On the cellular localization of cerebellar muscarinic receptors: an autoradiographic analysis of weaver, reeler, Purkinje cell degeneration and staggerer mice

Chronic exposure to methadone induces activated microglia and astrocyte and cell death in the cerebellum of adult male rats

Methadone is a centrally-acting synthetic opioid analgesic widely used in the methadone maintenance therapy (MMT) programs throughout the world. Considering its neurotoxic effects particularly on the cerebellum, this study aims to address the behavioral and histological alterations in the cerebellar cortex associated with methadone administration. Twenty-four adult male albino rats were randomized into two groups of control and methadone treatment. Methadone was subcutaneously administered (2.5-10 mg/kg) once a day for two consecutive weeks. The functional and structural changes in the cerebellum were compared to the control group. Our data revealed that treating rats with methadone not only induced cerebellar atrophy, but also prompted the actuation of microgliosis, astrogliosis, and apoptotic biomarkers. We further demonstrated that treating rats with methadone increased complexity of astrocyte processes and decreased complexity of microglia processes. Our result showed that methadone impaired motor coordination and locomotor performance and neuromuscular activity. Additionally, relative gene expression of TNF-α, caspase-3 and RIPK3 increased significantly due to methadone. Our findings suggest that methadone administration has a neurodegenerative effect on the cerebellar cortex via dysregulation of microgliosis, astrogliosis, apoptosis, and neuro-inflammation.

Regional brain variations of cytochrome oxidase activity inRelnrl-orl mutant mice

Cell malpositioning has been described in laminated structures of the spontaneous mutation, reeler, including the cerebellum, the hippocampus, and the neocortex. Despite the ectopic positions of different neuronal populations, the specificity of synaptic connections is maintained. The metabolic consequences of this form of neuropathology were examined in Reln(rl) mutant mice by quantitative measures of cytochrome oxidase (CO) activity, a mitochondrial enzyme essential for oxidative metabolism in neurons. Despite severe tissue disorganization but in line with the intact synaptic organization, the reeler mutation did not affect global metabolic activity of the laminated structures of the brain. CO activity, however, was altered in specific subregions of the cerebellum, hippocampus, and neocortex, as well as in septum and various brainstem (medial pontine, paramedial reticular, paragigantocellular reticular) regions anatomically related to these structures, attesting to large functional alterations in Reln(rl-orl) brain. Metabolic activity variations were also detected in the ventral tegmental area and ventral neostriatum of the mesolimbic dopaminergic pathway. The results are discussed and compared to the regional CO variations found in other ataxic mice, in regard to the structural defects, the integrity of the connections, and the mutation-specific effects.

Differential messenger RNA expression of complexins in mouse brain

Complexins (CPLXs) are small isomeric proteins that bind to the soluble NSF-attachment protein receptor (SNARE) complex and modulate neurotransmitter release. Two isoforms of CPLX exist in the brain, CPLXI and CPLXII. These are differentially distributed in the cortex and cerebellum, with CPLXI found in axosomatic terminals and CPLXII in axodendritic terminals. Since in cortex and cerebellum axosomatic terminals are inhibitory and axodendritic terminals are excitatory, it has been assumed that CPLXI modulates inhibitory and CPLXII modulates excitatory transmitter release. Here we used in situ hybridisation to study the mRNA distribution of CPLXI and CPLXII in mouse brain. We show that while CPLXs are expressed in distinct cell populations, they do not segregate with either particular neurotransmitters, or different classes of transmitter action. For example, while CPLXII is the dominant isoform in the output (glutamatergic excitatory) neurons of the cortex, it is also the dominant isoform in medium spiny (GABAergic inhibitory) neurons of the striatum. We suggest that the functional role of CPLXs depends not only on the identity of the neurotransmitter, but also upon the circuitry connecting the neurons in which they are expressed. Thus, the predominant expression of CPLXII in neurons of the basal ganglia and cortex suggests a role in cognition, emotional behaviour and control of voluntary movement, while the pattern of CPLXI expression suggests a primary role in motor learning programs and sensory processing.

