Galanin microinjected into the medial preoptic nucleus facilitates female- and male-typical sexual behaviors in the female rat

Vocal and Electric Fish: Revisiting a Comparison of Two Teleost Models in the Neuroethology of Social Behavior

The communication behaviors of vocal fish and electric fish are among the vertebrate social behaviors best understood at the level of neural circuits. Both forms of signaling rely on midbrain inputs to hindbrain pattern generators that activate peripheral effectors (sonic muscles and electrocytes) to produce pulsatile signals that are modulated by frequency/repetition rate, amplitude and call duration. To generate signals that vary by sex, male phenotype, and social context, these circuits are responsive to a wide range of hormones and neuromodulators acting on different timescales at multiple loci. Bass and Zakon (2005) reviewed the behavioral neuroendocrinology of these two teleost groups, comparing how the regulation of their communication systems have both converged and diverged during their parallel evolution. Here, we revisit this comparison and review the complementary developments over the past 16 years. We (a) summarize recent work that expands our knowledge of the neural circuits underlying these two communication systems, (b) review parallel studies on the action of neuromodulators (e.g., serotonin, AVT, melatonin), brain steroidogenesis (via aromatase), and social stimuli on the output of these circuits, (c) highlight recent transcriptomic studies that illustrate how contemporary molecular methods have elucidated the genetic regulation of social behavior in these fish, and (d) describe recent studies of mochokid catfish, which use both vocal and electric communication, and that use both vocal and electric communication and consider how these two systems are spliced together in the same species. Finally, we offer avenues for future research to further probe how similarities and differences between these two communication systems emerge over ontogeny and evolution.

Functions of galanin, spexin and kisspeptin in metabolism, mood and behaviour

The bioactive peptides galanin, spexin and kisspeptin have a common ancestral origin and their pathophysiological roles are increasingly the subject of investigation. Evidence suggests that these bioactive peptides play a role in the regulation of metabolism, pancreatic β-cell function, energy homeostasis, mood and behaviour in several species, including zebrafish, rodents and humans. Galanin signalling suppresses insulin secretion in animal models (but not in humans), is potently obesogenic and plays putative roles governing certain evolutionary behaviours and mood modulation. Spexin decreases insulin secretion and has potent anorectic, analgesic, anxiolytic and antidepressive-like effects in animal models. Kisspeptin modulates glucose-stimulated insulin secretion, food intake and/or energy expenditure in animal models and humans. Furthermore, kisspeptin is implicated in the control of reproductive behaviour in animals, modulation of human sexual and emotional brain processing, and has antidepressive and fear-suppressing effects. In addition, galanin-like peptide is a further member of the galaninergic family that plays emerging key roles in metabolism and behaviour. Therapeutic interventions targeting galanin, spexin and/or kisspeptin signalling pathways could therefore contribute to the treatment of conditions ranging from obesity to mood disorders. However, many gaps and controversies exist, which must be addressed before the therapeutic potential of these bioactive peptides can be established.

Galanin neuron activation in feeding, parental care, and infanticide in a mouthbrooding African cichlid fish

Galanin is a conserved neuropeptide involved in parental care and feeding. While galanin is known to mediate parental care and infanticide in rodents, its role in parental care and feeding behaviors in other taxa, particularly fishes, remains poorly understood. Mouthbrooding is an extreme form of parental care common in fishes in which caregivers carry offspring in their buccal cavity for the duration of development, resulting in obligatory starvation. In the cichlid fish Astatotilapia burtoni, females brood their young for ~2 wks and perform maternal care after release by collecting them into their mouth when threatened. However, females will cannibalize their brood after ~5 days. To examine the role of gal in feeding and maternal care, we collected mouthbrooding, fed, and starved females, as well as those displaying post-release maternal care and infanticide behaviors. Activation of gal neurons in the preoptic area (POA) was associated with parental care, providing the first link between gal and offspring-promoting behaviors in fishes. In contrast, activation of gal neurons in the lateral tuberal nucleus (NLT), the Arcuate homolog, was associated with feeding and infanticide. Overall, these data suggest gal is functionally conserved across vertebrate taxa with POA gal neurons promoting maternal care and Arc/NLT gal neurons promoting feeding.

