Distribution and brainstem origin of cholecystokinin-like immunoreactivity in the opossum cerebellum

Systemic cholecystokinin amplifies vago-vagal reflex responses recorded in vagal motor neurones

Cholecystokinin (CCK) is a potent regulator of visceral functions as a consequence of its actions on vago-vagal reflex circuit elements. This paper addresses three current controversies regarding the role of CCK to control gastric function via vago-vagal reflexes. Specifically: (a) whether CNS vs. peripheral (vagal afferent) receptors are dominant, (b) whether the long (58) vs. short (8) isoform is more potent and (c) whether nutritional status impacts the gain or even the direction of vago-vagal reflexes. Our in vivo recordings of physiologically identified gastric vagal motor neurones (gastric-DMN) involved in the gastric accommodation reflex (GAR) show unequivocally that: (a) receptors in the coeliac-portal circulation are more sensitive in amplifying gastric vagal reflexes; (b) in the periphery, CCK8 is more potent than CCK58; and (c) the nutritional status has a marginal effect on gastric reflex control. While the GAR reflex is more sensitive in the fasted rat, CCK amplifies this sensitivity. Thus, our results are in stark contrast to recent reports which have suggested that vago-vagal reflexes are inverted by the metabolic status of the animal and that this inversion could be mediated by CCK within the CNS.

Repeated administration of methamphetamine blocked cholecystokinin-octapeptide injection-induced c-fos mRNA expression without change in capsaicin-induced junD mRNA expression in rat cerebellum

In the cerebellum, there are numerous cholecystokinin (CCK-8)-containing fibers. Since systemic CCK-8 injection-induced anxiety (psychological stress) activates the locus coeruleus cells that send mossy fiber inputs to the cerebellum, we examined whether systemic CCK-8 injections activate the rat and mouse cerebellum. First, injections of CCK-8 were found to induce c-fos mRNA expression in a vague patchy pattern that is different from single methamphetamine-induced Zebrin band-like c-fos mRNA expression, suggesting that the CCK-8 activating mossy fibers induce gene expression differently from the dopamine-containing mossy fibers in the ventral tegmental area. Second, since CCK-8 facilitates neural activity of dopamine in the midbrain, we examined whether repeated methamphetamine administration that induced behavioral sensitization had similar effects on the cerebellar CCK system. Repeated administration of methamphetamine suppressed the CCK-8-induced c-fos mRNA expression in the rat cerebellum. Third, capsaicin injections (physical stress) into a hind limb of the rat increased junD mRNA expression with no effect on c-fos mRNA expression, and repeated methamphetamine injections had no effect on the capsaicin-induced expression of junD mRNA. Fourth, either single injection of methamphetamine or CCK-8 to mice increased c-fos mRNA expression in the locus coeruleus, and so noradrenalin, but not dopamine, might interact with CCK-8-activating system. However, we considered the possibility unlikely. Thus, we conclude that repeated methamphetamine administration though dopamine selectively inhibits the c-fos mRNA expression after CCK-8 injection in the cerebellum.

Mechanisms of action of CCK to activate central vagal afferent terminals

Cholecystokinin [CCK] is a peptide released as a hormone by the proximal gut in response to the presence of peptones and fatty acid in the gut. Considerable evidence suggests that CCK inhibits feeding behavior and gastric function by acting as a paracrine modulator of vagal afferents in the periphery, especially in the duodenum. CCK is also widely distributed throughout the mammalian brain and appears to function as a neurotransmitter and neuromodulator. More recent studies have suggested that CCK may act directly within the CNS to activate central vagal afferent terminal inputs to the solitary nucleus. We have developed an in vitro calcium imaging method that reveals, for the first time, the direct effects of this peptide on vagal terminals in the solitary nucleus. In vitro imaging reveals that CCK provokes increases in intracellular calcium in vagal afferent terminals as a consequence of a complex interaction between protein kinase A [PKA] and phospholipase C [PLC] transduction mechanisms that open L-type calcium channels and causes endoplasmic reticular [ER] calcium release. The subsequent activation of PKC may be responsible for initiating calcium spiking which is dependent on a TTX-sensitive mechanism. Thus, imaging of the isolated but spatially intact hindbrain slice has allowed a more complete appreciation of the interdependent transduction mechanisms used by CCK to excite identified central vagal afferent fibers and varicosities.

