Application of either high or low frequency TENS to the inflamed paw reduced both innocuous and noxious evoked responses of WDR and HT dorsal horn neurons immediately and 1 h after treatment with TENS. Comparison of responses after TENS with baseline responses showed that the evoked responses in the majority of WDR and HT cells returned to or fell below baseline responses. TENS had no effect on responses of LT neurons. In summary, central neuron sensitization is reduced by TENS and may underlie the reduction in hyperalgesia observed after treatment with TENS.

Visceral pain

Visceral pain, although different from somatic pain in several important features, is not as widely researched and consequently our knowledge of neurophysiologic mechanisms as well as clinical management of visceral pain states remains unsatisfactory. Several recent studies have employed different visceral pain animal models to provide insight into the peripheral and central nervous system mechanisms underlying pain originating from the urinary bladder, ureter, and gastrointestinal tract. The effects of opioid and nonopioid drugs in these models have also been evaluated and are reviewed in this article. The importance of anatomic pathways relaying pain sensation in the central nervous system, particularly the newly described dorsal column pathway, is also discussed. In human subjects, new techniques like positron emission tomography are now being used to better understand visceral pain perception. Such findings deriving from basic animal research and human studies summarized in the present overview lead to a better understanding of visceral pain states and may be helpful in developing better treatment strategies to combat visceral pain states in the clinical setting.

Compensatory responses in the aging hippocampal serotonergic system following neurodegenerative injury with 5,7-dihydroxytryptamine

This study utilized a multidisciplinary approach to examine injury-induced compensatory responses in the aging hippocampal serotonin transporter (5-HTT), a membrane protein implicated in a variety of neurodegenerative disorders. Age-dependent cellular, anatomical, and physiological changes of the 5-HTT were evaluated in female Fischer 344 rats (2 and 17 months) following denervation of the serotonergic afferents (fimbria-fornix and cingulum bundle) to the dorsal hippocampus using the neurotoxicant 5,7-dihydroxytryptamine (5,7-DHT). Seven days following 5,7-DHT administration, a uniform loss of the hippocampal 5-HTT immunoreactivity was observed in both age groups. However, at 21 days 5-HTT immunoreactivity in young 5,7-DHT-treated animals was similar to control levels, indicative of recovery, while older animals exposed to 5,7-DHT did not show recovery of hippocampal 5-HTT expression. 5-HTT binding site density, as determined by quantitative autoradiography ([3H]citalopram), supported the immunohistochemical results by demonstrating a recovery of 5-HTT binding sites in young, but not old animals, at 21 days following the lesion (P < 0.001). Furthermore, cellular electrophysiological function of hippocampal CA1 pyramidal neurons in 3- and 18-month-old F344 rats at 21 days following 5,7-DHT or vehicle treatment were assessed using in vivo microiontophoretic application of serotonin (5-HT). Independent of changes in sensitivity to the inhibitory effects of 5-HT application, the time to recovery of cell firing following application of 5-HT was significantly increased in the 18-month 5,7-DHT group compared to the 18-month vehicle and 3-month 5,7-DHT groups (60 and 59% increases, respectively; P < 0.05). Overall, these series of studies comprise a model which can be used to identify cellular events underlying both the formation of injury-induced compensatory processes in younger animals and the lack thereof with advancing age.

Biochemical evidence of crossed cerebellar diaschisis in terms of nitric oxide indicators and lipid peroxidation products in rats during focal cerebral ischemia

OBJECTIVES

Cerebral hypoperfusion in the contralateral cerebellar hemisphere after stroke is interpreted as a functional and metabolic depression, possibly caused by a loss of excitatory afferent inputs on the corticopontocerebellar pathway terminating in the cerebellar gray matter. This phenomenon is defined as crossed cerebellar diaschisis and can be diagnosed clinically by positron emission tomography, single-photon emission computed tomography, brain magnetic resonance imaging and electroencephalography in terms of regional cerebral blood flow or metabolic rate of oxygen measurements.

MATERIALS AND METHODS

In the present study, nitric oxide indicators (nitrite and cyclic guanosine monophosphate) and lipid peroxidation products (malondialdehyde and conjugated dienes) were measured in rat cerebral cortices and cerebella after permanent right middle cerebral artery occlusion in order to assess the crossed cerebellar diaschisis.

