Vigilence state modulation of paired-pulse response in the rat hippocampus

The paired-pulse technique was used to establish an index of inhibition/facilitation in the dentate gyrus (DG) by determining the ratio of inhibitory to facilitatory responses to perforant path stimulation in four behavioral states (immobile waking (IW), active waking (AW), slow wave sleep (SWS), and REM sleep). In normal rats (born and reared on a 25% protein diet) at 90-120 days of age, a stimulus-response curve was determined in each behavioral state before paired-pulse testing was done at interpulse intervals (IPIs) between 20 and 1000 ms. Paired-pulse tests provide evidence of a changing ratio of inhibition to facilitation of the population spike in the DG at several IPIs. The ratio of facilitatory to inhibitory responses at short IPIs is significantly greater during AS than during IW, SWS, and REM, suggesting that inhibition (recurrent or feed-forward) may be suppressed during AW. Since prenatal nutritional insults to the developing central nervous system have effects persisting into adulthood, especially in highly plastic structures such as the hippocampus, the paired-pulse procedure was used to assess the effects of prenatal protein malnutrition on the vigilance state modulation of this inhibition/facilitation index. The major finding is that prenatal protein malnutrition results in loss of the dependence of population spike amplitude on vigilance state