Tonic activity and GABA responsiveness of medial vestibular nucleus neurons in aged rats

The tonic discharge of rat medial vestibular nucleus (MVN) neurons, and their responsiveness to GABA receptor agonists were investigated in slices prepared from aged rats (24 months old). Aged MVN neurons showed regular spontaneous activity similar to that seen in slices from young adults. However the inhibitory effects of the GABA(A) agonist muscimol on the spontaneous activity of aged MVN neurons were significantly greater than in young MVN neurons. Inhibitory responses to the GABA(B) agonist baclofen also tended to be greater in slices from aged animals, but this difference was not statistically significant. The regular discharge of aged MVN neurons at firing rates similar to those in young animals suggests that the intrinsic excitability of MVN cells is maintained with age. The up-regulation of GABA(A) receptor efficacy in aged MVN neurons may compensate for changes in inhibitory inputs from vestibular commissures and cerebellum that may occur with neuronal loss in the aged brain.