RESULTS

Nitrite values in ipsilateral cortex were significantly higher than those in contralateral cortex at 10 (P < 0.001) and 60 (P < 0.05) min of ischemia but no significant changes were observed in both cerebellum compared to the 0 min values. In both cerebral cortex and cerebellum cGMP levels at 10 and 60 min were significantly increased (P < 0.001). This increase was marked in ipsilateral cortex and contralateral cerebellum when compared with opposite cortex and cerebellum (P < 0.001). MDA values in ipsilateral cortex were significantly higher than those in contralateral cortex at 60 min of ischemia (P < 0.05). Contralateral cerebellar MDA values were found significantly higher than those in ipsilateral cerebellum at 0 (P<0.001) and 60 (P < 0.05) min of ischemia. In ipsilateral cortex, conjugated diene values at 0, 10, 60 min of ischemia were higher than those in contralateral cortex. On the other hand 0, 10, 60 min conjugated diene levels in contralateral cerebellum were significantly higher than those in ipsilateral cerebellum (P < 0.001).

CONCLUSION

These findings support the interruption of the corticopontocerebellar tract as the mechanism of the crossed cerebellar diaschisis.

Confocal microscopic analysis reveals sprouting of primary afferent fibres in rat dorsal horn after spinal cord injury

Following high thoracic spinal cord transection (SCT) in rats, abnormal changes in arterial pressure in response to sensory stimulation (autonomic dysreflexia) are correlated with changes in neural circuitry in the injured spinal cord. Anterograde transport of wheat germ agglutinin conjugated to Texas Red (WGATR) and confocal microscopy were used to characterize the increased arbourization of Adelta and Abeta fibre populations in laminae III-V of the dorsal horn. In cord-injured animals, significantly greater areas of WGATR-labeled fibres were found in the deeper laminae of the dorsal horn than in control rats. This increased area likely reflects sprouting of the Adelta, Abeta, and possibly C fibre populations. The time course of sprouting matches the onset of autonomic dysreflexia, indicating a possible functional correlation between the two phenomena.

Corneal infection of herpes simplex virus type 2--induced neuronal apoptosis in the brain stem of mice with expression of tumor suppressor gene (p53) and transcription factors

To understand the mechanism of neuronal apoptosis induced by herpes simplex virus (HSV) infection in vivo, the distribution of viral antigen, the appearance of apoptotic bodies, and the expressions of the tumor suppressor gene p53 and several transcription factors such as c-fos, c-jun and NF-kappaB were examined immunohistochemically and histopathologically after corneal infection of mice with HSV type 2 strain 186. Five days after HSV infection, viral antigen was diffusely detected in the corneal epithelium, the trigeminal ganglion and the pars caudalis of the spinal trigeminal nucleus. Neuronal apoptosis was observed in the brain stem ipsilateral to the HSV-infected side with the immunoreactivities of c-fos, c-jun, NF-kappaB and p53. Dual-labeling immunohistochemical studies revealed that almost all of the viral antigen-positive neurons and glia in the brain stem also showed p53 immunoreactivity. On the other hand, no neuronal apoptosis but only with the expression of c-jun was found in the trigeminal ganglion. Our results suggest that the different expression of transcription factors between the brain stem and the trigeminal ganglion may influence the neuronal apoptosis induced by HSV infection.

Interruption of supramammillohippocampal afferents prevents the genesis and spread of limbic seizures in the hippocampus via a disinhibition mechanism

