Visual cells in the pontine nuclei of the cat.

Two hundred and thirty-two visually activated neurones were recorded in a small area of the rostral pontine nuclei of cats. The location of visually activated neurones was coextensive with the input from visual areas of cat's cortex as determined by degeneration studies. 2. Pontine visual cells could only be driven by visual stimuli. Cells responsive to somatosensory or auditory stimuli were also found in different regions in rostral pontine nuclei. They too responded to only one modality. 3. 96% of the cells were directionally selective. 4. Pontine visual cells were responsive to a wide range of stimulus speeds. Some cells responded to targets moving as fast as 1000 degrees/sec without losing directional selectivity. No pontine visual cells gave a clearly sustained response to a stationary stimulus. 5. Exact stimulus configurations were not critical. Large fields containing many spots were the most effective stimuli for 50% of the cells. Inhibition of responses depending upon stimulus dimensions, direction of movement, or location in the visual field was found for many cells. 6. Receptive field dimensions were large, ranging in size from 3 degrees X 4 degrees to more than an entire hemifield. 7. 94% of the cells had receptive fields which were centred in the contralateral hemifield. 8. 98% of the cells could be driven from both eyes. 9. The properties of the pontine visual cells suggest a corticopontocerebellar pathway sensitive to a wide range of speeds and directions of movement, but not sensitive to precise form.     

Synaptic influences of pontine nuclei on cochlear nucleus cells

Using the in vitro isolated whole brain preparation of the guinea pig, we tested the synaptic effects induced by the stimulation of pontine nuclei (PN) in intracellularly recorded and stained principal cells of the cochlear nucleus (CN). Twenty percent of the recorded cells in all CN subdivisions responded to stimulation of either ipsilateral or contralateral PN, and 12% of the cells exhibited convergence of inputs from both sides. The responses were recorded only in stellate cells of the ventral CN and in the pyramidal cells of the dorsal CN, whereas no responses were observed in bushy, octopus, and giant cells. PN stimulation produced excitatory and inhibitory postsynaptic potentials as well as mixed responses. The heterogeneous nature and the wide latency range (3.2–18 ms) of observed responses suggest significant variability in the underlying synaptic mechanisms and the implicated pathways. We propose that PN projections to the CN, terminating mainly in the granule cell domain (GCD), together with other non-auditory and auditory inputs contribute to multimodal convergence in the GCD leading ultimately to modulatory actions on the output activity of CN principal cells.     

A cerebellar projection onto the pontine nuclei in the albino rat

Summary Following removal of a significant part of the dentate nucleus and most of the interpositus nucleus in the rat cerebellum degenerated cerebellopontine fibres are shown to end in three fairly restricted regions in the contralateral pontine gray: in the paramedian position, in the middle and in the lateral third. The three regions are arranged in rostro-caudal longitudinal columns in the caudal three-quarters of the pons and these columns are continuous with one another by regions of scattered degeneration. The fibres appear to end in relation to distal dendrites of the pontine cells.This article has not been published in any journal before. The guiding principles in the care and use of animals approved by the American Physiological Society have been followed     

GABA-containing neurons in the pontine nuclei of rat, cat and monkey. An immunocytochemical study

