Electrophysiological test of an amphiphilic beta-structure in LHRH action

Micropipettes were used to record electrical activity from single neurons in hypothalamic tissue slices, in the hypothalamic arcuate nucleus (ARC), and in the periventricular and suprachiasmatic preoptic nuclei (POA). Responses were measured following in vitro application of luteinizing hormone releasing hormone (LHRH), and two analogues: LHRH models 1 and 3. Model 1 (pyroGlu-His-Trp-Ser-Phe-Thr-Ile-Lys-Ile-ThrNH2) had amino acid substitutions in residues 5-10 designed to form an amphiphilic beta-strand structure. Model 3 (pyroGlu-His-Trp-Ser-Phe-Gly-Ile-Lys-Pro-SerNH2) was also designed to possess amphiphilic characteristics, but also more closely to resemble the native peptide. Electrical recording results showed that LHRH was able both to excite or inhibit different hypothalamic neurons, and that it was more effective in the preoptic area than in the arcuate nucleus. Responses to LHRH model 3 were strongly correlated with responses to LHRH, in their occurrence and their direction, for both of the brain regions studied. Moreover, LHRH models 1 and 3 also retained the neuromodulatory effects of LHRH on cellular responses to norepinephrine and serotonin. Thus, LHRH analogues, designed to possess an amphiphilic beta-structure, preserved some of the properties of LHRH when tested electrophysiologically in the central nervous system.