Effects Of Deafferentation Research Articles

Tooth pulp deafferentation effects on trigeminal (V) brainstem neurons: Factors influencing magnitude and duration of neuronal changes

Tooth pulp deafferentation effects on trigeminal (V) brainstem neurons: Factors influencing magnitude and duration of neuronal changes

Beta 1- and beta 2-adrenergic 125I-pindolol binding sites in the interpeduncular nucleus of the rat: normal distribution and the effects of deafferentation

The plasticity of the beta 1- and beta 2-adrenergic receptor subtypes was examined in the interpeduncular nucleus (IPN) of the adult rat. The beta-adrenergic receptor antagonist 125I-pindolol (125I-PIN) was used in conjunction with the selective subtype antagonists ICI 118,551 and ICI 89,406 to determine the subnuclear distribution of beta 1- and beta 2-adrenergic receptors in this nucleus and to correlate the receptor distribution with the distribution of both noradrenergic afferents from the locus coeruleus (LC) and non-noradrenergic afferents from the fasiculus retroflexus (FR). The density of these binding sites was examined following lesions that decreased (LC lesions) or increased (FR lesions) the density of the noradrenergic projection in the IPN. Quantitative radioautography indicated that beta 1-labeled binding sites account for the larger percentage of binding sites in the IPN. The beta 1-binding sites are densest in the those subnuclei that receive a noradrenergic projection from the LC: the central, rostral, and intermediate subnuclei. beta 1-binding sites are algo homogeneously distributed throughout the lateral subnuclei, where there is no detectable noradrenergic innervation. beta 2-binding sites have a more restricted distribution. They are concentrated in the ventral half of the lateral subnuclei, where they account for 70% of total 125I-PIN binding sites. beta 2-binding sites are also present along the ventral border of the IPN. Some of this labeling extends into the central and intermediate subnuclei. Bilateral lesions of the LC, which selectively remove noradrenergic innervation to the IPN, result in an increase in the beta 1-binding sites. Bilateral lesions of the FR, which remove the major cholinergic and peptidergic input from the IPN, elicit an increase in noradrenergic projections and a decrease in beta 1-binding sites. beta 1-binding sites thus exhibit both up-regulation and down-regulation which is correlated with the density of the noradrenergic projection. Our results suggest, therefore, that the density of beta 1-binding sites is regulated by noradrenergic input. beta 2-binding sites increase in density in response to both the LC and FR lesions, suggesting that they are postsynaptic to both of these afferents. The distribution suggests that some of these binding sites may reflect binding to glial cells. The beta 2-binding sites may therefore be regulated by both noradrenergic and non-noradrenergic mechanisms.

Effects of tooth pulp deafferentation on nociceptive and nonnociceptive neurons of the feline trigeminal subnucleus caudalis (medullary dorsal horn).

1. Effects of deafferentation of the tooth pulps of the posterior mandibular teeth were studied in single neurons recorded in the ipsilateral subnucleus caudalis of the trigeminal (V) spinal tract nucleus of adult cats and kittens. The functional properties of neurons in each anesthetized animal were determined electro-physiologically in a series of microelectrode penetrations of the subnucleus. 2. The more than 800 neurons investigated could be subdivided on the basis of their cutaneous mechanoreceptive field properties into low-threshold mechanoreceptive (LTM) neurons, wide dynamic range (WDR) neurons, or nociceptive-specific (NS) neurons. Comparisons of neuronal properties were made between control (intact) cats and 7-15 day deafferented cats studied in a blind design, as well as groups of longer term deafferented cats, and kittens undergoing a "natural" deafferentation as a result of exfoliation of primary teeth. 3. There was no apparent change in the somatotopic pattern of organization of the subnucleus in the kittens and pulp-deafferented cats and no statistically significant differences were noted between kittens and control cats in any property except for alterations in the incidence of spontaneously active neurons. 4. Limited but statistically significant alterations were noted in some of the neuronal properties in the deafferented cats. These changes were especially apparent in the LTM neurons. The incidence of spontaneous activity was significantly decreased in the neurons of most long-term deafferented groups of cats. In the 7-15 day deafferented group, significantly more LTM neurons had a mechanoreceptive field involving all three divisions of the V nerve, and there was a significant increase in the incidence of LTM neurons activated by electrical stimulation of intraoral sites. Mechanosensitive neurons responsive only to tap stimuli were found only in the deafferented groups of cats. 5. These alterations in caudalis contrast with previous reports claiming marked hyperexcitability of caudal V brain stem neurons as a consequence of deafferentation and implicating such effects in the development of pain. However, some of the changes are in general not inconsistent with deafferentation-induced changes reported in spinal somatosensory neurons and with the pulp deafferentation-induced changes that we have recently documented in LTM neurons of subnucleus oralis of the V spinal tract nucleus of adult cats.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of deafferentation on the levels of uric acid in the spinal cord of the rat

