Development and localisation of GABAA receptor α1, α2, β2 and γ2 subunit mRNA in the chick optic tectum

An in situ hybridisation technique was used to analyse the spatial and temporal pattern of expression of the mRNA encoding the four γ-aminobutyric acid A (GABA A ) receptor subunits (α 1 , α 2 , β 2 , and γ 2 ) in the developing chick optic tectum. As a rule, layer i, layer h, and transient cell compartment 3 (TCC3) show the highest levels of expression, especially of α 1 , α 2 and β 2 , which undergo striking changes as a function of time. Apart from these common features, the global pattern is highly complex and dynamic. Such complexity derives from the fact that each subunit exhibits a characteristically distinct pattern of expression and the temporal evolution of each differs in the different layers of the tectum. The influence of several developmental cell behaviours such as proliferation, neuronal migration, programmed cell death, and differentiation must be taken into account to understand pattern complexity and dynamics. Our results suggest that differences in the rate of subunit expression, particularly of α 1 , α 2 , and β 2 , could have significant consequences on GABA A receptor complex subunit composition along development and on the functional properties of the GABA neurotransmitter system.