Olfactory preference in the male rat depends on multiple chemosensory inputs converging on the preoptic area

Both volatile and nonvolatile molecules are involved in chemosensory communication in rodents. Volatile odors from physically inaccessible estrous females induced increased numbers of c-Fos-positive cells in the preoptic area (POA) and in the cortical nucleus of the amygdala (CoA) of male rats. The numbers of c-Fos-positive cells in the medial nucleus of the amygdala (MeA) increased in response to the nonvolatile odors of bedding soiled with the excreta of estrous females. In an alternate choice paradigm, male rats carrying ibotenic acid lesions in either the MeA or the CoA--or a combination of both--distinguished the odors of estrous females from those of males, although the time spent sniffing the stimuli was diminished. Males with POA lesions showed complete loss of this capability. Males carrying either of the lesions did not detect differences between estrous and anestrous females or between intact and orchidectomized males. Lesions in the POA or MeA severely impaired male sexual behavior, whereas a CoA lesion had no effects. Thus, c-Fos-positive cells in the CoA might be involved in chemosensory transmission relevant to certain social contexts, but not in the execution of male sexual behavior. The POA is indispensable for both olfactory preferences and sexual behavior. The residual olfactory preference in males with MeA or CoA lesions or the combination of both could reflect an additional route for chemosensory transmission from the main olfactory bulb to the POA.

Mu-opioid receptor densities are depleted in regions implicated in agonistic and sexual behavior in male European starlings (Sturnus vulgaris) defending nest sites and courting females

Social status and resource availability can strongly influence individual behavioral responses to conspecifics. In European starlings, males that acquire nest sites sing in response to females and dominate other males. Males without nest sites sing, but not to females, and they do not interact agonistically with other males. Little is known about the neural regulation of status- or resource-appropriate behavioral responses to conspecifics. Opioid neuropeptides are implicated in birdsong and agonistic behavior, suggesting that opioids may underlie differences in the production of these behaviors in males with and without nest sites. Here, we examined densities of immunolabeled mu-opioid receptors in groups of male starlings. Males that defended nest boxes dominated other males and sang at higher rates when presented with a female than males without nest boxes, independent of testosterone concentrations. Multiple regression analyses showed nest box ownership (not agonistic behavior or singing) predicted the optical density of receptor labeling in the medial bed nucleus of stria terminalis, paraventricular nucleus, ventral tegmental area and the medial preoptic nucleus. Compared to males without nest boxes, males with nest boxes had lower densities of immunolabeled mu-opioid receptors in these regions. Singing additionally predicted the area covered by labeling in the ventral tegmental area. The results suggest that elevated opioid activity in these regions suppresses courtship and agonistic behavioral responses to conspecifics in males without nest boxes. The findings are consistent with a dynamic role for opioid receptors in adjusting social behavior so that it is appropriate given the resources available to an individual.

Seasonal changes in hypothalamic gonadotropin-releasing hormone-I immunoreactivity in relation with testicular volume in adult male free-living European starlings (Sturnus vulgaris)

Birds from the temperate and cold zones show annual sexual activity accompanied by gonadal changes and fluctuation in their brain gonadotropin-releasing hormone (GnRH) levels. However, most of the studies were done on captive birds where the constant environment can profoundly modify periodical changes. Therefore our aim was to reveal annual variations of hypothalamic and gonadal changes in male, free-living European starlings (Sturnus vulgaris) captured directly from their natural environment. We analyzed hypothalamic GnRH-I immunoreactivity and testes volume. Four key time points of the active reproductive cycle and the photorefractory phase were studied. GnRH-I immunoreactivity was analyzed in the preoptic area (POA) and the median eminence (ME). Photorefractory birds (August) with regressed gonads had the lowest level of GnRH-I immunoreactivity compared to other birds from the active reproductive phases. These results suggest that parallel with the gonadal volume GnRH-I undergoes seasonal changes in adult male free-living European starlings.

Differential regulation of female sexual behaviour by dopamine agonists in the medial preoptic area

The medial preoptic area (mPOA) is a brain region critical in the control of male sexual behaviour, and the neurotransmitter dopamine (DA) plays an important role within it. However, both the roles of DA and the mPOA in female sexual behaviour are not fully understood, with few studies producing consistent data. The present study examined the function of DA within the mPOA on the full cascade of female sexual behaviour. Ovariectomized female rats were bilaterally cannulated into the mPOA and partially hormonally primed with estradiol benzoate (EB). Different doses of a nonselective DA receptor agonist, and selective DA D1 and D2 receptor agonists (apomorphine, SKF 38393 and quinpirole, respectively) were infused bilaterally to the mPOA. Copulatory behaviour was then immediately tested over a period of 30 min in a bilevel chamber with a sexually experienced male. Precopulatory behaviours were increased in females following infusions of a low dose (0.25μg) of apomorphine and both a low (0.05μg) and a high dose (0.2μg) of quinpirole. However, hops and/or darts were decreased following infusion of a low dose (0.05μg) of SKF 38393. These results suggest that the ratio of DA D1/D2 activity within the mPOA of female rats is critical for the expression of precopulatory behaviours, and may work with other brain areas responsible for stimulating lordosis to control the timing of female sexual behaviour.

The medial preoptic area is necessary for motivated choice of pup- over cocaine-associated environments by early postpartum rats

Converging evidence suggests that the motivation to seek cocaine during the postpartum period is significantly impacted by the competing incentives of offspring, a stimulus unique to this life stage. In the present study, the functional role of the medial preoptic area (mPOA), a critical site involved in maternal responsiveness, on processing incentive value of pup-associated cues and influencing response allocation for pup- over cocaine-associated environments was investigated using a concurrent pup/cocaine choice conditioned place preference (CPP) paradigm. Early postpartum females with bilateral guide cannulae aimed into the mPOA or into anatomical control sites were conditioned, from postpartum days (PPD) 4 to 7, to associate different uniquely featured environments with pups or cocaine. CPP was tested on PPD8 following intra-mPOA infusions of either 2% bupivacaine or saline vehicle. In two additional experiments, the effects of intra-mPOA infusions of bupivacaine on expression of conditioned responding induced by environments associated with either pups or cocaine were examined separately. Transient inactivation of the mPOA selectively blocked the conditioned preferences for pup-associated environments, significantly contrasting the robust pup-CPP found in non-surgical and intra-mPOA vehicle-treated females. In contrast, mPOA inactivation failed to alter cocaine-CPP in postpartum females. When given a choice between environments associated with pups or cocaine, transient functional inactivation of the mPOA altered choice behavior, biasing the preference of females toward cocaine-associated environments, such that almost all preferred cocaine- and none the pup-associated option. The anatomical specificity was revealed when inactivation of adjacent regions to the mPOA did not affect CPP responses for pups. The findings support a critical role for the mPOA in mediating pup-seeking behavior, and further suggest that the competing properties of pups over alternative incentives, including drugs of abuse, rely on mPOA integrity to provide relevant pup-related information to the circuitry underlying the choice behavior between pups and alternative stimuli.

Gonadotrophin-releasing hormone (GnRH) exerts stimulatory effects on GnRH neurons in intact adult male and female mice

There is substantial evidence for a role of the neuropeptide gonadotrophin-releasing hormone (GnRH) in the regulation of GnRH neurone secretion but how this is achieved is not understood. We examined here the effects of GnRH on the electrical excitability and intracellular calcium concentration ([Ca2+](i)) of GnRH neurones in intact adult male and female mice. Perforated-patch electrophysiological recordings from GnRH-green fluorescent protein-tagged GnRH neurones revealed that 3 nm-3 mum GnRH evoked gradual approximately 3 mV depolarisations in membrane potential from up to 50% of GnRH neurones in male and female mice. The depolarising effect of GnRH was observed on approximately 50% of GnRH neurones throughout the oestrous cycle. However, at pro-oestrus alone, GnRH was also found to transiently hyperpolarise approximately 30% of GnRH neurones. Both hyperpolarising and depolarising responses were maintained in the presence of tetrodotoxin. Calcium imaging studies undertaken in transgenic GnRH-pericam mice showed that GnRH suppressed [Ca2+](i) in approximately 50% of GnRH neurones in dioestrous and oestrous mice. At pro-oestrus, 25% of GnRH neurones exhibited a suppressive [Ca2+](i) response to GnRH, whereas 17% were stimulated. These results demonstrate that nm to mum concentrations of GnRH exert depolarising actions on approximately 50% of GnRH neurones in males and females throughout the oestrous cycle. This is associated with a reduction in [Ca2+](i). At pro-oestrus, however, a further population of GnRH neurones exhibit a hyperpolarising response to GnRH. Taken together, these studies indicate that GnRH acts predominantly as a neuromodulator at the level of the GnRH cell bodies to exert a predominant excitatory influence upon GnRH neurones in intact adult male and female mice.

