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

Fundamental Mechanisms of Autoantibody-Induced Impairments on Ion Channels and Synapses in Immune-Mediated Cerebellar Ataxias

In the last years, different kinds of limbic encephalitis associated with autoantibodies against ion channels and synaptic receptors have been described. Many studies have demonstrated that such autoantibodies induce channel or receptor dysfunction. The same mechanism is discussed in immune-mediated cerebellar ataxias (IMCAs), but the pathogenesis has been less investigated. The aim of the present review is to evaluate what kind of cerebellar ion channels, their related proteins, and the synaptic machinery proteins that are preferably impaired by autoantibodies so as to develop cerebellar ataxias (CAs). The cerebellum predictively coordinates motor and cognitive functions through a continuous update of an internal model. These controls are relayed by cerebellum-specific functions such as precise neuronal discharges with potassium channels, synaptic plasticity through calcium signaling pathways coupled with voltage-gated calcium channels (VGCC) and metabotropic glutamate receptors 1 (mGluR1), a synaptic organization with glutamate receptor delta (GluRδ), and output signal formation through chained GABAergic neurons. Consistently, the association of CAs with anti-potassium channel-related proteins, anti-VGCC, anti-mGluR1, and GluRδ, and anti-glutamate decarboxylase 65 antibodies is observed in IMCAs. Despite ample distributions of AMPA and GABA receptors, however, CAs are rare in conditions with autoantibodies against these receptors. Notably, when the autoantibodies impair synaptic transmission, the autoimmune targets are commonly classified into three categories: release machinery proteins, synaptic adhesion molecules, and receptors. This physiopathological categorization impacts on both our understanding of the pathophysiology and clinical prognosis.

Nicotinic receptor modulation of neurotransmitter release in the cerebellum

Nicotinic ACh receptors (nAChRs) are formed by pentameric combinations of alpha and beta subunits, differentially expressed throughout the central nervous system (CNS), where they have been shown to play a role in the modulation of neurotransmitter release. nAChRs are also important during neuronal differentiation, regulating gene expression and contributing to neuronal pathfinding. The cerebellum, which is involved in the maintenance of balance and orientation as well as refinement of motor action, in motor memory and in some aspects of cognition, undergoes a significant process of development and maturation of its neuronal networks during the first three postnatal weeks in the rat. Autoradiographic as well as in situ hybridization and immunocytochemical studies have shown that several nicotinic receptor binding sites and subunits are expressed in the rat cerebellum from embryonic stage through to adulthood, with the highest expression levels seen during the development of the cerebellar cortex. A diffuse cholinergic afferent projection to all lobules of the cerebellar cortex has been described, with the uvulanodulus, flocculus and lobules I and II of the anterior vermis regions receiving a particularly dense projection. Low levels of nAChR subunit transcripts and immunoreactivity, particularly during adulthood, and the scattered distribution of immunoreactivity between neurons in the cerebellar cortex, can explain the difficulty in assessing electrophysiologically the presence of functional nAChRs in the cerebellar cortex and some contradictory results reported in the early-published papers. In recent years, several groups have shown that also in the cerebellum different nAChR subtypes modulate release of glutamate and GABA at different synapses. The possible role of these mechanisms in synaptic consolidation during development, as well as on plasticity phenomena and network activity at mature synapses, are discussed.

Whole-cell and single-channel currents activated by GABA and glycine in granule cells of the rat cerebellum

