Analysis of neurotransmitter receptors mediating changes in LH release induced by electrical stimulation of the dorsal raphe nucleus in the rat

Abstract

We report studies of neurotransmitter and receptor species mediating the inhibition of LH release in ovariectomized (OVX) rats and stimulation in OVX estrogen-primed rats induced by electrical stimulation of the dorsal raphe nucleus (DRN). Attempts were made to block effects of stimulation of the DRN in groups of four to nine ovariectomized rats with or without priming with estradiol benzoate (EB) by pretreatment with the 5HT receptor antagonists ketanserin, methysergide, or metergoline; the alpha-adrenergic antagonist phenoxybenzamine; or the opiate antagonist naltrexone. Blood samples were collected via jugular cannulae from the unanesthetized rats at 10-min intervals before and during electrical stimulation of the DRN, and assayed by double antibody radioimmunoassay for LH. To test the effect of stimulation, data from animals in each treatment group were subjected to analysis of variance to obtain the contrast matrix including prestimulation and stimulation time points of interest. The contrast matrix was then used to construct an F ratio and thereby to evaluate the level of significance. In unprimed OVX rats the sustained decrease in plasma LH concentration during stimulation was prevented in rats pretreated with ketanserin or phenoxybenzamine. Methysergide pretreatment delayed the inhibitory effect of DRN electrical stimulation for 30 min, whereas metergoline and naltrexone were ineffective. In EB-primed animals the increase in plasma LH observed during stimulation was prevented in rats pretreated with metergoline, and reversed in those receiving naltrexone. Ketanserin limited the duration of the increase to 10 min, while phenoxybenzamine and methysergide had no significant effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Serotonin Inhibits Luteinizing Hormone Release via 5-HT1A Receptors in the Zona incerta of Ovariectomised, Anaesthetised Rats Primed with Steroids

“…The system originating in the DRN also has an inhibitory effect on pulsatile release of LH via 5-HT but only in the absence of gonadal steroids [20, 21]. Correlating 5-HT activity with steroidal negative feedback effects on LH release show that an early effect (3 h) of oestrogen is to both depress LH and increase 5-HT turnover presumably in the MRN pathway [36].…”

“…The stimulatory effect appears to reside in a system originating in the dorsal raphe nucleus (DRN) and terminating in the pre-optic area (POA) and median eminence (ME) [16, 17, 18, 19], but this system is only active in the presence of oestrogen [20, 21]. This is based on a wide variety of experiments including electrical stimulation and lesions of the DRN [17, 21]and noting a positive correlation in 5-HT activity and LH release in the three areas mentioned above (DRN, POA and ME) in both intact proestrous rats and ovariectomised rats primed with gonadal steroids that induce an LH surge (DRN [22, 23]; POA [19, 23, 24]; ME [25, 26]).…”

“…This is based on a wide variety of experiments including electrical stimulation and lesions of the DRN [17, 21]and noting a positive correlation in 5-HT activity and LH release in the three areas mentioned above (DRN, POA and ME) in both intact proestrous rats and ovariectomised rats primed with gonadal steroids that induce an LH surge (DRN [22, 23]; POA [19, 23, 24]; ME [25, 26]). Pharmacological evidence in vivo [28, 29]and in vitro [30, 31]also supports the stimulatory role of 5-HT in regulating LH release.…”