Mating Behavioral Function of Preoptic Galanin Neurons Is Shared between Fish with Alternative Male Reproductive Tactics and Tetrapods

Understanding the contribution of neuropeptide-containing neurons to variation in social behavior remains critically important. Galanin has gained increased attention because of the demonstration that galanin neurons in the preoptic area (POA) promote mating and parental care in mammals. How widespread these mechanisms are among vertebrates essentially remains unexplored, especially among teleost fishes, which comprise nearly one-half of living vertebrate species. Teleosts with alternative reproductive tactics exhibit stereotyped patterns of social behavior that diverge widely between individuals within a sex. This includes midshipman that have two male morphs. Type I males mate using either acoustic courtship to attract females to enter a nest they guard or cuckoldry during which they steal fertilizations from a nest-holding male using a sneak or satellite spawning tactic, whereas type II males only cuckold. Using the neural activity marker phospho-S6, we show increased galanin neuron activation in courting type I males during mating that is not explained by their courtship vocalizations, parental care of eggs, or nest defense against cuckolders. This increase is not observed during mating in cuckolders of either morph or females (none of which show parental care). Together with their role in mating in male mammals, the results demonstrate an unexpectedly specific and deep-rooted, phylogenetically shared behavioral function for POA galanin neurons. The results also point to galanin-dependent circuitry as a potential substrate for the evolution of divergent phenotypes within one sex and provide new functional insights into how POA populations in teleosts compare to the POA and anterior hypothalamus of tetrapods.SIGNIFICANCE STATEMENT Studies of neuropeptide regulation of vertebrate social behavior have mainly focused on the vasopressin-oxytocin family. Recently, galanin has received attention as a regulator of social behavior largely because of studies demonstrating that galanin neurons in the preoptic area (POA) promote mating and parental care in mammals. Species with alternative reproductive tactics (ARTs) exhibit robust, consistent differences in behavioral phenotypes between individuals within a sex. Taking advantage of this trait, we show POA galanin neurons are specifically active during mating in one of two male reproductive tactics, but not other mating-related behaviors in a fish with ARTs. The results demonstrate a deep, phylogenetically shared role for POA galanin neurons in reproductive-related social behaviors with implications for the evolution of ARTs.

Galanin immunoreactivity is sexually polymorphic in neuroendocrine and vocal-acoustic systems in a teleost fish

Galanin is a peptide that regulates pituitary hormone release, feeding, and reproductive and parental care behaviors. In teleost fish, increased galanin expression is associated with territorial, reproductively active males. Prior transcriptome studies of the plainfin midshipman (Porichthys notatus), a highly vocal teleost fish with two male morphs that follow alternative reproductive tactics, show that galanin is upregulated in the preoptic area-anterior hypothalamus (POA-AH) of nest-holding, courting type I males during spawning compared to cuckolding type II males. Here, we investigate possible differences in galanin immunoreactivity in the brain of both male morphs and females with a focus on vocal-acoustic and neuroendocrine networks. We find that females differ dramatically from both male morphs in the number of galanin-expressing somata and in the distribution of fibers, especially in brainstem vocal-acoustic nuclei and other sensory integration sites that also differ, though less extensively, between the male morphs. Double labeling shows that primarily separate populations of POA-AH neurons express galanin and the nonapeptides arginine-vasotocin or isotocin, homologues of mammalian arginine vasopressin and oxytocin that are broadly implicated in neural mechanisms of vertebrate social behavior including morph-specific actions on vocal neurophysiology in midshipman. Finally, we report a small population of POA-AH neurons that coexpress galanin and the neurotransmitter γ-aminobutyric acid. Together, the results indicate that galanin neurons in midshipman fish likely modulate brain activity at a broad scale, including targeted effects on vocal motor, sensory and neuroendocrine systems; are unique from nonapeptide-expressing populations; and play a role in male-specific behaviors.

Neuroanatomical Framework of the Metabolic Control of Reproduction

A minimum amount of energy is required for basic physiological processes, such as protein biosynthesis, thermoregulation, locomotion, cardiovascular function, and digestion. However, for reproductive function and survival of the species, extra energy stores are necessary. Production of sex hormones and gametes, pubertal development, pregnancy, lactation, and parental care all require energy reserves. Thus the physiological systems that control energy homeostasis and reproductive function coevolved in mammals to support both individual health and species subsistence. In this review, we aim to gather scientific knowledge produced by laboratories around the world on the role of the brain in integrating metabolism and reproduction. We describe essential neuronal networks, highlighting key nodes and potential downstream targets. Novel animal models and genetic tools have produced substantial advances, but critical gaps remain. In times of soaring worldwide obesity and metabolic dysfunction, understanding the mechanisms by which metabolic stress alters reproductive physiology has become crucial for human health.