Putative GABAergic elements in the pontine nuclei have been studied in the rat, cat and two old world monkeys (Macaca mulatta and Papio papio) using an antiserum against GABA-glutaraldehyde-protein conjugates and the peroxidase-antiperoxidase method. In addition, an antiserum against glutamate decarboxylase has been used in the cat. For comparison, Golgi impregnated material from cat and macaque has been studied. In all species there is a moderately dense plexus of fibres with GABA-like immunoreactivity with only minor regional differences between different parts of the pontine nuclei. The number of cell bodies showing GABA-like immunoreactivity is, however, strikingly different. Thus, in the rat there are very few such neurons. In the cat, they make up about 1% of the total cell population, while the corresponding number in the two primate species is about 5%. The number is consistently somewhat higher in rostral than in caudal parts of the pontine nuclei. Numbers in the cat are essentially the same with the glutamate decarboxylase antiserum as with the GABA antiserum. The size of GABA-like immunoreactivity positive somata is very similar in cat, macaque and baboon, averaging about 160 micron2 in cross-sectional area. The average cross-sectional area of the total neuronal population as measured in adjacent thionin-stained sections is about 280 micron2. However, the range of sizes for GABA-like immunoreactivity positive cells is wide, so that size alone is not a good criterion for their identification. Although their dendritic morphology is varied, a significant proportion of GABA-like immunoreactivity positive cells have very long and straight dendrites. A few examples were found in the primate species of GABA-like immunoreactivity positive cells with processes tentatively identified as axons. Such processes could be seen to divide several times. No such branching processes could be identified, however, in Golgi impregnated material from the same species. In order to determine whether GABA-like immunoreactivity positive cells project to the cerebellum, retrograde tracing of horseradish peroxidase-wheat germ agglutinin was combined with immunocytochemistry. No double labelled cells could be found in the pontine nuclei. Comparison of size distribution of retrogradely labelled pontocerebellar and GABA-like immunoreactivity positive cell bodies showed a high degree of overlap, although the average size of projection neurons and GABA-like immunoreactivity positive ones is clearly different.(ABSTRACT TRUNCATED AT 400 WORDS)     

Vesicular acetylcholine transporter-immunoreactive axon terminals enriched in the pontine nuclei of the mouse

Information to the cerebellum enters via many afferent sources collectively known as precerebellar nuclei. We investigated the distribution of cholinergic terminal-like structures in the mouse precerebellar nuclei by immunohistochemistry for vesicular acetylcholine transporter (VAChT). VAChT is involved in acetylcholine transport into synaptic vesicles and is regarded as a reliable marker for cholinergic terminals and preterminal axons. In adult male mice, brains were perfusion-fixed. Polyclonal antibodies for VAChT, immunoglobulin G-peroxidase and diaminobenzidine were used for immunostaining. In the mouse brain, immunoreactivity was seen in almost all major cholinergic cell groups including brainstem motoneurons. In precerebellar nuclei, the signal could be detected as diffusely beaded terminal-like structures. It was seen heaviest in the pontine nuclei and moderate in the pontine reticulotegmental nucleus; however, it was seen less in the medial solitary nucleus, red nucleus, lateral reticular nucleus, inferior olivary nucleus, external cuneate nucleus and vestibular nuclear complex. In particular, VAChT-immunoreactive varicose fibers were so dense in the pontine nuclei that detailed distribution was studied using three-dimensional reconstruction of the pontine nuclei. VAChT-like immunoreactivity clustered predominantly in the medial and ventral regions suggesting a unique regional difference of the cholinergic input. Electron microscopic observation in the pontine nuclei disclosed ultrastructural features of VAChT-immunoreactive varicosities. The labeled bouton makes a symmetrical synapse with unlabeled dendrites and contains pleomorphic synaptic vesicles. To clarify the neurons of origin of VAChT-immunoreactive terminals, VAChT immunostaining combined with wheat germ agglutinin-conjugated horseradish peroxidase retrograde labeling was conducted by injecting a retrograde tracer into the right pontine nuclei. Double-labeled neurons were seen bilaterally in the laterodorsal tegmental nucleus and pedunculopontine tegmental nucleus. It is assumed that mesopontine cholinergic neurons negatively regulate neocortico-ponto-cerebellar projections at the level of pontine nuclei.     

