Subcellular fractionation of rat cerebellum: an electron microscopic and biochemical investigation. III. Isolation of large fragments of the cerebellar glomeruli

Ricardo Tapia (1940 - 2021)

This is an Obituary to Ricardo Tapia, one of the most prominent Latin American neuroscientists of the second half of the 20th century, initiator of neurochemical research in Mexico and a huge advocate for scientific-driven policy. Ricardo Tapia passed away on September 8th 2021, at the age of 81. He was an Emeritus Professor at the Institute of Cellular Physiology, which he co-founded in the National Autonomous University of Mexico (UNAM). Ricardo was an outstanding leader and mentor to a large community of neurochemists in Mexico. Photo credit: Linda Lasky.

Exploring Subcellular Cerebellar Fractions with the Electron Microscope

Differential ultracentrifugation and subcellular fractionation historically helped to study the components of the cell, to discover new cellular organelles, and to decipher their morphological and molecular properties. In neuroscience, the technique has yielded important results on neuron biochemistry and the mechanisms of synaptic transmission. This Cerebellar Classic is devoted to the pioneering work of Manuel del Cerro, Ray S. Snider, and Mary Lou Oster-Granite, who isolated purified fractions after successive centrifugations of the rat cerebellum from birth to adulthood and studied them under the electron microscope.

Commentary on "Subcellular Fractions of Adult and Developing Rat Cerebellum, by M. del Cerro, R. S. Snider and M. L. Oster, July 1969"

Subcellular fractionation by differential ultracentrifugation has allowed the study of the cell and its organelles from a morphological, physiological, and biochemical perspective. Combined with electron microscopy, and by using animals at different stages of postnatal development, these methods yielded useful results concerning the ontogeny of synaptosomes, mitochondria, and myelin and broadened the possibilities to investigate the molecular underpinnings of cerebellar histogenesis.

Comparison of simple sucrose and percoll based methodologies for synaptosome enrichment

Synaptosomes are isolated nerve terminals. They represent an extremely attractive in vitro model system to study synaptic physiology since they preserve morphological and functional characteristics of the synapse. As such they have been used to investigate synaptic dysfunctions associated with neuropathologies like Alzheimer's disease. In the present work two simple methodologies for isolating synaptosomal-enriched fractions were compared for the first time. The starting points of both protocols were rat cortical or hippocampal homogenized tissues that underwent several differential centrifugation steps followed by a final purification of synaptosomal-enriched fractions using either a Percoll gradient or a Sucrose gradient. Comparison of the fractions obtained was carried out, using both biochemical and electron microscopy approaches. In the biochemical analysis the protein levels of pre-synaptic, post-synaptic, nuclear and mitochondrial markers were evaluated. Additional characterization of the synaptosomal-enriched fractions was performed using transmission electron microscopy. In summary, the results indicate that under the conditions tested the Sucrose based protocol is more efficient for the isolation of synaptosomal-enriched fractions from both neuronal tissues, being particularly efficient for hippocampus that is a less abundant brain tissue. Further, the sucrose protocol apparently results in a higher yield of viable synaptosomes suitable for further assays, including structural and functional studies of synapses; making this an attractive procedure to study processes associated with neuropathologies.

A rapid Percoll gradient procedure for preparation of synaptosomes

Homogenization of fresh brain tissue in isotonic medium shears plasma membranes causing nerve terminals to become separated from their axons and postsynaptic connections. The nerve terminal membranes then reseal to form synaptosomes. The discontinuous Percoll gradient procedure described here is designed to isolate synaptosomes from brain homogenates in the minimum time to allow functional experiments to be performed. Synaptosomes are isolated using a medium-speed centrifuge, while maintaining isotonic conditions and minimizing mechanically damaging resuspension steps. This protocol has advantages over other procedures in terms of speed and by producing relatively homogeneous synaptosomes, minimizing the presence of synaptic and glial plasma membranes and extrasynaptosomal mitochondria. The purified synaptosomes are viable and take up and release neurotransmitters very efficiently. A typical yield of synaptosomes is between 2.5 and 4 mg of synaptosomal protein per gram rat brain. The procedure takes approximately 1 h from homogenization of the brain until collection of the synaptosomal suspension from the Percoll gradient.

