Differences induced by incubation temperature, versus androgen manipulation, in male leopard geckos (Eublepharis macularius)

A fundamental tenet of sexual selection is that in sexually dimorphic traits, there is variation within a sex. In leopard geckos (Eublepharis macularius), a species with temperature-dependent sex determination, embryonic temperature contributes both to sex determination and polymorphisms within each sex. In this study we report that males from different incubation temperatures, one hitherto untested, exhibit significant differences in behavior even when castrated. Further, treatment with dihydrotestosterone increases scent marking, a territorial behavior. This supports previous results indicating that temperature has a direct organizing action on brain and sociosexual behavior independent of gonadal hormones.     

Intermediate filament immunohistochemistry of astroglial cells in the leopard gecko, Eublepharis macularius

The distribution of intermediate filament molecular markers, glial fibrillary acidic protein (GFAP) and vimentin, has been studied in the central nervous system (CNS) of the adult leopard gecko, Eublepharis macularius. This immunohistochemical study points out the presence of different astroglial cell types. The main pattern is constituted by ependymal radial glia, which have their cell bodies located in the ependymal layer throughout the brain ventricular system. Radial glia proper or radial astrocytes show their cell bodies displaced from the ependymal layer into a periependymal zone and are observed only in the spinal cord. Star-shaped astrocytes are scarce. They are detected in the ventral and lateral regions of the diencephalon and mesencephalon, in the superficial layer of the optic tectum, in the ventral medulla oblongata, and in the ventral and lateral spinal cord. In the different regions of the CNS, the staining intensity appears not to be identical even in the same cellular type. The results reported in the present study show an heterogeneous feature of the astroglial pattern in E. macularius.     

Dopamine, the medial preoptic area, and male sexual behavior

The medial preoptic area (MPOA), at the rostral end of the hypothalamus, is important for the regulation of male sexual behavior. Results showing that male sexual behavior is impaired following MPOA lesions and enhanced with MPOA stimulation support this conclusion. The neurotransmitter dopamine (DA) facilitates male sexual behavior in all studied species, including rodents and humans. Here, we review data indicating that the MPOA is one site where DA may act to regulate male sexual behavior. DA agonists microinjected into the MPOA facilitate sexual behavior, whereas DA antagonists impair copulation, genital reflexes, and sexual motivation. Moreover, microdialysis experiments showed increased release of DA in the MPOA as a result of precopulatory exposure to an estrous female and during copulation. DA may remove tonic inhibition in the MPOA, thereby enhancing sensorimotor integration, and also coordinate autonomic influences on genital reflexes. In addition to sensory stimulation, other factors influence the release of DA in the MPOA, including testosterone, nitric oxide, and glutamate. Here we summarize and interpret these data.     

Inhibition of male sexual behavior by serotonin application in the medial preoptic area

The study investigated the possible involvement of serotonin in the medial preoptic area in the regulation of sexual behavior of male rats. Injection of serotonin in the medial preoptic area resulted in an inhibition, whereas cyproheptadine (a serotonin antagonist) produced a slight facilitation, of male sexual behavior.     

Orexin A (hypocretin-1) application at the medial preoptic area potentiates male sexual behavior in rats

The medial preoptic area plays an important role in the regulation of male sexual behavior in rats, and this area receives orexinergic inputs. The role of orexinergic inputs in the medial preoptic area in sexual behavior has not been studied, though they have been shown to play a role in some other physiological functions. In this study, the changes in male sexual behavior in rats were studied after local injection of orexin A (Hypocretin-1) at the medial preoptic area. The results of the study showed that orexin A application at the medial preoptic area increased sexual arousal as well as the copulatory performance. Sexual arousal is one of the physiological stimuli, which influences wakefulness. It is possible that the earlier reports showing increased wakefulness, on application of orexin A at the medial preoptic area/basal forebrain, has a contribution from sexual arousal.     

Effect of prepuberal medial preoptic area lesions on male rat sexual behavior

Studies have shown that the medial preoptic area (MPOA) is necessary for male sexual behavior in many species. Sparing of function occurs in rats which have MPOA-lesions made prepuberally and are reared in heterosexual group cages. In the present study, male rats with MPOA-lesions made prepuberally and control-operated animals were reared either in group or solitary cages. In three regular mating tests few MPOA-animals reared in isolation displayed sexual behavior, while those reared in groups performed no differently from control animals. Animals with MPOA-lesions that mated exhibited the same frequency and developmental progression of play behaviors as their control peers. In sexual exhaustion and postcastration tests, group-reared MPOA-animals performed at a lower level than control animals. The results are compatible with the hypothesis that play experiences have a role in sparing of copulatory behavior in rats with MPOA-lesions. Deficits in the MPOA-animals in the more challenging tests were discussed in relation to a possible decrease in responsiveness to gonadal or hypothalamic hormones.     

