Neonatal Rat Cerebellar Granule and Purkinje Neurons in Culture Express Different GABA_A Receptors

We have established a culture system for microexplants of rat cerebellar cortical tissue in which cells develop morphologically, express type‐A receptors for the inhibitory neurotransmitter γ‐aminobutyric acid (GABA) and form GABAergic synaptic connections. Criteria of cell size and shape allow reliable identification of granule and Purkinje neurons, criteria confirmed by studies of the binding of antibodies to calbindin D28K and GABA. Both granule and Purkinje neurons express GABA_A receptors, but granule neurons fall into two classes in terms of their sensitivity. Granule neurons which do not show spontaneous synaptic currents are relatively insensitive to GABA, while granule neurons with synaptic currents are much more sensitive. The responses of Purkinje neurons to applications of 1 μM GABA are relatively insensitive to Zn²⁺ ions (10 μM), and are potentiated by chlordiazepoxide (100 μM) and La³⁺ ions (100 μM). Responses of innervated granule neurons, on the other hand, are blocked more strongly by Zn²⁺ ions, are less affected by chlordiazepoxide and are equally potentiated by La³⁺ ions. Hence these cultures provide a source of identifiable, functionally innervated cells which express distinct types of GABA_A receptors.