In previous studies we reported that the rat spinal cord contains relatively high levels of uric acid and that the levels increase in a rat model of bilateral chronic pain, experimental adjuvant arthritis. In this report we evaluate the changes in UA in the unilaterally deafferented rat, a preparation which has also been used to study chronic pain. Uric acid was measured by high-pressure liquid chromatography with electrochemical detection in the spinal cord of rats that underwent unilateral, multiple cervical dorsal rhizotomy. compared to control and sham-operated rats, there was a significant increase in the level of uric acid in the dorsal quadrant of the spinal cord ipsilateral to the dorsal rhizotomy. This increase was present at 1 and 4 weeks after surgery. At 1 week, we also observed a small but statistically insignificant increase in uric acid levels in the dorsal quadrant contralateral to the deafferentation and in sham-operated rats. Four weeks after surgery the levels of UA in all regions except for the deafferented dorsal quadrant returned to normal. The possibility was raised that the changes in uric acid reflect an increase in purinergic metabolism in the spinal cord secondary to the increased activity of the dorsal horn neurons that occurs with deafferentation.

Combined effects of deafferentation and de-efferentation on isthmo-optic neurons during the period of their naturally occurring cell death.

We have studied the effects on the chick embryo's isthmo-optic nucleus of de-efferentation alone or in combination with deafferentation. De-efferentation was achieved by pharmacological destruction of the axonal target cells in the retina at E13, or by colchicine-blockade of axoplasmic transport in the intraocular parts of the isthmo-optic axons at E13; deafferentation was by a tectal lesion at E11 or E12. De-efferentation alone causes all the isthmo-optic neurons to die, and mostly by the "endocytic-autophagic" mode of cell death, which is characterized by pronounced endocytosis (of an intravascularly injected label) and by intense, clumped activity of two lysosomal enzymes (acid phosphatase and N-acetyl-beta-glucosaminidase). Deafferentation plus de-efferentation caused there to be less endocytic-autophagic dying cells in the isthmo-optic nucleus than after de-efferentation alone, but all the neurons still died. Our interpretation is that deafferentation switched many of the isthmo-optic neurons to a completely different (nonendocytic, nonautophagic) mode of cell death.

Sexual behavior of male dairy goats: Effects of deafferentation of the genitalia

The following study examines the effects of deafferentation of the penis, scrotum, prepuce and adjacent cutaneous surfaces on the development of mounting behavior in male dairy goats. Ten males underwent surgical deafferentations and 10 males received sham operations at 8 to 12 weeks of age. Mounting and other sexual behaviors were monitored while subjects were cohabiting with male and female penmates and when individually exposed to estrous females. Denervated males mounted penmates less frequently than sham controls and lacked vigorous thrusting behavior. When exposed to estrous females denervated goats did not exhibit the normal progression from shallow to deep thrusting with successive mounts and failed to attain intromissions and ejaculations. However, frequency of mounting was similar to that of controls when the latter were prevented from attaining intromissions. It was concluded that sensory feedback from the genitalia and surrounding cutaneous areas is not required for the initiation of leg-kicking behavior in male dairy goats but plays an important role in the development and maintenance of normal patterns of thrusting behavior. Because it was not possible to determine the rate at which reinnervation occurred, the extent to which mounting behavior depends on sensory feedback could not be determined.