Cholinergic innervation and receptors in the cerebellum

We have studied the source and ultrastructural characteristics of ChAT-immunoreactive fibers in the cerebellum of the rat, and the distribution of muscarinic and nicotinic receptors in the cerebellum of the rat, rabbit, cat and monkey, in order to define which of the cerebellar afferents may use ACh as a neurotransmitter, what target structures are they, and which cholinergic receptor mediate the actions of these pathways. Our data confirm and extend previous observations that cholinergic markers occur at relatively low density in the cerebellum and show not only interspecies variability, but also heterogeneity between cerebellar lobules in the same species. As previously demonstrated by Barmack et al. (1992a,b), the predominant fiber system in the cerebellum that might use ACh as a transmitter or a co-transmitter is formed by mossy fibers originating in the vestibular nuclei and innervating the nodulus and ventral uvula. Our results show that these fibers innervate both granule cells and unipolar brush cells, and that the presumed cholinergic action of these fibers most likely is mediated by nicotinic receptors. In addition to cholinergic mossy fibers, the rat cerebellum is innervated by beaded ChAT-immunoreactive fibers. We have demonstrated that these fibers originate in the pedunculopontine tegmental nucleus (PPTg), the lateral paragigantocellular nucleus (LPGi), and to a lesser extent in various raphe nuclei. In both the cerebellar cortex and the cerebellar nuclei these fibers make asymmetric synaptic junctions with small and medium-sized dendritic profiles. Both muscarinic and nicotinic receptor could mediate the action of these diffuse beaded fibers. In the cerebellar nuclei the beaded cholinergic fibers form a moderately dense network, and could in principle have a significant effect on neuronal activity. For instance, the cholinergic fibers arising in the PPTg may modulate the excitability of the cerebellonuclear neurons in relation to sleep and arousal (e.g. McCormick, 1989). Studies on the distribution of cholinergic markers in the cerebellum have proven valuable besides the issue whether cholinergic mechanism play a role in the cerebellar circuitry, because they illustrate a complexity of the cerebellar anatomy that extends beyond its regular trilaminar and foliar arrangement. For instance, AChE histochemistry has been shown to preferentially stain the borders of white matter compartments (the 'raphes', Voogd, 1967), and therefore is useful in topographical analysis of the cortico-nuclear and olivocerebellar projections (Hess and Voogd, 1986; Tan et al., 1995; Voogd et al., 1996; see Voogd and Ruigrok, 1997, this Volume). ChAT-immunoreactivity, at least in rat, appears to be a good marker to outline the morphological heterogeneity of mossy fibers, and m2-immunocytochemistry could be used to label (subpopulations of) Golgi cells, subsets of mossy fibers and, in the rabbit, a specific subset of Purkinje cells (Jaarsma et al., 1995).

Light-microscopic distribution and parasagittal organisation of muscarinic receptors in rabbit cerebellar cortex

Recent studies on the effects of intrafloccular injections of muscarinic agonists and antagonists on compensatory eye movements in rabbit, indicate that muscarinic receptors may play a modulatory role in the rabbit cerebellar circuitry. It was previously demonstrated by Neustadt et al. (1988), that muscarinic receptors in rabbit cerebellar cortex are distributed into alternating longitudinal zones of very high and very low receptor density. In the present study, the zonal and cellular distribution of muscarinic receptors in the rabbit cerebellar cortex is investigated in detail using in vitro ligand autoradiography with the non-selective high-affinity antagonist [3H]quinuclidinyl benzilate (QNB), and the M2-specific antagonist [3H]AF-DX384, and immunocytochemistry with a monoclonal antibody specific for the cloned m2 muscarinic receptor protein. [3H]QNB and [3H]AF-DX384 binding sites and m2-immunoreactivity had similar overall distributions: dense labeling occurred in the dendritic arbors of a subset of Purkinje cells that are organized into parasagittal bands. A high level of muscarinic receptor labeling was also observed in a thin substratum of the molecular layer immediately above the Purkinje cell layer of the vestibulo-cerebellar lobules, i.e. the nodulus, the ventral uvula and the flocculus. Labeling in this stratum was associated with densely packed fibres, which were putatively identified as parallel fibres. Also Golgi cells, which were localized in part in the molecular layer, and a subset of mossy fibre rosettes, primarily concentrated in lobule VI, were immunoreactive for the m2 receptor. The parasagittal band of labeled Purkinje cell dendrites were most prominent in the anterior lobe (lobules I-V), in crus 1 and 2, in the flocculus, the ventral paraflocculus and the rostral folium of the nodulus. In other lobules, only infrequent Purkinje cells contained muscarinic receptors. The parasagittal organisation of muscarinic receptors differed from that of zebrin I, a Purkinje cell-specific protein which is often used as a marker of parasagittal parcelation of the cerebellar cortex. In the anterior lobe, however, there was a partial correspondence between muscarinic receptor and zebrin I bands. In the flocculus the distribution of muscarinic-receptor-positive Purkinje cells was related to the distinct white matter compartments as revealed with acetylcholinesterase (AChE) histochemistry. Muscarinic receptor-containing Purkinje cells were located primarily in the floccular zone 1, which is implicated in the control of eye movements about a horizontal axis. In order to relate the distribution of muscarinic receptor labeling to that of cholinergic nerve terminals, [3H]QNB binding sites and sodium-dependent [3H]hemicholinium-3 binding were compared. Sodium-dependent [3H]hemicholinium-3 binding sites mainly occurred in the granule cell layer of the vestibulo-cerebellum, which corresponds well with the distribution of the acetylcholine synthesizing enzyme, choline acetyltransferase (ChAT). However, sodium-dependent [3H]hemicholinium binding complemented, rather than co-localized with, muscarinic receptors which were primarily distributed in the molecular layer of the lobules of the vestibulo-cerebellar lobules. Their functional significance is puzzling, since their distribution does not correspond to that of markers of cholinergic innervation.

