The Application of Sub-Perception Electrical Stimuli Elicits a Temporally Distinct Response from Restraint Stress: II. Neurochemical Considerations

Abstract

The concentration of noradrenaline (NA) and its principal metabolite methoxyhydroxyphenylglycol (MHPG) was determined in five brain regions of rats that received either no treatment, or restraint for 5, 10, 20, 40, 60 or 120 min. Similar groups of rats received a transcranial sub-perception electrical stimulation (TCET) while being restrained for a similar period of time. Plasma was analyzed by radioimmunoassay techniques for adrenocorticotropic hormone (ACTH), corticosterone (cort) and B-endorphin (BE). NA concentration in the hypothalamus was significantly higher than the basal values in both sham and treated rats at each time interval. With the exception of the hypothalamus and pituitary, MHPG concentration was significantly higher in all the restrained animals than the basal controls; at 10 and 20 min, the value in the rats receiving TCET was significantly lower than that of the sham-treated animals, thereafter increasing to levels significantly higher than that of the shams. The plasma ACTH, cort and BE immunoreactivity (-Ir) was generally higher than the basal controls in all except the last (120 min) sample. In the TCET-treated rats ACTH-Ir was significantly lower than the shams after 10 and 20 min, although the sham value declined below the basal at 120 min. In the TCET-treated rats plasma cort-Ir did not correspond with ACTH-Ir and was significantly higher than the shams at 10, 20 and 40 min. BE-Ir was significantly higher in the TCET-treated group in comparison with the shams at 5 min only. These data show temporal differences between concentrations of neurohumoral substances associated with the response to stressful stimuli in similarly restrained rats which differed only in whether or not they received a concomitant sub-perception microelectrostimulus.