Acetylcholine in the interpeduncular nucleus of the rat: normal distribution and effects of deafferentation

We studied the cholinergic projection to the interpeduncular nucleus (IPN) by examining localization of choline acetyltransferase (ChAT) in the habenula, fasciculus retroflexus (FR) and among the subnuclei of the IPN of the rat, using an antibody raised against ChAT. ChAT-containing neurons were present in the ventral portion of the medial hanenula, ChAT-stained axons were present in the FR and ChAT-stained axons and terminals were present in the rostral, central and intermediate subnuclei of the IPN. No ChAT staining was seen in the lateral or dorsal subnuclei. The pattern of ChAT localization was thus complementary to the pattern of the habenular substance P projection to the IPN. Lesions of the FR eliminated all ChAT from the IPN while lesions of the stria medullaris produced a modest decrease. Unilateral FR lesions indicated that the FR projection to the central and rostral subnuclei is largely bilateral and symmetrical and that to the intermediate subnuclei is largely ipsilateral. We found no evidence of lesion-induced plasticity, i.e. replacement of ChAT immunoreactivity, by surviving FR axons in these adult brains.

Norepinephrine in the interpeduncular nucleus of the rat: normal distribution and the effects of deafferentation

We used correlative biochemical and histochemical methods to examine (1) the norepinephrine (NE) projection from the paired locus coeruleus (LC) to the midline interpeduncular (IPN) of the adult rat and (2) the ability of the LC to respond to denervation of their target following removal of noradrenergic afferents (6-hydroxydopamine lesions of the LC) or non-noradrenergic afferents (lesion of the paired fasciculi retroflexi (FR)). Histofluorescence revealed that the NE innervation from the two LC to the IPN is symmetric and overlapping. This projection is confined to rostral, central, and intermediate subnuclei and is absent from lateral and dorsal subnuclei. We found no evidence for homotypic collateral sprouting of undamaged LC neurons into the IPN following unilateral LC lesion. Bilateral LC lesions also did not induce sprouting by NE-containing neurons from other systems (e.g. the superior cervical ganglion or the lateral tegmental group) or from those LC neurons that survived the 6-hydroxydopamine lesion. Histofluorescence following bilateral FR lesions confirmed an earlier observation that apparent hyperinnervation of the IPN by LC afferents is elicited following removal of non-noradrenergic afferents. Measurements of the turnover rate of NE in the IPN of control animals and those that received bilateral FR lesions indicate an increased NE content and increased turnover rate of NE in the IPN of lesioned animals. Taken together these results suggest an increased number of NE terminals and an increase in the activity of tyrosine hydroxylase. No change in NE content or turnover rate was seen in the frontal cortex from these same animals. This is consistent with a target-dependent regulation of heterotypic collateral sprouting.

Effect of deafferentation of the rat tongue on plasma corticosterone, aldosterone, angiotensin and ACTH levels

The role of serotonin receptors in the inhibitory effect of serotoninergic system on immunogenesis was studied using cyproheptadine, a specific blocker of 5-HT2 receptors. It was shown that cyproheptadine administration to CBA mice stimulated the immune response, which was dopamine-dependent and was realized via thymus. With the pituitary stalk destruction, the stimulatory effect of cyproheptadine was not observed, which suggests the participation of 5-HT2 brain receptors in immunogenesis.

Respiration in awake cats: sympathectomy and deafferentation of carotid bifurcations.

Respiratory effects of sympathectomy of the carotid bifurcations and, in a subsequent experiment, bilateral carotid sinus nerve section were examined in six awake resting cats. In each intact and denervated state, sequential breaths were analyzed at 10-min intervals up to 80 min. Individual breath frequency (f), tidal volume (VT), and ventilation (V = f X VT) were determined. In individual cats, sympathectomy or deafferentation could cause significant increases or decreases in ventilation or no change. Thus the range of spontaneous variability in breath V as well as minute ventilation (VE), averaged for the group, were not consistently altered in the same direction by either sympathectomy or deafferentation of the carotid bifurcations. Interestingly, in most cats after both sympathectomy (5 of 6) and deafferentation (4 of 6), VT increased and f decreased relative to V. Despite this, after sinus nerve section in two cats arterial PO2 decreased and arterial PCO2 tended to increase relative to VE, suggesting possible effects of deafferentation on ventilation-perfusion balance. Sympathectomy also affected timing such that inspiratory time began to exceed 0.5 of the breath duration at a lower breath f; this effect of sympathectomy was reversed to intact values by subsequent sinus deafferentation. Thus, in eupneic awake cats, sympathetics normally suppress reflex modulation of central timing from carotid chemoreceptors and/or baroreceptors.