Spatial distribution of corticotropin-releasing factor immunopositive climbing fibers in the mouse cerebellum: analysis by whole mount immunohistochemistry

This study examined the spatial organization of corticotropin-releasing factor (CRF) immunopositive climbing fibers in the mouse cerebellum by whole mount immunohistochemistry. A striking pattern of parasagittal stripes of CRF staining was revealed. Cryosections of whole mount CRF stained cerebellum showed that anti-CRF immunostaining is restricted to climbing fibers in the molecular layer and does not penetrate deeper into the granular layer. The array of CRF stripes was reminiscent of zebrin II immunopositive Purkinje cell stripes in the anterior vermis and the hemispherical lobules. However, a direct comparison of the two distributions showed that the CRF-defined parasagittal stripes and transverse zones in the posterior vermis are different from those defined by the expression of zebrin II: in particular, CRF immunostaining revealed a transverse boundary between lobules VIb and VII and the presence of four CRF-immunopositive climbing fiber stripes in lobule VIII. Furthermore, an array of CRF stripes was seen in lobule X, the flocculus and the paraflocculus, despite uniform zebrin II expression in these areas. In these cases some, but not all, CRF-immunopositive stripes shared boundaries with Purkinje cell stripes that were visualized by the expression of heat shock protein 25. The results reveal a reproducible pattern of CRF-immunopositive climbing fiber innervation in the mouse cerebellum that bears a complex relationship to the stripes delineated by Purkinje cell compartmentation antigens.

The distribution of corticotropin-releasing factor (CRF), CRF binding sites and CRF1 receptor mRNA in the mouse cerebellum

The purpose of the present study is to determine the distribution of CRF containing afferents, and correlate these findings with the distribution of CRF binding sites and the neuronal localization of mRNA for the CRF1 receptor in the cerebellum of a single species, the mouse. Corticotropin releasing factor (CRF) has been localized within climbing fibers and mossy fibers throughout the cerebellar cortex of the mouse using immunohistochemistry. CRF immunoreactive, axonal varicosities also are present within all four of the cerebellar nuclei. 125I-labeled CRF binding sites are evident throughout all three layers of the cerebellar cortex (molecular, Purkinje and granule cell layers), but are not seen within the cerebellar nuclei. In situ hybridization histochemistry was employed using an antisense riboprobe corresponding to the full length sequence of the rat mRNA for the CRF1 receptor. Positive signal is present throughout the cerebellum in Purkinje cells and the granule cell layer. CRF1 receptor mRNA also is expressed within all four of the cerebellar nuclei. Further experiments are required to reconcile the lack of CRF binding sites in the cerebellar nuclei with the positive mRNA receptor expression and the presence of immunoreactive axonal varicosities. In previous physiological experiments, iontophoretic application of CRF enhances spontaneous as well as quisqualate-induced activity of Purkinje cells in slice preparations of the mouse cerebellum. When the results of the anatomical techniques are compared to the physiological data, there is convergent evidence to suggest that CRF influences the firing rate or responsiveness of Purkinje cells directly via release of the peptide from the climbing fiber system and indirectly via the mossy fiber-granule cell-parallel fiber circuit. Taken together, these anatomical and physiological data provide strong evidence to suggest that, in the adult cerebellum, CRF functions as a neuromodulator.

Neuropeptide Y (NPY) expression is up-regulated in the rat inferior olive during development

The aim of this study was to analyse the developmental expression of the neuropeptide Y (NPY) in the rat inferior olivary (IO) complex by immunoperoxidase and immunofluorescence techniques. The spatial distribution of NPY-immunoreactivity (IR) did not vary during development, whereas NPY-IR intensity levels varied significantly. The peak of NPY-IR expression occurred during the second postnatal week, but differed in intensity in individual IO subnuclei, the highest levels being present in the dorsal fold of the dorsal accessory olive and in the ventro-lateral outgrowth. In the adult, NPY-IR could only be rescued in colchicine pretreated animals, but its distribution overlapped the one found during development. These findings show that NPY-IR is transiently up- regulated, during development, in specific compartments of the IO complex, and that the peptide is rescued in the same specific olivocerebellar compartments in the adult. These observations are here taken to support the hypothesis that NPY may exert different trophic-differentiating and/or neuromodulatory roles during development, when its expression is transiently up-regulated, or at adult stages, when it can be rescued, according to the different biological contexts.

