Large GABA cells of chick ectostriatum: anatomical evidence suggesting a double GABAergic disinhibitory mechanism. An electron microscopic immunocytochemical study.
In an extension of our previous light microscopic observations, a type of neuron which shows GABA-like immunoreactivity was identified and described in the ectostriatal core of young domestic chicks, using pre- and postembedding electron microscopic immunocytochemistry. Large GABA immunopositive (GABA+) cells are characterized by an ovoidal or polygonal soma of 12-16 micron diameter, uniformly distributed nuclear chromatin, a prominent Golgi apparatus and an abundance of rough endoplasmic reticulum. In addition to axodendritic terminals, large GABA neurons receive numerous axosomatic synapses of both symmetrical and asymmetrical types covering a substantial part of their perikaryal surface. Axosomatic terminals with symmetrical junctions are usually immunoreactive to GABA whereas the boutons with asymmetrical synaptic specialization are immunonegative. GABA+ boutons also synapse with dendritic spine necks presumably belonging to projection neurons. These terminals usually contain loosely packed synaptic vesicles without any marked accumulation near the synaptic cleft. Large GABA+ terminals with densely packed vesicles were found to synapse with axon hillocks. Based on known descriptions of ectostriatal cytoarchitecture and synaptology, it is suggested that the GABA+ cells of chick ectostriatum represent inhibitory interneurons which may be equivalent to GABAergic non-pyramidal neuronal types of mammalian visual cortex. GABA+ axosomatic synapses afferent to large GABA cells are likely to form the structural basis for a disinhibitory mechanism in the avian ectostriatum.
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First Department of Anatomy, Semmelweis University of Medicine, Budapest, Hungary.
D000818:Animals; D001369:Axons / Q000648:ultrastructure; D002645:Chickens; D004721:Endoplasmic Reticulum / Q000648:ultrastructure; D005260:Female; D006056:Golgi Apparatus / Q000648:ultrastructure; D007124:Immunoenzyme Techniques; D008297:Male; D016253:Microscopy, Immunoelectron; D013569:Synapses / Q000648:ultrastructure; D013687:Telencephalon / Q000033:anatomy & histology / Q000648:ultrastructure*; D005680:gamma-Aminobutyric Acid / Q000032:analysis*
D005680:gamma-Aminobutyric Acid