Responses of medullary reticulospinal and other reticular neurons to somatosensory and brainstem stimulation in anesthetized or freely-moving ovariectomized rats with or without estrogen treatment

Summary The medial medullary reticular formation (mMRF) is probably involved in controlling lordosis, a feminine mating reflex which requires both estrogen priming and appropriate somatosensory input(s). We have recorded single-unit activity of antidromically identified reticulospinal (RS) and unidentified (UI) neurons in mMRF of ovariectomized rats with or without estrogen treatment to investigate neurohormonal mechanisms regulating lordosis. The units were recorded in both acute and chronic preparations, the latter involving implanted floating wire electrodes to allow the influence of estrogen on a particular unit to be followed for several days.A substantial number of RS and UI units in both acute and chronic preparations were either excited or inhibited by a lordosis-eliciting somatosensory stimulation, indicating that the lordosis-eliciting sensory inputs did reach mMRF. The majority of these units responded promptly to the stimulation, and could participate in triggering the short-latency lordosis reflex. Electrical stimulation of several brainstem locations revealed that there was an extensive and specific convergence on mMRF neurons between inputs from the lordosis-eliciting stimulation and mesencephalic central gray, which has been shown to relay lordosis-inducing estrogen influence from hypothalamus to lower brainstem. Therefore, mMRF neurons can receive both the estrogen influence and the lordosis-eliciting inputs and integrate them. Although no apparent estrogen influence was detected in chronic preparations, statistical comparisons of results from acute preparations with or without estrogen treatment suggest that estrogen can increase the proportion of the neurons excited by the lordosis-eliciting stimulation and facilitate neuronal excitability. Both effects are consistent with the prevailing notion that the net lordosis-inducing influence of estrogen is facilitatory, and they may be mechanisms for making lordosis elicitable.Supported by NIH grant HD 05751     

Progesterone: examination of its postulated inhibitory actions on lordosis during the rat estrous cycle.

Three experiments tested whether the inhibitory effects of progesterone could be of physiological significance in regulating the duration of behavioral estrus in female rats. In animals displaying 5 day estrous cycles, a second period of sexual receptivity, one day following the occurrence of spontaneous estrus, could be induced by exogenous hormone administration, regardless of whether the ovaries were intact or were removed during the period over which the exogenous hormones were acting. In a second experiment, acute ovariectomy at various times during the progesterone surge acted only to degrade the quality of receptive behavior subsequently observed, never to enhance it by removing a postulated inhibitory influence. In the final experiment there was some suggestion that progesterone's facilitating effect on lordosis during the later portions of spontaneous estrus were attenuated by prior exposure to ovarian secretions during the early period of behavioral estrus. Our results are consistent with the hypothesis that the duration of receptive behavior under physiological conditions is not primarily regulated by inhibitory actions of progesterone, but rather by the quantity and duration of estrogen secretions during the conditioning period.     

Intracerebral implantation of the anti-estrogen CN-69, 725-27: Effects on female sexual behavior in rats

Ovariectomized adult female rats were stereotaxically implanted with double walled cannulas (22 ga outer and 27 ga inner) and tested for sexual receptivity (lordosis behavior) following SC estradiol benzoate and progesterone priming. Implantation of the anti-estrogen CN-69,725-27 (c. 6.5 μg) immediately after the first of 3 daily estrogen injections produced a dramatic inhibition of sexual receptivity when these implants were placed in the preoptic and anterior hypothalamic areas. CN-69,725-27 implants had no effect on receptivity when implanted in the middle hypothalamus, mesencephalon or frontal cortex. All inhibitory effects of the anti-estrogen were reversible within one day after removal of the CN-69,725-27 cannula from the brain.     

Facilitation of sexual receptivity in the rat by an ovulation-inhibiting analog of LHRH

An LHRH analog known to inhibit ovulation the rat ([N-Ac-Phe¹, D-p-Cl-Phe², D-Trp^3,6]LHRH) was tested for its effects on sexual receptivity. The dose of 500 ng/rat was found in dose-response experiments to be most active and was further investigated for its behavioral effects in rats treated with either estrogen or estrogen plus progesterone. The analog significantly facilitated the behavior of rats in regimens producing low [estradiol benzoat (EB) (2μg)] and intermediate [EB (2 μg) plus progesterone (2.5 mg)] levels of sexual behavior. In rats given regimens producing high behavioral scores [EB (5 μg) plus progesterone (1 mg)], the peptide did not reduce mating behavior. In the same experiment, rats given EB (5 μg) but not progesterone showed significantly higher scores after the LHRH analog only if they had been designated ”responders” by a previous screening test with 1 μg LHRH. These results demonstrate that in animals showing low, intermediate, or high levels of sexual behavior, the LHRH analog can affect mating behavior in a direction quite different from that exerted on pituitary reproductive functions.     

Role of the adrenal glands, repeated matings and monoamines in lordosis behavior of rats

Tetrabenazine, a potent monoamine depletor, was administered to estrogen-primed rats which were ovariectomized or ovariectomized and adrenalectomized. The drug treatment facilitated sexual receptivity in the nonadrenalectomized rats but had no such effects in adrenalectomized ones. Injection of saline, the solvent of tetrabenazine, in combination with repeated mating exerted the same facilitatory effect as the drug on the lordosis behavior. As in the case of tetrabenazine the effects only occurred in the presence of the adrenals. The facilitatory effect on the lordosis behavior was interpreted as due to adrenal steroids with progestational action which were secreted as a response to tetrabenazine, saline or/and repeated mating.     

