Inputs to testosterone‐sensitive stria terminalis neurones in the rat brain and the effects of castration.

Abstract

SUMMARY1. The inputs to cortico-medial amygdala neurones which project directly to the area of the medial preoptic/anterior hypothalamic junction were studied electrophysiologically in urethane anaesthetized male rats.2. In experiments with fifteen male rats it was found that none of these neurones was responsive to electrical stimulation of the ipsilateral olfactory bulb or accessory olfactory bulb or odour stimulation.3. Experiments with four rats showed that electrical stimulation of the lateral portion of the contralateral fimbria excited 81 % of these cortico-medial amygdala neurones. Their typical response to stimulation of the contralateral fimbria was a single action potential followed by an inhibitory period (20-1000 ms).4. Analysis of the polarity of evoked waves in the amygdala suggested that the fimbria input terminated in the basolateral nucleus of the amygdala and that this nucleus subsequently projected to the cortico-medial amygdala. The fimbria input was found to be contralateral in origin, crossing the mid line in the anterior fornical commissure.5. In a further experiment 118 identified cortico-medial amygdala neurones were recorded from twelve rats (six gonadally intact and six castrated). Castration significantly decreased the percentage of these neurones responding to stimulation of the ipsilateral fimbria (20 vs. 97 %) and lengthened post-excitatory inhibitory periods.6. Results are discussed with respect to the initial finding by Kendrick & Drewett (1979) of testosterone-sensitive absolute refractory periods in cortico-medial amygdala neurones.

Effect of castration on medial preoptic/anterior hypothalamic neurone responses to stimulation of the fimbria in the rat

“…There was no significant difference between the two groups for the number of orthodromically stimulated neurones encountered during each electrode penetration In the previous paper (Kendrick, 1982) it was concluded that there was a fimbria input to the cortico-medial amygdala (c.m.a.) probably via the basolateral nucleus of the amygdala (b.l.n.).…”

“…to the m.p.o.a.h., via, presumably, the corticohypothalamic tract (Raisman, Cowan & Powell, 1966). This direct projection via the corticohypothalamic tract is, however, ipsilateral (Raisman et al 1966) whereas the present projection via the amygdala is contralateral in origin (Kendrick, 1982). Hubbard et al (1981) reported that for more anterior locations the most effective part of the i.f.i.m.b.…”

“…could be stimulated antidromically simply by raising the current. The previous paper (Kendrick, 1982) showed that castration reduced the percentage of cortico-medial amygdala (c.m.a.) neurones projecting to the medial preoptic/anterior hypothalamic junction (m.p.…”

“…Driven unit activity is characterized in the previous paper (Kendrick, 1982). For those neurones showing post-stimulus inhibition the length of the inhibitory period was measured by plotting a post-stimulus histogram using an averager (Neurolog NL 750; Digitimer Ltd.).…”

“…Anaesthesia, stimulation, recording and histological techniques are described in the previous paper (Kendrick, 1982). Stimulating electrodes were placed either in the ipsilateral fimbria, contralateral fimbria, ipsilateral stria terminalis, basolateral amygdala, cortico-medial amygdala or medial forebrain bundle at the level of the lateral hypothalamus.…”