In this study we describe the preventive effect of interruption of the supramammillohippocampal afferents on the Fos expression in the forebrain and epileptic discharges in the hippocampal electroencephalogram in rat model of kainic acid-induced limbic seizure. Little was known about the contribution of different degrees of neural activity of hippocampal principal cells to the genesis and spread of limbic seizures in the forebrain structures. Following kainic acid injection to the amygdala with or without concurrent injection of muscimol to the supramammillary nucleus, behavioral changes and electroencephalograms were observed in freely moving rats. The animals were processed for Fos immunocytochemical analysis at several time points. The latest expression of Fos at 2h was seen in hippocampal CA1-CA3, ventrolateral thalamic nuclei and mediodorsal caudate putamen, while the early Fos expression at 0.5h was seen in the piriform, entorhinal and other cortices, the thalamic midline nuclei and hypothalamic nuclei. Muscimol injection to the supramammillary nucleus prevented Fos expression in the CA1-CA3 region and reduced that in the forebrain regions with the latest Fos expression, but did not affect Fos expression in other forebrain regions with early Fos expression. This treatment also eliminated epileptic discharges and attenuated all waves in hippocampus. These findings indicate that an acute interruption of the facilitatory hypothalamic afferents by intrasupramammillary injection of muscimol may cause the inactivation of the disinhibition mechanism for hippocampal throughput at the dentate gyrus, resulting in the blockade of the genesis and spread of limbic seizures in the hippocampus.

Up-regulation of pituitary adenylate cyclase-activating polypeptide in urinary bladder pathways after chronic cystitis

These studies examined changes in the expression of pituitary adenylate cyclase-activating polypeptide (PACAP) in micturition reflex pathways after chronic cystitis induced by cyclophosphamide (CYP). In control Wistar rats, PACAP immunoreactivity was expressed in fibers in the superficial dorsal horn at all segmental levels examined (L1, L2, and L4-S1). Bladder afferent cells (40-45%) in the dorsal root ganglia (DRG; L1, L2, L6, and S1) from control animals also exhibited PACAP immunoreactivity. After chronic, CYP-induced cystitis, PACAP immunoreactivity increased dramatically in spinal segments and DRG (L1, L2, L6, and S1) involved in micturition reflexes. The density of PACAP immunoreactivity was increased in the superficial laminae (I-II) of the L1, L2, L6, and S1 spinal segments. No changes in PACAP immunoreactivity were observed in the L4-L5 segments. Staining also increased dramatically in a fiber bundle extending ventrally from Lissauer's tract in lamina I along the lateral edge of the dorsal horn to the sacral parasympathetic nucleus in the L6-S1 spinal segments (lateral collateral pathway of Lissauer). After chronic cystitis, PACAP immunoreactivity in cells in the L1, L2, L6, and S1 DRG increased significantly (P </= 0.0001), and the percentage of bladder afferent cells expressing PACAP immunoreactivity also increased significantly (P </= 0.0001; 70-85%). No changes were observed in the L3-L5 DRG. These studies suggest that the neuropeptide, PACAP, may play a role in urinary bladder afferent pathways after visceral (urinary bladder) inflammation. Changes in PACAP expression after cystitis may play a role in altered visceral sensation (allodynia) and/or urinary bladder hyperreflexia in the clinical syndrome, interstitial cystitis.

Differential effects of trigeminal tractotomy on Adelta- and C-fiber-mediated nociceptive responses

In this study we have tested in the rat, whether trigeminal tractotomy, which deprives the spinal trigeminal nucleus caudalis (Sp5C) of its trigeminal inputs, affected differentially nociceptive responses mediated by C- vs. Adelta-nociceptors from oral and perioral regions. Tractotomy had no effect on the threshold of the jaw opening reflex, induced by incisive pulp stimulation (Adelta-fiber-mediated), but blocked the formalin response (mainly C-fiber-mediated). These results suggest that nociceptive responses mediated by trigeminal C-fibers completely depend on the integrity of the Sp5C, while intraoral sensations triggered Adelta-fibers (especially of dental origin) are primarily processed in the rostral part of the spinal trigeminal nucleus.

Calcitonin gene-related peptide and substance P immunoreactivity in rat trigeminal ganglia and brainstem following adjuvant-induced inflammation of the temporomandibular joint