Clitoral stimulation induces conditioned place preference and Fos activation in the rat

The present study examined the ability of clitoral stimulation (CLS) to induce conditioned place preference (CPP) and Fos protein in the brain. Ovariectomized, hormone-primed Long-Evans rats were randomly assigned to receive either distributed CLS (1 stimulation every 5 s for 1 min prior to being placed in one distinctive side of a nonbiased CPP box for 2 min, after which the cycle of stimulation and CPP exposure were repeated for 4 more cycles, totaling 60 stimulations) or continuous CLS (1 stimulation per second for 1 min with 2 min in one side of the CPP box, repeated for 4 more cycles, totaling 300 stimulations). Two days later, females were placed into the other side of the CPP box without prior stimulation. CPP was tested after 5 sequential exposures each of CLS and no stimulation. Females given distributed stimulation developed a significant CPP whereas females given continuous stimulation did not. CLS induced Fos in hypothalamic and limbic structures, including the nucleus accumbens, piriform cortex, arcuate nucleus, and dorsomedial portion of the ventromedial hypothalamus, compared to no stimulation. However, distributed CLS induced more Fos in the medial preoptic area than continuous CLS or no stimulation. In contrast, continuous CLS induced more Fos in the posteroventral medial amygdala compared to no stimulation. These data indicate that CLS induces a reward state in the rat and a pattern of Fos activation in regions of the brain that process genitosensory input, incentive salience, and reward.

Interactions between neurotensin and GnRH neurons in the positive feedback control of GnRH/LH secretion in the mouse

In female mammals, increased ovarian estradiol (E(2)) secretion triggers GnRH release from neurons in the basal forebrain, which drives LH secretion from the pituitary and subsequently induces ovulation. However, the neural circuits that activate this preovulatory GnRH/LH surge remain unidentified. Neurotensin is expressed in neurons of the anteroventral periventricular nucleus (AVPV), a region thought to be critical for generating the preovulatory GnRH/LH surge. E(2) induces neurotensin (Nts) gene expression in this region, and blockade of neurotensin signaling reduces the LH surge in the rat. We postulated that neurotensin signaling plays a similar role in generating the E(2)-induced GnRH/LH surge in mice. We used in situ hybridization (ISH) to determine whether E(2) induces Nts expression in the mouse and found evidence to support this proposition. Next, we determined that the neurotensin receptor (Ntsr2) is present in many GnRH-expressing neurons. Since the kisspeptin gene (Kiss1) is expressed in the AVPV and is responsive to E(2), we predicted that some neurons in this region express both Kiss1 and Nts; however, by double-label ISH, we observed no coexpression of the two mRNAs. We also postulated that Nts mRNA expression would increase in parallel with the E(2)-induced LH surge and that the central (icv) administration of neurotensin would stimulate LH secretion and activation of GnRH neurons but found no evidence to support either of these hypotheses. Together, these findings suggest that, although neurotensin neurons in the AVPV are targets for regulation by E(2), neurotensin does not appear to play a direct role in generating the GnRH/LH surge in the mouse.

Insulin causes hyperthermia by direct inhibition of warm-sensitive neurons

OBJECTIVE

Temperature and nutrient homeostasis are two interdependent components of energy balance regulated by distinct sets of hypothalamic neurons. The objective is to examine the role of the metabolic signal insulin in the control of core body temperature (CBT).

RESEARCH DESIGN AND METHODS

The effect of preoptic area administration of insulin on CBT in mice was measured by radiotelemetry and respiratory exchange ratio. In vivo 2-[(18)F]fluoro-2-deoxyglucose uptake into brown adipose tissue (BAT) was measured in rats after insulin treatment by positron emission tomography combined with X-ray computed tomography imaging. Insulin receptor-positive neurons were identified by retrograde tracing from the raphe pallidus. Insulin was locally applied on hypothalamic slices to determine the direct effects of insulin on intrinsically warm-sensitive neurons by inducing hyperpolarization and reducing firing rates.

RESULTS

Injection of insulin into the preoptic area of the hypothalamus induced a specific and dose-dependent elevation of CBT mediated by stimulation of BAT thermogenesis as shown by imaging and respiratory ratio measurements. Retrograde tracing indicates that insulin receptor-expressing warm-sensitive neurons activate BAT through projection via the raphe pallidus. Insulin applied on hypothalamic slices acted directly on intrinsically warm-sensitive neurons by inducing hyperpolarization and reducing firing rates. The hyperthermic effects of insulin were blocked by pretreatment with antibodies to insulin or with a phosphatidylinositol 3-kinase inhibitor.

CONCLUSIONS

Our findings demonstrate that insulin can directly modulate hypothalamic neurons that regulate thermogenesis and CBT and indicate that insulin plays an important role in coupling metabolism and thermoregulation at the level of anterior hypothalamus.

Relative role of neural substrates in the aggressive behavior of rats

Early animal studies have shown an association between aggression and brain dysfunction. The goal of the present study was to compare the effects of lesions of different parts of brain on aggression in rats. Adult rats (n = 40, weighing 200-260 g) were randomly divided into four groups of ten animals each and subjected to lesions of the septum (Group I), medial preoptic area (Group II), medial accumbens (Group III), and bed nucleus of stria terminalis (Group IV), using stereotaxy apparatus. Aggression toward an unfamiliar male intruder was observed before and after the lesion. The aggression score of each animal was recorded three times before lesion and averaged for use in analysis. Analysis of variance (ANOVA) was applied for finding homogeneity of the groups. Postoperative scores were also similarly recorded and summarized as mean +/- standard deviation. Pre- and post-lesion scores were compared using the t test. The scores were significantly reduced in Group I, II, and III, but increased in Group IV. We can conclude that the septum, medial preoptic area, medial accumbens, and bed nucleus of stria terminalis, by virtue of their interconnections, influence aggressive behavior.

The changing role of the medial preoptic area in the regulation of maternal behavior across the postpartum period: facilitation followed by inhibition

Maternal behavior in rats undergoes considerable plasticity in parallel to the developmental stage of the pups, resulting in distinct patterns of maternal behavior and care at different postpartum time points. The medial preoptic area (mPOA) of the hypothalamus is one critical neural substrate underlying the onset and early expression of maternal behavior in rats but little is known about its specific functional role in the evolving expression of maternal behavior across the postpartum period. The present study uses a reversible local neural inactivation method to examine the role of the mPOA in the regulation of maternal behavior throughout the postpartum period, particularly extending into the late postpartum, a little examined period. This approach avoids the compensatory plasticity in CNS that occurs after permanent lesions, and allows the repeated testing of same individuals. Early (PPD7-8) and late (PPD13-14) postpartum maternal behavior was evaluated in female rats following infusions of bupivacaine or vehicle into the mPOA or into control areas. As expected, mPOA inactivation severely but transiently disrupted early postpartum maternal behavior whereas infusion of vehicle or inactivation of adjacent control sites did not. Later in the postpartum period, however, transient mPOA inactivation facilitated the expression of maternal behaviors, highly contrasting the behavioral expression levels characteristic of late postpartum. Results strongly demonstrate that the mPOA is differentially engaged throughout postpartum in orchestrating appropriate maternal responses with the developmental stage of the pups.

Possible involvement of microglia containing cyclooxygenase-1 in the accumulation of gonadotrophin-releasing hormone in the preoptic area in female rats

Prostaglandins (PGs), especially PGE(2), are involved in the hypothalamic control of gonadotrophin-releasing hormone (GnRH) release, acting at least in part on the terminal of GnRH axons in the median eminence. The present study aimed: (i) to clarify the role of PG(s) in regulating GnRH cell function at the level of the perikarya in the preoptic area; (ii) to determine the cyclooxygenase (COX) isozyme responsible for producing PG(s) that regulates GnRH perikarya; and (iii) to identify cell types that contain the responsible COX isozyme in female rats. A surge of luteinising hormone (LH) secretion was induced by oestrogen and progesterone in ovariectomised rats. Treatment of the rat before the LH surge with indomethacin, a nonselective COX inhibitor, or NS-398, a selective COX-2 inhibitor, did not interfere with the surge. However, treatment with indomethacin or flurbiprofen, a selective COX-1 inhibitor, significantly reduced the number of GnRH-immunoreactive cells in the preoptic area at the time of peak LH secretion during the surge. NS-398 did not affect the GnRH immunoreactivity. Double-labelled immunofluorescent histochemistry revealed COX-1 immunoreactivity in the vicinity of, but not within, GnRH containing neurones in the preoptic area. COX-2 immunoreactivity was not found in the same area. The COX-1 immunoreactivity was almost entirely localised in microglia in the preoptic area, but not in neurones or astrocytes. These results suggest that microglia in the preoptic area containing COX-1 are responsible for producing PG(s), which, in turn, facilitates the accumulation of GnRH during the gonadotrophin surge in female rats.