Peptide localization in the mouse inferior olive

The inferior olivary complex is the sole source of climbing fibers to the cerebellar cortex. Physiologically these afferents have been shown to have a powerful excitatory effect on their target neurons, namely Purkinje cells. Thus, any modulation of olivary firing rate or responsiveness will alter Purkinje cell firing and ultimately cerebellar function. Neuropeptides have been shown to modulate neuronal activity in several systems. The intent of the present study is to determine the olivary distribution of five peptides previously shown to be present and functional in cerebellar circuitry including cholecystokinin, calcitonin gene-related peptide, corticotropin releasing factor, enkephalin and substance P. These studies were carried out in the adult C57BL/6J mouse using the peroxidase anti-peroxidase immunohistochemical technique. All five peptides labeled varicosities of varying sizes. Varicosities labeled for cholecystokinin, calcitonin gene-related peptide and corticotropin releasing factor were densely distributed throughout the inferior olive. In contrast, varicosities immunostained for substance P and enkephalin, were more restricted in their distribution. The overlap in the distribution of these peptides suggests that they may be colocalized with each other as well as with excitatory or inhibitory amino acids known to be present in afferents to the inferior olive. Because of the extensive distribution of the peptides, it is likely that they are derived from multiple brainstem sources. These findings serve as baseline data for future physiological studies designed to address the functional role of peptides in olivary circuitry.

Cholecystokinin modulation of spontaneous and excitatory amino acid-induced activity in the opossum cerebellum

Cholecystokinin-B (CCK-8) is an octapeptide that was initially described in the gastrointestinal tract. Recent studies have shown that this peptide also has an extensive distribution in the central nervous system, including the cerebellum of the opossum. In addition to the protein, binding sites for CCK-8 also have been described in the granule cell and molecular layer of this species. These anatomical data suggest that CCK-8 has a functional role in cerebellar circuitry. In the present study we have determined the physiological effects of CCK-8 on spontaneous and amino acid-induced activity. The results indicate that this peptide has both excitatory and inhibitory effects on spontaneous activity as well as the excitatory responses elicited by application of the excitatory amino acids aspartate, glutamate and quisqualate. The data suggest that CCK-8 may influence more than one population of cerebellar neurons. The findings support a neuromodulatory role for this peptide in cerebellar circuitry.

Calcitonin gene-related peptide modulates neuronal activity in the mammalian cerebellar cortex

Calcitonin gene related peptide (CGRP) has been localized within specific populations of mossy fibers in the cat's cerebellar cortex. The intent of the present study was to determine the physiological role of this peptide in cerebellar circuitry. CGRP was iontophoretically applied and its effects on spontaneous, amino acid-induced, and synaptically-mediated activity were recorded. In addition, interactions between CGRP and serotonin (5HT), another neuromodulator in cerebellar circuitry, also were analyzed. The findings of this study reveal that the primary effect of CGRP is to suppress spontaneous and excitatory amino acid-induced activity. However, CGRP has a more potent effect in suppressing aspartate- and quisqualate-induce activity as compared to that elicited by glutamate. CGRP slowed or completely blocked synaptic activity mediated by stimulation of the inferior cerebellar peduncle. Finally, the individual suppressive effects of 5HT and CGRP were potentiated when both were applied simultaneously. However, the potentiation was greater when the neuron was exposed to 5HT before CGRP was applied. In summary, the presence of CGRP in selected populations of mossy fibers, together with serotoninergic afferents, decreases the responsiveness of Purkinje cells to excitatory amino acids as well as synaptically-driven activity. Thus, activation of an afferent system to the cerebellum can elicit distinct effects on different populations of neurons that are dependent on the microenvironment of the cell at a particular point in time.