1. Patch-clamp methods have been used to characterize GABA-and glycine-activated channels and spontaneous synaptic currents in granule cells in thin cerebellar slices from 7- to 20-day-old rats. 2. All granule cells responded to 10 microM GABA, while approximately 60% responded to 100 microM glycine. With repeated against application, whole-cell responses to GABA, but not those to glycine, declined over a period of minutes unless the pipette solution contained Mg-ATP. 3. Whole-cell concentration-response curves gave EC50 values at 45.2 and 99.6 microM and Hill slopes of 0.94 and 2.6 for GABA and glycine, respectively. At saturating concentrations, currents evoked by GABA were fivefold larger than those evoked by glycine. 4. Whole-cell current-voltage (I-V) relationships of GABA- and glycine-activated currents reversed close to the predicted Cl- equilibrium potential. Partial replacement of intracellular Cl- with F- shifted the GABA reversal potential to a more negative value. 'Instantaneous' I-V relationships produced by ionophoretic application of GABA were linear, while 'steady-state' I-V relationships produced by ramp changes in potential showed outward rectification. For glycine, 'steady-state' I-V plots were linear. 5. Responses to GABA were blocked by the GABAA receptor antagonists bicuculline (15 microM), SR-95531 (10 microM) and picrotoxinin (100 microM) while responses to glycine were selectively blocked by strychnine (200 nM), indicating the presence of two separate receptor types. 6. In outside-out membrane patches, GABA opened channels with conductances of 16 and 28 pS. The proportion of openings to each of the conductances varied between patches, possibly indicating the activation of two distinct channel types. Glycine-activated single-channel currents had conductances of 32, 55 and 104 pS. Single-channel I-V relationships were linear. 7. Spontaneous synaptic currents with a rapid rise time and biexponential decay were present in more than half of the cells examined. These currents were eliminated by bicuculline (15 microM) or SR-95331 (10 microM) and were greatly reduced in frequency by tetrodotoxin (TTX; 300 nM), suggesting that they were mediated by GABA and arose from spontaneous activity in Golgi interneurones. In granule cells where this spontaneous synaptic activity was apparent, glycine and low concentrations of GABA increased the frequency of the synaptic currents.(ABSTRACT TRUNCATED AT 400 WORDS)

Autoradiographical evaluation of [3H]glycine uptake in rat forebrain: cellular localization in the hippocampus

The cellular elements responsible for the uptake of [3H]glycine into rat hippocampal slices were investigated. The diffuse laminar distribution of labelling observed under control conditions was greatly reduced seven days after intrahippocampal injection of a neurotoxic dose of quinolinic acid, suggesting a neuronal localization. Glycine was also taken up into glial cells, since dense clusters of silver grains were present on small sized cells throughout the hippocampus which were apparently increased in number after the lesion. The pattern of [3H]glycine uptake into rat cerebral cortex and cerebellar slices was also consistent with both neuronal and glial localization. These glycine transport sites may be strategically located to control excitatory neurotransmission mediated by the N-methyl-D-aspartate sub-type of glutamate receptors.

Effects of excitotoxic lesions of the nucleus basalis magnocellularis on conditioned taste aversion and inhibitory avoidance in the rat

The role of the nucleus basalis magnocellularis (NBM) in a variety of learning tasks is well known. Lesions of this nucleus result in a reduction of cholinergic transmission throughout a vast portion of the cortex. Because cholinergic transmission in the insular cortex seems to be important for the acquisition of conditioned taste aversion, the aim of the present work was to study the effects of bilateral chemically induced lesions of the NBM on this conditioning, as correlated with some cholinergic markers in the insular cortex. The effect on inhibitory avoidance was also studied. Lesions prevented the acquisition of the aversion and disrupted retention of the task in previously trained animals. Learning in the inhibitory avoidance paradigm was also notably affected. Postlesion reductions of choline acetyltransferase and acetylcholinesterase activities and of K(+)-stimulated [3H]acetylcholine release were found in the insular cortex. Further, in intact rats labeling of NBM neurons was observed by retrograde tracing after injection of Fluoro-Gold into the insular cortex. These findings indicate that the NBM is involved in the neural integration of feeding behavior and that its cholinergic projection to the insular cortex is one of the implicated neurotransmitter systems.

Cholinergic innervation of the human cerebellum

Cholinergic innervation of the human cerebellum was investigated immunocytochemically by using a polyclonal rabbit antiserum against choline acetyltransferase. Immunoreactive structures were found throughout the cerebellar cortex but were localized predominantly in the vermis, flocculus, and tonsilla. These included 1) a population of Golgi cells in the granular layer; 2) a subpopulation of mossy fibers and glomerular rosettes; 3) thin, varicose fibers closely associated with the Purkinje cell layer and the molecular layer; and 4) a relatively dense network of fibers and terminals contributing to the glomerular formations in the granular layer. In the cerebellar nuclei, some cells stained positively for choline acetyltransferase, and a terminal field pattern could be detected with a distinct but sparse network of varicose fibers. Acetylcholine appears to be a primary transmitter in the vestibulocerebellar pathways at several levels, which may account for the potent effects of muscarinic antagonists in diminishing vestibular vertigo in humans.