Quantitative histochemical and microchemical changes in the adult mouse central nervous system after section of the infraorbital and optic nerves

The sensory projections from the whiskers of mice and other rodents synapse somatotopically in 3 subnuclei in the brainstem trigeminal complex, in the ventrobasal complex of the thalamus and in the somatosensory cortex. Deafferentation of the whiskers in adult animals results in qualitative and quantitative changes in activities of the metabolic enzymes in the somatosensory cortex (e.g. J. Neurosci., 1 (1981) 929–935). We determined the time course and extent of changes in the subcortical trigeminal centers of adult mice after deafferentation. The right infraorbital nerve was sectioned in mice under surgical anesthesia; the animals survived for periods up to 26 weeks. The optic nerve was also cut to evaluate the effects of central tract section. Some brains were prepared histochemically for the mitochondrial enzymes cytochrome oxidase (CO) and succinic dehydrogenase (SDH), and some were prepared for microchemical analysis of the enzymes citrate synthase (CS), malate dehydrogenase (MDH) and phosphorylase. All deafferented and intact nuclei were examined in each animal quantitatively. The oxidative enzymes (CO, SDH, CS and MDH) that were analyzed by histochemical and microchemical approaches showed a decrease in activities as early as 3 weeks postdeafferentation, a trend that continued up to 12 weeks in all the subcortical trigeminal stations and lateral geniculate nucleus (LGN) when compared with the intact side. By 25 weeks postlesion, the levels were comparable to the intact side except that in the LGN, the levels remained depressed. The phosphorylase levels increased at around 3 weeks postoperation and remained elevated 25 weeks postlesion. Each case provided results on the effects of deafferentation at a given time point throughout the trigeminal pathway. Direct quantitative correlation of histochemical and microchemical approaches for glycolytic enzymes is consistent with a coordinate regulation of these molecules. The changes in enzyme levels in all nuclei occur simultaneously and to a similar degree. This strongly suggests that neuronal activity plays an important role in regulating metabolic machinery throughout this pathway in adults.

A reconsideration of the central pattern generator concept for locust flight

Although it is generally agreed that locusts can generate flight similar rhythmic motor activity in the absence of sensory feedback from the wings, recent studies indicate that functional deafferentation produces significant changes in the flight motor pattern (Hedwig and Pearson 1984). These findings have raised doubts on the adequacy of the central pattern generator concept for the locust flight system (Pearson 1985). In this paper, we re-investigate the effects of deafferentation on the capacity of adult migratory locusts to generate the flight motor pattern. For this purpose, the experimental animals were dissected to various degrees, ranging from head-ventral nerve cord, to isolated pterothoracic nerve cord, and finally single isolated ganglion preparations. Flight motor activity was released by either wind stimulation, the more traditional method, or by applying octopamine (Sombati and Hoyle 1984; Stevenson and Kutsch 1986). In all cases the released motor activity was analysed, giving details of latency, and phase relationships between specific synergistic and antagonistic motor units, and then compared with the flight motor pattern generated by intact tethered locusts.

Plasticity of expression of a synaptic vesicle antigen in adult rat superior cervical ganglion

The effects of deafferentation and alterations of synaptic activity on levels of a synaptic vesicle-specific membrane protein (SV) were studied in the adult rat superior cervical ganglion (SCG) in vivo, using a monoclonal antibody directed against the protein. Levels of SV were quantified by radioimmunoassay. Deafferentation of the SCG results in a transient increase in SV levels in the SCG on days 7 and 10 after surgery, with levels then dropping below control levels on days 14, 21, and 30 after surgery. Immunohistochemical labeling of deafferented ganglia indicates that the increase is confined to the perikarya of principal ganglionic neurons. Levels of SV in an SCG target tissue, the iris, do not differ from control levels on day 7 after deafferentation, but are elevated at days 10, 14, and 30 after surgery. After reinnervation of the SCG, levels of SV in the SCG are elevated above control values, but do not differ from control values in the iris. Treatment with chlorisondamine, which blocks synaptic transmission in sympathetic ganglia, produces a significant increase in SV levels in the SCG after 7 d of treatment. Long-term chlorisondamine treatment results in reductions in SV in the SCG after 14 and 28 d. Treatment with phenoxybenzamine for 6 d, which reflexly increases synaptic activity, produces a marked decrease in SV in the SCG. These results suggest that activity, mediated by transsynaptic factors, contributes to the regulation of synthesis of a synaptic vesicle protein in the SCG. The results further suggest that accumulation of synaptic vesicles in terminals of the principal ganglion neurons may help regulate the maintenance of normal synaptic vesicle pools within sympathetic neurons.

