Reduction in cold-water swim analgesia following hypothalamic paraventricular nucleus lesions.

The analgesic response following cold-water swims (CWS) has been shown to be mediated through neurohormonal mechanisms and independently of opioid systems. The hypothalamic paraventricular nucleus (PVN) appears to be important in autonomic, hypophysial and medial-basal hypothalamic function. The present study examined whether lesions placed in the PVN in rats would alter CWS analgesia on the tail-flick test. Animals with lesions placed in the PVN displayed significant reductions in analgesic magnitude 30 (66%) and 60 (54%) min following CWS relative to sham-treated rats without alterations in baseline latencies. In contrast, CWS analgesia was not altered in animals with lesions placed dorsal and/or lateral to the PVN. These data are discussed in terms of the roles of PVN projections to the median eminence and brainstem/spinal structures as well as roles for neuropeptides in the PVN.