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).

Secondary vestibular cholinergic projection to the cerebellum of rabbit and rat as revealed by choline acetyltransferase immunohistochemistry, retrograde and orthograde tracers

Previously we have shown that four regions of the cerebellum, the uvula-nodulus, flocculus, ventral paraflocculus, and anterior lobe 1, receive extensive, but not exclusive, cholinergic mossy fiber projections. In the present experiment we have studied the origin of three of these projections in the rat and rabbit (uvula-nodulus, flocculus, ventral paraflocculus), using choline acetyltransferase (ChAT) immunohistochemistry in combination with a double label, retrogradely transported horseradish peroxidase (HRP). We have demonstrated that in both the rat and rabbit the caudal medial vestibular nucleus (MVN) and to a lesser extent the nucleus prepositus hypoglossus (NPH) contain ChAT-positive neurons. Neurons of the caudal MVN are double-labeled following HRP injections into the uvula-nodulus. HRP injections into the uvula-nodulus also labeled less than 5% of the neurons in the cholinergic vestibular efferent complex. Fewer ChAT-positive neurons in the MVN and some ChAT-positive neurons in the NPH are double-labeled following HRP injections into the flocculus. Almost no ChAT-positive neurons in the MVN and some ChAT-positive neurons in the NPH are double-labeled following HRP injections into the ventral paraflocculus. Injections of Phaseolus leucoagglutinin (PHA-L) into the caudal MVN of both the rat and rabbit demonstrated projection patterns to the uvula-nodulus and flocculus that were qualitatively similar to those observed using ChAT immunohistochemistry. We conclude that the cholinergic mossy fiber pathway to the cerebellum in general and the uvula-nodulus in particular is likely to mediate secondary vestibular information related to postural adjustments.

An improved method for the preparation of rat cerebellar glomeruli

Cerebellar glomeruli consist of large portions of the mossy fiber giant terminal, granule cell dendrites and Golgi neuron terminals. By modifying previously reported procedures we have developed a new method for bulk preparation of this polysynaptic complex from rat cerebellum. We obtained well preserved isolated glomeruli of satisfactory purity and homogeneity as indicated by electron microscopy and by determination of appropriate biochemical markers. The method is fast and simple, and it provides a glomerular fraction suitable for investigation of neurotransmitter receptors.

Non-NMDA excitatory amino acid receptors in a subcellular fraction enriched in cerebellar glomeruli

In the internal granular layer of the cerebellar cortex the polysynaptic complexes called glomeruli consist mainly of homogeneous populations of glutamatergic and GABAergic synapses, both located on granule cell dendrites. A subcellular fraction enriched in glomeruli was prepared from rat cerebellum, and the distribution of the different types of NMDA and non-NMDA glutamate binding sites was studied in the membranes derived from this fraction (fraction G) as compared to that in the membranes prepared from a total cerebellar homogenate (fraction T). Cl-/Ca2+ independent [3H]glutamate binding sites were not abundant and could be reliably measured only in fraction G. Cl- dependent/Ca2+ activated [3H]glutamate binding sites were more abundant and exhibited a single KD in both fractions G and T. Quisqualate, NMDA, kainate, L-AP4 and trans-ACPD inhibited [3H]glutamate binding to different extents in the two membrane fractions. Quisqualate sensitive sites were predominant in all cases but more abundant in fraction T than in fraction G. An opposite distribution was observed for the NMDA sensitive binding sites while kainate sensitive binding sites were scarce everywhere. Trans-ACPD, a ligand presumed selective for metabotropic glutamate binding sites, displaced [3H]glutamate from fraction T but nor from fraction G, suggesting the absence of these sites from glomeruli. Similarly, no L-AP4 sensitive sites were present in fraction G while they were abundant in fraction T. Binding sites associated with ionotropic receptors of the quisqualate type were determined by measuring [3H]AMPA binding. The density of the high affinity [3H]AMPA binding sites in fraction T was twice as high as in fraction G, indicating that these sites are abundant in structures other than glomeruli.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic dietary choline influences the permeability of nerve cell membranes as revealed by in vivo Rb+ uptake and release