The immunoreactivity of two inflammatory mediators, calcitonin gene-related peptide (CGRP) and substance P, was measured in the trigeminal ganglia and brainstem to characterize an adjuvant-induced inflammation within the rat temporomandibular joint at various acute (6, 24 and 48 h) and intermediate (10 day) time intervals. Concentrations of adjuvant-related neuropeptides were compared to those in both contralateral vehicle-related tissues and non-injected controls. By 6 h, CGRP immunoreactivity in the trigeminal ganglia was significantly above that in contralateral vehicle-injected tissue. The CGRP had decreased at each of the following time-points, but remained significantly elevated at 10 days. Substance P in the ganglion on the injected side was significantly increased for all four time periods. In brainstem subnucleus caudalis, CGRP was significantly increased for all four time periods. Substance P immunoreactivity in the subnucleus caudalis was significantly increased for the initial three time periods, but by day 10 had been reduced to that of the control. These data show that the pattern of changes in neuropeptides following the induction of inflammation is different between substance P and CGRP. Moreover, the pattern of change varies between the brainstem and the trigeminal ganglion. This suggests that the two neuropeptides may have different roles in the inflammatory process, and that this process may be modulated by different mechanisms at the brainstem and ganglion.

Apoptosis and impaired axonal regeneration of sensory neurons after nerve crush in diabetic rats

We investigated the possible induction of apoptosis of dorsal root ganglion (DRG) neurons and the defect of nerve regeneration after crush injury with reference to the JNK/c-jun and cAMP pathway in streptozocin-induced diabetic rats. In addition, the effects of a PGE1 analogue were tested in diabetic rats. At day 0 (before axonal injury), no TUNEL-positive DRG neurons were observed in any group. From day 1 to 7 after axonal injury, TUNEL-positive DRG neurons were seen in diabetic rats, but not in non-diabetic or PGE1-treated diabetic rats. The regeneration distance at day 7 after crush injury was shorter in diabetic rats than in the other groups of rats. The time course of JNK/c-jun phosphorylation did not parallel apoptosis. At day 7, the cAMP content of DRG was higher than that at day 0 in non-diabetic and PGE1-treated rats, whereas it was not increased after 7 days in diabetic rats. These results indicate that in diabetic rats apoptosis of DRG neurons is induced by axonal injury independently of the JNK/c-jun and cAMP pathway and that PGE1 rescues DRG neurons from apoptosis and improves axonal regeneration in diabetic rats.

Injury to dorsal root ganglia alters innervation of spinal cord dorsal horn lamina involved in nociception

STUDY DESIGN

A study of the relation between the development of mechanical allodynia and the reorganization of primary afferent terminals in the sensory lamina of the rat spinal cord dorsal horn after partial dorsal root ganglion injury in rats.

OBJECTIVES

To investigate the pathologic mechanisms of mechanical allodynia after partial dorsal root ganglion injury.

SUMMARY OF BACKGROUND DATA

After experimental peripheral nerve injury causing neuropathic pain, myelinated afferent fibers sprout into lamina II of the dorsal horn. This lamina is associated with nociceptive-specific neurons that generally are not stimulated by myelinated fiber input from mechanical receptors. These morphologic changes are suggested to have significance in the pathogenesis of chronic mechanical allodynia, although it is not known whether this kind of morphologic change occurs after dorsal root ganglion injury.

METHODS

After partial dorsal root ganglion crush injury, the mechanical force causing footpad withdrawal was measured with von Frey hairs, and myelinated primary afferents were labeled with cholera toxin B subunit horseradish peroxidase, a selective myelinated fiber tracer that identifies transganglionic synapses.

RESULTS

After partial dorsal root ganglion injury, mechanical allodynia developed in the corresponding footpad within 3 days and persisted throughout the experimental period. At 2 and 4 weeks after the injury, B subunit horseradish peroxidase-positive fibers, presumably myelinated afferents, were observed to be sprouting into lamina II of the dorsal horn on the injured side, but not on the contralateral control side.

CONCLUSIONS

Morphologic change in spinal cord dorsal horn lamina II occurs after partial dorsal root ganglion injury. This change may have significance in the pathogenesis of chronic mechanical allodynia after partial dorsal root ganglion injury.