Early development of cerebellar afferent systems that contain corticotropin-releasing factor

Corticotropin-releasing factor (CRF) and CRF binding sites have been described in the cerebellum of several species, including the North American opossum (Didelphis marsupialis virginiana), the species used in the present study. Inotophoretic application of this peptide in the adult cerebellum enhances the spontaneous and amino acid-induced firing rate of Purkinje cells and overcomes the GABA-induced suppression of Purkinje cell activity. The present account provides immunohistochemical evidence for the localization of CRF in the North American opossum within developing axons and their growth cones prior to the formation of the Purkinje cell and granule cell layers. CRF mRNA is present on postnatal day (PD) 1 within the internal migratory stream of the ventral lateral medulla, which contains migrating olivary neurons, and within the ventral medulla in the region, where inferior olivary neurons first aggregate to form the inferior olivary complex. The olivary complex can first be identified on PD2 and is well defined by PD3. CRF-immunoreactive axons are evident within the cerebellar primordium on PD4 and penetrate the nascent Purkinje cell layer between PD14 and PD26. By PD26, CRF-immunoreactive puncta are organized within the Purkinje cell layer as parasagittal bands. Thus, olivary neurons express CRF mRNA prior to the time that the first CRF-labeled axons are present in the cerebellar anlage (PD4), suggesting that olivary axons are among the first to reach the developing cerebellum. Coincident (PD1-3) with the early transcription of CRF mRNA in the inferior olive, cells in the medullary reticular formation (PD1) and locus coeruleus (PD2) also transcribe CRF mRNA. These brainstem sites also could provide CRF-immunoreactive axons to the developing cerebellum; however, based on the results of this study and correlative data reported in the literature, we propose that the primary source of early-arriving CRF fibers is the inferior olivary complex. The early arrival of CRF-containing axons in the cerebellum prior to synaptogenesis and migration of both granule cells and Purkinje cells suggests a role for this peptide in target recognition and synaptic organization.

Comparative distribution of N-acetylaspartylglutamate and GAD67 in the cerebellum and precerebellar nuclei of the rat utilizing enhanced carbodiimide fixation and immunohistochemistry

The most prevalent peptide in the nervous system, N-acetylaspartylglutamate (NAAG), specifically activates N-methyl D-aspartate (NMDA) receptors and a subclass of metabotropic glutamate receptors. One action of this peptide may be to modulate the release of other neurotransmitters, including gamma-aminobutyric acid (GABA). The present study describes the cellular distribution of NAAG, relative to GABA, in the cerebellum and precerebellar nuclei as a foundation for further physiological investigations. Numerous cells of origin for mossy fibers, including many of the larger neurons of the pontine nuclei, lateral reticular nuclei, vestibular nuclei, reticulotegmental nuclei, and spinal grey, were moderately to strongly stained for NAAG. Many NAAG-labeled fibers were clearly visible in the cerebellar peduncles and central white matter. Mossy fibers and mossy endings were among the most prominent NAAG-immunoreactive elements in the cerebellar cortex. Most neurons in the inferior olive were not stained for NAAG, and only sparse, lightly immunoreactive, climbing fiber-like endings could be identified in restricted regions of the cortical molecular layer. Purkinje neurons ranged from nonreactive to moderately positive, with the great majority being unstained. Cerebellar granule cells did not exhibit any NAAG immunoreactivity. A population of neurons in the deep cerebellar nuclei was highly immunoreactive for NAAG. Additionally, many neurons of the red nucleus were intensely stained for NAAG. Comparisons with staining for the 67 kD form of glutamic acid decarboxylase in serial sections revealed complementary distributions, with NAAG in excitatory pathways and cell groups, and glutamic acid decarboxylase in inhibitory systems. These findings suggest a significant functional involvement of NAAG in the excitatory afferent and efferent projection systems and provide an anatomical basis for investigations into the interactions of NAAG and GABA in the cerebellum.

Distribution of cholecystokinin binding sites in the North American opossum cerebellum

Previous studies in our laboratory have reported on the differential distribution of several neuropeptides, including the octapeptide cholecystokinin (CCK8), in the cerebellar cortex and nuclei of the North American opossum (Didelphis marsupialis virginiana). The present account reports on the distribution of CCK8 binding sites as determined from serial autoradiographic images of the cerebellum which were labelled by using [125I]Bolton Hunter sulfated CCK8. Evidence for the limited presence of CCK8-like immunoreactivity and CCK8 binding sites in several other species suggests that the distribution of this peptide and its receptor(s) may be species specific. In the opossum, CCK8-like immunoreactivity is present in mossy fiber terminals that distribute throughout the cerebellar cortex; it has a very limited distribution in climbing fibers (King and Bishop (1990) J. Comp. Neurol. 238, 373-384. CCK8 binding sites are present throughout all lobules of the cerebellar cortex and the cerebellar nuclei, which correlates well with the distribution of the peptide. CCK8-like immunoreactivity is located primarily in the granule cell layer, although the greatest density of binding sites is in the molecular layer. The presence of CCK8 is mossy fiber terminals, coupled with the presence of CCK8 binding sites in the cerebellar cortex, and the fact that CCK8 alters the firing rate of Purkinje cells (Madtes et al. (1992) Neurosci. Abstr. 18, 853) indicate this peptide may function as a neuromodulator in the cerebellum of the North American opossum.(ABSTRACT TRUNCATED AT 250 WORDS)