The effect of chronic choline supplementation on the in vivo Rb+ uptake and release of rat brain cortical cells was investigated. Adult (11 months old) and old (22 months old) controls as well as old (22 months old) female rats treated with choline (approximately 100 mg/day in the drinking water) by the age of 11 months, were used. All the animals received a daily dose of 30 mg RbCl/100 g body weight for 14 days, given intraperitoneally, half in the morning, half in the evening. After discontinuation of the RbCl treatment, the animals were killed at intervals of 2, 4, 9 and 16 days, respectively. The intracellular Rb+ and K+ contents were analyzed by energy dispersive X-ray microanalysis, whereas concentrations of these two elements were determined by atomic absorption spectrophotometry in the cerebrospinal fluid. Old animals accumulate more Rb+ than the adult ones at any time taken into account. Choline treatment was able to reduce the amount of accumulated Rb+ in the old rats. Rb+-discrimination ratios calculated on the basis of Rb+ and K+ contents of both cortical cells and cerebrospinal fluid, is higher in old rats as compared to both adult and old choline treated rats. Present findings support that chronic choline treatment is effective improving the passive membrane permeability of nerve cells for Rb+ (and K+) in the old animals.

Neurotransmitters of the cerebellar glomeruli: uptake and release of labeled gamma-aminobutyric acid, glycine, serotonin and choline in a purified glomerulus fraction and in granular layer slices

We have studied some properties of the uptake and release of labeled gamma-aminobutyric acid (GABA), glycine, serotonin and choline in a purified fraction of glomeruli and in slices of the granular layer of the rat cerebellum. The uptake of both GABA and glycine into the glomerulus particles was dependent on the presence of Na+ in the medium. In contrast, the uptake of both serotonin and choline was Na+-independent. In slices of the granular layer also a slight Na+-dependence was observed for both serotonin and choline uptake; imipramine and hemicholinium partially inhibited the uptake of serotonin and choline, respectively. Choline uptake into the glomerulus particles showed two components, with apparent Km values of 16.8 and 102 microM. GABA release was stimulated by K+-depolarization about 100% (peak stimulation) and this value was reduced to 50% when Ca2+ was omitted. The release of glycine was stimulated more rapidly and notably than GABA (200%) and this stimulation was completely abolished in the absence of Ca2+. Serotonin release from the glomerulus particles was only slightly stimulated by depolarization, but this stimulation was strictly Ca2+-dependent. In slices of the granular layer, this stimulation was considerably larger (about 40%) and it was also almost totally dependent on Ca2+. In contrast, after loading with labeled choline the release of radioactivity from both the glomerulus particles and the cerebellar slices was not stimulated at all by K+-depolarization, either in the presence or in the absence of Ca2+. Most of the radioactivity released spontaneously corresponded to choline, and only a small proportion (8-14%) to acetylcholine. From the results of the release experiments and taking into account the pertinent data from the literature, it is concluded that GABA and glycine are probably the transmitters of different populations of Golgi axon terminals, whereas serotonin might be the transmitter of at least a certain population of the mossy fiber giant terminals, in the rat cerebellar glomeruli. In contrast, acetylcholine does not seem to have any transmitter role in the synaptic structures of the glomeruli.

Isolation of glomeruli from areas of bovine cerebellum and comparison of [3H]serotonin uptake

A method for bulk preparation of glomerular particles from subdivisions of the bovine cerebellum is presented. This method represents a modification of that previously reported by Hajos et al. [8], which increases the yield of glomerular protein by five-fold (5.5 mg/g wet wt) without compromising structural integrity or homogeneity. In addition, it offers the advantage of allowing one to study intraregional variations in the metabolic properties of cerebellar glomeruli. [3H]Serotonin (5-HT) uptake was measured in this preparation and it was demonstrated that glomeruli possess an active high affinity mechanism for this substrate. Comparison of [3H]5-HT uptake by glomeruli isolated from the cerebellar cortices of the lateral hemispheres and vermis revealed no differences in their kinetic properties.