Nitric oxide mediates noradrenaline-induced hypothermic responses and opposes prostaglandin E2-induced fever in the rostromedial preoptic area

Noradrenaline (NA) microinjected into the rostromedial preoptic area (POA) elicits heat loss responses and opposes prostaglandin E(2)-induced fever. Here, I tested the hypothesis that local synthesis and release of nitric oxide (NO) mediates the NA-induced effects. The unilateral microinjection of the NO donor sodium nitroprusside (SNP, 8.4 nmol), but not that of saline solution, into the NA-sensitive site elicited an increase in tail skin temperature and decreases in the whole-body O(2) consumption rate, heart rate, and colonic temperature simultaneously in urethane-chloralose-anesthetized rats. Pretreatment with SNP greatly attenuated the thermogenic, tachycardic, and hyperthermic effects of prostaglandin E(2) (140 fmol) microinjected into the same site. Furthermore, the NA-induced hypothermic responses were largely blocked by a prior microinjection of an NO synthase inhibitor N(G)-monomethyl-L-arginine (L-NMMA, 5 nmol), but not by that of its inactive enantiomer, N(G)-monomethyl-D-arginine (D-NMMA, 5 nmol), at the same site. These results suggest that the hypothermic and antipyretic effects of NA are mediated by NO in the rostromedial POA.

In vivo circadian rhythms in gonadotropin-releasing hormone neurons

Although it is generally accepted that the circadian clock provides a timing signal for the luteinizing hormone (LH) surge, mechanistic explanations of this phenomenon remain underexplored. It is known, for example, that circadian locomotor output cycles kaput (clock) mutant mice have severely dampened LH surges, but whether this phenotype derives from a loss of circadian rhythmicity in the suprachiasmatic nucleus (SCN) or altered circadian function in gonadotropin-releasing hormone (GnRH) neurons has not been resolved. GnRH neurons can be stimulated to cycle with a circadian period in vitro and disruption of that cycle disturbs secretion of the GnRH decapeptide. We show that both period-2 (PER2) and brain muscle Arnt-like-1 (BMAL1) proteins cycle with a circadian period in the GnRH population in vivo. PER2 and BMAL1 expression both oscillate with a 24-hour period, with PER2 peaking during the night and BMAL1 peaking during the day. The population, however, is not as homogeneous as other oscillatory tissues with only about 50% of the population sharing peak expression levels of BMAL1 at zeitgeber time 4 (ZT4) and PER2 at ZT16. Further, a light pulse that induced a phase delay in the activity rhythm of the GnRH-eGFP mice caused a similar delay in peak expression levels of BMAL1 and PER2. These studies provide direct evidence for a functional circadian clock in native GnRH neurons with a phase that closely follows that of the SCN.

Sexual experience changes sex hormones but not hypothalamic steroid hormone receptor expression in young and middle-aged male rats

Testosterone is well known to regulate sexual behavior in males, but this is dependent upon prior sexual experience. Aging is associated with decreased libido and changes in testosterone, but the role of experience in these age-related processes has not been systematically studied. We examined effects of age and sexual experience on serum hormones (total testosterone, free testosterone, estradiol, LH) and on numbers of androgen receptor (AR) and estrogen receptor alpha (ERalpha) immunoreactive cells in the hypothalamus. Extensive sexual experience was given to male rats at 4 months of age. Rats were euthanized at either 4 months (young) or 12 months (middle-aged (MA)). Comparable sexually naïve male rats were handled and placed into the testing arena but did not receive any sexual experience. Thus, we had four groups: young-naïve, young-experienced, MA-naïve and MA-experienced. Serum hormone levels were assayed, and numbers of AR and ERalpha cells were quantified stereologically in the medial preoptic nucleus (MPN) and the anteroventral periventricular nucleus (AVPV). Sexually experienced males had significantly elevated serum testosterone and free testosterone in both age groups. Both total and free testosterone were higher, and estradiol lower, in middle-aged than young rats. Experience did not alter either AR or ERalpha expression in the preoptic brain regions studied. Aging was associated with increased expression of AR, but no change in ERalpha. These results show that sexual experience can induce short-term and long-term alterations in serum hormones but these effects are not manifested upon their receptors in the hypothalamus.

Sleep-waking behavior following a lesion in the median preoptic nucleus in the rat

Hypnogenic structures are mainly located in the preoptic area of the hypothalamus. The number of Fos-immunoreactive neurons in the ventrolateral preoptic area (vlPOA) and in the median preoptic nucleus (MnPN) is positively correlated with the amount of preceding sleep. Majority of neurons recorded in these nuclei exhibit elevated discharge rates during sleep. Present study examined the effects of MnPN electrolytic lesion on the sleep-waking behavior in the rat. Experiments were performed on adult Mongrel albino male rats. Rats were implanted with EEG/EMG electrodes and with an electrode for MnPN lesion. Following a post-surgery recovery, rats were adapted to the recording environment, recorded for a baseline sleep-wakefulness cycle and then assigned to two groups. One group of rats was subjected to MnPN lesion and recorded for spontaneous sleep on the third, seventh and fourteenth days following the lesion procedure. Other rats served as a control group. The control and the MnPN-lesion rats exhibited different profiles of sleep-wakefulness organization. MnPN-lesion rats had significantly higher amounts of wakefulness and lower amounts of sleep, compared to control animals. Our findings support a view that the activity of a subset of MnPN neurons is strongly related to sleep regulation.

Sexual behavior in lactating rats: role of estrogen-induced progesterone receptors

Lactation is associated with suppression of reproductive function, the duration of which depends on the number of young suckled and food availability. Although previous studies have documented increasing responsivity to the positive feedback effects of estrogen on luteinizing hormone (LH) secretion with time postpartum, changes in the ability of estrogen to stimulate sexual behavior across these time points and the influence of food restriction on response to estrogen have not been investigated. Thus, we compared the ability of exogenous estrogen administration to stimulate proceptive and receptive behavior in ad libitum fed and food restricted rats on Days 15 and 20 postpartum. Because the ability of estrogen to induce sexual behavior depends on activation of both estrogen receptors and estrogen-induced progesterone receptors, a second study compared estrogen and progesterone-ir within the VMH and MPOA in similar groups. Finally, we investigated the role of the high levels of progesterone typical of lactation in the suppression of estrogen-induced sexual behavior by transient blockade of the progesterone receptor using RU486. As expected there was an increase across time in the ability of estrogen to stimulate sexual behavior that correlated with an increased ability of estrogen to induce progesterone receptors in the MPOA that was most evident in ad libitum fed rats. RU486 administration concomitant with estrogen administration increased solicitation behavior and was most effective in ad libitum fed rats suggesting an inhibitory role of progesterone on estrogen-induced sexual proceptivity in lactating rats.

From here to paternity: neural correlates of the onset of paternal behavior in California mice (Peromyscus californicus)

In a minority of mammalian species, including humans, fathers play a significant role in infant care. Compared to maternal behavior, the neural and hormonal bases of paternal care are poorly understood. We analyzed behavioral, neuronal and neuropeptide responses towards unfamiliar pups in biparental California mice, comparing males housed with another male ("virgin males") or with a female before ("paired males") or after ("new fathers") the birth of their first litter. New fathers approached pups more rapidly and spent more time engaging in paternal behavior than virgin males. In each cage housing two virgin males, one was spontaneously paternal and one was not. New fathers and paired males spent more time sniffing and touching a wire mesh ball containing a newborn pup than virgin males. Only new fathers showed significantly increased Fos-like immunoreactivity in the medial preoptic nucleus (MPO) following exposure to a pup-containing ball, as compared to an empty ball. Moreover, Fos-LIR in the bed nucleus of the stria terminalis (STMV and STMPM) and caudal dorsal raphe nucleus (DRC) was increased in new fathers, independent of test condition. No differences were found among the groups in Fos-LIR in oxytocinergic or vasopressinergic neurons. These results suggest that sexual and paternal experiences facilitate paternal behavior, but other cues play a role as well. Paternal experience increases Fos-LIR induced by distal pup cues in the MPO, but not in oxytocin and vasopressin neurons. Fatherhood also appears to alter neurotransmission in the BNST and DRC, regions implicated in emotionality and stress-responsiveness.