Glutamate-immunoreactive climbing fibres in the cerebellar cortex of the rat

The climbing fibre system, one of the two main excitatory inputs to the cerebellar cortex, is anatomically and physiologically well characterized, while the nature of its neurotransmitter is still a matter of debate. We wished to determine whether glutamate-immunoreactive profiles with the morphological characteristics of climbing fibres could be found in the rat cerebellar cortex. For this purpose, a monoclonal 'anti-glutamate' antibody has been used in combination with a sensitive postembedding immunoperoxidase method on semi-thin sections or in combination with a postembedding immunogold method on ultrathin sections. At the light microscopic level, climbing fibres appeared as strongly stained fibrous profiles, chains of interconnected varicosities or heavily labelled dots of various sizes, often in close apposition to principal Purkinje cell dendrites. At the electron microscopic level, certain labelled varicosities or more elongated profiles resembling climbing fibre terminals were in synaptic contact with dendritic spines of Purkinje cells. Quantitative analysis of gold particle densities showed that such elements were about three to four times more heavily labelled than their postsynaptic partners. The results obtained in this study demonstrate that at least a subset of climbing fibres and their terminals contain relatively high levels of glutamate-like immunoreactivity and provide additional evidence for a role of glutamate as transmitter in these cerebellar afferents.

A subpopulation of olivocerebellar projection neurons express neuropeptide Y

By neuropeptide Y (NPY) immunohistochemistry and in situ hybridization histochemistry with digoxigenin-labeled oligonucleotide probes for this peptide, a subpopulation of neurons in the caudal portions of the rat dorsal and medial accessory olives were found to express NPY immunoreactivity and mRNA. In the cerebellum, NPY-immunolabeled climbing fibers were distributed to the flocculus and parts of vermal cortex. The results suggest particular association of NPY with the climbing fiber system presumably mediating spinal, visual and vestibular inputs.

Localization of cholecystokinin binding sites in the adult and developing Brazilian opossum brain

Cholecystokinin (CCK) is now recognized as one of the most abundant peptides in the mammalian central nervous system. We have previously used immunohistochemistry to localize CCK in the adult and developing Brazilian opossum brain. However, little is known about the distribution of CCK binding sites in the developing mammalian brain. Therefore, to further our knowledge of the sites of action for CCK during development, we initiated a series of studies to localize CCK binding sites in the adult and developing Brazilian opossum. This species was chosen because pups are born in a fetus-like state. Receptor autoradiography was performed on coronally sectioned brains of 1 to 60 day postnatal (PN) animals and adults with 125I-Bolton Hunter-CCK-8 as the radioligand. Binding is evident in the 1PN opossum brainstem and is observed in the developing forebrain by 5PN. Region-specific binding increases during development, and binding in the 35PN brain resembles the adult pattern. Binding is evident prior to the detection of CCK-like immunoreactivity in many areas. The facial motor nucleus is identifiable and exhibits high levels of binding in Brazilian opossum pups of 10 to 35 days of age. However, binding is undetectable in the facial motor nucleus of 45 and 60PN pups. In general, the binding patterns for CCK in the adult opossum resemble those of other mammals and likely mediate similar physiological functions. However, some cholecystokininergic pathways appear to be unique to neonatal mammals.

Development of the olivocerebellar projection in the rat: I. Transient biochemical compartmentation of the inferior olive

In the present study the early phases of the development of the inferior olive were examined by using immunocytochemical techniques. We observed that, from embryonic day 16 onward, antibodies against the calcium binding proteins parvalbumin and calbindin and the calcitonin gene related peptide stain partially overlapping territories of the inferior olive. This staining delimits a biochemical zonation of the inferior olive which is combinatory and transient. We have previously observed a biochemical parcellation of the cerebellar Purkinje cells which, like that of the inferior olive, is first observed at E16, involves the combined expression of marker proteins and is also transient. In order to know whether the biochemical compartmentations of the cerebellum and inferior olive arise independently, the time course of the development of the olivocerebellar projection was studied by anterograde and retrograde in vitro axonal tracing by using the fluorescent carbocyanine dye DiI. The olivocerebellar axons were found to reach the limit of the cerebellar plate at E16 and to enter it at E17. Even at this age the great majority of the climbing fibers are tightly fasciculated, which minimizes their interactions with the PC clusters. These observations indicate that the topographical heterogeneity of Purkinje cells and inferior olive neurons arise independently. The transient biochemical individualization of subgroups of neurons during development could contribute to recognition mechanisms.