Behavioural tactic predicts preoptic-hypothalamic gene expression more strongly than developmental morph in fish with alternative reproductive tactics

Reproductive success relies on the coordination of social behaviours, such as territory defence, courtship and mating. Species with extreme variation in reproductive tactics are useful models for identifying the neural mechanisms underlying social behaviour plasticity. The plainfin midshipman (Porichthys notatus) is a teleost fish with two male reproductive morphs that follow widely divergent developmental trajectories and display alternative reproductive tactics (ARTs). Type I males defend territories, court females and provide paternal care, but will resort to cuckoldry if they cannot maintain a territory. Type II males reproduce only through cuckoldry. We sought to disentangle gene expression patterns underlying behavioural tactic, in this case ARTs, from those solely reflective of developmental morph. Using RNA-sequencing, we investigated differential transcript expression in the preoptic area-anterior hypothalamus (POA-AH) of courting type I males, cuckolding type I males and cuckolding type II males. Unexpectedly, POA-AH differential expression was more strongly coupled to behavioural tactic than morph. This included a suite of transcripts implicated in hormonal regulation of vertebrate social behaviour. Our results reveal that divergent expression patterns in a conserved neuroendocrine centre known to regulate social-reproductive behaviours across vertebrate lineages may be uncoupled from developmental history to enable plasticity in the performance of reproductive tactics.

Maternally involved galanin neurons in the preoptic area of the rat

Recent selective stimulation and ablation of galanin neurons in the preoptic area of the hypothalamus established their critical role in control of maternal behaviors. Here, we identified a group of galanin neurons in the anterior commissural nucleus (ACN), and a distinct group in the medial preoptic area (MPA). Galanin neurons in ACN but not the MPA co-expressed oxytocin. We used immunodetection of phosphorylated STAT5 (pSTAT5), involved in prolactin receptor signal transduction, to evaluate the effects of suckling-induced prolactin release and found that 76 % of galanin cells in ACN, but only 12 % in MPA were prolactin responsive. Nerve terminals containing tuberoinfundibular peptide 39 (TIP39), a neuropeptide that mediates effects of suckling on maternal motivation, were abundant around galanin neurons in both preoptic regions. In the ACN and MPA, 89 and 82 % of galanin neurons received close somatic appositions, with an average of 2.9 and 2.6 per cell, respectively. We observed perisomatic innervation of galanin neurons using correlated light and electron microscopy. The connection was excitatory based on the glutamate content of TIP39 terminals demonstrated by post-embedding immunogold electron microscopy. Injection of the anterograde tracer biotinylated dextran amine into the TIP39-expressing posterior intralaminar complex of the thalamus (PIL) demonstrated that preoptic TIP39 fibers originate in the PIL, which is activated by suckling. Thus, galanin neurons in the preoptic area of mother rats are innervated by an excitatory neuronal pathway that conveys suckling-related information. In turn, they can be topographically and neurochemically divided into two distinct cell groups, of which only one is affected by prolactin.

Brain Transcriptional Profiles of Male Alternative Reproductive Tactics and Females in Bluegill Sunfish

Bluegill sunfish (Lepomis macrochirus) are one of the classic systems for studying male alternative reproductive tactics (ARTs) in teleost fishes. In this species, there are two distinct life histories: parental and cuckolder, encompassing three reproductive tactics, parental, satellite, and sneaker. The parental life history is fixed, whereas individuals who enter the cuckolder life history transition from sneaker to satellite tactic as they grow. For this study, we used RNAseq to characterize the brain transcriptome of the three male tactics and females during spawning to identify gene ontology (GO) categories and potential candidate genes associated with each tactic. We found that sneaker males had higher levels of gene expression differentiation compared to the other two male tactics. Sneaker males also had higher expression in ionotropic glutamate receptor genes, specifically AMPA receptors, compared to other males, which may be important for increased spatial working memory while attempting to cuckold parental males at their nests. Larger differences in gene expression also occurred among male tactics than between males and females. We found significant expression differences in several candidate genes that were previously identified in other species with ARTs and suggest a previously undescribed role for cAMP-responsive element modulator (crem) in influencing parental male behaviors during spawning.