Androgen- and estrogen-independent regulation of copulatory behavior following castration in male B6D2F1 mice

Male reproductive behavior is highly dependent upon gonadal steroids. However, between individuals and across species, the role of gonadal steroids in male reproductive behavior is highly variable. In male B6D2F1 hybrid mice, a large proportion (about 30%) of animals demonstrate the persistence of the ejaculatory reflex long after castration. This provides a model to investigate the basis of gonadal steroid-independent male sexual behavior. Here we assessed whether non-gonadal steroids promote mating behavior in castrated mice. Castrated B6D2F1 hybrids that persisted in copulating (persistent copulators) were treated with the androgen receptor blocker, flutamide, and the aromatase enzyme inhibitor, letrozole, for 8 weeks. Other animals were treated with the estrogen receptor blocker, ICI 182,780, via continual intraventricular infusion for 2 weeks. None of these treatments eliminated persistent copulation. A motivational aspect of male sexual behavior, the preference for a receptive female over another male, was also assessed. This preference persisted after long-term castration in persistent copulators, and administration of ICI 182,780 did not influence partner preference. To assess the possibility of elevated sensitivity to sex steroids in brains of persistent copulators, we measured mRNA levels for genes that code for the estrogen receptor-alpha, androgen receptor, and aromatase enzyme in the medial preoptic area and bed nucleus of the stria terminalis. No differences in mRNA of these genes were noted in brains of persistent versus non-persistent copulators. Taken together our results suggest that non-gonadal androgens and estrogens do not maintain copulatory behavior in B6D2F1 mice which display copulatory behavior after castration.

Influence of neurotransmitters on sexual differentiation of brain structure and function

Newborn rats received daily subcutaneous treatment with compounds which influence serotoninergic, cholinergic, alpha-adrenergic and beta-adrenergic activity. In adulthood luteinizing hormone (LH) secretion pattern, female sexual behavior, and the volume of the sexually dimorphic nucleus of the preoptic are (SDN-POA) were determined. Postnatal administration of l-tryptophan increased the volume of the SDN-POA significantly when given alone or when given simultaneously with testosterone propionate (TP). Para-chlorophenyl-alanine (pCPA) also increased SDN-POA volume, but did not potentiate the stimulating influence of TP. Clonidine had no effect per se on SDN-POA development, but it significantly potentiated the effect of TP in females. Salbutamol increased SDN-POA volume in females and in males. Postnatal treatment of female rats with the alpha-adrenergic receptor antagonists prazosine and yohimbine or with the nicotin receptor antagonist mecamylamine had permanent potentiating effects on the pattern of LH secretion, whereas postnatal treatment with beta-adrenergic compounds reduced the LH-release response to gonadal steroids in adulthood. Postnatal treatment with clonidin or l-tryptophane inhibited differentiation of the capacity for lordosis behavior. Beta-receptor agonists postnatally had a potentiating effect on the capacity for lordosis behavior in female and male rats. Cholinergic stimulation postnatally inhibited differentiation of the capacity for lordosis behavior in female rats, but prevented the inhibitory effect of postnatal androgenization. There was no correlation between SDN-POA volume and any of the two functional parameters.

The inhibitory effect of beta-endorphin on LH release in ovariectomized rats does not involve the preoptic GABAergic system

In rats, beta-endorphin (beta-END) and gamma-aminobutyric acid (GABA) suppress LH secretion by hypothalamic mechanisms involving the preoptic area (POA). Systemic injection of naloxone (NAL) increases LH secretion in male rats, an effect which can be prevented by coadministration of GABA agonists. Application of NAL into the POA of ovariectomized (ovx), progesterone substituted sheep modulates preoptic GABA release. These findings have been interpreted such that the endogenous opioids act via the preoptic GABAergic system to regulate LH release. To evaluate this hypothesis we implanted ovx rats with push pull cannula into the POA and measured GABA secretion prior to and during the preoptic application of either NAL or beta-END. Blood samples were collected to assess the effects of the drugs on LH secretion. In addition, ovx rats were substituted with estradiol (E2) to induce a negative feedback effect on LH release. Intrapreoptic application of beta-END caused a rapid decline of LH release in ovx rats which was completely reversible after termination of beta-END perfusion. Though LH levels were clearly suppressed, no change of GABA release in the POA was observed. During preoptic NAL perfusion both LH secretion and GABA release remained unaffected. Likewise, during beta-END perfusion into the POA of E2 treated rats neither LH nor GABA secretion changed. In contrast, NAL perfusion rapidly increased LH release but again this action of the opioidergic drug was not accompanied by alterations of GABA release. We conclude from these data: 1) Intrapreoptically applied beta-END inhibits LH release only in the absence of steroids. In turn, blockade of opioid receptors is effective only in the presence of steroids. Both findings indicate that in the POA opioidergic activity is low in ovx rats, but high during negative feedback of E2. 2) No changes of GABA secretion were observed during manipulations of the opioidergic tonus in the POA suggesting that both beta-END and GABA do not interact to regulate LH release. Thus, beta-END may directly inhibit the activity of GnRH neurons located in the POA or acts via a neurotransmitter other than GABA.

Effects of angiotensin II and atrial natriuretic peptide on LH release are exerted in the preoptic area: possible involvement of gamma-aminobutyric acid (GABA)

The preoptic/anterior hypothalamic area (PO/AH) contains the majority of LHRH neurons of which the function is regulated by a variety of neurotransmitters and peptides. In this area, numerous estrogen-receptive neurons utilize gammaaminobutyric acid (GABA) as neurotransmitter and these neurons communicate directly with LHRH neurons. Angiotensin II (AII) and atrial natriuretic peptide (ANP) are known to be involved in the regulation of LH secretion. The site of action of these peptides and the mechanisms by which they influence LHRH neurons, are largely unknown. Therefore the effects of intrapreoptic application of AII and ANP on serum LH levels of ovariectomized (ovx) and of ovx estrogen-primed rats were investigated. The peptides were applied into the PO/AH by means of push-pull cannula and in the effluent fractions GABA was measured. In the ovx estrogen-primed rat, prominent LH and prolactin surges were observed. At the time of increased LH levels preoptic GABA release was significantly reduced. At this time application of AII or ANP into the PO/AH was without effect on either LH or prolactin levels in the serum or on preoptic GABA release rates. In ovx, not steroid-primed rats intrapreoptic AII application suppressed serum LH levels significantly and this treatment had a slight stimulatory effect on preoptic GABA release rates. This effect of AII could be antagonized by prior preoptic treatment with saralasin, a specific AII receptor blocking peptide. Preoptic treatment with ANP resulted in a slight increase in serum LH levels which was accompanied by a slight, but significant reduction of preoptic GABA release rates.(ABSTRACT TRUNCATED AT 250 WORDS)

Postnatal development of an estradiol-kisspeptin positive feedback mechanism implicated in puberty onset

The regulation of GnRH neurons by kisspeptin is critical for normal puberty onset in mammals. In the rodent the kisspeptin neurons innervating GnRH neurons are thought to reside in the rostral periventricular area of the third ventricle (RP3V). Using kisspeptin immunocytochemistry we show that kisspeptin peptide expression in the RP3V of female mice begins around postnatal d 15 (P15) and rapidly increases to achieve adult-like levels by P30, the time of puberty onset. Ovariectomy of female pups at P15 resulted in a 70-90% reduction (P < 0.01) in kisspeptin peptide expression within the RP3V of P30 or P60 mice. Replacement of 17-beta-estradiol (E2) in P15-ovariectomized mice from P15-30 or P22-30 resulted in a complete restoration of kisspeptin peptide expression in the RP3V (P < 0.01). Kisspeptin-immunoreactive fibers throughout the hypothalamus, including the arcuate nucleus, followed the same pattern of estrogen-dependent expression. To test the absolute necessity of estrogen for kisspeptin expression in the RP3V, aromatase knockout mice were examined. Kisspeptin-immunoreactive cells were detected in the arcuate nucleus, but there was a complete absence of kisspeptin peptide in RP3V neurons of aromatase knockout adult females. These results demonstrate that E2 is essential for the prepubertal development of kisspeptin peptide within RP3V neurons and suggest that an E2-kisspeptin positive feedback mechanism exists before puberty. This implies that RP3V kisspeptin neurons are E2-dependent amplifiers of GnRH neuron activity in the prepubertal period.