Chronic dietary choline modulates synaptic plasticity in the cerebellar glomeruli of aging mice

A morphometric investigation was carried out on ethanolic phosphotungstic acid (E-PTA) stained synaptic junctions in the cerebellar glomeruli of adult, old, old choline-deficient and old choline-supplemented mice. Numerical (Nv) and surface (Sv) density as well as average length (L) of the synapses were calculated on 100 pictures per group. A significant reduction of Nv and Sv, as well as an increase of L was found during aging. Choline deficient animals did not show any change as compared to old animals of the same age. In choline supplemented mice Nv and Sv were significantly increased and L significantly decreased, respectively, as compared to old control littermates. No difference was found between adult and choline supplemented mice. In the cerebellar glomeruli only a small fraction of fibers are cholinergic, therefore the present findings support the idea that dietary choline can influence systems other than cholinergic. The possible role of choline supplementation in the modulation of synaptic plasticity via the synthesis and/or turnover of neuronal membrane choline phospholipids, is discussed.

Muscarinic receptor during postnatal development of rat cerebellum: an index of cholinergic synapse formation?

Quantitative and qualitative modifications of the specific binding sites for [3H]quinuclidinyl benzylate (QNB), a muscarinic antagonist, were studied during rat cerebellar postnatal development. Specific binding sites for QNB (QNB-sbs), regardless of whether they correspond to muscarinic acetylcholine receptors, are present with the highest density in the archicerebellar cortex, but the total amount per region is about the same in the archi -, paleo-, and neocerebellar cortex regions. Large amounts of QNB-sbs are also present in a cerebellar fraction including central white matter and deep cerebellar nuclei. QNB-sbs are low but present at birth and then accumulate during ontogenic development according to a curve which duplicates, with a delay of a few days, the curve of DNA accumulation. Dissection studies indicated that this curve does not depend on the preferential localization of QNB-sbs in a specific cerebellar region nor on the particular development of this region. The similarity of the QNB-sbs and the DNA developmental curves might indicate that the QNB-sbs are present on granule cells; however, a comparative analysis of the data in the literature suggests that a great many QNB-sbs are located on the Purkinje cell dendrites in the molecular layer, where all or some of them might correspond to the extrajunctional muscarinic acetylcholine receptor detected there by electrophysiology. It would appear that only a small percentage of cerebellar QNB-sbs corresponds to the cholinergic synapses present in cerebellar cortex; hence, the question of muscarinic receptors in the cerebellum should be re-examined.

Immunohistochemical localization of choline acetyltransferase in rabbit forebrain

uinea pig antiserum specific to the purified bovine choline acetyltransferase was used to demonstrate the localization of this enzyme in rabbit forebrain by the peroxidase-antiperoxidase immunohistochemical method. Choline acetyltransferase was localized in olfactory bulb, olfactory tract, olfactory tubercle, piriform cortex, septum, diagonal band, basal ganglia, thalamus, hypothalamus, subthalamus, habenula, cerebral cortex, hippocampal region, corpus callosum, internal capsule, fornix, longitudinal striae and other areas. The findings reflect the distribution of cholinergic axons and, possibly, their terminals. These observations correlate well with biochemical determinations of choline acetyltransferase and with previously proposed cholinergic pathways.