Tooth pulp deafferentation is associated with functional alterations in the properties of neurons in the trigeminal spinal tract nucleus.

The effects of deafferentation of the tooth pulps of mandibular or maxillary teeth were investigated on the functional properties of single neurons recorded in the subnucleus oralis of the trigeminal (V) spinal tract nucleus of adult cats. Deafferentation was produced by endodontic removal, under sterile conditions, of the coronal pulp of the canine, premolar, and molar teeth. The subnucleus oralis of each animal was then studied electrophysiologically in a series of microelectrode penetrations of the subnucleus at a single postoperative time that varied between 3 days and 2 yr. Data from deafferented cats were compared with those obtained from control (unoperated) animals. The study was based on an examination of over 2,000 single units recorded on the side ipsilateral to the pulp deafferentation. In animals deafferented 7-15 days prior to brain stem neuron recording, tooth pulp deafferentation was associated with a statistically significant decrease compared with control animals in the incidence of neurons having a mechanoreceptive field localized within the mandibular or maxillary division; this decrease in incidence was coincident with a significant increase in the occurrence of neurons having a mechanoreceptive field involving two or three V divisions. Linear trend analysis indicated a progressive return to control values from the 7- to 15-day postoperative period. In deafferented cats there were also statistically significant increases in the incidence of neurons having spontaneous activity or showing rapidly habituating responses to brisk tap stimuli applied to the orofacial region; neurons having a receptive field consisting of discontinuous zones of mechanosensitivity were also encountered. The mean impulse frequency of spontaneous activity was not, however, significantly different between control and deafferented animals. The responsiveness of the habituating tap-sensitive neurons was further quantified and compared with neurons showing normal rapidly adapting (RA) features of their responses to mechanical orofacial stimuli. Whereas most (85%) of the RA neurons could faithfully follow stimuli applied by a mechanical stimulator at a mean maximal following frequency of 6.6 Hz and showed entrainment and 'turning curve' profiles comparable to those previously described for oralis neurons in normal animals, most of the habituating tap-sensitive neurons could not follow mechanical stimulus frequencies greater than 1 Hz (mean maximal following frequency 0.3 Hz) and none could be entrained sufficiently to allow for a determination of their tuning curve.(ABSTRACT TRUNCATED AT 400 WORDS)

Plasticity in the olfactory cortex: age-dependent effects of deafferentation.

In order to assess the role of input-target interactions in the development of olfactory cortex, the primary afferent fibers from the olfactory bulb to the superficial part of layer I of the cortex (layer Ia) were removed in developing and mature rats. After survival periods that vary from a few days to 2-6 months, changes were assessed in (1) the radial thickness of layer I, (2) the laminar distribution of intracortical associational fibers, which normally terminate in a deep part of layer I (layer Ib), and (3) the distribution of glia in layer I. The findings indicate that the lamination of fibers within layer I is not intrinsically prespecified, but gradually becomes "set" during the first month after birth. If the fibers from the olfactory bulb are removed, the dendrites of cortical cells are capable of accepting inputs from other fiber systems, depending on the maturational state of the dendrites and the ingrowing axons. Development of the abnormal inputs is associated with relatively normal dendritic growth, whereas lack of adequate input results in dendritic atrophy. Thus, after neonatal bulb ablation, the intracortical fibers occupy both superficial and deep parts of layer I, and a normal synaptic density is established throughout the layer. Layer I also develops to nearly its normal adult thickness, although the high density of glia that normally characterizes layer Ia is not apparent. With bulb ablation at progressively older ages (from postnatal day (P-) 3 to 21), the cortical associational fibers show progressively less extension into the denervated layer Ia. Layer I continues to grow, but not to the same extent as after P-1 ablations. In these experiments the glia distribution resembles the pattern present at the time of denervation. After adult olfactory bulb ablation, the long intracortical fibers extend very little into layer Ia, which undergoes pronounced shrinkage and becomes filled with a high concentration of glia. However, partial reinnervation of layer Ia is accomplished by the proliferation of a normally sparse native fiber system, which has been identified only with the Timm method. These results are interpreted as evidence that the normal development of lamination of afferent fibers to the olfactory cortex depends on axodendritic interaction during development.