Galanin and Cognition

Since the neuropeptide galanin’s discovery in 1983, information has accumulated that implicates it in a wide range of functions, including pain sensation, stress responses, appetite regulation, and learning and memory. This article reviews the evidence for specific functions of galanin in cognitive processes. Consistencies as well as gaps in the literature are organized around basic questions of methodology and theory. This review shows that although regularities are evident in the observed behavioral effects of galanin across several methods for measuring learning and memory, generalization from these findings is tempered with concerns about confounds and a restricted range of testing conditions. Furthermore, it is revealed that many noncognitive behavioral constructs that are relevant for assessing potential roles for galanin in cognition have not been thoroughly examined. The review concludes by laying out how future theory and experimental work can overcome these concerns and confidently define the nature of the association of galanin with particular cognitive constructs.

Temporal and concentration-dependent effects of oestradiol on neural pathways mediating sexual receptivity

The acceptance of oestradiol signalling through receptors found in the cell membrane, as well as, the nucleus, has provided for a re-examination of the timing and location of the actions of oestradiol on neural circuits mediating sexual receptivity (lordosis). Oestradiol membrane signalling involves the transactivation of metabotrophic glutamate receptors (mGluRs) that transduce steroid information through protein kinase C signalling cascades producing rapid activation of lordosis-regulating circuits. It has been known for some time that oestradiol initially produces an inhibition of the medial preoptic nucleus. We have demonstrated that underlying this inhibition is oestradiol acting in the arcuate nucleus to induce β-endorphin release, which inhibits the medial preoptic nucleus through a μ-opioid receptor mechanism. This transient inhibition is relieved by either subsequent progesterone treatment or longer exposure to higher doses of oestradiol to facilitate lordosis behaviour. We review recent findings about oestradiol membrane signalling inducing dendritic spine formation in the arcuate nucleus that is critical for oestradiol induction of sexual receptivity. Moreover, we discuss the evidence that, in addition to oestrogen receptor α, several other putative membrane oestrogen receptors facilitate lordosis behaviour through regulation of the arcuate nucleus. These include the GRP30 and the STX activated Gq-mER. Finally, we report on the importance of GABA acting at GABAB receptors for oestradiol membrane signalling that regulates lordosis circuit activation and sexual receptivity.

Neuropeptides and central control of sexual behaviour from the past to the present: a review

Of the numerous neuropeptides identified in the central nervous system, only a few are involved in the control of sexual behaviour. Among these, the most studied are oxytocin, adrenocorticotropin, α-melanocyte stimulating hormone and opioid peptides. While opioid peptides inhibit sexual performance, the others facilitate sexual behaviour in most of the species studied so far (rats, mice, monkeys and humans). However, evidence for a sexual role of gonadotropin-releasing hormone, corticotropin releasing factor, neuropeptide Y, galanin and galanin-like peptide, cholecystokinin, substance P, vasoactive intestinal peptide, vasopressin, angiotensin II, hypocretins/orexins and VGF-derived peptides are also available. Corticotropin releasing factor, neuropeptide Y, cholecystokinin, vasopressin and angiotensin II inhibit, while substance P, vasoactive intestinal peptide, hypocretins/orexins and some VGF-derived peptide facilitate sexual behaviour. Neuropeptides influence sexual behaviour by acting mainly in the hypothalamic nuclei (i.e., lateral hypothalamus, paraventricular nucleus, ventromedial nucleus, arcuate nucleus), in the medial preoptic area and in the spinal cord. However, it is often unclear whether neuropeptides influence the anticipatory phase (sexual arousal and/or motivation) or the consummatory phase (performance) of sexual behaviour, except in a few cases (e.g., opioid peptides and oxytocin). Unfortunately, scarce information has been added in the last 15 years on the neural mechanisms by which neuropeptides influence sexual behaviour, most studied neuropeptides apart. This may be due to a decreased interest of researchers on neuropeptides and sexual behaviour or on sexual behaviour in general. Such a decrease may be related to the discovery of orally effective, locally acting type V phosphodiesterase inhibitors for the therapy of erectile dysfunction.

siRNA silencing of estrogen receptor-α expression specifically in medial preoptic area neurons abolishes maternal care in female mice

