Effects of periventricular lesions on the release of somatostatin during perifusion

Hypothalamic periventricular (PV) nucleus lesions reduce median eminence (ME) SRIF content by approximately equal to 80% without affecting non-stress plasma growth hormone (GH) levels or the GH response to stress. Our aim was to study the effects of PV lesions on SRIF released during perifusion of preoptic-anterior hypothalamic (PO-AH) tissue. Female rats received anterior or posterior PV lesions; sham-lesioned and intact rats served as controls. Non-stress and stress plasma GH levels were similar in all groups at 2, 4 and 16 weeks after surgery. At 18 weeks after surgery, the perifused PO-AHs of the PV- and sham-lesioned rats released similar amounts of SRIF, and these were higher (P less than 0.001) than amounts released from PO-AHs of intact rats. The PO-AHs from all groups showed similar increases in SRIF release after 56 mM K+. Two rats were chosen randomly from each group to assess ME SRIF content; PV lesions caused almost 80% depletion of SRIF, sham lesions did not. These results confirm that most SRIF neurons in the PV nucleus and 80% of ME SRIF content are not essential for the control of GH levels under non-stress conditions or for the GH response to stress and indicate that PV or sham lesions in the rostral forebrain enhance in vitro SRIF release, perhaps from neurons outside the PV nucleus.