Age-dependent cell death in the olfactory cortex: lack of transneuronal degeneration in neonates.

Adult olfactory cortical neurons in layer IIa undergo fulminant transneuronal degeneration after removal of afferent olfactory bulb fibers (Price, '76, Neurosci Abst. 2:161; Heimer and Kalil, '78, J. Comp. Neurol. 178:559-609). This provides an unusual example of dependence of a mature population of neurons on axonal input. In order to investigate whether similar transneuronal degeneration occurs in immature animals, a series of rats were subjected to unilateral olfactory bulb removal at various ages during the first 3 postnatal weeks. The brains were examined for degeneration after short survivals by use of the de Olmos cupric silver method, which selectively stains degenerating neurons. In addition, animals with long survivals were examined with the HRP retrograde tracing method, in order to determine if cells that survive the acute effects of deafferentation develop normal patterns of connections. Young neurons are more resistant to the effects of olfactory bulb removal than more mature neurons. There was little degeneration of cortical neurons after bulb ablation during the first 2 postnatal weeks. Although layer IIa does not become distinct from layer IIb in these experimental animals, cells that have connections normally characteristic of the cells of layer IIa, and are situated at the superficial edge of layer II, were identified with the HRP method. The severity of transneuronal degeneration increases and becomes adultlike between the second and third postnatal weeks. This increase in transneuronal degeneration is temporally associated with a progressive reduction in axonal sprouting following deafferentation during the first 3 postnatal weeks, as described in the companion paper (Friedman and Price, '86). Thus, axon sprouting may "protect" the immature IIa neurons from the effects of removal of the fibers from the olfactory bulb. A period of normal cell death has also been identified in olfactory cortex by the use of the de Olmos cupric silver method. This cellular degeneration is much less severe and has a different time course and laminar distribution than the transneuronal degeneration produced by olfactory bulb ablation in adults. Although normal cell death appears to be potentiated by removal of the olfactory bulb on postnatal day 1, it is clearly a different process from the transneuronal reaction.

Contextual control of trigeminal sensorimotor function

Simple actions, such as rhythmic tongue protrusions, forelimb facial strokes, and forelimb flails, are emitted by rats both during taste-elicited ingestion/aversion and during postprandial grooming. This study combined peripheral trigeminal deafferentation with a computer-assisted video analysis of action form to examine the use of cutaneous feedback from the face in action production. Changes in action form after deafferentation were found to be context-dependent: Deformations characterized rhythmic tongue protrusions when emitted in ingestive but not in grooming contexts. The opposite was true for alterations in forelimb action. Further, postprandial grooming as a whole was found to comprise distinct sequentially defined phases. Actions occurring in one highly stereotyped sequence phase were protected from deafferentation effects, although the same actions occurring outside of this phase were not. The results suggest that behavioral context (e.g., grooming versus ingestive set, sequence phase) can shift the integration of sensory guided and endogenous mechanisms that pattern simple actions.

Substance P in the interpeduncular nucleus of the rat: normal distribution and the effects of deafferentation.