Cholinergic innervation of the cerebellum of the rat by secondary vestibular afferents

The cholinergic innervation of the cerebellar cortex of the rat was studied by immunohistochemical localization of choline acetyltransferase, radiochemical measurement of ChAT activity, and double labeling of ChAT-positive neurons with HRP injected into the cerebellum. ChAT immunohistochemistry revealed large mossy fiber rosettes as well as finely beaded terminals with different morphological characterization, laminar distribution within the cerebellar cortex, and regional differences within the cerebellum. Large "grapelike" ChAT-positive mossy fiber rosettes that were distributed primarily in the granule cell layer were concentrated, but not exclusively located, in three separate regions of the cerebellum: (1) the uvula-nodulus (lobules 9 and 10); (2) the flocculus, and (3) the anterior lobe vermis (lobules 1 and 2). Regional differences in ChAT-positive afferent terminations in the cerebellar cortex demonstrated by immunohistochemistry were confirmed by regional biochemical measurements of ChAT activity. Using ChAT immunohistochemistry in combination with HRP injections into the uvula-nodulus, we have studied the origin of the cholinergic projection. The caudal medial vestibular nucleus and to a lesser extent the nucleus prepositus hypglossus contain ChAT-positive neurons that were double labeled following HRP injections into the uvula-nodulus. We conclude that (1) there is a prominent cholinergic mossy fiber pathway to the vestibulocerebellum, (2) this pathway originates primarily in the caudal third of the medial vestibular nucleus, and (3) this cholinergic pathway likely mediates secondary vestibular information related to postural adjustment.

Levels, uptake, and release of glycine and glutamate in the rat pontine reticular formation

In this work we have determined the levels of glycine, glutamate, and other amino acids in the rat pontine reticular formation (PRF), in addition to some properties of the uptake and release of labeled glycine and glutamate in slices of this region. Glutamate was the most concentrated amino acid in the PRF, although its content was about half that of the striatum. Surprisingly, glycine levels in the PRF were 3.2-fold higher than in the striatum, whereas GABA content was similar in both regions. The uptake of both glycine and glutamate by PRF slices was strictly Na(+)-dependent. Their release was stimulated by K(+)-depolarization, but only the release of glycine was Ca(2+)-dependent. These findings suggest that glycine is a strong candidate for a neurotransmitter role in the PRF and that glutamate might also play such a role in this region.

Cholinergic innervation of the cerebellum of rat, rabbit, cat, and monkey as revealed by choline acetyltransferase activity and immunohistochemistry

The cholinergic innervation of the cerebellar cortex of the rat, rabbit, cat and monkey was studied by immunohistochemical localization of choline acetyltransferase (ChAT) and radiochemical measurement of regional differences in ChAT activity. Four antibodies to ChAT were used to find optimal immunohistochemical localization of this enzyme. These antibodies selectively labeled large mossy fiber rosettes as well as finely beaded terminals with different morphological characterization, laminar distribution within the cerebellar cortex, and regional differences within the cerebellum. Large "grape-like" classic ChAT-positive mossy fiber rosettes that were distributed primarily in the granule cell layer were concentrated, but not exclusively located in three separate regions of the cerebellum in each of the four species studied: 1) The uvula-nodulus (lobules 9 and 10); 2) the flocculus-ventral paraflocculus, and 3) the anterior lobe vermis (lobules 1 and 2). No intrinsic cerebellar neurons were labeled. No cells in either the inferior olive (the origin of cerebellar climbing fibers) or in the locus coeruleus (an origin of noradrenergic fibers) were ChAT-positive. Thin, finely beaded axons, similar to cholinergic axons of the cerebral cortex of the rat, were observed in both the granule cell layer and molecular layer of the cerebellar cortex of the rat, rabbit and cat. The regional differences in ChAT-positive afferent terminations in the cerebellar cortex was for the most part confirmed by regional measurements of ChAT activity in the rat, rabbit, and cat. The three cholinergic afferent projection sites correspond to regions of the cerebellar cortex that receive vestibular primary and secondary afferents. These data imply that a subset of vestibular projections to the cerebellar cortex are cholinergic.

