GABAERGIC INTERNEURONS OF THE STRIATUM EXPRESS THE SHAW-LIKE POTASSIUM CHANNEL KV3.1

In addition to numerous GABA-ergic efferent neurons, the striatum cont ains a subpopulation of fast-firing GABA-ergic interneurons characteri zed by the presence of immunoreactivity for the calcium-binding protei n, parvalbumin. Double-label in situ hybridization with digoxigenin- a nd radiolabelled cRNA probes was performed on striatal sections of adu lt rats to identify mRNAs expressed by striatal GABA-ergic interneuron s. In the dorsolateral striatum, only parvalbumin mRNA-positive neuron s expressed the mRNA encoding the potassium channel Kv3.1, a member of the Shaw family of potassium channels with rapid activation and inact ivation kinetics, usually found in fast-firing neurons such as the bas ket cells of the hippocampus. Colocalization of the parvalbumin and Kv 3.1 proteins was confirmed by double-label immunohistochemistry. Parva lbumin mRNA-positive neurons expressed very high levels of the mRNA en coding glutamic acid decarboxylase (Mr 67,000: GAD67) in the dorsolate ral striatum. A smaller proportion of double-labelled neurons was foun d in the ventrolateral striatum. A small number of densely labelled ne urons for GAD67 mRNA also expressed the mRNA encoding the dopamine D2 receptor, but none expressed detectable levels of the dopamine D1 rece ptor mRNA. This indicates major differences in the expression of dopam ine receptor mRNA in a majority of GABA-ergic interneurons vs. GABA-er gic efferent neurons of the striatum. The results suggest that distinc t molecular characteristics are associated with the distinct electroph ysiological properties of striatal GABA-ergic neurons. (C) 1994 Wiley- Liss, Inc.