Luteinizing hormone release in the anaesthetised cat following electrical stimulation of limbic structures

The release of luteinizing hormone (LH) in response to electrical stimulation of limbic centres, namely the medial preoptic region (MPO) medial basal hypothalamus (MBH) and the medial amygdala (AME) has been studied in the anaesthetised gonadectomized cat. Chronically gonadectomized cats were anaesthetised with pentobarbitone or Althesin and paired bipolar stimulating electrodes were aimed at the MPO, AME or MBH. The effect of electrical stimulation of these regions on the secretion of LH was studied by radio-immunoassay of LH in serial blood samples taken before, during and after stimulation. No change in plasma LH in response to electrical stimulation was ever recorded during pentobarbitone anaesthesia. During Althesin anaesthesia stimulation in the MPO more often than not resulted in a peak of LH release during stimulation. A peak release of LH during stimulation was also recorded when electrodes were placed in the arcuate-median eminence region of the MBH. The time-course of these peaks in LH secretion was similar to the time-course of the plasma LH responses recorded following a single intravenous injection of gonadotrophin-releasing hormone (GnRH). In contrast, electrodes placed in AME had no effect on plasma LH during electrical stimulation, but immediately after stopping it, a small LH peak was recorded. The time-course of these responses suggests a pulse release of GnRH, the rapid response to MPO and MBH stimulation possibly being the result of a direct action on GnRH neurons while the delayed AME response may be produced by AME projections to the GnRH release system. These responses could be likened to the surge of LH which in the cat occurs post-coitus.