Glutamate, GABA, and glycine in the human retina: an immunocytochemical investigation

The distribution of the neuroactive amino acids glutamate, GABA, and glycine in the human retina was examined in consecutive semithin sections treated with antisera specific for fixed glutamate, GABA, and glycine, respectively. Glutamate immunoreactivity was conspicuous in all photoreceptor cells (rods more strongly labelled than cones), and in a majority (85-89%) of the cells in the inner nuclear layer (INL). Rod spherules and cone pedicles showed a greater enrichment of glutamate immunoreactivity than the parent cell bodies and inner segments. Also, structures of the inner plexiform layer (IPL) were labelled. A large majority (83-91%) of cells in the ganglion cell layer (GCL) was strongly stained, as were most axons in the nerve fibre layer. Müller cell processes appeared unstained. GABA immunoreactivity was present in presumed amacrine but not in bipolar-like cells. The stained cells were restricted to the inner 1/3 of the INL and were more frequent in central than in peripheral retina (40% and 26% of all cells in the inner 1/2 of INL, respectively). GABA positive cell processes, probably originating from interplexiform cells, appeared to traverse the INL and end in the outer plexiform layer. Dense immunolabeling was found in the IPL. GABA immunoreactive cells (some also stained for glutamate) comprised 23% of all GCL cells in the peripheral retina, but only 5% in the central retina. Most of them were localized adjacent to the IPL. A few GABA positive (possibly ganglion) cells extended a single fibre toward the nerve fibre layer. Solitary GABA positive fibres were seen in this layer and in the optic nerve. Glycine immunoreactivity was observed in cells with the location typical of amacrine and bipolar (peripheral retina) cells, as well as in punctate structures of the IPL. In contrast to the GABA positive cells, the glycine positive cells were more frequent in the peripheral than in the central retina (42% and 23% of all cells in inner 1/3 of INL, respectively). A few cells in the GCL (0.5-1.5%) were glycine positive. Glutamate colocalized with GABA or glycine in a majority of the cells stained for either of these inhibitory transmitters (90-95% of the GABA positive cells, and 80-86% of the glycine positive cells, in the INL). Some bipolar cells were stained for both glutamate and glycine. Colocalization of GABA and glycine occurred in a subpopulation (3-4%) of presumed amacrine cells, about half of which was also glutamate positive.

Release of acetylcholine and GABA, and activity of their synthesizing enzymes in the rat pontine reticular formation

The aim of this study was to obtain neurochemical information on the possible role of acetylcholine (ACh) and gamma-aminobutyric acid (GABA) as neurotransmitters in the pontine reticular formation (PRF). We studied the uptake of labeled choline and GABA, as well as the release of this amino acid and of ACh, in PRF slices of the rat. In addition, choline acetyltransferase, acetylcholinesterase and glutamate decarboxylase activities were assayed in PRF homogenates. The uptake of GABA was strictly Na(+)-dependent, whereas choline uptake was only partially Na(+)-dependent. The release of both ACh and GABA was stimulated by K(+)-depolarization, but only the former was Ca(2+)-dependent. Choline acetyltransferase activity in the PRF was 74% of that in the striatum, whereas acetylcholinesterase activity was considerably lower. Glutamate decarboxylase activity in the PRF was about half that observed in the striatum. These findings support the possibility that both ACh and GABA may act as neurotransmitters in the rat PRF.

Release of acetylcholine, gamma-aminobutyrate, dopamine and glutamate, and activity of some related enzymes, in rat gustatory neocortex

The gustatory neocortex (GN), final relay along the gustatory pathway, is a region of the brain involved in the neural integration of feeding behavior. Since information on the neurotransmitters in this nucleus is scarce, the aim of the present work was to establish whether acetylcholine (ACh), gamma-aminobutyric acid (GABA), dopamine and glutamate may act as transmitters within this structure. It was found that GN slices are able to release labeled GABA, ACh and glutamate but not dopamine. Additionally, it was possible to detect significant glutamic acid decarboxylase, choline acetyltransferase and acetylcholinesterase activities in GN homogenates. The activity of the two enzymes involved in acetylcholine metabolism was higher than that observed in other cortical regions. These findings suggest that GABA, ACh and glutamate probably are neurotransmitters in the GN, whereas dopamine is not.