Organization of projections from the raphe nuclei to the vestibular nuclei in rats

Previous anatomic and electrophysiological evidence suggests that serotonin modulates processing in the vestibular nuclei. This study examined the organization of projections from serotonergic raphe nuclei to the vestibular nuclei in rats. The distribution of serotonergic axons in the vestibular nuclei was visualized immunohistochemically in rat brain slices using antisera directed against the serotonin transporter. The density of serotonin transporter-immunopositive fibers is greatest in the superior vestibular nucleus and the medial vestibular nucleus, especially along the border of the fourth ventricle; it declines in more lateral and caudal regions of the vestibular nuclear complex. After unilateral iontophoretic injections of Fluoro-Gold into the vestibular nuclei, retrogradely labeled neurons were found in the dorsal raphe nucleus (including the dorsomedial, ventromedial and lateral subdivisions) and nucleus raphe obscurus, and to a minor extent in nucleus raphe pallidus and nucleus raphe magnus. The combination of retrograde tracing with serotonin immunohistofluorescence in additional experiments revealed that the vestibular nuclei receive both serotonergic and non-serotonergic projections from raphe nuclei. Tracer injections in densely innervated regions (especially the medial and superior vestibular nuclei) were associated with the largest numbers of Fluoro-Gold-labeled cells. Differences were observed in the termination patterns of projections from the individual raphe nuclei. Thus, the dorsal raphe nucleus sends projections that terminate predominantly in the rostral and medial aspects of the vestibular nuclear complex, while nucleus raphe obscurus projects relatively uniformly throughout the vestibular nuclei. Based on the topographical organization of raphe input to the vestibular nuclei, it appears that dense projections from raphe nuclei are colocalized with terminal fields of flocculo-nodular lobe and uvula Purkinje cells. It is hypothesized that raphe-vestibular connections are organized to selectively modulate processing in regions of the vestibular nuclear complex that receive input from specific cerebellar zones. This represents a potential mechanism whereby motor activity and behavioral arousal could influence the activity of cerebellovestibular circuits.     

Neuronal death and the development of the pontine nuclei and inferior olive in the chick

The cerebellar inputs from the chick's inferior olive and medial pontine nucleus are largely or entirely crossed, and those from the lateral pontine nucleus are partly (probably more than 50%) crossed. The neurons of these cell groups leave their last generation cycle between stages 20–25 (inferior olive); stages 24–29 (medial pontine nucleus); and stages 25–30 (lateral pontine nucleus). During normal development, about one-third of the cells in the inferior olive are lost, presumably through their death, over the 4 days before hatching; this corresponds to the previously demonstrated time of induced cell loss in the olive following cerebellar lesions. There is normally no cell loss, however, in the developing pontine nuclei.The absence of cell death in the pontine nuclei is of special interest, since this is the first report of such an absence for a brain nucleus. It may be due to the great abundance of potential synaptic sites available to the mossy fibres from the pons. All this lends weight to the view that for a neuron to survive during normal development it is more critically important for its axon to make synapses than for its dendrites and soma to receive synapses.     

A cerebellar projection onto the pontine nuclei an experimental anatomical study in the cat

Summary Fibres passing from the intracerebellar nuclei to the pontine nuclei proper have been noted only by few students. In the present study this projection is analysed by mapping with the Nauta (1957) and Fink and Heimer (1967) methods the degeneration which occurs in the pontine nuclei following stereotactically placed electrolytic lesions in different parts of the intracerebellar nuclei in the cat. Cerebellopontine fibres come from the lateral cerebellar nucleus (NL) except its ventralmost part, and from the rostral but probably not from the caudal part of the interpositus anterior (NIA) and the interpositus posterior.The fibres end in three fairly well circumscribed regions of the pontine nuclei: a longitudinal column in the paramedian pontine nucleus, a column in the dorsolateral nucleus and one in the dorsal peduncular nucleus. Fibres from the NL as well as the NIA appear to end in all three regions, but the possibility of a more specific distribution cannot be excluded. Parts of the projection areas in the pons appear to be specific to cerebellar afferents, while other parts overlap with terminations of cerebropontine fibres, especially from SmI and SmII.The findings support the conclusions arrived at in recent studies of the cerebral corticopontine projections by P. Brodal (1968a, 1968b, 1971a, 1971 b) that the pontine nuclei are very precisely organized. The general principles in the organization of the corticopontine and cerebellopontine projections appear to be similar.Working in the Anatomical Institute, University of Oslo, with leave of absence from the Laboratory of Normal Anatomy, University of Coimbra, Portugal, with a grant from the Portugese Institute for Higher Culture.     