Synaptic reorganization in the substantia gelatinosa after peripheral nerve neuroma formation: aberrant innervation of lamina II neurons by Abeta afferents

Intracellular recording and extracellular field potential (FP) recordings were obtained from spinal cord dorsal horn neurons (laminae I-IV) in a rat transverse slice preparation with attached dorsal roots. To study changes in synaptic inputs after neuroma formation, the sciatic nerve was sectioned and ligated 3 weeks before in vitro electrophysiological analysis. Horseradish peroxidase labeling of dorsal root axons indicated that Abeta fibers sprouted into laminae I-II from deeper laminae after sciatic nerve section. FP recordings from dorsal horns of normal spinal cord slices revealed long-latency synaptic responses in lamina II and short-latency responses in lamina III. The latencies of synaptic FPs recorded in lamina II of the dorsal horn after sciatic nerve section were reduced. The majority of monosynaptic EPSPs recorded with intracellular microelectrodes from lamina II neurons in control slices were elicited by high-threshold nerve stimulation, whereas the majority of monosynaptic EPSPs recorded in lamina III were elicited by low-threshold nerve stimulation. After sciatic nerve section, 31 of 57 (54%) EPSPs recorded in lamina II were elicited by low-threshold stimulation. The majority of low-threshold EPSPs in lamina II neurons after axotomy displayed properties similar to low-threshold EPSPs in lamina III of control slices. These results indicate that reoccupation of lamina II synapses by sprouting Abeta fibers normally terminating in lamina III occurs after sciatic nerve neuroma formation. Furthermore, these observations indicate that the lamina II neurons receive inappropriate sensory information from low-threshold mechanoreceptor after sciatic nerve neuroma formation.

Survival effects of BDNF and NT-3 on axotomized rubrospinal neurons depend on the temporal pattern of neurotrophin administration

This study shows that both BDNF and NT-3 can prevent cell death in axotomized adult rat rubrospinal neurons (RSNs), but that the efficacy of neuroprotection depends on the temporal pattern of treatment. At 8 weeks after cervical spinal cord injury, 51% of the RSNs had died. Subarachnoidal BDNF infusion into the cisterna magna for 4 weeks resulted in neuronal hypertrophy and 71% survival. Continuous infusion for 8 weeks into the lumbar subarachnoidal space with either BDNF or NT-3 gave similar survival rates, while a combination of BDNF and NT-3 resulted in 96% survival, although the cells were atrophic. When administration of either BDNF or NT-3 was delayed and performed during postoperative weeks 5-8, the number of surviving neurons was increased compared to early treatment. Delayed treatment with a combination of BDNF and NT-3 resulted in complete survival and a reduction in neuronal atrophy. A decreased expression of TrkB receptors and microtubule-associated protein-2 in the RSNs after axotomy was counteracted by BDNF and NT-3. Microglial activity remained increased even when complete cell survival was achieved. Thus, the combination of neurotrophins as well as the temporal pattern of treatment need to be adequately defined to optimize survival of injured spinal tract neurons.

Visceral nociception

Visceral pain is of great concern to the medical community because it remains particularly resistant to current clinical treatments. A serendipitous and initially unexplainable clinical finding that a punctate midline dorsal column lesion is effective in eliminating visceral pain, however, has initiated a resurgence of interest in the study of the basic mechanisms of visceral nociception. Clinical and anatomic findings have determined that visceral pain either of thoracic or pelvic origin can be relieved by carefully placed lesions directed at the lateral edge or the medial edge of the gracile fasciculus, respectively. Studies are demonstrating that visceral pain is quite unique from cutaneous pain.

Cross-modal reorganization of callosal connectivity without altering thalamocortical projections

Mammalian cerebral cortex is composed of a multitude of different areas that are each specialized for a unique purpose. It is unclear whether the activity pattern and modality of sensory inputs to cortex play an important role in the development of cortical regionalization. The modality of sensory inputs to cerebral cortex can be altered experimentally. Neonatal diversion of retinal axons to the auditory thalamus (cross-modal rewiring) results in a primary auditory cortex (AI) that resembles the primary visual cortex in its visual response properties and topography. Functional reorganization could occur because the visual inputs use existing circuitry in AI, or because the early visual inputs promote changes in AI's circuitry that make it capable of constructing visual receptive field properties. The present study begins to distinguish between these possibilities by exploring whether the callosal connectivity of AI is altered by early visual experience. Here we show that early visual inputs to auditory thalamus can reorganize callosal connections in auditory cortex, causing both a reduction in their extent and a reorganization of the pattern. This result is distinctly different from that in deafened animals, which have widespread callosal connections, as in early postnatal development. Thus, profound changes in cortical circuitry can result simply from a change in the modality of afferent input. Similar changes may underlie cortical compensatory processes in deaf and blind humans.

