Dopamine and GABA receptors in cultured substantia nigra neurons: correlation of electrophysiology and immunocytochemistry.

Primary neuron cultures were made separately from the substantia nigra pars compacta and the substantia nigra pars reticulata of neonatal rats. Using the whole-cell patch-clamp, we tested for the presence of dopamine and GABA receptor subtypes by applying dopamine receptor agonists [the D2 receptor agonist quinpirole and the D1 receptor agonist R(+)-SKF-38393] and GABA receptor agonists (GABA and baclofen). The D2 agonists and the GABA(B) agonist increased an inward rectifier K+ conductance, while the D1 agonist decreased this K+ conductance. Application of GABA increased membrane conductance, probably by increasing Cl- permeability through GABA(A) receptors. Following the physiological tests, the same neuron was examined by double immunocytochemical labeling for antibody to tyrosine hydroxylase and antibody to GABA. Neurons which responded to the D2 agonist were dopaminergic neurons, while neurons which did not respond to D2 agonist were mostly GABAergic or non-dopaminergic/non-GABAergic. Neurons which responded to the D1 agonist were non-dopaminergic/non-GABAergic. GABA(A) receptors were present in all types of neurons, while GABA(B) receptors were located on some dopaminergic neurons and some GABAergic neurons. These results largely agree with the published data on in vivo or brain slice preparations, indicating that these neurons of neonatal rat brains, after being dissociated, produce the same transmitters and the same receptors in culture as those in vivo.