Inactivation of the medial preoptic area/anterior hypothalamus by lidocaine reduces male sexual behavior and sexual incentive motivation in male rats

Permanent bilateral lesions of the medial preoptic area anterior hypothalamus (MPOA/AH) produce a drastic inhibition of male sexual behavior in all species studied to date. The present experiment was designed to evaluate if temporal inactivation of the MPOA/AH by infusions of lidocaine also inhibits sexual behavior in male rats. This would allow us to rule out the possibility that the behavioral effects observed after damage of the MPOA/AH could be associated with plastic changes induced by the lesion in other brain regions. We also evaluated sexual incentive motivation in males after the infusion of lidocaine in a test in which copulation is not possible but where males maintain approach behavior to the estrous females despite repeated testing. The percentage of animals displaying mounts, intromissions and ejaculation was significantly reduced while mount and intromission latency were prolonged after infusion of lidocaine. No changes were observed in sexual behavior after infusion of lidocaine in animals with cannulae outside the MPOA/AH suggesting that the inhibitory effects are specific to this brain region. Sexual incentive motivation was also affected by administration of lidocaine. Males consistently showed a clear preference for the sexually receptive female except when infused with lidocaine. After the infusion of the compound a significant reduction in the time spent in the incentive zone of the stimulus female was observed. These results support the hypothesis that neurons of the MPOA/AH are involved in the control of male sexual motivation.     

Effects of two-stage lesions of the medial preoptic area on sexual behavior of male rats

The effects of lesions of the medial preoptic area (MPOA) on sexual behavior of adult male rats were examined. Bilateral lesions were performed in either one or two stages. Bilateral, but not unilateral, destruction of the MPOA virtually eliminated mounts, intromissions, and ejaculation. No sparing of the male rats' sexual behavior was observed after two-stage MPOA lesions.     

The relation between sexual behavior and seminal fructose in intact and castrated rabbits

Seminal fructose and sexual behavior were studied in intact and castrated, testosterone treated rabbits. Both seminal fructose and the intensity of sexual behavior increased after testosterone treatment. The dose-response relations were quite different for the two variables. A dose of 7.5 mg testosterone propionate injected every third day during the experiment restored the sexual behavior to precastrational levels, whereas a dose of 30 mg TP was insufficient to give seminal fructose concentrations comparable to those in the intact animals. There were no correlations between sexual behavior and seminal fructose in individual animals. Neither were any such correlations found in the intact animals. The data seem to support the idea of different hormonal mechanisms controlling sexual behavior and activity in the accessory sexual glands.     

Effect of bicuculline on sexual activity in castrated male rats

The GABA antagonist (+) bicuculline methiodide (30 ng/cannula) was injected in the medial preoptic-anterior hypothalamic area of castrated rats treated with subthreshold dosages of testosterone propionate (150 micrograms/kg/day). The treatment resulted in a facilitation of sexual activity suggesting a role of GABA as a neurotransmitter in neural processes determining sexual arousal.     

Medial preoptic connections with the midbrain tegmentum are essential for male sexual behavior

The medial preoptic area appears to play a major role in the control of sexual behavior. Efferents from the medial preoptic area course through the medial forebrain bundle to pass through and/or terminate in the dorsolateral and ventral tegmentum of the midbrain. Bilateral lesions of the dorsolateral tegmentum eliminate mating behavior in male rats, reproducing the effect of bilateral medial preoptic lesions. Sexual behavior is also eliminated when a preoptic lesion on one side of the brain is combined with a lesion of the dorsolateral tegmentum on the other side of the brain. In other words, asymmetric brain damage which bilaterally destroys the preoptic connections with the dorsolateral tegmentum eliminates male sexual behavior, and we conclude that the connections between these two regions are essential for copulation.     

Neuropsychological correlates of platelet monoamine oxidase (MAO) activity in female and male subjects

Platelet monoamine oxidase (MAO) activity has been found to have behavioral (psychiatric and personality) correlates and is assumed to be linked to central transmitter systems and thus presumably to neuropsychological processes. In the present study, computerized neuropsychological tests, a reaction time (RT) test and a visuo-spatial problem solving test, the Perceptual Maze Test (PMT), were given to 32 female and 29 male students, each sex group divided into three subgroups on the basis of platelet MAO activity. The tests yield measures of laterality (reaction time for left- versus right-sided stimuli) and different aspects of cognitive strategy and skill, e.g. time used for inspection of the maze, for processing the stimulus pattern, and for checking the correctness of solutions. Low MAO female subjects had shorter RTs, pronounced for left-sided stimuli, and shorter inspection times in the PMT compared to other female subjects. Low and high MAO males had difficulties in inhibiting responses, when required, and low MAO males were more rapidly prepared to respond to new stimuli after short intervals than other males. In the PMT, high MAO male subjects spent a smaller part of the total time on inspection in relation to other male groups and had more rubouts than low MAO males, whose maze solving behavior indicated higher visuo-spatial ability. The results are discussed in terms of possible neurochemical bases of impulsivity and psychopathy, and of spatial skill.     