Calcitonin gene-related peptide in afferents to the cat's cerebellar cortex: distribution and origin

In the present study, the distribution and origin of calcitonin gene-related peptide (CGRP) were analyzed in the cat's cerebellum. Following incubation in an antibody generated against rat CGRP and processing with the peroxidase anti-peroxidase (PAP) technique, CGRP immunoreactivity (IR) is found in profiles that have morphological characteristics of both simple and complex mossy fibers. However, all mossy fibers are not CGRP-positive. Further, CGRP-IR mossy fibers have a heterogeneous distribution in the cerebellum. In the vermis, the majority of immunoreactive profiles are in lobules VII, VIII, and the dorsal folia of IX. In anterior vermal lobules, only scattered terminals, located primarily at the apex and along the shoulder of the folia, are present. Laterally, CGRP-IR mossy fibers are located in the paramedian lobule, paraflocculus, and crus II. No CGRP fibers or varicosities are observed in any of the cerebellar nuclei. However, CGRP-positive cell bodies are scattered throughout the nuclear neuropil. A double label technique revealed that CGRP-IR mossy fibers arise from neurons located in the lateral reticular nucleus, external cuneate nucleus, inferior vestibular nucleus, and basilar pons. The present findings, taken together with previous data, indicate that cerebellar afferents are chemically heterogeneous. The findings of the present study suggest that precerebellar nuclei that give rise to the mossy fibers that contain CGRP have the potential for playing a complex role in modulating circuitry in the cerebellar cortex of the cat.

Distribution and cerebellar projections of cholinergic and corticotropin-releasing factor-containing neurons in the caudal vestibular nuclear complex and adjacent brainstem structures

By using immunohistochemistry combined with lesioning and retrograde neuronal labeling techniques, cholinergic neurons and corticotropin-releasing factor-immunoreactive neurons were examined for their distribution, coincidence and cerebellar projections in feline vestibular nuclear complex and adjacent brainstem structures. Cholinergic neurons as revealed here with choline acetyltransferase immunoreactivity were found massively in the abducens and hypoglossal nuclei, dorsal motor nucleus of the vagus nerve and nucleus of Roller; less numerously in the medial vestibular, prepositus hypoglossi and solitary nuclei and the caudal two-thirds of descending vestibular nucleus; and only occasionally in the intercalated and supravestibular nuclei and cell groups f, x and z. Corticotropin-releasing factor-immunoreactive neurons were found clustered in the prepositus hypoglossi nucleus and also in cell groups f and x and the rostral two-thirds of descending vestibular nucleus, less numerously in the medial vestibular, intercalated and solitary nuclei and nucleus of Roller, and only occasionally in the caudal one-third of descending vestibular nucleus, the dorsal motor nucleus of the vagus nerve, supravestibular nucleus and cell group z. The lateral and superior vestibular nuclei did not contain either type of neuron. The two types of immunopositive neurons observed in most of the brainstem nuclei differed in cell size, distribution-pattern and rostrocaudal level of occurrence. While there were many regions which exhibited both types of immunopositive neurons, perikarya colocalizing the cholinergic and peptide markers were not detected in the brainstem. Following unilateral, partial lesioning of the vestibular nuclear complex, corticotropin-releasing factor-immunoreactive mossy fiber terminals (rosettes) disappeared from the ipsilateral flocculus. However, such lesions did not produce clear-cut changes of cholinergic terminals in the vermis. Following retrograde neuronal labeling combined with immunohistochemistry, the two types of immunopositive neurons observed in most of the brainstem sites were found to project to the vermal lobules I-III, IX and X. On comparison of these immunopositive projection neurons with non-immunoreactive, retrogradely labeled neurons, the cholinergic neurons and the peptide-immunoreactive neurons were found to constitute a major part of the total vestibulocerebellar neuronal population. The results indicate chemical heterogeneity in vestibular nuclear complex and cerebellar afferents.