Correlation between acetylcholine release and recovery of conditioned taste aversion induced by fetal neocortex grafts

Rats with lesions of the gustatory neocortex (GN) show deficits in the acquisition of taste aversion. Fetal GN grafts to a lesioned animal restore taste aversion learning and establish connections with the host brain. In this work, we examined whether the grafts are biochemically functional and whether this fact can be related to behavioral recovery. Gustatory or occipital cortices from rat fetuses were transplanted to GN-lesioned rats. Two months later, taste aversion recovery was tested and the release of labeled gamma-aminobutyric acid (GABA), acetylcholine (ACh), dopamine and glutamate from the grafted tissue was assayed. Fetal GN grafts promoted recovery of learning and released GABA, ACh and glutamate in response to K+ depolarization. Occipital cortex grafts did not induce behavioral recovery, although they were capable of releasing GABA. In contrast, these grafts did not release ACh. Moreover, GN-grafted rats in which behavioral recovery was not seen also failed to release ACh. These results are in agreement with previous findings that cholinergic transmission is important in the GN and suggest that ACh may play a role in the graft-mediated behavioral recovery observed in this model.

The expression of excitatory amino acid binding sites during neuritogenesis in the developing rat cerebellum

The present study has examined excitatory amino acid transmitter binding sites as measured autoradiographically in cryostat sections prepared from developing rat cerebella during the period of granule cell neuritogenesis. The external germinal layer (EGL) and molecular layer (ML), which during development contain granule cells at early stages of axon growth, contained only low levels of NMDA-displaceable L-[3H]glutamate binding sites. Similarly, [3H]glycine binding to the NMDA receptor linked binding site was not enriched in the EGL. Radioligand binding to the NMDA receptor was always greater in the granular layer (GL) than in the ML. The developmental increases in NMDA-displaceable L-[3H]glutamate and in [3H]glycine binding to the GL were similar but NMDA displaceable L-[3H]glutamate binding density increased before [3H]glycine binding sites. Glycine increased NMDA-displaceable L-[3H]glutamate binding only in the adult cerebellum. These results suggest that NMDA stimulation of neuritogenesis in granule cell cultures may reflect stimulation of dendritogenesis in the developing glomerulus rather than a stimulation of axon growth in the EGL. Also, NMDA receptors may be present in an immature form during cerebellar development and have different properties to the adult receptor. Binding sites for [3H]kainate and [3H]AMPA were present in both the GL and ML and increased during development. At all times the amount of binding sites for [3H]kainate were highest in the GL whereas those for [3H]alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate were highest in the ML.

Transmitter release in hippocampal slices from rats with limbic seizures produced by systemic administration of kainic acid

The systemic injection of kainic acid (KA) has been shown to destroy neurons in the hippocampus and to induce limbic-type seizure activity. However, little is known on the neurochemical events that are associated with this convulsant effect. In the present work we studied the spontaneous and the K(+)-stimulated release of labeled tau-aminobutyric acid (GABA), glutamate, serotonin and dopamine, in hippocampal slices of KA-treated rats, at the moment of clinical seizures (2 h) and 72 h later. At the onset of convulsions we found a 40-45% decrease in the K(+)-stimulated release of GABA. The release of the other neurotransmitters was not significantly affected by KA treatment. After 72 h GABA release was still reduced by 30-40%. It is concluded that the epileptogenic effect of KA in the hippocampus is probably related to a diminished inhibitory GABAergic neurotransmission.

Circling behavior induced by intranigral administration of ruthenium red and 4-aminopyridine in the rat

We have studied the effects of the unilateral intranigral microinjection of Ruthenium Red and 4-aminopyridine in the rat, as compared with that of muscimol. The three drugs produced contralateral turning when injected into the central nigra reticulata. Muscimol was the most effective but its effect disappeared in 3-4 h, whereas that of Ruthenium Red lasted for up to 3 days. When injected into the caudoventromedial nigra, Ruthenium Red produced intense ipsiversive turning, 4-aminopyridine weak ipsiversive turning and muscimol intense contraversive turning. Pretreatment with haloperidol (i.p.) abolished the effect of Ruthenium Red after injection into the caudoventromedial nigra but only partially reduced it after administration into the central nigra. The effect of muscimol, when injected into either of the nigral regions studied, was only slightly diminished by haloperidol. The release of [3H]GABA in slices of the Ruthenium Red-injected substantia nigra was not altered. Histological examination showed that the microinjected Ruthenium Red was located mainly inside the soma of nigral neurons. It is concluded that alterations of transmitter release are probably responsible for the circling behavior induced by 4-aminopyridine, but the effects of Ruthenium Red seem to be secondary to its penetration into the neuronal somas. Dopaminergic neurons seem to play an important role in the ipsilateral turning induced by Ruthenium Red when injected into the caudoventromedial nigra.