Infusions of bicuculline to the ventral tegmental area attenuates sexual, exploratory, and anti-anxiety behavior of proestrous rats

Actions of 5α-pregnan-3α-ol-20-one (3α,5α-THP), in the midbrain ventral tegmental area (VTA) modulate sexual receptivity of female rats. Actions of 3α,5α-THP at GABAergic substrates in the VTA are known to modulate consummatory aspects of sexual behavior among rodents, such as lordosis. However, the extent to which GABA_A receptors in the VTA are important for appetitive (exploratory, anti-anxiety, social) aspects of sexual receptivity is not well-understood. Proestrous rats were bilaterally-infused with saline or bicuculline (100 ng), a GABA_A receptor antagonist, to the VTA or missed control sites. Rats were assessed for exploratory/anti-anxiety (open field/elevated plus maze), social (social interaction), and sexual (paced-mating) behavior. Compared to saline or missed site controls, intra-VTA bicuculline significantly reduced the number of central entries in an open field, time spent on the open arms of an elevated plus maze, frequency and intensity of lordosis, anti-aggression towards a male, pacing of sexual contacts, and 3α,5α-THP concentrations in midbrain and hippocampus. Bicuculline-infused rats also displayed less affiliation with a novel conspecific, fewer sexual solicitations, and had lower 3α,5α-THP concentrations in diencephalon and cortex, albeit these were not significant differences. Thus, actions at GABA_A receptors in the midbrain VTA are essential for appetitive and consummatory aspects of sexual receptivity among rats.     

胸腰段后凸畸形对腰椎前凸角度的影响及其临床意义

目的 :了解腰椎对胸腰段后凸畸形的代偿性改变及其临床意义。方法 :收集 12例具备胸腰椎和腰骶椎正侧位X线片的胸腰段后凸畸形病例 ,就其腰脊柱和每一节段腰椎的Cobb角、胸腰段的Cobb角、椎体滑移情况进行分析研究 ,并与 2 0例正常对照组进行相应比较。结果 :患病组平均腰椎前凸角度与正常对照组相比有极显著性差异 (P <0 .0 0 1)。患病组单节段腰椎前凸角度以上腰椎变化更为明显 ,L2～ 3 和L3～ 4分别是正常组相应节段的 4.2和 2 .4倍。结论 :腰椎过度前凸是胸腰段后凸畸形后为维持脊柱平衡的一个重要的代偿改变 ,而且以上腰椎的改变更为明显。     

Psychoneuroendocrine effects of neurotoxic lesions in the septum and striatum of rats

The psychoneuroendocrine effects of electrolytic septal lesions were compared with neurotoxic lesions in the lateral septum or striatum of rats induced by 6-hydroxydopamine (6-OHDA) or kainic acid (KA). Lesion effects were examined in terms of changes in body weight (BWt) regulation, ovarian compensatory hypertrophy (OCH) and female sexual behavior. Septal injections of 6-OHDA selectively reduced septal levels of dopamine (DA) by 60% whereas striatal injections reduced striatal levels of DA by 77% and septal levels by 30%. Significant effects of these various lesions were relative to controls (1) KA lesions in the septum increased and 6-OHDA lesions in the striatum decreased BWt; (2) 6-OHDA lesions in the striatum reduced ovarian weight and KA lesions in the septum increased OCH; (3) electrolytic septal lesions increased and KA septal lesions decreased female sexual behavior; (4) the effects of estrogen on food intake and BWt were attenuated in KA septal lesioned rats. Since this experiment failed to show an inhibitory role for DA on lordotic behavior, in a second experiment brain levels of DA were depleted by 6-OHDA injections in the ventral tegmental area or substantia nigra. Levels of female sexual behavior for these animals were comparable to controls. Thus, decreases in brain levels of DA previously shown to associated with electrolytic septal lesions may not be causally related to the observed increase in lordotic behavior. Lateral septal damage induced by KA appears to modify a variety of estrogen-sensitive systems.     

Effects of progesterone on lordotic responses to specific mating stimuli in hamsters

Mating-induced inhibition of sexual receptivity was examined in ovariectomized, estrogen (E) treated and estrogen plus progesterone (E + P) treated hamsters given 10 min of exposure to male mounting stimulation alone or to mounts, intromissions, and ejaculations at eight hourly intervals. In E + P treated females, no differential effects of exposure to full mating stimulation vs. mounting stimulation alone were observed. In contrast, females given E treatment alone showed a marked differential response. Fully mated, E-treated females showed more lordosis than E-treated females exposed to mounts alone during the initial test. However, total lordosis duration declined precipitiously in the fully mated group by 2 hr and remained significantly below that in other groups during subsequent tests. Levels of receptivity in E-treated females mounted-only remained relatively constant until 8 hr. These results suggest that P reduces the inhibitory effects of vaginocervical cues received during mating without affecting the response to mounting stimulation alone. In addition, vaginocervical stimulation may initially facilitate lordosis in E-treated females.     

Leumorphin, a novel opioid peptide, promotes lordosis in female rats

The actions of leumorphin, a recently characterized endogenous opioid peptide, oppose those of most opioid peptides in facilitating lordosis reflex, a major component of female sexual behavior in the rat. Maximal lordosis appeared promptly after infusion of 1 nmol leumorphin into the ventromedial hypothalamus of ovariectomized estrogen-primed rats. This facilitation lasted for as long as 5 h, unless interrupted by midbrain infusion of an antiserum to prolactin. The result is a discovery of a novel substance of remarkable strength in facilitating lordosis, an effect presumably mediated by midbrain release of prolactin.