Oestrogenic influences on the electrical activity of the olfactory pathway

CARTAS-HEREDIA, L., R. GUEVARA-AGUILAR AND H. U. AGUILAR-BATURONI. Oestrogenic influences on theelectrical activity of the olfactory pathway. BRAIN RES. BULL. 3(6) 623–630, 1978.—The influence of the Oestrogenic hormones over the spontaneous and induced activity of the olfactory pathway was studied in normal female cats. Electrodes were placed chronically or acutely in the olfactory bulb (OB), olfactory tubercle (OT) and in the prepyriform cortex (PPC). Oestrogenic hormones were applied locally in the posterior hypothalamic region. Recordings were made during the two different phases of the oestral cycle. In addition, another group of castrated animals was studied. The oestral phase was induced in these cats by the subcutaneous administration of 17-β-oestradiol. Results indicate that the pattern of the electroencephalographic spontaneous activity as well as the response induced by hypothalamic stimulation changed. The number of the bursts for each 10 sec trace was higher in oestrus than in anoestrus for all the structures studied. The duration of each burst also changed, being shorter in oestrus than in anoestrus cats. The threshold for significant bursting in the olfactory structures following hypothalamic stimulation was lower in oestrus than in anoestrus. The evoked potentials recorded in the same three olfactory structures by hypothalamic stimulation exhibited changes in correlation with the hormonal administration. In all the structures studied the amplitude of the different components of the evoked potentials increased immediately after the hormones were administered. However, the most dramatic increase was observed in the olfactory tubercle. In order to further investigate these changes in acute preparations, a study evaluating the excitability changes was conducted. Applied pulse pairs, with different interpulse intervals between 200 to 1000 msec, were delivered in the hypothalamus before and after 200 μg of the hormone were administered into the posterior hypothalamus. Results illustrate that a significant increase in the amplitude of evoked potentials occurred following the smaller interpulse intervals in the OB. In the OT, the administration of the hormone resulted in a decrease in the amplitude of the potentials for all interpulse intervals studied. A relatively smaller decrease in evoked potential amplitude was observed for longer interpulse intervals in the PPC.