Multiple single units and population responses during inhibitory gating ofhippocampal auditory response in freely-moving rats

Paired clicks were presented to awake, freely-moving rats to examine neuron al activity associated with inhibitory gating of responses to repeated audi tory stimuli. The rats had bundles of eight microwires implanted into each of four different brain areas: CA3 region of the hippocampus, medial septal nucleus, brainstem reticular nucleus, and the auditory cortex. Single-unit recordings from each wire were made while the local auditory-evoked potent ial was also recorded. The response to a conditioning stimulus was compared to the response to a test stimulus delivered 500 ms later: the ratio of th e test response to the conditioning response provided a measure of inhibito ry gating. Auditory-evoked potentials were recorded at all sites. Overall, brainstem reticular nucleus neurons showed the greatest gating of local aud itory-evoked potentials, while the auditory cortex showed the least. Howeve r, except for the auditory cortex, both gating and non-gating of the evoked response were recorded at various times in all brain regions. Gating of th e hippocampal response was significantly correlated with gating in the medi al septal nucleus and brainstem reticular nucleus, but not the auditory cor tex. Single-unit neuron firing in response to the clicks was most pronounce d in the brainstem reticular nucleus and the medial septal nucleus, while r elatively few neurons responded in the CA3 region of the hippocampus and th e auditory cortex. Taken together, these data support the hypothesis that i nhibitory gating of the auditory-evoked response originates in the non-lemn iscal pathway and not in cortical areas of the rat brain. (C) 1999 Elsevier Science B.V. All rights reserved.