The medial preoptic area has been shown to be intricately involved in many behaviors, including locomotion, sexual behavior, maternal care, and aggression. The gene encoding estrogen receptor-α (ERα) protein is expressed in preoptic area neurons, and a very dense immunoreactive field of ERα is found in the preoptic region. ERα knockout animals show deficits in maternal care and sexual behavior and fail to exhibit increases in these behaviors in response to systemic estradiol treatment. In the present study, we used viral-vector mediated RNA interference to silence ERα expression specifically in the preoptic area of female mice and measured a variety of behaviors, including social and sexual aggression, maternal care, and arousal activity. Suppression of ERα in the preoptic area almost completely abolished maternal care, significantly increasing the latency to pup retrieval and significantly reducing the time the moms spent nursing and licking the pups. Strikingly, maternal aggression toward a male intruder was not different between control and preoptic ERα-silenced mice, demonstrating the remarkably specific role of ERα in these neurons. Reduction of ERα expression in preoptic neurons significantly decreased sexual behavior in female mice and increased aggression toward both sexual partners and male intruders in a seminatural environment. Estrogen-dependent increases in arousal, measured by home cage activity, were not mediated by ERα expression in the preoptic neurons we targeted, as ERα-suppressed mice had increases similar to control mice. Thus, we have established that a specific gene in a specific group of neurons is required for a crucially important natural behavior.

Puberty onset in female rats: relationship with fat intake, ovarian steroids and the peptides, galanin and enkephalin, in the paraventricular and medial preoptic nuclei

Puberty is a time of rapid change, including a marked increase in fat consumption and body fat accrual, particularly in females. The mechanisms underlying these changes are unknown. Building on the results obtained in adult rats, the present study in pubertal rats focused on the orexigenic peptides, galanin (GAL) and enkephalin (ENK), in the paraventricular nucleus (PVN) and medial preoptic nucleus (MPN), which are known to be responsive to female steroids and have a role in both energy balance and reproductive function. The present study examined female rats maintained on pure macronutrient diets from before weaning (day 15) to day 70. After an initial burst in protein intake (days 21-35), rats showed an increase, specifically in preference for fat, from 15% to 30%. In rats examined at different ages before (day 30) and after (days 45 and 60) puberty, this rise in fat intake was associated with a marked increase, from days 30-45, in levels of oestradiol and progesterone and in GAL and ENK mRNA or peptide levels, specifically in the PVN and MPN, but not other hypothalamic areas examined. This positive relationship with increased fat intake, steroids and peptides across ages was also observed when comparing pubertal rats that naturally preferred fat (> 25% of total diet) with those consuming little fat (< 15%) or rats that reached puberty at an early age (days 30-34) with those that were late (days 37-40). These rats with early puberty onset exhibited a strong fat preference 3-4 days before vaginal opening, which was positively related to steroid levels, GAL, fat intake and body fat accrual after puberty. These findings suggest that, in addition to providing a signal for puberty onset, early fat ingestion acting through mechanisms involving the steroids and orexigenic peptides may be related to long-term patterns of eating and body weight regulation.

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.

A preprogalanin cDNA from the turtle pituitary and regulation of its gene expression

Galanin is a hormone 29 or 30 amino acids (aa) long that is widely distributed within the body and exerts numerous biological effects in vertebrates. To fully understand its physiological roles in reptiles, we analyzed preprogalanin cDNA structure and expression in the turtle pituitary. Using the Chinese soft-shell turtle ( Pelodiscus sinensis order Testudines), we obtained a 672-base pair (bp) cDNA containing a 99-bp 5′-untranslated region, a 324-bp preprogalanin coding region, and a 249-bp 3′-untranslated region. The open-reading frame encoded a 108-aa preprogalanin protein with a putative 23-aa signal sequence at the NH2 terminus. Based on the location of putative Lys-Arg dibasic cleavage sites and an amidation signal of Gly-Lys-Arg, we propose that turtle preprogalanin is processed to yield a 29-aa galanin peptide with Gly1 and Thr29 substitutions and a COOH-terminal amidation. Sequence comparison revealed that turtle preprogalanin and galanin-29 had 48–81% and 76–96% aa identities with those of other vertebrates, respectively, suggesting their conservative nature. Expression of the turtle galanin gene was detected in the pituitary, brain, hypothalamus, stomach, liver, pancreas, testes, ovaries, and intestines, but not in the adipose or muscle tissues, suggesting tissue-dependent differences. An in vitro study that used pituitary tissue culture indicated that treatment with 17β-estradiol, testosterone, or gonadotropin-releasing hormone resulted in increased galanin mRNA expression with dose- or time-dependent differences, whereas leptin and neuropeptide Y reduced galanin mRNA levels. These results suggest a hormone-dependent effect on hypophyseal galanin mRNA expression.

Physiology of female sexual function: animal models

INTRODUCTION

Data concerning the physiology of desire, arousal, and orgasm in women are limited because of ethical constraints. Aim. To gain knowledge of physiology of female sexual function through animal models.

