Suppression of neuronal hyperexcitability and associated delayed neuronal death by adenoviral expression of GABAc receptors

Abstract

The excessive neuronal excitation underlying several clinically important diseases is often treated with GABA allosteric modulators in an attempt to enhance inhibition. An alternative strategy would be to enhance directly the sensitivity of postsynaptic neurons to GABA. The GABAC receptor, normally found only in the retina, is more sensitive to GABA and demonstrates little desensitization compared with the GABAA receptor. We constructed an adenovirus vector that expressed cDNA for both the GABAC receptor ρ1 subunit and a green fluorescent protein (GFP) reporter and used it to transduce cultured hippocampal neurons. Transduced neurons were identified by fluorescence, double immunocytochemistry proved colocalization of the ρ1 protein and the reporter, Western blot verified the expected molecular masses, and electrophysiological and pharmacological properties confirmed the presence of functional GABAC receptors, ρ1-GFP transduction resulted in an increased density of GABAA receptors as well as expression of novel GABAC receptors. This effect was not reproduced by addition of TTX or Mg2+ to the culture medium to reduce action potentials or synaptic activity. In a model of neuronal hyperexcitability induced by chronic blockade of glutamate receptors, expression of GABAC receptors abolished the hyperactivity and the consequent delayed neuronal death. Adenovirus-mediated neuronal GABAC receptor engineering, via its dual mechanism of inhibition, may offer a way of inhibiting only those hyperexcitable neurons responsible for clinical problems, avoiding the generalized nervous system depression associated with pharmacological therapy.