Decreased expression of the mRNA for somatostatin in the periventricular nucleus of depression-model rats

Expression of the mRNA for somatostatin (SRIF) in the periventricular nucle us (PeN), the level of SRIF in the stalk-median eminence (SME) and the conc entration of growth hormone (GH) in the plasma were examined in depression- model rats in an attempt to confirm the hypothesis that SRIF neurons in the hypothalamus are hypofunctional in this model. We exposed male Wistar rats to intermittent walking stress for two weeks and then we measured their sp ontaneous running activity for 12 days. We divided the rats into a depressi on-model group and a partial-recovery group according to the spontaneous ru nning activity of each rat after the termination of exposure to stress. Exp ression of SRIF mRNA in the PeN of the hypothalamus was monitored by in sit u hybridization and relative levels were determined with an image analysis system. The relative level of expression of SRIF mRNA in the PeN was lower in rats in the depression-model group than in the control group and the par tial-recovery group. The level of SRIF in the SME was lower and the plasma concentration of GH was higher in the depression-model group than in the ot her groups. Our findings suggest that reduced expression of mRNA for SRIF i n the PeN might be associated with the pathophysiology of rats with this pa rticular model of depression, (C) 1999 Elsevier Science Inc.