The interpeduncular nucleus (IPN) is a midbrain structure that receives its major afferents from the medial habenulae via the fasciculi retroflexi. Among the axons projecting to the IPN is a population of substance P (SP)-containing axons. The IPN has been subdivided into the central, dorsal, intermediate, rostral, and lateral subnuclei using cytoarchitectonic criteria. The distribution of SP among these subnuclei was determined by using Sternberger's ('79) peroxidase-antiperoxidase technique. In the normal IPN the rostral subnucleus can be subdivided into two sectors on the basis of SP content. The ventral sector contains a moderate amount of SP and scattered SP positive perikarya. The dorsal cap of the rostral subnucleus contains denser SP than the ventral sector and it is continuous with the SP found in the dorsal subnucleus. The lateral subnuclei contain the densest SP found in the IPN and appear as laterally placed columns that expand in size caudally. The central and intermediate subnuclei contain very sparse SP. The fasciculus retroflexus was destroyed in 30 animals unilaterally or bilaterally and animals were perfused 4 days to 3 months postoperatively. After unilateral fascicular lesion, the SP in the rostral part of the ipsilateral lateral subnucleus is almost abolished, but caudally the decrease is confined to its lateral aspect. There is no visible decrease contralateral to the lesion. SP in the rostral part of the cap of the rostral subnucleus is decreased ipsilaterally but no loss is seen contralaterally or caudally. Animals with bilateral lesions show a great decrease in staining in the dorsal cap of the rostral subnucleus and the lateral subnuclei, with no decrease seen in the central, dorsal, or intermediate subnuclei. These results confirm that the origin of most of the SP in the IPN is fasciculus retroflexus fibers, but some of the SP arises from intrinsic SP perikarya located in the ventral sector of the rostral subnucleus and some may also arise from other sources. The areas of the IPN that receive bilateral SP projections from the fasciculus retroflexus (parts of the lateral and rostral subnuclei) show evidence for replacement of SP after lesion. This replacement implies sprouting or an increase in production of SP by remaining systems.

Deafferentation and axotomy of neurons in cat striate cortex: Time course of changes in binocularity following corpus callosum transection

Single neurons were recorded in the callosal terminal and cell zones of area 17 in the cat to assess the time course of changes in the proportion of binocular neurons produced by corpus callosum transection. The callosal terminal zone contains all the degenerating terminals in area 17 after corpus callosum transection. The callosal cell zone contains all the cells in area 17 which contribute axons to the corpus callosum. The cell zone is larger than, and partially overlaps, the callosal terminal zone. After corpus callosum transection there was an initial change in ocular dominance of neurons in both callosal zones. This initial change was followed by a reduction in the proportion of binocular neurons in both zones. This reduction became maximal 2–4 weeks after transection. In the callosal terminal zone, binocularity did not recover even at the longest postoperative periods examined (31–42 weeks). In the part of the callosal cell zone outside of the callosal terminal zone, the proportion of binocular neurons began to recover after 5 weeks and was at normal levels at the longest survival periods studied. Corpus callosum transection deafferents and axotomizes cells in the callosal terminal zone and, since central neurons do not regenerate their long-ranging axons, the combined effects of deafferentation and axotomy in this zone are permanent. The callosal cell zone outside of the callosal terminal zone contains axotomized cells and no degenerating terminals following transection. The recovery of binocularity in this region may be attributed to the transient changes which axotomized cells undergo. The zone which contains no callosal cells or terminals is unaffected by transection of the corpus callosum.

Influence of neonatal cochlear removal on the development of mouse cochlear nucleus. III. Its efferent projections to inferior colliculus

In order to determine the transneuronal developmental influences of auditory deafferentation, the right cochleas, with the first order spiral ganglion neurons, were removed in 6-day-old mice to eliminate all peripheral input to the right cochlear nucleus (CN). At 45 days, some of the efferent projections of right CN in these unilaterally lesioned mice and their unoperated controls were identified by retrograde transport of horseradish peroxidase from the contralateral (left) inferior colliculus (IC). In both groups of animals, reaction product was observed in neurons of the right CN, contralateral to the injection, and no labeling was seen in the ipsilateral left CN in either group. Contralaterally labeled were the fusiform cells of dorsal CN, the globular cells of ventral CN, and neurons within the nucleus of the intermediate acoustic stria. Quantification revealed significantly fewer fusiform and globular cells labeled in the deafferented CN, whereas the number of labeled acoustic stria neurons was the same in both groups. Although the deafferented CN had 65.4% fewer labeled neurons, the proportions projecting to IC were similar in the two groups, 7.8%. Because of this significant reduction in the number of deafferented CN neurons projecting to the contralateral IC, it was concluded that the transneuronal effects of deafferentation would be to deprive or deafferent developing neurons within the higher auditory brainstem nuclei.