Neural correlates of sensory gating in the rat: Decreased Fos induction inthe lateral septum

In the P-50 gating or conditioning-testing paradigm in the rat, two identic al click stimuli are presented with an inter-click interval of 500 ms. The reaction towards the second click, as measured with evoked potentials, is r educed in respect to that towards the first click; this phenomenon is calle d sensory gating. In the present experiments, the inter-click interval was varied systematically and auditory evoked potentials were measured. Sensory gating was found to occur only at intervals between 500 and 1000 ms, but n ot at longer intervals. Fos immunohistochemistry was then performed using t wo groups of rats exposed to double clicks: the inter-click interval was 50 0 ms in the experimental group and 2500 ms in the control group. Fos induct ion was analyzed in selected brain structures. In the auditory pathways, Fo s-immunoreactive neurons were found in both groups of rats in the inferior colliculus and medial geniculate body. Fos-immunoreactive cells were also e xamined in the septum and hippocampus. In the ventral part of the lateral s eptal nucleus, the labeled neurons were significantly fewer in the experime ntal animals compared to the control group. Smaller and non-significant qua ntitative differences of Fos-positive neurons were documented in the medial septum and hippocampal CA1 region. These data point out a selective decrea se in the lateral septum of Fos induced by auditory sensory gating, and sug gest an involvement of this structure, and possibly of other parts of the s epto-hippocampal system, in sensory gating mechanisms. The results might be relevant for theories on sensory gating deficits in schizophrenia. (C) 200 1 Elsevier Science Inc.