Catecholaminergic activity in the medial preoptic area and nucleus infundibularis-median eminence of anestrous ewes in normal physiological state and under stress condition.

Abstract

The stressful events induce in organism both excitatory and inhibitory mechanisms for rapid physiological adjustment to environmental stressors. Pull-push technique was used to determine extracellular concentrations of NE, DA, and their metabolites MHPG and DOPAC in the medial preoptic area (MPOA) and nucleus infundibularis-median eminence (NI/ ME) of anestrous ewes in normal physiological state and under stress condition. In non-stressed ewes the level of NE in the MPOA was substantially lower than in the NI/ME, whereas DA was found only in the NI/ME. No regional differences in the concentrations of MHPG, DOPAC in these structures were found. On the first day, footshock stimulation activated noradrenergic system in the MPOA and both noradrenergic and dopaminergic system in the NI/ME during the first 1.5 h followed by gradual desensitisation of these systems. On the third day during whole period of stimulation the concentration of all these neurochemical compounds were significantly lower than in controls. It indicates that prolonged intermittent stress elicits a neurochemical processes in the MPOA and NI/ME whose effects lead to the suppression of catecholamines release and their metabolism. The basal concentration and stress induced changes of NE, DA, MHPG, DOPAC in the fluid of the III-rd brain ventricle (V-III) reflect a dynamic relationship between extracellular levels of catecholamines and their metabolites in the hypothalamus and cerebral fluid. The consequences of these long-term response of catecholaminergic system in the MPOA and NI/ME may be essential for changes in LHRH release from the hypothalamus which we observed in ewes subjected to prolonged stressful experience (Tomaszewska et al., 1999).