Levels of somatostatin and cholecystokinin in the brain of ataxic mutant mice

Changes in immunoreactive somatostatin (SOM) and cholecystokinin (CCK-8) levels in the cerebellum and cerebrum were investigated in three types of genetically-determined ataxic mutant mice: rolling mouse Nagoya (RMN), weaver, and Purkinje cell degeneration (PCD) mice. The cerebellar pathology in each of these types differs. The concentration of both SOM and CCK-8 (ng/mg weight) was significantly higher in the cerebellum and the cerebrum of the three types of ataxic mutant mice than in these regions in the respective controls. SOM and CCK-8 content (ng/organ) was significantly higher in PCD and RMN than in controls but this was not in the weaver mice. The possible involvement of both peptides in manifestations of ataxia is discussed.

Age-related changes in cholinergic and noradrenergic transmission in the rat cerebellum. A histochemical and immunocytochemical study

The histochemical and immunocytochemical distribution of some cholinergic and noradrenergic markers was compared in the cerebellum of young adult (3-month old) and aged (24-month old) Wistar rats. A decrease in the density and staining of acetyl cholinesterase (AChE) positive fibers, puncta and Golgi cells was found in both the cerebellar cortex and nuclei of aged rats. The age-related changes in choline acetyltransferase immunoreactivity were less pronounced than the changes in AChE activity. A reduction in the density of catecholamine fluorescent fibers and puncta was observed in the cerebellar cortex during aging. In aged rats the increase in monoamine oxidase (MAO)-A activity was more pronounced than the increase in MAO-B activity.

Distribution of muscarinic receptors in the developing rodent cerebellum

The distribution of muscarinic receptors in the developing rodent cerebellum was studied by light microscopic autoradiography of [3H]quinuclidinyl benzilate binding sites. Muscarinic receptors were not detected in the mouse cerebellar plate until embryonic day 16, at which time they were clustered in the ventromedial region of the cerebellar anlagen. At postnatal day 1, additional areas of higher grain density became visible in the dorsolateral medullary zone, internal to the newly forming granular layer. Labeling increased throughout the entire cerebellum between postnatal days 5 and 10, becoming markedly higher in the lateral hemispheres than in the vermis. This elevated density of binding sites in the hemispheres became reduced to that of the vermis by postnatal day 13 in the mouse, and PD20 in the rat. In adult animals, the cortical grain density was highest in the granule and Purkinje cell layers, low in the molecular layer and absent from the white matter. Receptor labeling was, however, observed over many areas of white matter throughout early development; this became more restricted to specific tracts during the third postnatal week. At no time during development were binding sites observed in the external germinal layer. Microvessels and capillaries, structures which have been shown to contain [3H]quinuclidinyl benzilate binding sites, may partially account for the observed ontogenic pattern.

Topographical distribution of muscarinic cholinergic receptors in the cerebellar cortex of the mouse, rat, guinea pig, and rabbit: a species comparison

Light microscopic autoradiography of [3H]quinuclidinyl benzilate (QNB) binding sites was used to study the distribution of muscarinic acetylcholine receptors in the mouse, rat, guinea pig, and rabbit cerebellar cortex. In the mouse, the laminar distribution of grain density was similar throughout the cortex, with slightly higher levels over lobules IX and X. The highest [3H]QNB labeling was present over the granule cell layer, and low levels were observed over the molecular layer. In the rat, the general distribution was similar to that of the mouse in that the granule cell layer was most densely labeled and the highest concentration of [3H]QNB binding sites was present in lobules IX and X of the archicerebellum. In these lobules, however, the laminar distribution of grain density was reversed so that the molecular layer was more densely labeled than the granule cell layer. In addition, several discrete columns of elevated grain density traversed the granule cell layer in caudal regions of lobule IX. The distribution of [3H]QNB binding sites in the guinea pig cerebellum was similar to that of the rat in that the molecular layer of lobules IX and X was again more intensely labeled than other cerebellar regions. In the remaining lobules, grain density was equal over the granule cell and molecular layers. In the rabbit cerebellar cortex, slightly higher grain density was observed in the granule cell layer than in the molecular layer. In lobules IX and X and in the hemisphere of X, the Purkinje cell layer was most densely labeled; parasagittal columns of very high grain density were present over the molecular layer of several cortical regions, including lobules, I, II, III, IV, V, IX, X, and the hemispheres of IX and X. Since muscarinic receptors have previously been found on blood vessels, there is a possibility that some proportion of receptor labeling may be localized to these structures. Microvessels and capillaries in each of the species examined were more numerous in the granule cell layer than in the molecular layer and white matter. The distribution of blood vessels in many cerebellar lobules of mice, rats, and guinea pigs corresponded quite closely to the general distribution of [3H]QNB binding sites. Unique patterns of labeling in lobules IX and X were not accompanied by corresponding patterns of blood vessel distribution, however. In the mouse, there was a slight increase in muscarinic receptor density observed in the archicerebellum, with no corresponding increase in the density of blood vessels.(ABSTRACT TRUNCATED AT 400 WORDS)