Differential modulation of Purkinje cell activity by enkephalin and corticotropin releasing factor

Several peptides have been localized within afferents to the opossum's cerebellum, including cholecystokinin (15), enkephalin (16, 17) and corticotropin releasing factor (7, 9). Each of these peptides has a heterogeneous laminar and lobular distribution. Two peptide, enkephalin (ENK) and corticotropin releasing factor (CRF) are present in specific populations of climbing fibers and mossy fibers, which have an overlapping distribution in several areas of the cerebellum, in particular the lateral aspect of vermal lobules VII and VIII. Within this location ENK and CRF are co-localized in individual climbing fibers and mossy fibers (7). In the present study, the physiological effects of these peptides on Purkinje cell activity were analyzed. The data indicate that ENK and CRF have opposite effects on Purkinje cell activity. ENK suppresses spontaneous activity as well as that induced by application of glutamate and aspartate, as described previously (5). In contrast, CRF enhances both spontaneous and amino acid-induced unit activity. Further, when applied simultaneously, CRF blocks the suppressive effect induced by ENK. Previous studies have shown that climbing fibers, as well as the mossy fiber-parallel fiber pathway, are excitatory to Purkinje cells (11). However, immunohistochemical data have shown that these afferents are heterogeneous with respect to their chemical content (7-9, 15-17, 25). As found in the current and previous studies (3, 5) peptides in climbing and mossy fibers modulate the responsiveness of Purkinje cells to primary excitatory neurotransmitters in selected areas of the cerebellar cortex. However, the firing rate of individual Purkinje cells is differentially altered depending on which neurochemical messenger(s) are released.(ABSTRACT TRUNCATED AT 250 WORDS)

Ontogenesis of cerebellar afferents identified by cholecystokinin-like immunoreactivity

The present account provides a developmental timetable for the maturation of cholecystokinin (CCK)-positive fibers in the cerebellar cortex and cerebellar nuclei of the opossum. CCK-positive fibers are in the cerebellar peduncle by postnatal day (PD) 1, however they wait until PD 7 to penetrate the cerebellar anlage. Between PD 7 and PD 20 the fibers wait again in the medullary core of the cerebellum. After PD 20, there are 2 distinct patterns of CCK localization within the overlying cortical layers. The first pattern develops between PD 20-26 when CCK puncta are present in restricted foci within the Purkinje cell layer of the anterior lobe vermis. They distribute in 4 parasagittal bands, 2 on either side of the midline, that extend from the primary fissure rostrally into the anterior lobe of the cerebellum. By PD 33 two additional parasagittal bands are present in the posterior lobe vermis. The vast majority of these CCK puncta are transient in nature as all but a few disappear by PD 84. Those that remain progress through a series of developmental stages characteristic of climbing fiber ontogeny. These climbing fibers persist in lobules V, VII and VIII of the adult cerebellum. Further, there is a transient expression of CCK-immunoreactivity within inferior olivary neurons. These observations support the interpretation that the transient population of CCK-IR puncta are immature climbing fiber axons derived from the inferior olive. The second pattern of CCK localization is evident between PD 30-33, the time when granule cells first can be recognized in a histologically distinct internal granule cell layer (IGL). Between PD 30 and PD 68 there is a differential pattern of distribution of CCK-IR profiles within the lobules of the cerebellum. Initially, CCK-IR axons are only present in the anterior vermis where they are aligned in register with the bands of CCK puncta in the Purkinje cell layer. CCK-IR puncta are not present in the posterior lobe vermis or hemispheres until later stages of development. Further, a sagittal organization is not evident in either of these latter 2 areas. Initially, CCK-IR profiles in the IGL cannot be identified as mossy fibers based on their terminal morphology. When they first enter the IGL they appear as punctate elements. Over time they become increasingly more complex in shape and between PD 68-84 develop morphological characteristics of adult mossy fiber rosettes. The cerebellar nuclei can be distinguished histologically by PD 18, but CCK-IR fibers are not evident among these neurons until PD 36 which corresponds to about the time they can be visualized in the IGL. In addition, CCK-IR cell bodies first appear in the cerebellar nuclei between PD 26-30; these are present in the adult.(ABSTRACT TRUNCATED AT 400 WORDS)