Cortical neurons projecting to the pontine nuclei in the cat. An experimental study with the horseradish peroxidase technique

Summary Horseradish peroxidase (HRP) injections in various portions of the cat pontine nuclei resulted in retrograde labeling of neurons in layer V of the ipsilateral cerebral cortex.Corticopontine neurons, pyramidal in type, have been found to be labeled in the entire cortex, confirming the previous findings of anterograde degeneration studies. Most (91%) of the labeled cells were 14–26 m in diameter (mean 19.4±4.5 m SD). Small (10–20 m) and medium (20–40 m) cells represent 51.5% and 47.7%, respectively, of the total number of the labeled neurons. The populations of the neurons of various sizes were almost identical in different cortical areas, and were different from the populations of corticoreticular and corticospinal cells.Corticopontine cells were well labeled in experimental cases of 3-days' survival time, confirming the topographical organization established previously by degeneration studies for this projection system. However, in cases of shorter survival time (20–27 h), the number of labeled neurons was very small.The relative paucity of labeled Corticopontine neurons in the sigmoid and lateral gyri is discussed with reference to other cortical descending neurons (e.g., the corticotectal, corticoreticular and corticospinal) which have hitherto been identified morphologically as well as physiologically.Abbreviations AL gyrus lateralis anterior - ASigm gyrus sigmoideus anterior - ASup gyrus suprasylvius anterior - Br.p. brachium pontis - Cor gyrus coronalis - L left - L.m. lemniscus medialis - MEct gyrus ectosylvius medius - MSup gyrus suprasylvius medius - N.dl. nucleus dorsolateralis - N.l. nucleus lateralis - N.m. nucleus medianus - N.p. nucleus peduncularis - N.pm. nucleus paramedianus - N.r.t. nucleus reticularis tegmenti pontis - N.v. nucleus ventralis - Ped corticospinal and corticopontine fibers in cerebral peduncle - PSigm gyrus sigmoideus posterior - R right     

The mode of synaptic linkage in the cerebro-ponto-cerebellar pathway of the cat. II. Responses of single cells in the pontine nuclei

Extracellular and intracellular recordings were made from single cells in the pontine nuclei (PN) of the cat. PN cells were identified by antidromic invasion from the cerebellum by stimulating either the brachium pontis (BP) or the white matter near the cerebellar nuclei. The cerebrally-induced impulses excited PN cells postsynaptically with a monosynaptic latency. Both fast and slow conducting cortical fibres contributed to the corticopontine excitation, so that the latency varied over a wide range. Measurements of the latencies for antidromic and corticopontine excitation and of the distances between stimulated sites permitted the calcuation of conduction velocities of PN cell axons and of their cortical input fibres. PN cells with fast conducting axons received convergence from both fast and slow cortical fibres, whereas PN cells with slow axons were innervated only by slow cortical fibres. The majority of PN cells were also excited by stimulating the medullary pyramid through collaterals of the pyramidal tract. Evidence of abundant pyramidal collaterals was provided by the collision technique. The functional role of the PN is discussed in connection with the cerebro-cerebellar loop circuits.     

GAD-immunoreactive neural elements in the basilar pontine nuclei and nucleus reticularis tegmenti pontis of the rat. I. Light microscopic studies