METHODS

To provide state-of-the-art knowledge concerning female sexual function in animal models, representing the opinions of seven experts from five countries developed in a consensus process over a 2-year period.

MAIN OUTCOME MEASURE

Expert opinion was based on the grading of evidence-based medical literature, widespread internal committee discussion, public presentation, and debate.

RESULTS

Sexual desire may be considered as the presence of desire for, and fantasy about, sexual activity. Desire in animals can be inferred from certain appetitive behaviors that occur during copulation and from certain unconditioned copulatory measures. Proceptive behaviors are dependent in part on estrogen, progesterone, and drugs that bind to D1 dopamine receptors, adrenergic receptors, oxytocin receptors, opioid receptors, or gamma-amino butyric acid receptors. Peripheral arousal states are dependent on regulation of genital smooth muscle tone. Multiple neurotransmitters/mediators are involved including adrenergic, and nonadrenergic, noncholinergic agents such as vasoactive intestinal polypeptide, nitric oxide, neuropeptide Y, calcitonin gene-related peptide, and substance P. Sex steroid hormones, estrogens and androgens, are critical for structure and function of genital tissues including modulation of genital blood flow, lubrication, neurotransmitter function, smooth muscle contractility, mucification, and sex steroid receptor expression in genital tissues. Orgasm may be investigated by urethrogenital (UG) reflex, in which genital stimulation results in rhythmic contractions of striated perineal muscles and contractions of vagina, anus, and uterine smooth muscle. The UG reflex is generated by a multisegmental spinal pattern generator involving the coordination of sympathetic, parasympathetic, and somatic efferents innervating the genital organs. Serotonin and dopamine may modulate UG reflex activity.

CONCLUSIONS

More research is needed in animal models in the physiology of female sexual function.

Effects of galanin-like peptide (GALP) on locomotion, reproduction, and body weight in female and male mice

Galanin-like peptide (GALP) has been implicated in the neuroendocrine regulation of both feeding and reproduction. In male rodents and primates, intracerebroventricular (icv) infusions of GALP stimulate luteinizing hormone (LH) release, induce Fos expression in brain areas implicated in feeding and reproduction, and affect food intake and body weight in rodents. In gonad-intact and castrated male rats, icv administration of GALP also stimulates male sexual behavior. While the effects of GALP on male physiology and behavior are well documented, no studies have addressed such a role of GALP in females. We tested the effects of icv GALP infusions on LH release, locomotor activity, motor control, and body weight regulation in adult ovariectomized female mice hormonally primed with estradiol benzoate and progesterone. In addition, sexually-experienced male and female mice were treated with GALP and tested for sexual behavior. In females, GALP reduced open-field locomotor activity, the ability to maintain grip on an accelerating rotarod, and 24-h body weight in a dose-dependent manner. GALP also increased LH secretion in female mice, an effect that was blocked by pre-treatment with Antide, a gonadotropin-releasing hormone (GnRH) type-1 receptor antagonist. GALP infusions slightly decreased the occurrence of lordosis behavior in female mice and significantly increased the latencies with which females displayed receptivity. Unlike previous reports in male rats, GALP inhibited male sexual behavior in mice. Our data indicate that in female mice, GALP stimulates LH release via GnRH, and decreases body weight, motor control, and locomotor activity via GnRH-independent pathways. Furthermore, our sexual behavior and locomotor findings suggest species-specific differences in the mechanism and/or location of GALP action in the brains of rats and mice.

Animal models of attention-deficit hyperactivity disorder

Attention-deficit hyperactivity disorder (ADHD) involves clinically heterogeneous dysfunctions of sustained attention, with behavioral overactivity and impulsivity, of juvenile onset. Experimental models, in addition to mimicking syndromal features, should resemble the clinical condition in pathophysiology, and predict potential new treatments. One of the most extensively evaluated animal models of ADHD is the spontaneously hypertensive rat. Other models include additional genetic variants (dopamine transporter gene knock-out mouse, coloboma mouse, Naples hyperexcitable rat, acallosal mouse, hyposexual rat, and population-extreme rodents), neonatal lesioning of dopamine neurons with 6-hydroxydopamine, and exposure to other neurotoxins or hippocampal irradiation. None is fully comparable to clinical ADHD. The pathophysiology involved varies, including both deficient and excessive dopaminergic functioning, and probable involvement of other monoamine neurotransmitters. Improved models as well as further testing of their ability to predict treatment responses are required.