Cholinergic innervation of the rat cerebellum: qualitative and quantitative analyses of elements immunoreactive to a monoclonal antibody against choline acetyltransferase

Cholinergic innervation of the rat cerebellum was investigated immunohistochemically by using a monoclonal antibody against choline acetyltransferase. Immunoreactive structures included: 1) a subpopulation of mossy fibers and glomerular rosettes; 2) thin varicose fibers, which were closely associated with the Purkinje cell layer and also found in the molecular layer; and 3) relatively dense networks of varicose fibers distributing in the cerebellar nuclei. Quantitative analysis indicated that a great many immunoreactive rosettes were localized in lobules IXc and X, although their density in lobule X was approximately four times that in the lobule IXc. A considerable number of immunoreactive structures were also present in all other lobules. In the hemispheres they were confined to a zone immediately beneath the Purkinje cell layer, whereas in the vermis they were scattered throughout the granular layer. Most of the immunoreactive fibers found in the molecular layer coursed toward the pial surface and were distributed within the inner half of the molecular layer. In the cerebellar nuclei, portions of the medial nucleus and magnocellular portion of the lateral nucleus had moderately dense networks of immunoreactive fibers, whereas loose networks of fibers were observed in the posterior interposed nucleus. Other parts of the cerebellar nuclei contained a smaller number of varicose fibers.

Development of monoamine oxidase activity and monoamine effects on glutamate release in cerebellar neurons and astrocytes

Activities of monoamine oxidase (MAO) A and B were measured during the first month of postnatal development in mouse cerebellum and in primary cultures of either cerebellar granule cells or cerebellar astrocytes, derived from 7-day-old cerebella. In addition, effects of the two monoamines, serotonin (a MAO A substrate) and phenylethylamine (a MAO B substrate) on the release of glutamate under resting conditions and in a transmitter related fashion (i.e., potassium-induced, calcium-dependent glutamate release) were studied during the same period. Both MAO A and MAO B activities increased during in vivo development (beginning around postnatal day 14) and in cultured astrocytes (during a comparable time period and to a similar extent), but remained constant at a low level in granule cells. In 4-day-old cerebellar granule cell cultures there was no potassium-induced glutamate release but serotonin as well as phenylethylamine reduced the release in both the presence and absence of excess potassium. In 8- and 12-day-old granule cell cultures and in 8- and 18-day old astrocyte cultures there was a pronounced glutamate release during superfusion with 50 mM K+. In both neurons and astrocytes this response was inhibited by 1 nM of either serotonin or phenylethylamine. In the astrocytes the inhibition was followed by an increased release of glutamate in both the presence and absence of the high potassium concentration, whereas the 8-day-old neurons showed only a slight increase in glutamate release after the withdrawal of the monoamine and only in the absence of excess potassium. The response was almost identical in 8- and 18-day-old astrocytes in spite of the marked difference in MAO activities.

Quantitative electron microscopic immunocytochemistry of neuroactive amino acids

Amino acids are of crucial importance in brain function, not only as metabolic intermediates and building blocks of proteins, but also as mediators of interneuronal communication. This dual role of the amino acids distinguishes them from other neurotransmitter candidates, and implies that they are unlikely to be restricted to neurons using them as transmitters. This calls for a quantitative approach when attempts are made to analyse the distribution of transmitter amino acids by means of immunocytochemistry. The present review deals with recent methodological developments that have made it possible to utilize specific antisera to explore the cellular and subcellular distribution of neuroactive amino acids in a quantitative manner.

Glutaminase in the postnatally developing rat cerebellum: comparison of staining and immunocytochemistry activity

Distribution patterns and developmental profiles of phosphate activated glutaminase (PAG) in the cerebellar cortex of the rat were demonstrated by enzyme activity staining (tetrazolium salt technique) and immunolabeling. Histochemical evaluation of enzyme activity stained sections revealed in the molecular and granular layer (i.e. premigratory zone and external germinal zone in neonate rats) an increase from postnatal day 2 to day 50 by 350 and 400%, respectively. The smallest elevation was found in Purkinje cell bodies (140%). Maximum rise of PAG-activity was observed for all of the areas examined between day 12 and 15. The immunocytochemical visualisation of PAG-like immunoreactivity resulted in spatial and developmental patterns which differed from those of PAG-activity staining and displayed, to some extent, dependency on the way of tissue preparation, especially the fixation procedure.