Different primary target cells are important for fiber lamination in the fascia dentata: a lesson from reeler mutant mice

The factors determining the lamina-specific termination of entorhinal and commissural afferents to the fascia dentata are poorly understood. Recently it was shown that early generated Cajal-Retzius (CR) cells in the outer molecular layer and reelin, synthesized by CR cells, play a role in the lamina-specific termination of entorhinal fibers which form transient synapses with CR cells before establishing their definite contacts with granule cell dendrites (J. A. del Rio et al., 1997, Nature 385, 70-74). By using anterograde tracing with Phaseolus vulgaris leukoagglutinin we show that the normal, sharply delineated entorhinal projection to the outer molecular layer is retained in reeler mutant mice lacking reelin. This coincides with the regular presence of CR cells, the primary, transient target cells of entorhinal fibers. In contrast, the commissural fibers were found to terminate in an abnormal broad, not clearly defined area. This widespread projection coincides with the distribution of granule cells which in the mutant do not form a dense cell layer but are scattered all over the hilus due to a migration defect. Unlike the entorhinal fibers, the commissural fibers arrive in their target layer late in development, when granule cell dendrites are already there. We hypothesize from these results that the presence of the adequate postsynaptic element at the time of fiber ingrowth, CR cells for the early ingrowing entorhinal fibers and granule cells for the late-arriving commissural fibers, is crucial for the normal formation of these layer-specific projections.

The hippocampus of the reeler mutant mouse: fiber segregation in area CA1 depends on the position of the postsynaptic target cells

Area CA1 of the rodent hippocampus is characterized by a highly lamina-specific and nonoverlapping termination of afferent fiber tracts. Entorhinal fibers terminate in stratum lacunosum-moleculare and commissural/associational fibers terminate in strata radiatum and oriens. It has been hypothesized that this fiber lamination depends on specific signals for the different afferent fiber tracts that are located on distinct dendritic segments of the postsynaptic neuron. In order to test this hypothesis, entorhinal and commissural/associational afferents to Ammon's horn were investigated in the adult reeler mutant mouse, in which developmental cell migration defects have disrupted the normal array of cells. Golgi staining revealed a deep and a superficial principal cell layer in the mutant. The morphology of the cells located in the deep pyramidal cell layer was considerably abnormal, whereas most cells located in the superficial pyramidal cell layer showed an almost normal cellular and dendritic morphology. Anterograde tracing with Phaseolus vulgaris leukoagglutinin revealed that the duplication and disorganization of the pyramidal cell layer in area CA1 are mirrored by the duplication and disruption of afferent fiber termination zones. In the zone above the abnormal deep pyramidal cell layer, i.e., between the two cell layers, entorhinal fibers as well as commissural/associational fibers terminate and intermingle. In contrast, in the zone above the fairly normal superficial pyramidal cell layer, entorhinal and commissural/associational fibers retain their normal fiber segregation. These data suggest that the normal laminar organization of the murine hippocampus depends on positional cues presented by their target cells.

Effects of neonatal attenuation of axoplasmic flow or transection of the rat's infraorbital nerve on the morphology of individual trigeminal primary afferent terminals in the brainstem

Attenuation of axoplasmic transport in the infraorbital nerve (ION), or transection of this trigeminal (V) branch at birth, results in degradation of the central cellular aggregates related to the mystacial vibrissae. However, blockade of axoplasmic transport does not result in the nearly 90% loss of ION ganglion cells that follows neonatal transection of this nerve. The present study was undertaken to further characterize the response of individual ION axons to attenuation of axoplasmic transport and to compare these effects to the changes observed following nerve transection. Neurobiotin injections were made into the V ganglion on postnatal day (P-) 6 in normal rats and animals that had vinblastine applied to the ION or received transection of the ION on P-0. Individual labeled fibers in the portions of V nucleus principalis (PrV) and subnucleus interpolaris (SpI) innervated by the ION were drawn from single sections with the aid of a computer. Morphological analysis of fibers drawn in SpI indicated no significant differences between axons from normal and vinblastine-treated animals. The fibers drawn from rats that sustained ION transection had significantly more branch points (P < 0.05) than those from either normal or vinblastine-treated animals. In PrV, fibers drawn from vinblastine-treated rats had a slightly, but significantly, larger total process length and cross-sectional area than those from the normal animals (P < 0.05). There were no other significant differences among the three groups of axons. These results support the conclusion that application of vinblastine to the developing ION does not dramatically alter the morphologic patterning of the central arbors of its axons.

