Suppression of neuronal hyperexcitability and associated delayed neuronal death by adenoviral expression of GABA(C) receptors

The excessive neuronal excitation underlying several clinically important d iseases is often treated with GABA allosteric modulators in an attempt to e nhance inhibition. An alternative strategy would be to enhance directly the sensitivity of postsynaptic neurons to GABA. The GABA(C) receptor, normall y found only in the retina, is more sensitive to GABA and demonstrates litt le desensitization compared with the GABA(A) receptor. We constructed an ad enovirus vector that expressed cDNA for both the GABA(C) receptor rho (1) s ubunit and a green fluorescent protein (GFP) reporter and used it to transd uce cultured hippocampal neurons. Transduced neurons were identified by flu orescence, double immunocytochemistry proved colocalization of the rho (1) protein and the reporter, Western blot verified the expected molecular mass es, and electrophysiological and pharmacological properties confirmed the p resence of functional GABA(C) receptors. rho (1)-GFP transduction resulted in an increased density of GABA(A) receptors as well as expression of novel GABA(C) receptors. This effect was not reproduced by addition of TTX or Mg 2+ to the culture medium to reduce action potentials or synaptic activity. In a model of neuronal hyperexcitability induced by chronic blockade of glu tamate receptors, expression of GABA(C) receptors abolished the hyperactivi ty and the consequent delayed neuronal death. Adenovirus-mediated neuronal GABA(C) receptor engineering, via its dual mechanism of inhibition, may off er a way of inhibiting only those hyperexcitable neurons responsible for cl inical problems, avoiding the generalized nervous system depression associa ted with pharmacological therapy.