Summary Immunocytochemical procedures employing the unlabeled antibody enzyme (PAP) method were used to visualize those neuronal elements in the basilar pontine nuclei (BPN) and nucleus reticularis tegmenti pontis (NRTP) of the rat which contain glutamic acid decarboxylase (GAD), a key enzyme involved in the synthesis of the neurotransmitter gamma-aminobutyric acid (GABA). Neuronal somata, axons, and axon terminals in the BPN and NRTP exhibited GAD-immunoreactivity. Both thick and thin varieties of labeled axons and terminals were distributed in varying densities throughout the BPN and NRTP. The greatest accumulation of labeled terminals was noted in the ventrolateral and lateral border regions of the BPN while a slightly less dense aggregation was observed along the ventral, ventromedial and midline regions of the pontine gray. Labeled fibers and terminals were also observed in the dorsal and ventral peduncular regions as well as central portions of the lateral, ventral, and medial pontine areas. Axonal and terminal labeling was present throughout the NRTP but no focal increases in density similar to those in the BPN were apparent. No obvious GAD-labeled fiber bundles could be observed to enter the BPN or NRTP. However, small fascicles of labeled axons were seen to course ventrally around the dorsolateral aspect of the cerebral peduncle to reach lateral pontine areas while other labeled axons descended through clefts in the mid-portion of the cerebral peduncle or passed through the medial lemniscus and around the medial portion of the cerebral peduncle to enter the pontine gray. The number of GAD-positive neuronal somata in the BPN and NRTP is quite sparse in comparison to that of neighboring brainstem regions such as the ventral nucleus of the lateral lemniscus and the pontine reticular formation. The majority of labeled neuronal somata were less than 20 m in diameter although some, particularly in NRTP, were as large as 28 m. A variety of morphologies was represented in the population of labeled somata ranging from spheroidal to spindle-shaped or polygonal. GAD labeled somata were distributed throughout the BPN and NRTP but were most numerous in the rostral medial pontine region and the lateral, ventral, and medial border areas of the BPN, adjacent to the fibers of the brachium pontis. From these observations it is proposed that the population of GAD positive cells in the BPN and NRTP gives rise to at least a portion of the labeled axon terminals while other GABA-ergic neurons extrinsic to the pontine gray serve as a source of the remainder of the labeled axons and terminals.     

Corticofugal effects from sensorimotor area I and somatosensory area II on neurones of the pontine nuclei in the cat.

1. The objective of the present experiments was to study the cortical influence from sensorimotor area I (SM I) and from somatosensory area II (S II) on single neurones of the pontine nuclei (PN) in cats under N2--thiamylal anaesthesia. 2. Extracellular single unit recordings revealed a considerable convergence from S II and SM I. Out of ninety-one PN neurones (identified as ponto-cerebellas neurones by antidromic stimulation of the contralateral brachium pontis), fifty-seven neurones were influenced by stimulation of at least one cortical site. Slightly less than half of these neurones (twenty-five) had a convergent input from SM I and S II; twenty-three PN neurones were excited by SM I only and nine PN neurones by S II only. The proportion of PN neurones excited via collaterals of cortico-spinal neurones was small and restricted to those neurones which had an input from SM I. 3. Sixty per cent of the ponto-cerebellar neurones were reliably activated by natural stimulation such as tapping or passive manipulations of limbs of various joints. The vast majority (thirty-three out of thirty-six PN neurones) which had receptive fields were also influenced by electrical stimulation of one or both cortical areas. The long latency and low probability of discharge to peripheral nerve stimulation suggest a complex, probably transcortical, pathway from the periphery to the PN. 4. The distribution of latencies to both cortical and brachium pontis stimulation indicates that the PN are a relay for fast and slow cerebro-cerebellar connexions. 5. The convergence from cortical areas on PN indicates that the neurones influenced from somatic areas SM I and S II transmit integrated patterns of activity to the cerebellum.     

Microinjections of local anesthetic into the pontine nuclei reduce the amplitude of the classically conditioned eyelid response

Seventeen rabbits were implanted bilaterally with cannulae into the pontine nuclei, and were then trained in the classically conditioned eyeblink procedure. Nine of the rabbits were trained with a tone as a conditioned stimulus (CS), and eight were trained with both tone and a light CS. After each rabbit had learned the conditioned response (CR) well, testing began. One microliter of 5% lidocaine injected bilaterally significantly impaired the CR amplitude for both tone and light as a CS, although unconditioned response amplitude was not affected. Injection of 1 microliter of isotonic saline did not impair CR amplitude, suggesting that the impairment seen after lidocaine injection was due to the anesthetic action of lidocaine in the pons, and not to nonspecific effects distal to the site of injection. These results support and extend the lesion data which shows that the pontine nuclei and their mossy fiber projection to the cerebellum are necessary for eyeblink conditioning using a peripheral CS.     

