Repeated restraint stress enhances glutamatergic transmission in the paraventricular nucleus of the rat hypothalamus.

Corticotropin-releasing hormone (CRH)-synthesizing parvocellular neuroendocrine neurons of the hypothalamic paraventricular nucleus (PVN) play a key role in the activation of the hypothalamic-pituitary-adrenal axis (HPA). It is well known that excitatory and inhibitory inputs that regulate the activity of these neurons may undergo stress-related modifications; however, the effect of repeated restraint stress on the function of glutamatergic and GABAergic synapses on PVN parvocellular neuroendocrine neurons has not been fully understood so far. Adolescent male Wistar rats were subjected to restraint lasting 10 min and repeated twice daily for 3 days. Brain slices were prepared 24 hours after the last restraint session and were studied ex vivo. Whole-cell patch-clamping was used to record spontaneous excitatory and inhibitory postsynaptic currents (sEPSCs and sIPSCs) from parvocellular neuroendocrine neurons of the PVN. Repeated restraint stress resulted in an increase in the mean frequency of sEPSCs and in a decrease in the rise time and the decay time constant of sEPSCs. There was no change in the mean amplitude of sEPSCs. The parameters characterizing sIPSCs also remained unaltered. In addition, the injected current vs. spiking rate ratio of parvocellular neurons was decreased. In conclusion, restraint stress, repeated for 3 days, selectively enhances excitatory synaptic inputs to parvocellular neurons of the PVN, these modifications being accompanied with a decrease in the intrinsic excitability of PVN neuroendocrine parvocellular neurons.