Gamma-aminobutyric acid pathways in the cerebellum studied by retrograde and anterograde transport of glutamic acid decarboxylase antibody after in vivo injections

The cerebellar nucleo-cortical projection in the rat studied by the retrograde fluorescent double-labelling method

Injection of true blue into rat cerebellar cortex and nuclear yellow into either the superior cerebellar peduncle or the ventral thalamus produced double-labelled neurones in the cerebellar deep nuclei. This suggests that the nucleo-cortical projection arises from collaterals of cerebellofugal fibres. The topography of this projection, and differences in collateralization between thalamic and other cerebellofugal fibres are discussed.

Gamma-aminobutyric acid interneurons in the rat hippocampal region studied by retrograde transport of glutamic acid decarboxylase antibody after in vivo injections

The retrograde axonal labeling of hippocampal GABA-ergic neurons was studied after in vivo injections of a characterized antibody against glutamic acid decarboxylase (GAD) into different parts of the hippocampal region. Small injections (50 nl) of undiluted GAD antibody into the area dentata (AD) labelled fusiform and dentate pyramidal basket cells within the AD and fusiform and multipolar cells in subfields CA2/CA3 (a and b) of Ammon's horn. The labeled cells were characterized by intense immunoreactivity of the soma and proximal parts of the dendrites, while the nucleus contained little or none. The morphological appearance and laminar positions of these cells corresponded to hippocampal GAD-positive neurons, as shown previously (Ribak et al. 1978) with immunocytochemistry. Injections of anti-GAD into the medial entorhinal area, subiculum, and CA1 region labeled cells in strata oriens, pyramidale and radiatum of CA2 and CA3a, but injections of the antibody into these latter areas failed to label cells in the medial CA1 and subiculum, thus suggesting a preferential organization of hippocampal GABA neuronal projections in a lateral to medial direction. Injections of preimmune sera or antiserum preabsorbed with the pure enzyme antigen GAD failed to label cells in a manner similar to that described for the anti-GAD injections. These observations, taken together with the finding that injections of anti-GAD into the terminal field of non-GABA-ergic pathways never resulted in retrograde axonal transport of the antibody-antigen complex, suggest that the in vivo injection of GAD antibody is a useful method to study the organization of hippocampal GABA-ergic neurons and their projections.

Neurotoxic effect of kainic acid on ultrastructure and GABAergic parameters in the goldfish cerebellum

Kainic acid administration into the cerebellar dorsal lobe of the goldfish causes selective degeneration of some neuronal types. Stellate and Golgi neurons are very sensitive to the neurotoxin and undergo rapid degeneration. On the basis of their differential responses to kainic acid, Purkinje cells can be divided in two distinct sub-populations (i.e. sensitive and insensitive neurons). The degenerative changes of the Purkinje neurons are in addition remarkably slow in comparison with the same cells in mammals or with stellate and Golgi neurons in the goldfish. Granule cells, as well as the cerebellar afferent fiber system, are not significantly affected. Six days after kainic acid administration, the level of glutamate decarboxylase in the cerebellar dorsal lobe drops to about 40% of the control value. This result suggests that the neurons sensitive to kainic acid neurotoxicity are, at least in part, GABAergic. Light- and electron-microscopic autoradiography of cerebellar elements selectively accumulating [3H]GABA, supports this idea. Moderate decreases of acetylcholinesterase and protein content were also noticed in the kainic acid-treated cerebellar dorsal lobe.

Chemical heterogeneity in cerebellar Purkinje cells: existence and coexistence of glutamic acid decarboxylase-like and motilin-like immunoreactivities

Purkinje neurons of the cerebellar cortex from a chemically and morphologically heterogeneous population containing some members that have gamma-aminobutyric acid (GABA), others that have immunoreactivity for motilin, and a small number that have both. The remaining 30-40% of all Purkinje cells have neither of these two neuroactive substances, leaving possibilities for other transmitter candidates. The evidence was compiled from double-staining immunocytochemical procedures performed on single sections of the cerebellum and brain stem in rat, mouse, and monkey. Two polyclonal antibodies were applied in succession, one directed against the midregion and COOH terminus of the 22-amino acid polypeptide motilin and the other against glutamic acid decarboxylase (glutamate decarboxylase; L-glutamate 1-carboxy-lyase, EC 4.1.1.15), the rate-limiting enzyme in the synthesis of the neurotransmitter GABA. The staining combinations employed the immunoperoxidase method, with different chromogens for distinguishing the motilin-like immunoreactivity from glutamic acid decarboxylase immunoreactivity by different colors, or the immunoperoxidase method for one antiserum and immunofluorescence for the other. The locations of both motilin and GABA cell types were mapped. The recognition of motilin in Purkinje cells calls for experimental definition of the role of this substance in the cerebellum and for reevaluation of the roles of Purkinje cells and of GABA in cerebellar function. The significant motilin representation in the flocculus, paraflocculus, and vermis suggests that it may be the Purkinje cell mediative chemical in the vestibular parts of the cerebellum. However, the presence of GABA as well in the same regions indicates that the chemical preference may be at least bimodal.

EM-autoradiography of cerebellar nucleocortical terminals in the cat

The findings from the present EM-autoradiography experiments identify the cerebellar nucleocortical projection as a mossy fiber-type pathway. In these studies orthogradely labelled axons and terminals were observed in the folial white matter and granule cell layer, with only background levels of silver grains over the Purkinje cell and molecular layers. Most nucleocortical axons synapsed within cerebellar glomeruli either at en passant contacts along dilated segments of unmyelinated axons or at multilobulated (terminal) expansions of the axons. Typically these synaptic junctions were of the asymmetrical type containing clear round vesicles. Usually, each labelled mossy fiber rosette synapsed on a large number of small terminal dendrites of granule cells; however, occasionally a series of 4-8 asymmetric contacts were noted on a single large dendrite. Labelled nucleocortical terminals were occasionally present in the nonglomerular neuropil between granule cell bodies where they contacted large dendrites of Golgi cells.

Autoradiographic experiments to examine uptake, anterograde and retrograde transport of tritiated serotonin in the mammalian brain

In an attempt to define the potential application of neurotransmitter-specific transport as a method of tracing fiber connections, we have examined the uptake and subsequent ortho- and retrograde transport of tritium-labeled serotonin (3H-5HT) in the cerebellum-raphe pallidus system. Injection of various concentrations of 3H-5HT followed by different post-injection survival times revealed different labeling patterns in the injected sites and different patterns of transport. The most striking feature is that nonseroitonin neurons as well as serotonin cells were able to take up and transport the tritium label in both otho- and retrograde fashion. The non-sertonin-specific nature of this uptake and transport is more obvious at higher concentrations of 3H-5HT (more than 9 X 10(-5) M), with longer survival times and following pretreatment with monoamine oxidase inhibitors. At a concentration of 9 X 10(-6) M 3H-5HT, only specific uptake seems to take place as evidenced by label in known serotinin cells and fiber systems; however, it was impossible to detect by autoradiography any ortho- or retrograde transport at this low concentration. Non-specific uptake and transport were observed following injection into the vestibular nuclei and oculomotor complex. This suggests that non-specific uptake and the transport of 3H-5HT or metabolites may also occur in other regions of the central nervous system.