Afferent connections to the pontine nuclei from the cortex of the anterior ectosylvian sulcus in the cat

Following injections of horseradish peroxidase conjugated with wheatgerm agglutinin (HRP-WGA) in different sectors of the cortex of the anterior ectosylvian sulcus (SEsA), anterograde labeling was observed in the pontine nuclei (PN) of the cat. Labeled fibers were identified in a wide area which covers the entire rostro-caudal extent of the PN. The various sectors of the SEsA, which differ in their associative, cortico-cortical connections with the somatosensory, auditory and visual cortices, also were shown to differ in their projection patterns to the PN. These corticopontine projections of the SEsA were compared to those from the modality specific areas.     

Immunohistochemical study on the distribution of neuropeptides within the pontine tegmentum--particularly the parabrachial nuclei and the locus coeruleus of the human brain.

The topographical distribution of neuropeptide-containing cell bodies, fibers and terminals was studied in human parabrachial nuclei and the pontine tegmentum with immunohistochemical stainings. Brains of seven adult human subjects of 35-72 years were fixed within 2 h post mortem. Serial sections were immunostained by antisera of 14 different neuropeptides--oxytocin, vasopressin, thyrotropin-releasing hormone, angiotensin II, calcitonin gene-related peptide, beta-endorphin, dynorphin A, dynorphin B, leucine-enkephalin, alpha-melanocyte stimulating hormone, substance P, neuropeptide Y, cholecystokinin and galanin--alternately. All of these peptides were found to be present in nerve fibers and terminals, but only two, angiotensin II and dynorphin B, in cell bodies of the parabrachial nuclei. Calcitonin gene-related peptide-, neuropeptide Y-, cholecystokinin- and galanin-immunoreactive cells were present in other areas of the pontine tegmentum, like the motor trigeminal nucleus, locus coeruleus, periventricular gray matter but not in the parabrachial nuclei. Peptidergic fibers were distributed unevenly throughout the pontine tegmentum having unique, individual distribution patterns. In the parabrachial nuclei, substance P, neuropeptide Y, cholecystokinin and galanin showed the highest density of immunoreactive neuronal networks. Moderate to low concentrations of immunoreactive processes were detected by calcitonin gene-related peptide, alpha-melanocyte stimulating hormone, dynorphin B, thyrotropin releasing hormone, leucine-enkephalin, dynorphin A, angiotensin II, beta-endorphin, vasopressin and oxytocin antisera, respectively. Other pontine tegmental areas, like the locus coeruleus, dorsal tegmental, pontine raphe and motor trigeminal nuclei as well as the central gray of the tegmental region exhibited a varying assortment of neuropeptides with distinct, individual localization patterns. Their detailed topographical distributions are mapped and given in coronal sections.     

大鼠前庭脊核和X细胞群向脑桥核的直接投射

目的:应用菜豆白细胞凝集素(PHA-L)顺行追踪和荧光金(FG)逆行追踪技术研究前庭脊核和X细胞群向脑桥核的直接投射.方法:SD大鼠随机分为PHA-L注射组和FG注射组.将顺行神经追踪剂PHA-L电泳至前庭脊核和X细胞群,逆行神经追踪剂FG分别电泳至脑桥核的外侧亚核和内侧亚核,动物存活7 d,灌流固定后,脑干作冠状冷冻切片,然后进行免疫组织化学显色.结果:PHA-L注射于前庭脊核后,顺行标记纤维和终末主要分布在对侧脑桥核的外侧亚核、内侧亚核及脑桥网状被盖核;FG分别注射于脑桥核的外侧和内侧亚核后,逆行标记细胞仅分布在对侧前庭脊核和X细胞群.结论:前庭脊核和X细胞群向对侧脑桥核的外侧和内侧亚核有直接的纤维投射,该投射可能与前庭-眼反射的调节有关.     