Localization of high affinity [3H]glycine transport sites in the cerebellar cortex

A study was made of [3H]glycine uptake sites in a preparation greatly enriched in large pieces of the cerebellar glomeruli (glomerulus particles) and in morphologically well preserved slices of rat cerebellum. Electron microscopic autoradiography revealed that of the neurones in the cerebellar cortex only Golgi cells transported [3H]glycine at the low concentration used. Glial cells also took up [3H]glycine but to a lesser extent than the Golgi neurons. It was also confirmed that under comparable conditions Golgi cells transport [3H]GABA. Kinetic studies utilizing the Golgi axon terminal-containing glomerulus particles showed that glycine is a weak non-competitive inhibitor of [3H]GABA uptake (Ki over 600 microM vs the Kt of about 20 microM) and that GABA is an even weaker inhibitor of [3H]glycine uptake. These observations indicated that glycine and GABA do not share the same carrier. Quantitative electron microscopic autoradiography showed that the uptake of the two amino acids, in terms of the unit area of labelled Golgi axon terminals, was not additive. In contrast, their uptake in terms of unit protein was strictly additive. These observations, the first relating to unit volume and the latter to the total volume of Golgi terminals, are consistent with the view that there are two biochemically separate populations of Golgi neurons, one transporting glycine the other GABA. Saturable [3H]strychnine binding was detected in the preparations of glomerulus particles, but in comparison with those from the spinal cord the affinity was lower and [3H]strychnine was not displaced by glycine. Available information on glycine receptors, however, suggest that this should not exclude the possibility of strychnine resistant glycine receptors in the rat cerebellum.

Antibodies to synaptic vesicles purified from Narcine electric organ bind a subclass of mammalian nerve terminals

Antibodies were raised in rabbits to synaptic vesicles purified to homogeneity from the electric organ of Narcine brasiliensis, a marine electric ray. These antibodies were shown by indirect immunofluorescence techniques to bind a wide variety of nerve terminals in the mammalian nervous system, both peripheral and central. The shared antigenic determinants are found in cholinergic terminals, including the neuromuscular junction, sympathetic ganglionic and parasympathetic postganglionic terminals, and in those synaptic areas of the hippocampus and cerebellum that stain with acetylcholinesterase. They are also found in some noncholinergic regions, including adrenergic sympathetic postganglionic terminals, the peptidergic terminals in the posterior pituitary, and adrenal chromaffin cells. They are, however, not found in many noncholinergic synapse-rich regions. Such regions include the molecular layer of the cerebellum and those laminae of the dentate gyrus that receive hippocampal associational and commissural input. We conclude that one or more of the relatively small number of antigenic determinants in pure electric fish synaptic vesicles have been conserved during evolution, and are found in some but not all nerve terminals of the mammalian nervous system. The pattern of antibody binding in the central nervous system suggests unexpected biochemical similarities between nerve terminals heretofore regarded as unrelated.

Immunohistochemical localization of choline acetyltransferase in the human cerebellum

Guinea pig antiserum specific to purified bovine choline acetyltransferase was found to cross-react with human enzyme. The peroxidase-antiperoxidase immunohistochemical method was then used to demonstrate the localization of choline acetyltransferase in formalin-fixed and paraffin-embedded human cerebellum from normal as well as from Huntington's disease brains. Choline acetyltransferase was localized exclusively in the mossy fibers and the glomeruli of the cerebellar folia. These immunohistochemical findings reveal the distribution of cholinergic axons and their terminals. The results are not only similar to our previous studies using the same method on the localization of choline acetyltransferase in rabbit cerebellum, but also demonstrate that some mossy fibers are cholinergic as suggested by others.

Subcellular fractionation of rat cerebellum: separation of synaptosomal populations and heterogeneity of mitochondria