A role for the medial preoptic area in CGRP-induced suppression of pulsatile LH secretion in the female rat

Calcitonin gene-related peptide (CGRP) is involved in a variety of stress responses and plays a pivotal role in stress-induced suppression of the GnRH pulse generator in the rat. Intracerebroventricular administration of CGRP suppresses luteinizing hormone (LH) pulses and increases Fos expression within the medial preoptic area (mPOA) and paraventricular nucleus (PVN). The aims of the present study were to investigate whether the mPOA or PVN are sites of action for CGRP-induced suppression of LH pulses and whether lipopolysaccharide (LPS), restraint or insulin-induced hypoglycaemia, stressors known to suppress LH pulses, affect mRNA expression for CGRP and its receptor subunits (calcitonin receptor-like receptor (CL) and RAMP-1) in the mPOA and PVN. Micro-infusion of CGRP (50, 250 or 500 pmol) into the mPOA, but not the PVN, dose-dependently suppressed LH pulse frequency. LPS, restraint and hypoglycaemia suppressed RAMP-1 mRNA, but not CL or CGRP mRNA expression in the mPOA. In the PVN, all three stressors suppressed CL mRNA expression, but only LPS or restraint suppressed RAMP-1 mRNA, and CGRP mRNA was unaffected. These results provide evidence that, unlike the PVN, the mPOA might play an important role in the inhibitory effect of CGRP on pulsatile LH secretion. Additionally, CGRP receptor function may be involved in this brain region in stress-induced suppression of the GnRH pulse generator.

Three types of gonadotrophin-releasing hormone neurones and steroid-sensitive sexually dimorphic kisspeptin neurones in teleosts

In general, the gonadotrophin-releasing hormone (GnRH) neuronal systems of vertebrates consist of one group of hypothalamic neuroendocrine and one or two group(s) of extrahypothalamic neuromodulatory GnRH neurones. By taking advantage of the brains of dwarf gourami and GnRH-green fluorescent protein transgenic medaka, the spontaneous electrical activities of all three different types of GnRH neurones have now been characterised. The hypophysiotrophic preoptic area-gnrh1 neurones show irregular and episodic spontaneous electrical activities, whereas extrahypothalamic midbrain gnrh2 and terminal nerve-gnrh3 neurones show regular pacemaker potentials. It is suggested that these spontaneous electrical activities are related to their different functions as neuroendocrine hormones (gnrh1 neurones) and neuromodulators (gnrh2 and gnrh3 neurones). On the other hand, recent evidence strongly suggests that the GnRH neurones are regulated by another class of peptidergic neurones, the kisspeptin neurones. The gene encoding kisspeptin (kiss1 gene) has been cloned, and the anatomical distribution of kiss1 mRNA expressing neurones (kiss1 neurones) has recently been studied in brains of several fish species. In medaka, two kiss1 neuronal populations in hypothalamic areas, called the nucleus ventral tuberis (NVT) and nucleus posterioris periventricularis (NPPv), have been identified. The NVT kiss1 neurones are sexually dimorphic in number (male >> female) under breeding conditions and are sensitive to ovarian oestrogens, whereas the NPPv kiss1 neurones are neither sexually dimorphic, nor sensitive to steroids. The steroid-sensitive changes in kiss1 mRNA expression in the NVT occur physiologically, closely linked to the reproductive state. As in the mammalian counterpart, the medaka kiss1 neuronal system is suggested to be involved in the central regulation of reproductive functions. Interestingly, kiss2, another gene paralogous to kiss1, has been cloned in some fish species. The possible regulation of reproduction and other unknown functions by kiss1 and kiss2 neurones may be the focus of future studies.

Sex differences and the roles of sex steroids in apoptosis of sexually dimorphic nuclei of the preoptic area in postnatal rats

The brain contains several sexually dimorphic nuclei that exhibit sex differences with respect to cell number. It is likely that the control of cell number by apoptotic cell death in the developing brain contributes to creating sex differences in cell number in sexually dimorphic nuclei, although the mechanisms responsible for this have not been determined completely. The milieu of sex steroids in the developing brain affects sexual differentiation in the brain. The preoptic region of rats has two sexually dimorphic nuclei. The sexually dimorphic nucleus of the preoptic area (SDN-POA) has more neurones in males, whereas the anteroventral periventricular nucleus (AVPV) has a higher cell density in females. Sex differences in apoptotic cell number arise in the SDN-POA and AVPV of rats in the early postnatal period, and an inverse correlation exists between sex differences in apoptotic cell number and the number of living cells in the mature period. The SDN-POA of postnatal male rats exhibits a higher expression of anti-apoptotic Bcl-2 and lower expression of pro-apoptotic Bax compared to that in females and, as a potential result, apoptotic cell death via caspase-3 activation more frequently occurs in the SDN-POA of females. The patterns of expression of Bcl-2 and Bax in the SDN-POA of postnatal female rats are changed to male-typical ones by treatment with oestrogen, which is normally synthesised from testicular androgen and affects the developing brain in males. In the AVPV of postnatal rats, apoptotic regulation also differs between the sexes, although Bcl-2 expression is increased and Bax expression and caspase-3 activity are decreased in females. The mechanisms of apoptosis possibly contributing to the creation of sex differences in cell number and the roles of sex steroids in apoptosis are discussed.

Gonadal steroid action and brain sex differentiation in the rat

Gonadal steroids that establish sexually dimorphic characteristics of brain morphology and physiology act at a particular stage of ontogeny. Testosterone secreted by the testes during late gestational and neonatal periods causes significant brain sexual dimorphism in the rat. This results in both sex-specific behaviour and endocrinology in adults. Sexual differentiation may be due to neurogenesis, migration or survival. Each mechanism appears to be uniquely regulated in a site-specific manner. Thus, the volume of an aggregate of neurones in the rat medial preoptic area (POA), termed the sexually dimorphic nucleus of the POA (SDN-POA), is larger in males than in females. The anteroventral periventricular nucleus (AVPV) is packed with neurones containing oestrogen receptor (ER)beta in female rats but, in males, ERbeta-positive neurones scatter into the more lateral portion of the POA. POA neurones are born up to embryonic days 16-17 and not after parturition. Therefore, neurogenesis is unlikely to contribute to the larger SDN-POA in males. DNA microarray analysis for oestrogen-responsive genes and western blotting demonstrated site-specific regulation of apoptosis- and migration-related genes in the SDN-POA and AVPV.

Vasotocin neurons in the bed nucleus of the stria terminalis preferentially process social information and exhibit properties that dichotomize courting and non-courting phenotypes

Neurons within the medial bed nucleus of the stria terminalis (BSTm) that produce arginine vasotocin (VT; in non-mammals) or arginine vasopressin (VP; in mammals) have been intensively studied with respect to their anatomy and neuroendocrine regulation. However, almost no studies have examined how these neurons process stimuli in the animals' immediate environment. We recently showed that in five estrildid finch species, VT-immunoreactive (-ir) neurons in the BSTm increase their Fos expression selectively in response to positively-valenced social stimuli (i.e., stimuli that should elicit affiliation). Using male zebra finches, a highly gregarious estrildid, we now extend those findings to show that VT-Fos coexpression is induced by a positive social stimulus (a female), but not by a positive non-social stimulus (a water bath in bath-deprived birds), although the female and bath stimuli induced Fos equally within a nearby control region, the medial preoptic nucleus. In concurrent experiments, we also show that the properties of BSTm VT-ir neurons strongly differentiate males that diverge in social phenotype. Males who reliably fail to court females ("non-courters") have dramatically fewer VT-ir neurons in the BSTm than do reliable courters, and the VT-ir neurons of non-courters fail to exhibit Fos induction in response to a female stimulus.

Infusions of naloxone into the medial preoptic area, ventromedial nucleus of the hypothalamus, and amygdala block conditioned place preference induced by paced mating behavior

Paced mating induces positive affect as revealed by conditioned place preference (CPP) in female rats. It has been suggested that endogenous opioids are involved in the generation of this positive affect since systemic administration of the opioid antagonist naloxone blocks mating-induced CPP. Several brain structures, including the medial preoptic area (mPOA), the ventromedial nucleus of the hypothalamus (VMH), the amygdala (Me), and the nucleus accumbens (Acb) have been implicated in the control of female sexual behavior. However, it is not known if these structures also participate in the positive affect produced by paced mating. To this end we determined the effects of intracranial administration of naloxone methiodide into the mPOA, VMH, Me and Acb on conditioned place preference induced by paced mating in female rats. Regardless of the site of infusion 5 micro of naloxone did not affect any of the sexual behavior parameters measured during copulation. When CPP was evaluated, the groups infused with naloxone into the mPOA, the VMH, and the Me before each conditioning session did not develop place preference. Only the group infused with naloxone in the Acb and the control groups did so. These results demonstrate that opioid receptors within the mPOA, VMH and Me are necessary for the rewarding aspects of paced mating. We suggest that the Me and VMH are important for the transmission of sensory information produced by copulation while the mPOA is the site where the positive affect is originated.

Estrogen-sensitive projections from the medial preoptic area to the dorsal pontine tegmentum, including Barrington's nucleus, in the rat

AIM

Urinary incontinence affects a significant number of post-menopausal women. There is conflicting evidence whether voiding symptoms in these women are related to hypoestrogenism or aging itself. This neuroanatomical study was designed to determine whether a specific central nervous system (CNS) pathway that projects to the pontine micturition center (PMC, also known as "Barrington's nucleus") is estrogen sensitive in a rat model.