Immunohistochemical localization of glutamate, glutaminase and aspartate aminotransferase in neurons of the pontine nuclei of the rat

The pontine nuclei form the key relay nuclei in the cerebropontocerebellar pathway. Although a great deal of information is available regarding the anatomy of this region, the identity of the neurotransmitter(s) contained in the neurons of the pontine gray are not known. The aim of the present investigation is to utilize immunohistochemical techniques to determine whether glutamate, a putative excitatory transmitter, and the enzymes responsible for its metabolism, are found in pontine neurons. Both glutaminase, an enzyme which converts glutamine to glutamate, and aspartate aminotransferase, an enzyme which is involved in the interconversion between glutamate and aspartate, have been proposed to be markers of neurons which use excitatory amino acids as neurotransmitters. The present study utilizes a monoclonal antibody against carbodiimide-fixed glutamate and polyclonal antisera against glutaminase and aspartate aminotransferase in conjunction with the indirect peroxidase technique or the peroxidase-labeled biotin-avidin procedure to localize glutamatergic neurons in the pontine nuclei of the rat. Numerous neurons in all subdivisions of the pontine nuclei were found to contain carbodiimide-fixed glutamate-like immunoreactivity, glutaminase-like immunoreactivity or aspartate aminotransferase-like immunoreactivity. Horseradish peroxidase was injected into the cerebellum of four rats for use with a combined retrograde transport-immunohistochemical procedure. Double-labeled neurons were observed in all subdivisions of the pontine nuclei, indicating that pontine neurons which contain glutamate-like immunoreactivity project to the cerebellum. Based on the hypothesis that increased levels of glutamate, glutaminase and aspartate aminotransferase reflect a transmitter role for glutamate, the present data raise the possibility that glutamate may be a major neurotransmitter of pontocerebellar fibers.     

Two types of degenerating axon terminals in the basilar pontine nuclei of the opossum following cerebral cortical lesions

Subsequent to large cerebral cortical lesions in adult opossums, small boutons (less than 2 μm) contacting small dendritic profiles were observed to undergo the dark, electron dense type of degeneration in most cases. When lesions were restricted to post-orbital (sensorimotor) regions, the majority of degenerating boutons were again small and dark. However, if the lesion was restricted to occipital (visual) regions, most degenerating boutons were somewhat larger (1–3 μm), contacted some intermediate and proximal dendrites and underwent an initial filamentous reaction before becoming electron dense. Thus, it was postulated that at least two different systems of corticofugal axons reach the pontine nuclei, one (small dark boutons) perhaps arising as collaterals or corticospinal axons, the other (filamentous boutons) representing a more direct corticobulbar or corticopontine system.     

Collateral axons of cholinergic pontine neurones projecting to midline, mediodorsal and parafascicular thalamic nuclei in the rat

The organization of collateral axons projecting from neurones in the pontine laterodorsal tegmental nucleus (LDTg) has been examined using combinations of retrograde neuronal tracers with immunocytochemical markers for the acetylcholine-synthesizing enzyme choline acetyltranferase (CHAT), focussing on projections to the midline, mediodorsal and parafascicular thalamic nuclei and the ventral tegmental area. 25–59% of LDTg neurones projecting to the mediodorsal nucleus provided collaterals to the midline nuclei. Virtually all (87–96%) of these double retrogradely labelled neurones appeared cholinergic. 9–18% of LDTg neurones projecting to the parafascicular nuclei also provided a collateral to the midline nuclei and 50–78% of these double retrogradely labelled neurones stained for CHAT. 26–29% of the single LDTg neurones which projected collaterals to both the mediodorsal and midline nuclei, were found to project a third collateral to the ventral tegmental area. These anatomical findings, taken together with functional evidence, suggest that cholinergic terminals arising from LDTg are involved in coordinating thalamic mechanisms of brain state control; and in regulating dopaminergic pathways, both directly and via the thalamus.