Restricted distribution of galanin receptor 3 (GalR3) mRNA in the adult rat central nervous system

Recent molecular cloning studies have established the existence of a third rat galanin receptor subtype, GalR3, however its precise distribution in the mammalian central nervous system (CNS) is not well established. In the present study, we examined the regional and cellular distribution of GalR3 mRNA in the CNS of the rat by in situ hybridization. Our findings indicate that GALR3 mRNA expression in the rat brain is discrete and highly restricted, concentrated mainly in the preoptic/hypothalamic area. Within the hypothalamus, GalR3 expression was confined to the paraventricular, ventromedial and dorsomedial hypothalamic nuclei. In addition to these hypothalamic nuclei, GalR3 mRNA-expressing cells were observed in the medial septum/diagonal band of Broca complex, the bed nucleus of the stria terminalis, the medial amygdaloid nucleus, the periaqueductal gray, the lateral parabrachial nucleus, the dorsal raphe nucleus, the locus coeruleus, the medial medullary reticular formation and in one of the circumventricular organs, the subfornical organ. In the spinal cord, a faint but specific ISH signal was observed over the laminae I-II with a few moderately labeled cells distributed in laminae V and X. The neuroanatomical distribution of GalR3 suggests it might be involved in mediating documented effects of galanin on food intake, fluid homeostasis, cardiovascular function and nociception.

Sexually dimorphic activation of galanin neurones in the ferret's dorsomedial preoptic area/anterior hypothalamus after mating

Male ferrets in breeding condition possess three times as many galanin-immunoreactive (IR) neurones as oestrous females in the sexually dimorphic dorsomedial preoptic area/anterior hypothalamus (dmPOA/AH). Using Fos-IR as a marker of activation, we investigated whether mating with intromission differentially activates this sexually dimorphic group of galanin-IR neurones in male and female ferrets. Male ferrets that intromitted had a significantly greater percentage of galanin-IR neurones in the dmPOA/AH that were colabelled with nuclear Fos-IR than oestrous females that received an intromission. Intromissive stimulation augmented Fos-IR in an equal percentage of galanin-IR neurones in both sexes in the medial amygdala (MA) and bed nucleus of the stria terminalis (BNST). Peripheral anosmia induced by bilateral occlusion of males' nares did not reduce the mating-induced activation of galanin-IR neurones in the dmPOA/AH, and there was a significant correlation among individual males between intromission duration and the percentage of dmPOA/AH galanin-IR neurones colabelled with Fos-IR. Exposure of castrated, testosterone propionate-treated male ferrets to either soiled bedding or to volatile odours from oestrous females failed to induce nuclear Fos-IR in galanin-IR neurones located in the dmPOA/AH, BNST or MA, suggesting that the mating-induced activation of galanin-IR forebrain neurones in male ferrets depends more on genital-somatosensory than on olfactory inputs. The observed sex dimorphism in the mating-induced activation of galanin-IR neurones in the dmPOA/AH raises the possibility that these neurones perform a mating-dependent function that occurs only in males.

Neuropeptides and sexual behaviour

Many neuropeptides are involved in the control of sexual behaviour at the central level. Among these, the most studied are adrenocorticotropin, alpha-melanocyte stimulating hormone, oxytocin and opioid peptides. This attempt to review old and new neuropharmacological, biochemical and psychobiological studies in this field, shows that all these neuropeptides apparently facilitate sexual behaviour, except for opioid peptides, which inhibit sexual performance, in most of the species studied so far (rats, mice, monkeys and humans). However, gonadotropin-releasing hormone, corticotropin releasing factor, neuropeptide Y, galanin, cholecystokinin, substance P and vasoactive intestinal peptide may be also involved in the control of sexual behaviour. Apparently, corticotropin releasing factor, neuropeptide Y and cholecystokinin inhibit, while substance P and vasoactive intestinal peptide facilitate, sexual behaviour. In contrast, gonadotropin-releasing hormone has been reported to exert a facilitative, inhibitory or no effect at all on sexual behaviour. Galanin was also shown either to facilitate or inhibit sexual behaviour. The above-mentioned putative role of the neuropeptides in sexual behaviour derives mainly from studies done in rats. In these studies, neuropeptides, their antisera or drugs that act as agonists or antagonists of neuropeptide receptors, were tested for their effect on sexual behaviour after systemic, intracerebroventricular, or intracerebral administration. The latter were infused into brain areas relevant for sexual behaviour, such as the medial preoptic area, and the ventromedial and paraventricular nuclei of the hypothalamus. The above studies show that little information is available on the mechanisms by which neuropeptides influence sexual behaviour. Also unclear is whether the above neuropeptides influence the anticipatory phase (sexual arousal and/or motivation) or the consummatory phase (performance) of sexual behaviour, except for opioid peptides. New information about the role of neuropeptides may come from the application of molecular biology and genetic manipulation techniques to the study of sexual behaviour. Of these, FOS protein determination, antisense oligonucleotides aimed at the neutralisation of neuropeptide and/or neuropeptide receptor mRNAs in specific brain areas, and gene ablation seem the most promising. Although still in the early stages, it is likely that these methodologies will provide new insights into the role of neuropeptides in the control of sexual behaviour.