METHODS

A fluorescent retrograde tracer was injected into the dorsal pontine tegmentum of adult female Sprague-Dawley rats to identify neurons in the medial preoptic area (MPA) that project to the PMC. Immunohistochemistry was performed using antibodies directed against estrogen receptor-alpha (ERalpha) and estrogen receptor-beta (ERbeta) to identify estrogen-sensitive neurons. The brain sections were examined using fluorescence microscopy to identify cells that project to the PMC (contain fluorescent tracer) and also express ER (are immunoreactive for ER).

RESULTS

There are neurons in the MPA that are double labeled (contain fluorescent tracer and express ERalpha, but not ERbeta), showing that a subset of neurons projecting from the MPA to the PMC is estrogen sensitive.

CONCLUSIONS

A subset of estrogen-sensitive neurons projects from the MPA to the PMC in rats, raising the possibility that indirect estrogenic regulation of forebrain neuronal function may modulate the micturition reflex. Future development of drugs that alter the function of this estrogen-sensitive CNS pathway may provide therapeutic strategies to treat post-menopausal incontinence.

Angiotensin and NMDA receptors in the median preoptic nucleus mediate hemodynamic response patterns to stress

The brain renin-angiotensin system plays an important role in the regulation of arterial pressure in response to stress, in part due to activation of AT1 receptors in the hypothalamic median preoptic nucleus (MnPO) by endogenous angiotensin II (ANG II). N-methyl-d-aspartate (NMDA) receptors are also involved in the angiotensinergic signaling pathway through the MnPO. We investigated whether AT1 and NMDA receptors in the MnPO are responsible for variable hemodynamic response patterns to stress. Cocaine or startle with cold water evoked a pressor response in Sprague-Dawley rats due, in some rats [vascular responders (VR)], to a large increase in systemic vascular resistance (SVR) and, in other rats [mixed responders (MR)], to small increases in SVR and cardiac output (CO). Microinjection of the GABAA agonist muscimol into the MnPO to block synaptic transmission attenuated the cocaine- or stress-induced increase in SVR and the decrease in CO seen in VR without altering either response in MR. Likewise, administration of either an AT1 receptor antagonist, losartan, or an NMDA receptor antagonist, MK-801, attenuated the increase in SVR and the decrease in CO in VR in response to either cocaine (losartan and MK-801) or startle with cold water (losartan) without altering either response in MR. We propose that the MnPO is responsible for greater SVR responses in VR and that AT1 and NMDA receptors play an important role in greater SVR responses in VR. These data provide additional support for the critical role of the MnPO in cardiovascular responses to stress.

[Cholinergic mechanisms of the hypothalamus medial preoptic area in control of thermoregulation and of wakefulness-sleep states in pigeons]

The data obtained show that cholinergic mechanisms of the medial preoptic area of hypothalamus participate in control of wakefulness-sleep states and thermoregulation parameters in pigeons. Muscarinic and nicotinic cholinergic receptors are established to be involved in the wakefulness maintenance. The muscarinic cholinergic receptor activation of the medial preoptic area is accompanied by an elevation of the brain temperature, by development of peripheral vasoconstriction, and by an in increase in level of the muscle contractile activity. During the nicotinic cholinergic receptor activation of the area, a decrease in the brain temperature and an increase in level of the muscle contractile activity are found. A comparative analysis of experiments and early investigation suggests that during the cholinergic receptors activation changes in the brain temperature of pigeons depend on type of the cholinergic receptors but not on their localization in the preoptic area of hypothalamus.

Regulation of progesterone receptor expression by estradiol is dependent on age, sex and region in the rat brain

Progesterone receptor (PR) expression is highly dependent on estradiol in the medial preoptic nucleus (MPN) and the ventromedial nucleus (VMN) of the adult rat brain. During development, males express high levels of PR in the MPN, whereas females have virtually no PR, a sex difference resulting entirely from differential exposure to estradiol. Because PR is also estradiol dependent in the adult VMN, the present study examined the regulation of PR immunoreactivity (PRir) in the developing VMN. Surprisingly, PRir was present at high levels in the VMN of both neonatal males and females. In the neonatal VMN, PR expression was dependent on gonadal hormones in males but not females. When females were ovariectomized and exposed to estradiol at various ages from neonatal to adulthood, estradiol reliably induced PRir in the MPN at postnatal d 7 but failed to induce PRir in the VMN of the same animals. Only later in development, around postnatal d 14, did estradiol increase PRir in the female VMN. There appears to be a developmental switch in the VMN when PR expression changes from estradiol independent to estradiol dependent. Furthermore, this switch is anatomically specific and does not exist in the MPN. The present results indicate that the regulation of PR expression by estradiol is dependent on age, sex, and brain region, suggesting that PR may play a critical but specific role in the normal development of these reproductively important brain areas. In addition, the neonatal female VMN may provide a unique model in which to examine the mechanisms underlying the specificity of steroid-induced gene expression.

[Effects of strong and weak electroacupuncture on endotoxin-induced changes of electrical activities of heat-sensitive neurons in preoptic area and anterior hypothalamus in rabbits]

OBJECTIVE

To observe the effects of weak and strong electroacupuncture (EA) on endotoxin (ET) thermolysis-induced changes of discharges of neurons in the preoptic region and anterior hypothalamus (PO-AH) so as to explore its underlying mechanism in antipyretic and thermolytic actions and its relation to the receptive system of acupoints.

METHODS

Eighteen New Zealand rabbits were randomly divided into ET group, ET + weak-EA group and ET + strong-EA group. Extracellular discharges of the PO-AH neurons were recorded by using tungsten microelectrodes. A "U"-shape stainless steel tube was implanted in the region (P0.4-A4.4, L0.5-1.7) crossing the hypothalamus for changing local temperature by perfusion of cool (25 degrees C) or warm (41 degrees C) solution in order to distinguish the heat sensitive neurons (HSN), cold sensitive neurons (CSN) and insensitve neurons to temperature changes. Intravenous injection of endotoxin (25 EU/rabbit) was given to rabbits to induce increase of tempe rature. EA (8 Hz, wave width 0.1 ms, weak stimulation: 4.5 V, strong stimulation: 25 V) was applied to bilateral "Yongquan" (KI 1) for observing changes of firing rates of HSN in PO-AH.

RESULTS

Compared with the basal values of firing rates of PO-AH neurons in each group, the average changing ratios of both ET and ET + weak-EA groups decreased significantly from 55-60 min on in ET group and from 40-45 min on in ET + weak-EA group after intravenous injection of ET (P<0.05), suggesting no marked effect of weak EA for preventing discharges of PO-AH neurons from decrease. While in ET + strong-EA group, the firing rates of HSN of PO-AH kept stable after injection of ET during EA and after cease of EA (P>0.05 vs basal value), suggesting that strong EA could antagonize ET thermolysis-induced decrease of firing rates of PO-AH neurons.

CONCLUSION

Stronger EA stimulation of KI1 can antagonize ET thermolysis-induced effect on electrical activities of PO-AH HSN, which may be initiated by the activation of the high-threshold thin nerve fibers in the acupoint region.

Kisspeptin acts directly and indirectly to increase gonadotropin-releasing hormone neuron activity and its effects are modulated by estradiol

GnRH neurons play a pivotal role in the central regulation of fertility. Kisspeptin greatly increases GnRH/LH release and GnRH neuron firing activity and may be involved in estradiol feedback, but the neurobiological mechanisms for these actions are unknown. G protein-coupled receptor 54, the receptor for kisspeptin, is expressed by GnRH neurons as well as other hypothalamic neurons, suggesting both direct and indirect effects are possible. To investigate this and determine whether kisspeptin activation of GnRH neurons is estradiol sensitive, we recorded the firing rate of GnRH neurons in brain slices from adult female mice that were ovariectomized (OVX) and either treated with estradiol (E) capsules (OVX+E) or left without further treatment. Kisspeptin increased GnRH neuronal activity in a dose-dependent manner in cells from both OVX and OVX+E mice, and estradiol significantly potentiated the response. To begin to distinguish direct from indirect actions of kisspeptin, fast synaptic transmission mediated by ionotropic gamma-aminobutyric acid and glutamate receptors was pharmacologically blocked (blockade). Blockade reduced GnRH response to kisspeptin in OVX+E but not in OVX mice. Actions of kisspeptin were also assessed using whole-cell voltage- and current-clamp recording in slices from OVX animals. Kisspeptin application depolarized GnRH neurons in current-clamp and generated inward current in voltage-clamp recordings, even after blocking action potential-dependent neural communication, consistent with a direct effect. Blockers of potassium channels abolished the inward current. Together our data indicate that kisspeptin activates GnRH neurons via both direct and transsynaptic mechanisms and that transsynaptic mechanisms are either enabled and/or potentiated by estradiol.