Inhibition of evoked C-fibre responses in the dorsal horn after contralateral intramuscular injection of capsaicin involves activation of descending pathways

In this study extracellular recordings of nociceptive dorsal horn neurones driven by electrical stimulation of the sciatic nerve were performed in intact urethane-anaesthetized Sprague-Dawley rats. Spikes 0-40, 40-250 and 250-800 ms after stimulus were defined as A- and C-fibre responses and post-discharge, respectively, and the effect of 200 microg capsaicin (8-methyl-N-vanillyl-6-noneamide) injected into the contralateral gastrocnemius-soleus muscle was investigated. In most cells tested, regardless of the size or location of their receptive fields, the injection of capsaicin caused a clear inhibition of the electrically evoked C-fibre responses. In animals with intact descending pathways the mean C-fibre response was inhibited to 51% of baseline 15 min after injection of capsaicin. In contrast, when capsaicin was given during cold block of the spinal cord between the brainstem and the site of recording in the dorsal horn, the same response was inhibited to 91% of baseline. A significant interaction between cold block and capsaicin was detected. We conclude that stimulation of capsaicin-sensitive afferents in the deep tissue in the hind limb can inhibit the electrically evoked C-fibre responses in the dorsal horn by activating inhibitory descending projections from higher centres. The model presented here may be an important tool for further investigations of the endogenous descending antinociceptive system.

The sensory trigeminal system in birds: input, organization and effects of peripheral damage. A review

The primary sensory trigeminal system in birds comprises the mesencephalic trigeminal nucleus and the trigeminal ganglion with projections to the principal sensory nucleus (PrV) and the descending tract with its subnuclei. Other cranial nerves can contribute to PrV and the descending system that together form the somatosensory system of the head. There is also a proprioceptive component. The somatosensory system comprises a component serving tactile sense and a nociceptive component. The former processes information from many mechanoreceptors in beak and tongue; both PrV and subnuclei of the descending system are involved. The nociceptive component consists of small ganglion cells projecting presumably to layers I and II of the caudal subnucleus of the descending trigeminal system and cervical dorsal horn; this is the only trigeminal region showing immunoreactivity for substance P. The effects of amputation of the tips of the beak of chickens (debeaking) are estimated by fiber counts in electron microscopic preparations of the trigeminal branches innervating that area, and by cell counts in Nissl stained sections of the trigeminal ganglion. Our data indicate that debeaking causes a loss of exteroceptive units, but not of nociceptive units. Comparison of sections stained for the presence of substance P (immunohistochemistry) did not reveal a long-term effect on the nociceptive system suggestive of the occurrence of chronic pain.

Anatomic and technical considerations in needle electromyography of the lumbar spine

Interpretation of the paraspinal needle electromyographic examination requires knowledge of complex and specialized anatomy and pathophysiological processes. The purpose of this article is to elucidate the anatomy and physiology of the lumbar paraspinal needle examination and apply this knowledge to accurate needle technique and rational clinical interpretation of the paraspinal examination.

Transsynaptic changes of neurons and associated microglial reaction in the spinal cord of rats following middle cerebral artery occlusion

This study investigated transsynaptic neuronal damage and microglial reaction in the spinal cord contralateral to focal cerebral ischaemia in rats induced by permanent occlusion of the right middle cerebral artery (MCA). Three and five days after MCA occlusion, some neurons in the dorsal horn of lumbar spinal cord underwent degeneration and they appeared to be engulfed by reactive microglia; on the other hand, the ventral horn neurons remained ultrastructurally intact. It is suggested that the neuronal degeneration in the dorsal horn was attributed to deafferentation of the local neurons following ischaemic lesion of the corticospinal neurons which are the main source of afferent inputs.

