Negative feedback functions in chronically stressed XXXX : role of the posterior paraventricular thalamus.

@entity2819 @entity619 @entity2339 @entity35
A gradual decrement in @entity2339 is observed following repeated exposure to the same stressor, such as repeated restraint. This decrement, termed habituation, may be partly due to alterations in @entity2819 -mediated negative feedback inhibition of the @entity2339 . We have previously found that the posterior division of the paraventricular thalamus (pPVTh) regulates habituated HPA activity without altering HPA responses to acute stress. Therefore, in the present study, we examined the role of the pPVTh in delayed feedback inhibition of plasma @entity2819 responses to repeated restraint. @entity619 was administered subcutaneously 2 h prior to 30 min restraint to induce delayed negative feedback inhibition of the @entity2339 . In the first experiment, we determined that a 0.05-mg/kg dose of @entity619 produced submaximal suppression of @entity2819 responses to acute restraint and used this dose in the remainder of the experiments. In Experiment 2, we examined @entity619 -induced feedback inhibition to @entity2819 responses to a single or eighth restraint exposure since negative feedback functions in chronically stressed @entity35 are not well studied. We found that @entity2819 levels following @entity619 treatment were similar in repeatedly restrained compared to acutely restrained @entity35 . In Experiment 3, we lesioned the pPVTh and examined @entity619 -induced feedback inhibition of @entity2819 responses to a single or eighth exposure to restraint. pPVTh lesions attenuated @entity619 -induced inhibition of @entity2819 at 30 min in chronically stressed @entity35 but had no effect in acutely stressed @entity35 . These data suggest that negative feedback functions are maintained in @entity35 exposed to repeated restraint and implicate the pPVTh as a site that contributes to these negative feedback functions specifically under chronic stress conditions.