A crude mitochondrial fraction (M) derived from manually disrupted cerebellar tissue and enriched in choline acetyltransferase (ChAT) activity was fractionated by centrifugation in discontinuous and continuous sucrose gradients. Further purification of 'cholinergic' synaptosomes was achieved (relative specific activity (RSA) of ChAT greater than 3), but the overlap with other synaptosomal populations was still considerable. Hand-homogenized cerebella processed through the full fractionation procedure described here and in previous papers yielded preparations enriched in certain neuronal structures and a fraction in which 'heavy' free mitochondria was concentrated. To characterize these preparations the activities of two transmitter enzymes (CHAT and glutamate decarboxylase, GAD) and 6 mitochondrial enzymes (succinate dehydrogenase (SDH), glutamate dehydrogenase (GDH), monoamine oxidase, citrate synthase, fumarase and GABA-aminotransferase) were determined. The distribution of the transmitter enzymes was clearly different in the preparations containing various neuronal structures. The GAD:ChAT RSA ratio was 2.4 for the glomerulus particles, 1.3 for the molecular layer fragments, 0.6 for the myelinated axon segments, and 0.2 for the 'cholinergic' synaptosomes. The mitochondrial enzyme profile of the preparations comprising mainly neuronal structures differed markedly from that of the 'free' mitochondrial fraction. Notably the latter was greatly enriched in GDH (RSA 5.6), whereas the SDH:GDH RSA ratio was relatively high in the former preparations. Nevertheless there were notable differences in the enzyme profile of the fractions of predominantly neuronal origin indicating that the enzyme composition of mitochondria of neuronal processes is not uniform.

Immunohistochemical localization of choline acetyltransferase in rabbit spinal cord and cerebellum

Guinea pig antiserum specific for purified bovine choline acetyltransferase has been shown to cross-react with rabbit enzyme. We used the peroxidase-antiperoxidase immunohistochemical method to demonstrate the localization of choline acetyltransferase in formalin-fixed and paraffin-embedded sections of rabbit spinal cord and cerebellum. In the spinal cord, in agreement with our and others' previous results using immunofluorescent techniques, choline acetyltransferase was found in the cell bodies of the ventral horn motor neurons. In the cerebellum, choline acetyltransferase was localized exclusively in the mossy fibers and the glomeruli of the cerebellar folia. The immunohistochemical findings in the cerebellum reveal the morphological detail of cholinergic axons and their terminals. The results are consistent with published biochemical data on the cerebellar distribution of choline acetyltransferase.

Morphological and biochemical studies on isolated molecular and granular layers from bovine cerebellum

Molecular layer, granular layer and white matter are dissected from bovine cerebellum under optical microscope and without freezing under conditions which preserve their main anatomical features. Polyacrylamide gel electrophoresis in sodium dodecyl sulphate of the isolated layers reveal that the P400 protein characteristic of the Purkinje cells is found in the isolated molecular layer and in the molecular layer free from Purkinje cell soma, but not in the granular layer or white matter. The histones (F1, F2A1,2, F2B, F3) are abundant in the granular layer and myelin proteins in the white matter. The DNA content per wet weight is 10 times greater in the isolated granular layer than in the other layers and the RNA content twice as great in the granular layer than in any other layer. The specific activity of acetylcholinesterase is 4 times greater in the granular layer than in the other layers. Homogenates of the isolated layers take up labeled amino-acids and the velocity of glutamate incorporation is 9 times greater in the molecular layer than in the granular layer, while GABA incorporation is about twice as great in the granular layer than in the molecular layer. Homogenates of isolated molecular layer are centrifuged on discontinuous Ficoll gradient after incubation with L[3H]glutamate and [14C]GABA. The analysis of the distribution of glutamate and GABA after centrifugation reveals that the particles which incorporate glutamate can be separated from those which take up GABA.

Characterization of an antiserum to synaptic glomeruli from rat cerebellum

Rabbit anti-rat cerebellar synaptic glomeruli antiserum when absorbed with non-neural tissues reacts only with neural tissues when tested by indirect immunofluorescence on tissue sections. Further absorption with forebrain results in the antiserum which detectably reacts only with synaptic glomeruli and soma of Purkinje cells of both rat and mouse. The developmental expression of the synaptic glomeruli antigen(s) parallels the formation of synapses between mossy fibers and granule cells. Immature synaptic contacts do not contain recognizable antigen(s), whereas only at postnatal Day 15 glomeruli become antigen-positive. At this stage antigen in Purkinje cells is no longer carried in their dendrites, but becomes confined to the cell soma. Staggerer mutant mice still express the immature pattern of antigen distribution on postnatal Day 18.