Heads or tails? Stressor-specific expression of corticotropin-releasing factor and urotensin I in the preoptic area and caudal neurosecretory system of rainbow trout

Corticotropin-releasing factor (CRF)- and urotensin I (UI)-expressing cells of the preoptic area (POA) and caudal neurosecretory system (CNSS) are considered key contributors to the regulation of the stress response in fish; however, the expression pattern of these neurons to environmental and social challenges have not been compared in a single study. Therefore, we characterized in rainbow trout (Oncorhynchus mykiss) the central distribution of CRF and UI expression and quantified the POA and CNSS mRNA levels of both transcripts in response to hyperammonemia, hypoxia, isolation, or subordination. The tissue distribution demonstrated that the POA and the CNSS are dominant sites of CRF and UI expression. Comparison of the plasma cortisol levels in response to the diverse treatments showed that subordination was the most severe stressor followed by hyperammonemia, isolation, and hypoxia. In the POA, with the exception of subordination that had no effect on UI expression, all stressors resulted in increase in CRF and UI mRNA levels. In the CNSS, while hyperammonemia was associated with increase in CRF and UI mRNA levels, and hypoxia induced an increase in CRF expression, isolation caused a decrease in the expression of both transcripts, and subordination had no effect. Independent of the stressor, we found strong positive correlations between CRF and UI expression in the POA and the CNSS, and no correlation in the expression of either gene between regions. Overall, the results demonstrate that the contribution of POA and CNSS CRF and UI neurons to the stress response in rainbow trout is stressor-, time-, and region-specific.

Gonadotropin-releasing hormone neuron requirements for puberty, ovulation, and fertility

The absolute requirement for reproduction implies that the hypothalamo-pituitary-gonadal axis, controlling fertility, is an evolutionary robust mechanism. The GnRH neurons of the hypothalamus represent the key cell type within the body dictating fertility. However, the level of functional redundancy within the GnRH neuron population is unknown. As a result of a fortuitous transgene insertion event, GNR23 mice exhibit a marked allele-dependent reduction in GnRH neuron number within their brain. Wild-type mice have approximately 600 GnRH neurons, compared with approximately 200 (34%) and approximately 70 (12%) in GNR23(+/-) and GNR23(-/-) mice, respectively. Using these mice, we examined the minimal GnRH neuron requirements for fertility. Male GNR23(-/-) mice exhibited normal fertility. In contrast, female GNR23(-/-) mice were markedly subfertile, failing to produce normal litters, have estrous cycles, or ovulate. The failure of ovulation resulted from an inability of the few existing GnRH neurons to generate the LH surge. This was not the case, however, for the first cycle at puberty that appeared normal. Together, these observations demonstrate that 12% of the GnRH neuron population is sufficient for pulsatile gonadotropin secretion and puberty onset, whereas between 12 and 34% are required for cyclical control in adult female mice. This indicates that substantial redundancy exists within the GnRH neuronal population and suggests that the great majority of GnRH neurons must be dysfunctional before fertility is affected.

Administration of the protein synthesis inhibitor, anisomycin, has distinct sleep-promoting effects in lateral preoptic and perifornical hypothalamic sites in rats

Although a robust relationship between sleep and increased brain protein synthesis is well-documented, there have been few reports of the effects of local application of a protein synthesis inhibitor (PSI) on sleep. In this study, we compared the effects of local microdialytic administration of the protein synthesis inhibitor, anisomycin (ANI) into the lateral preoptic area (LPOA), a sleep promoting area vs. the perifornical/lateral hypothalamus (PF/LH), a wake and rapid eye movement (REM) sleep-promoting area. ANI administered to the LPOA at night resulted in an increase in stage 2 of rat non-REM sleep, whereas ANI delivered into the PF/LH during the daytime increased REM sleep. ANI microdialysis into hippocampus did not affect sleep or waking. These differential effects of local protein synthesis inhibition on sleep support a hypothesis that mechanisms controlling protein synthesis are critically involved in the regulation of both NREM sleep and REM sleep.

Gonadal steroids regulate neural plasticity in the sexually dimorphic nucleus of the preoptic area of adult male and female rats

BACKGROUND

The densely staining sexually dimorphic nucleus of the preoptic area (SDNPOA) is profoundly affected by gonadal steroids during perinatal development.

METHODS

We tested whether the SDNPOA in rats also remains responsive to gonadal hormones in adulthood.

RESULTS

Castration of 60-day-old male rats led to a reduction of soma size in SDNPOA neurons 28 days later, but not 14 days later. In contrast, the SDNPOA volume in males was unaffected by adult castration, increasing somewhat between 60 and 88 days of age in both castrated males and sham controls. For female rats ovariectomized at 60 days of age, testosterone treatment resulted in a significantly larger SDNPOA soma size after either 14 or 28 days of treatment, compared to blank-treated controls. Testosterone-treated ovariectomized females also had a modestly larger SDNPOA volume after 28 days, but not 14 days, of treatment compared to blank-treated ovariectomized animals. A second experiment revealed that these effects in females were due to ovariectomy: both SDNPOA soma size and regional volume shrank in females that were ovariectomized compared to females subjected to sham surgery. The effects of ovariectomy were blocked by testosterone treatment. The cessation of testosterone treatment in females returned SDNPOA soma size and regional volume to that of control-treated ovariectomized females.

CONCLUSION

These results indicate considerable plasticity of the adult rat SDNPOA, and that (1) circulating androgens are required to maintain soma size, but not regional volume in males, and (2) ovarian steroids maintain both soma size and regional volume of the SDNPOA in females, an effect that can be mimicked with testosterone treatment and is fully reversible in adulthood.

Serotonergic modulation of GABAergic and glutamatergic synaptic transmission in mechanically isolated rat medial preoptic area neurons

The medial preoptic area (MPOA) of the hypothalamus is critically involved in the regulation of male sexual behavior and has been implicated in several homeostatic processes. Serotonin (5-hydroxytryptamine, 5-HT) inhibits sexual behavior via effects in the MPOA, where there are high densities of 5-HT(1A) and 5-HT(1B) receptor subtypes. We used whole-cell recordings under voltage-clamp conditions to investigate the serotonergic modulation of gamma-aminobutyric acid (GABA)ergic and glutamatergic synaptic transmission in mechanically dissociated rat MPOA neurons with native presynaptic nerve endings. Spontaneous GABAergic miniature inhibitory postsynaptic currents (mIPSCs) in the MPOA were completely blocked by bicuculline. Serotonin reversibly reduced the GABAergic mIPSC frequency without affecting the mean current amplitude. Serotonergic inhibition of mIPSC frequency was mimicked by (+/-)-8-hydroxy-2-dipropylaminotetralin hydrobromide, a specific 5-HT(1A) receptor agonist, and blocked by 1-(2-methoxyphenyl)-4-[4-(2-phthalimido)butyl] piperazine hydrobromide, a specific 5-HT(1A) receptor antagonist. 6-Cyano-7-nitroquinoxaline-2,3-dione completely blocked spontaneous glutamatergic miniature excitatory postsynaptic currents (mEPSCs) in the MPOA. Serotonin reversibly decreased the glutamatergic mEPSC frequency without affecting the mean current amplitude. Serotonergic inhibition of mEPSC frequency was mimicked by CGS 12066B, a specific 5-HT(1B) receptor agonist, and blocked by SB 216641, a specific 5-HT(1B) receptor antagonist. Stimulation of adenylyl cyclase with forskolin increased the frequencies of GABAergic mIPSCs and glutamatergic mEPSCs, and blocked the inhibitory effects of 5-HT. H-89, a selective protein kinase A (PKA) inhibitor, decreased the frequencies of GABAergic mIPSCs and glutamatergic mEPSCs, and blocked their reduction by 5-HT. These findings suggest that 5-HT reduces the frequency of GABAergic mIPSCs and glutamatergic mEPSCs through 5-HT(1A) and 5-HT(1B) receptor-mediated inhibition, respectively, of the PKA-dependent pathway in the presynaptic nerve terminals of MPOA neurons.

