Development of gamma-aminobutyric acid immunoreactivity in chick hyperstriatum ventrale and cerebellum: light and...

The presence of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) in the avian hyperstriatum ventrale and dorsal cerebeller vermis was investigated immunocytochemically using a recently characterized antiserum raised against GABA. Tissue from domestic chicks aged from 19 days in ovo to 28 days posthatch was studied with both light and electron microscopy using pre-embedding immunocytochemistry. Basket, stellate and Golgi cells in the cerebellum, considered to be GABA-ergic, exhibited specific GABA-like immunolabelling in perikarya and in axonal and dendritic processes throughout the developmental period investigated. Purkinje cells also exhibited specific GABA-like immunoreactivity in both pre- and posthatch birds but the distribution and intensity of the immunolabelling varied with age and also in its location within the Purkinje neuron. In prehatch birds Purkinje perikarya exhibited heavy immunostaining which was substantially reduced posthatch, whereas the Purkinje primary dendrites remained immunopositive throughout the developmental period. A small population of cells in the medial hyperstriatum ventrale (mHV) were GABA-positive prehatch, but no immunopositive perikarya were evident in any posthatch samples. Small GABA-positive punctate profiles, representing boutons and transversely sectioned axons or dendrites, were present in the neuropil of all age groups studied. Possible reasons for these findings are discussed and it is suggested that the loss of perikaryal immunostaining, both in the cerebellar Purkinje cells and in those of the mHV, may be governed by maturational processes.