GABAergic neurons in the rat hippocampal formation: ultrastructure and synaptic relationships with catecholaminergic terminals

摘要: Numerous studies indicate that gamma-aminobutyric acid (GABA) can either hyperpolarize or depolarize hippocampal pyramidal and granule cells. While the inhibitory action of GABA may occur directly on these cells, excitatory be mediated by interactions GABAergic neurons with each other catecholaminergic afferents. We sought to examine cellular basis for their relative frequency. Thus, ultrastructural morphology relation terminals exhibiting immunoreactivity catecholamine-synthesizing enzyme tyrosine hydroxylase (TH) were examined in rat formation using combined immunoautoradiographic peroxidase-antiperoxidase labeling methods. By light microscopy, perikarya processes codistributed most noticeably TH-containing hilus dentate gyrus (DG) strata lucidum, radiatum, lacunosum-moleculare CA3 region hippocampus. regions further electron microscopy. In analysis, GABA-like (GABA-LI) was detected neuronal perikarya, dendrites, axons, axon terminals. The GABA-containing large, ovoid (20-40 microns diameter), contained abundant cytoplasm an indented nucleus one nucleolus. Synaptic junctions dendrites GABA-LI both symmetric asymmetric. Approximately equal numbers TH-labeled (19% 133 DG; 39% 26 CA3) DG, 15% formed synapses GABA-labeled perikarya. remainder presynaptic (62% 46% unlabeled, i.e., unidentified transmitters. Terminals (0.5-1.6 microns) numerous small clear vesicles from 0 2 large dense-core vesicles. types associations remarkably similar DG hippocampus proper despite differences intrinsic cell type function. unlabeled (24% 151 25% 75 (18% 5% CA3). Additionally, converged upon same dendrite as a terminal (15% 21% direct apposition 20% remaining 28% without any apparent synaptic relations. CA3, symmetric. showing colocalization TH-I also although rarely.(ABSTRACT TRUNCATED AT 400 WORDS)