Neural injury, repair, and adaptation in the GI tract. II. The elusive action of capsaicin on the vagus nerve

Capsaicin is an excitotoxin for primary afferent neurons, and perivagal administration of capsaicin is frequently used to ablate afferent fibers from the vagus nerve in an attempt to elucidate the role of afferent fibers in gastrointestinal (GI) regulation. However, this method has recently been called into question by research demonstrating that the molecular target of capsaicin on spinal and trigeminal afferents, vanilloid receptor subtype 1 (VR1), is absent from vagal afferents. Although some concerns about selectivity exist, the available information suggests that perineural capsaicin defunctionalizes afferent neurons of the vagus nerve by acting on a vanilloid receptor subtype that is structurally different from VR1.

Dysfunction of Ib (autogenic) spinal inhibition in patients with progressive supranuclear palsy

We compared the activity of Ib spinal interneurons in five patients with progressive supranuclear palsy (PSP) with six age-matched control subjects. Stimulation of the medial gastrocnemius nerve at motor threshold intensity activated Ib afferents that in turn inhibit H reflexes from the soleus muscle. Maximum inhibition occurred at interstimulus intervals of 6 and 8 ms for both control subjects and PSP patients and was significantly greater in the PSP patients. Increased Ib activity of PSP patients may be caused by loss of inhibition of Ib interneurons through degeneration of the medullary reticulospinal pathway. The corticospinal pathways, unopposed by the medullary reticulospinal tract, may excessively activate Ib interneurons.

[Lesions of ponto-cerebellar and olivo-cerebellar afferents demonstrated by neurophysiologic analysis]

We describe a 52-year-old woman presenting a 2-year history of limb clumsiness and gait difficulties, characterized by progressive worsening. Neurological examination revealed cerebellar intention tremor, cerebellar dysmetria of all 4 limbs and ataxic gait. However, brain MRI was normal. Analysis of fast wrist flexion movements demonstrated hypometric movements, with decreased intensities of agonist EMG activities and increased durations of antagonist EMG activities. Such EMG abnormalities have been demonstrated in patients presenting lesions of the middle cerebellar peduncle, affecting the crossed cerebellopontine projections. Moreover, adaptation motor learning during a pinch task (isometric force) showed a severe inability to adapt motor programming, indicating a disruption of cerebellolivary and cerebellopontine afferent systems. We suggest that our patient presented an exceptional brainstem syndrome involving the function of cerebellar inflow tracts. Such electrophysiological findings are not encountered in patients presenting a cerebellar cortical degeneration or cerebellovlivopontine atrophy, and might have important implications in the treatment of cerebellar ataxia in the future.

Chemoafferent degeneration and carotid body hypoplasia following chronic hyperoxia in newborn rats

1. To define the role of environmental oxygen in regulating postnatal maturation of the carotid body afferent pathway, light and electron microscopic methods were used to compare chemoafferent neurone survival and carotid body development in newborn rats reared from birth in normoxia (21 % O2) or chronic hyperoxia (60 % O2). 2. Four weeks of chronic hyperoxia resulted in a significant 41 % decrease in the number of unmyelinated axons in the carotid sinus nerve, compared with age-matched normoxic controls. In contrast, the number of myelinated axons was unaffected by hyperoxic exposure. 3. Chemoafferent neurones, located in the glossopharyngeal petrosal ganglion, already exhibited degenerative changes following 1 week of hyperoxia from birth, indicating that even a relatively short hyperoxic exposure was sufficient to derange normal chemoafferent development. In contrast, no such changes were observed in the vagal nodose ganglion, demonstrating that the effect of high oxygen levels was specific to sensory neurones in the carotid body afferent pathway. Moreover, petrosal ganglion neurones were sensitive to hyperoxic exposure only during the early postnatal period. 4. Chemoafferent degeneration in chronically hyperoxic animals was accompanied by marked hypoplasia of the carotid body. In view of previous findings from our laboratory that chemoafferent neurones require trophic support from the carotid body for survival after birth, we propose that chemoafferent degeneration following chronic hyperoxia is due specifically to the loss of target tissue in the carotid body.