Role of the uterine cervix in inhibition of sexual behaviour in lactating rats

Sympathetic efferent pathways projecting to the vagina in the dog

The level of the thoracolumbar sympathetic outflow projecting to the vagina and the laterality of the signals passing through the splanchnic nerves to the vagina have not been well understood. This study was undertaken to explore the sympathetic innervation of the canine vagina by measuring intraluminal pressure of the vagina and contraction of the vaginal wall by electrical stimulation of each of the thoracolumbar splanchnic nerves with or without transection of unilateral hypogastric nerve (HGN). The 2nd-4th lumbar splanchnic nerve (LSN) stimulation elicited elevation of intraluminal pressure of the vagina and contraction of the vaginal wall. In contrast, intermesenteric plexus stimulations caused no response in both the vaginal pressure and the wall itself. On the right side, 12 of 27 LSNs that were stimulated elicited elevation of vaginal pressure and 16 of 32 LSN stimulations caused contraction of the wall, 10 increases in tension and 6 reductions. On the left side, 14 of 26 LSN stimulations elicited elevation of vaginal pressure and 12 of 27 LSN stimulations caused contraction of the wall, 5 increases in tension and 7 reductions. After transection of the right HGN, 6 of 14 right LSN stimulations elicited elevation of vaginal pressure and 10 of 15 right LSN stimulations caused contraction of the wall, 9 increases in tension and 1 reduction. After transection of the left HGN, 13 of 19 left LSN stimulations elicited elevation of vaginal pressure and 10 of 18 left LSN stimulations caused contraction of the wall. 4 increases in tension and 6 reductions. The results indicate that each of the L2-L4 LSNs on either side sends signals to the canine vagina via multiple routes with a crossing site at the level of the caudal mesenteric plexus (CMP).

Determination of Enkephalins in Rat Cerebrospinal Fluid with High-Performance Liquid Chromatography-Electrochemical Detection: Increased Concentrations During Lactation are Controlled by Sucking

Abstract Methionine- and leucine-enkephalin were measured in the cerebrospinal fluid of lactating rats by high-performance liquid chromatography and electrochemical detection. The concentration of both peptides was high while the rats were nursing their litter. The concentration of methionine-enkephalin decreased rapidly when the mother left her litter and increased equally rapidly after mother-young reunion, provided the pups were allowed direct contact with the nipples of the mother. The level of leucine-enkephalin did not change during the period of time the lactating rat normally stayed away from its litter but decreased after prolonged (12 h) mother-pup separation. These results show that the concentration of methionine-, but not leucine-enkephalin in the cerebrospinal fluid fluctuates as the lactating rat interacts with its litter and is directly dependent upon the suckling stimulus. Although methionine-enkephalin may contribute to the inhibition of sexual behaviour which occurs during lactation, the role of the enkephalins in the other behavioural and endocrine adaptations of lactation is unknown.

beta-Endorphin acts on the reproductive tract of female rats to suppress sexual receptivity

Sexual receptivity was suppressed in female rats immediately after the male had ejaculated. The inhibition was prevented by intravaginal injection of naloxone (100 micrograms) before testing and intravaginal injection of beta-endorphin (1.0 micrograms) inhibited sexual behavior in female rats in a manner comparable to that of ejaculation by the male. beta-Endorphin was present in ejaculatory plugs collected from the vagina of female rats (8.2 +/- 0.6 pM) and in seminal fluid collected from male rats (7.7 +/- 0.2 pM). The results suggest that beta-endorphin in the ejaculate of the male rat can act on the reproductive tract of the female rat to suppress her sexual behavior.

Selective effects of beta-endorphin infused into the hypothalamus, preoptic area and bed nucleus of the stria terminalis on the sexual and ingestive behaviour of male rats

beta-Endorphin was infused bilaterally into the medial preoptic area-anterior hypothalamic continuum at doses of 5, 10 and 40 pmol each side. The highest dose selectively abolished mounting, intromitting and ejaculating in sexually experienced male rats paired with an oestrous female. Males infused with 40 pmol beta-endorphin still followed the female, investigated her anogenital region and other parts of her body, but made abortive attempts to mount. A dose of 5 pmol beta-endorphin had no effect, but 10 pmol proved partially effective. The same males, in other tests, were allowed to ingest a highly preferred, sweet, non-calorific solution (acesulfame-K) in the absence of a female. beta-Endorphin infusions (up to 40 pmol) into the same area of the hypothalamus had no effect on this behaviour. Control males allowed simultaneous access both to an oestrous female and to the sweet solution copulated normally but reduced their ingestive behaviour, despite there being sufficient time during tests for both to occur. beta-Endorphin (40 pmol) infused into the preoptic area-anterior hypothalamic continuum under these conditions suppressed sexual interaction, but ingestion of acesulfame-K increased to values observed when the female was absent. beta-Endorphin infused into neighbouring areas of the brain had different behavioural effects. Sexual behaviour was not inhibited, and ingestion of acesulfame-K was unaltered, when beta-endorphin was infused either into the bed nucleus of the stria terminalis or the rostral ventromedial hypothalamus. However, infusions of cholecystokinin-8 into the ventromedial hypothalamus suppressed acesulfame-K ingestion in most animals, showing that the cannulae were placed in an area regulating ingestive behaviour. The inhibition of sexual behaviour after preoptic area-anterior hypothalamic continuum infusions of beta-endorphin was prevented by either pretreating rats with 1 mg/kg naloxone intraperitoneally, or by infusing a putative delta opiate receptor blocker (0.5 pmols ICI 174864) into the preoptic area-anterior hypothalamic continuum 5 min prior to beta-endorphin treatment. ICI 174864 administered alone significantly increased mount rate and reduced the post-ejaculatory refractory period in copulating males. These experiments suggest that there is both neurochemical and neuroanatomical specificity relating beta-endorphin to sexual behaviour in the male rat.