Mating activates NMDA receptors in the medial preoptic area of male rats

Studies have emphasized the role of the medial preoptic area (MPOA) as an important site for the regulation of male sexual behavior. Indeed, ablations of the MPOA impair sexual behavior, whereas stimulation of the MPOA enhances behavior. Furthermore, neural activity in the MPOA increases with mating. The current study tested the hypothesis that activation of N-methyl-D-aspartate (NMDA) receptors occurs in MPOA neurons and is essential for the expression of male sexual behavior in rats. Results indicate that nearly all MPOA neurons that expressed Fos following mating also contained the NR1 subunit of NMDA receptors. Furthermore, mating increased phosphorylation, thus activation, of NR1 in the MPOA. Additionally, blocking NMDA receptors significantly decreased mating-induced Fos expression and mating-induced phosphorylation of NMDA receptors and impaired male sexual behavior. These results provide evidence that mating activates NMDA receptors in the MPOA and that this activation is important for the expression of male sexual behavior.

Dopamine D1 receptor stimulation of the nucleus accumbens or the medial preoptic area promotes the onset of maternal behavior in pregnancy-terminated rats

There is good evidence that interference with the mesolimbic dopamine (DA) system results in impaired maternal responding in postpartum female rats. However, whether activation of the mesolimbic DA system is capable of promoting maternal behavior has not been investigated. This study examined whether increasing DA activity in various brain regions of pregnancy-terminated, naive female rats would stimulate the onset of maternal behavior. Experiments 1 and 2 examined the effects of microinjection of various doses (0, 0.2, or 0.5 microg/0.5 microl/side) of a D1 DA receptor agonist, SKF 38393, or a D2 DA receptor agonist, quinpirole, into the nucleus accumbens (NA) on latency to show full maternal behavior, and Experiment 3 determined the effects of SKF 38393 injection into a control site. Finally, because the medial preoptic area (MPOA) is also important for maternal behavior, receives DA input, and expresses DA receptors, the authors examined whether microinjection of SKF 38393 into MPOA was capable of stimulating the onset of maternal behavior. Results indicated that microinjection of SKF 38393 into either the NA or the MPOA facilitates maternal responding in pregnancy-terminated rats.

Comparison of medial preoptic, amygdala, and nucleus accumbens lesions on parental behavior in California mice (Peromyscus californicus)

We have previously shown that medial preoptic area (MPOA) lesions disrupt parental behavior in both male and female California mice (P. californicus). In the present study, we compare the effects of lesions in the MPOA, with those in the basolateral amygdala (BA) and nucleus accumbens (NA) on male and female parental behaviors in the biparental California mouse. A male or multiparous female from each male-female pair was given an electrolytic or sham lesion in the MPOA, BA, or NA and tested for parental responsiveness. Since female P. californicus show postpartum estrus, they were likely pregnant during parental testing. MPOA lesions produced deficits in both male and female parental behaviors, and BA lesions disrupted male, and to a lesser extent, female parental behavior. NA lesions produced mild effects on pup-retrieval in males and no effect on parental behavior in females. However, NA lesions incompletely destroyed the NA shell, the region most relevant for maternal behavior in rats, and should be investigated further. These results support a role for the MPOA and BA in both male and female parental behaviors.

Inactivation of the medial preoptic area or the bed nucleus of the stria terminalis differentially disrupts maternal behavior in sheep

The present study was designed to investigate the role of the medial preoptic area (MPOA) and the bed nucleus of the stria terminalis (BNST) in the onset and maintenance of maternal behavior in sheep. In a first experiment, the MPOA or BNST were transiently inactivated during the first 2 h postpartum in primiparous ewes with the use of the anaesthetic lidocaine. MPOA inactivation greatly impaired the display of maternal behavior whereas inactivation of BNST or of adjacent sites (septum or diagonal band of Broca) or infusion of cerebrospinal fluid did not. In a separation/reunion lamb test (S/R) performed at 2 h postpartum, ewes with MPOA inactivation exhibited little reaction after separation of their lambs and did not show any motivation to reunite with them. Ewes with BNST inactivation showed intermediate performances in the S/R test. Moreover, in control ewes that were maternal for the first 2 h postpartum, MPOA or BNST inactivation performed in the following 12 h induced deficits in the S/R test, indicating that the MPOA and to a lesser extent BNST are also involved in the maintenance of maternal behavior. A second experiment showed that, in multiparous ewes, MPOA inactivation at parturition induced less deficit in the display of maternal behavior and in the S/R test than in primiparous mothers. These findings indicate that the MPOA and, to some extent, the BNST are functionally involved in the initiation and in the maintenance of maternal behavior in sheep, but this involvement is influenced by maternal experience.

Increased caloric intake on a fat-rich diet: role of ovarian steroids and galanin in the medial preoptic and paraventricular nuclei and anterior pituitary of female rats

Previous studies in male rats have demonstrated that the orexigenic peptide galanin (GAL), in neurones of the anterior parvocellular region of the paraventricular nucleus (aPVN) projecting to the median eminence (ME), is stimulated by consumption of a high-fat diet and may have a role in the hyperphagia induced by fat. In addition to confirming this relationship in female rats and distinguishing the aPVN-ME from other hypothalamic areas, the present study identified two additional extra-hypothalamic sites where GAL is stimulated by dietary fat in females but not males. These sites were the medial preoptic nucleus (MPN), located immediately rostral to the aPVN, and the anterior pituitary (AP). The involvement of ovarian steroids, oestradiol (E(2)) and progesterone (PROG), in this phenomenon was suggested by an observed increase in circulating levels of these hormones and GAL in MPN and AP with fat consumption and an attenuation of this effect on GAL in ovariectomised (OVX) rats. Furthermore, in the same four areas affected by dietary fat, levels of GAL mRNA and peptide immunoreactivity were stimulated by E(2) and further by PROG replacement in E(2)-primed OVX rats and were higher in females compared to males. Because both GAL and PROG stimulate feeding, their increase on a fat-rich diet may have functional consequences in females, possibly contributing to the increased caloric intake induced by dietary fat. This is supported by the findings that PROG administration in E(2)-primed OVX rats reverses the inhibitory effect of E(2) on total caloric intake while increasing voluntary fat ingestion, and that female rats with higher GAL exhibit increased preference for fat compared to males. Thus, ovarian steroids may function together with GAL in a neurocircuit, involving the MPN, aPVN, ME and AP, which coordinate feeding behaviour with reproductive function to promote consumption of a fat-rich diet at times of increased energy demand.

Topography in the preoptic region: differential regulation of appetitive and consummatory male sexual behaviors

Several studies have suggested dissociations between neural circuits underlying the expression of appetitive (e.g., courtship behavior) and consummatory components (i.e., copulatory behavior) of vertebrate male sexual behavior. The medial preoptic area (mPOA) clearly controls the expression of male copulation but, according to a number of experiments, is not necessarily implicated in the expression of appetitive sexual behavior. In rats for example, lesions to the mPOA eliminate male-typical copulatory behavior but have more subtle or no obvious effects on measures of sexual motivation. Rats with such lesions still pursue and attempt to mount females. They also acquire and perform learned instrumental responses to gain access to females. However, recent lesions studies and measures of the expression of the immediate early gene c-fos demonstrate that, in quail, sub-regions of the mPOA, in particular of its sexually dimorphic component the medial preoptic nucleus, can be specifically linked with either the expression of appetitive or consummatory sexual behavior. In particular more rostral regions can be linked to appetitive components while more caudal regions are involved in consummatory behavior. This functional sub-region variation is associated with neurochemical and hodological specializations (i.e., differences in chemical phenotype of the cells or in their connectivity), especially those related to the actions of androgens in relation to the activation of male sexual behavior, that are also present in rodents and other species. It could thus reflect general principles about POA organization and function in the vertebrate brain.

Receptors and neural effects of oxytocin in the rodent hypothalamus and preoptic region

Vasopressin and oxytocin are produced in and secreted from not only hypothalamo-hypophysial neurons which shed their products into the circulation to act as hormones or releasing factors, but also from neurons whose axons form tracts which remain within the central nervous system. Using tritiated or radioiodinated ligands, binding sites for vasopressin and for oxytocin have been detected by in vitro autoradiography. In the rat hypothalamus binding sites for vasopressin are present in the suprachiasmatic, sigmoid and arcuate nuclei, and oxytocin receptors in the area of the ventromedial nucleus. Electrophysiological evidence obtained using single cell recordings in slices suggests that oxytocin-binding sites present in the ventromedial hypothalamus and in the bed nucleus of the stria terminalis mostly represent functional, neuronal receptors. The expression of these receptors (but not of the vasopressin receptors) depends on gonadal steroid hormones, as does that of uterine and mammary gland oxytocin receptors. Modifications of the hormonal status associated with, for example, puberty and lactation cause 'up-regulation' of central and peripheral oxytocin receptors. The central administration of oxytocin facilitates (and the administration of oxytocin agonists inhibits) maternal behaviour and the milk ejection reflex, therefore the hormonal and neural actions of oxytocin appear to be complementary in ensuring the birth and development of the offspring.