Galanin-like peptide stimulates feeding and sexual behavior via dopaminergic fibers within the medial preoptic area of adult male rats

Galanin-like peptide (GALP) is located in the arcuate nucleus (Arc) of the hypothalamus and is known to regulate both food intake and sexual behaviors in adult male rats. We have previously demonstrated that ICV GALP administration elicits a significant fos response within the medial preoptic area (mPOA). GALP is known to stimulate both food intake and male-typical sex behavior, presumably by direct actions within the mPOA. Recent data from our and other labs have led us to suspect that GALP effects on sex behaviors are due to activation of incertohypothalamic dopaminergic neurons that terminate within the mPOA. To test the hypothesis that GALP activates mPOA dopaminergic systems, we utilized an immunolesion technique to eliminate dopaminergic fiber input to the mPOA via a dopamine transporter-specific toxin (DATSAP, n = 8) and compared to control injections (SAP, n = 8). All animals were sexually experienced adult male Long-Evans rats. DATSAP-treated male rats showed a significant (p < 0.001) reduction in male sexual behaviors compared to SAP controls. We found that elimination of dopaminergic fibers within the mPOA significantly (p < 0.001) eliminated all aspects of male sexual behavior under normal mating paradigms. Injections of GALP (5.0 nmol) significantly increased (p < 0.01) male sex behavior and food intake in SAP control male rats but GALP did not stimulate the expression of these behaviors in DATSAP-treated rats. The orexigenic and anorexigenic effects of GALP were significantly (p < 0.001) attenuated in DATSAP-treated male rats compared to SAP controls; however, ICV GALP was still able to significantly (p < 0.05) reduce 24 h body weight in both DATSAP and SAP rats. ICV GALP significantly (p < 0.05) stimulated fos within the mPOA of SAP rats but not in DATSAP-treated male rats. These data suggest that GALP activates feeding and sexual behaviors in male rats by stimulating dopaminergic neurons that terminate within the mPOA.     

Stimulation of the medical preoptic area facilitates sexual behavior but does not reverse sexual satiation

The aim of the present study was to establish whether electrical and/or drug stimulation of the medial preoptic area/anterior hypothalamus (mPOA/AH) surmounts the sexual behavior inhibition that results from copulation to exhaustion. Thus, intermittent electrical stimulation of the mPOA/AH (alone or combined with the systemic injection of yohimbine or apomorphine, at doses that were subthreshold for reversing sexual exhaustion) or intrapreoptic treatments to block GABAergic transmission were applied to sexually satiated rats. The results suggest that the mPOA/AH is not responsible for male sexual behavior inhibition or for the pharmacologically induced sexual behavior expression in satiated rats. Data are discussed in terms of the roles ascribed to the mPOA/AH, both in the control of sexual behavior expression and in the regulation of the postejaculatory interval.     

Prepuberal social rearing conditions and sexual behavior in control and neonatally castrated male rats

Male and female sexual behaviors were assessed in control and neonatally castrated male rats that had been housed with a female, a control male, or a neonatally castrated male from day 16 until adulthood. Prepuberal housing conditions had no differential effect on lordosis or ejaculatory potentials of neonatally castrated males tested as adults. A smaller percentage of control males raised with a neonatal castrate ejaculated than did animals housed with a female or a control male. However, a greater proportion of control males caged with a female showed lordosis than did those living with another control male or with a neonatal castrate. The data demonstrate the modulating effects which specific types of social stimulation experienced during early life have on sexual behaviors displayed in adulthood.     

Facilitation of male rat copulatory behavior by electrical stimulation of the medial preoptic area

Lesion studies have demonstrated that the medial preoptic area (MPO) plays a critical role in male rat copulatory behavior. The present study attempted to better localize the neural elements mediating this behavior pattern and to determine the influence of preoptic area stimulation on particular aspects of copulatory behavior. Monopolar stimulating electrodes were implanted in the medial preoptic-anterior hypothalamic continuum or the lateral preoptic-medial forebrain bundle region. The effects of stimulating a particular locus were measured by comparing each animal's behavior on repeated stimulation and control tests. All measures of copulatory activity taken were facilitated by medial, but not by lateral, preoptic stimulation. The most common change produced by MPO stimulation was a reduction in both the number of mounts and intromissions preceding ejaculation. Short-latency approach and mounting of the female and greatly reduced refractory periods were also seen in two MPO animals. No evidence of a post-stimulation inhibition of copulatory behavior resulting from the stimulation itself was seen in these two animals. Most animals in both the medial and lateral groups learned to self-stimulate (SS) using the same 30-sec trains of stimulation as used in earlier tests of copulatory activity. SS rate, stimulation-bound copulation, and degree of facilitation of ejaculation were positively correlated in MPO, but not in lateral preoptic animals.     

Neural transection between preoptic area and septum inhibits maternal behavior in female and male rats

Artificially-induced maternal behavior was examined in inexperienced female and male rats following neural transection between the preoptic area and the septum. Anterior roof deafferentation (ARD) of the preoptic area (POA) was performed with an L-shaped microknife. Virgin female and male rats with or without ARD were exposed to the continuous presence of normal pups to induce maternal behavior 3 weeks after surgery. ARD resulted in a significant delay of the onset of maternal behavior in females and a lack of complete development of maternal behavior in males, compared with corresponding sham-operated and intact controls. The results indicate that neural substrates dorsal to the POA play an important role in modulating the expression of maternal behavior in the rat.