Evidence for expression of galanin receptor Gal-R1 mRNA in certain gonadotropin releasing hormone neurones of the rostral preoptic area

Previous studies have shown that galanin plays an important role in the regulation of gonadotropin releasing hormone (GnRH) release. At present, it is not known if this role is exerted by direct or indirect interactions between galanin producing neurones and GnRH neurones. The objective of this study was to determine whether or not GnRH neurones could express galanin receptor Gal-R1 mRNA. Dual in-situ hybridization experiments were carried out with digoxigenin-labelled cRNA probes encoding GnRH in combination with 35S-labelled riboprobe encoding the galanin receptor Gal-R1. In order to detect possible variations in the expression of the Gal-R1 mRNA under different physiological conditions, male rats, intact female rats throughout the phases of the oestrous cycle, ovariectomized (OVX) and steroid-treated rats were analysed. The results show that many cells expressing Gal-R1 mRNA were present throughout the preoptic area. Gal-R1 mRNA-expressing cells were observed in very close proximity with GnRH neurones. In the female rat, some GnRH neurones located in the rostral preoptic area/vascular organ of the lamina terminalis expressed Gal-R1 mRNA. These double-labelled cells were observed at all times of the oestrous cycle, except during diestrus at 08.00 h and pro-oestrus at 18.00 h. Conspicuously, at oestrus 1800 h, we found that 21.6% of rostral GnRH neurones expressed the Gal-R1 mRNA. In addition, dual-labelled GnRH neurones were seen in OVX animals but not in oestrogen plus progesterone-treated ones. In the male rat, colocalization of GnRH mRNA and Gal-R1 receptor mRNA was not observed. In the medial preoptic area, no double-labelled GnRH neurones were detected regardless of the endocrine conditions. These results suggest that, in addition to a possible indirect action of galanin on GnRH cells via neurones located at close proximity, the effects of galanin on GnRH can be mediated by direct activation of galanin receptors in rostral GnRH neurones. This study also shows that expression of Gal-R1 mRNA in GnRH cells is influenced by the levels of circulating gonadal steroids.

Gonadal steroid-dependent GAL-IR cells within the medial preoptic nucleus (MPN) and the stimulatory effects of GAL within the MPN on sexual behaviors

More GAL-I cells exist within sexually dimorphic cell groups of the medial preoptic nucleus (MPN) in male rate than females, a large percentage of estrogen-concentrating cells within MPN cell groups are also GAL-immunoreactive (GAL-IR), and significantly more GAL-IR cells are visible with estrogen or its precursor, testosterone. Gonadal steroids also increase the size (diameter) of MPN GAL-IR cells and the number of GAL-IR cell processes within a portion of the MPN called the "GAL-IR MPOA plexus," which exists in males only. GAL microinjected into the MPN stimulated male-typical sexual behaviors, with more testosterone required in females than males. Immunoneutralization with anti-GAL serum inhibited male-typical sexual behavior, indicating a role for endogenous GAL within the MPN. Microinjection of GAL into the MPN also stimulated female-typical sexual behaviors in estrogen-treated females and males, and GAL within the MPN dramatically overrode an inhibition of lordosis by dihydrotestosterone in rats of both sexes.

Presence of mu and kappa opioid receptor mRNAs in galanin but not in GnRH neurons in the female rat

Using a combination of radioactive and non-radioactive in situ hybridizations, the expression of mu and kappa opioid receptor mRNA was investigated in neurons in the female rat preoptic nucleus expressing galanin and gonadotropin-releasing hormone (GnRH) mRNA. Numerous cells expressing both mu or kappa and galanin were found in the intermediate and rostral regions of the preoptic area whereas little co-localization was observed at the rostral level. The number of kappa/galanin expressing cells was greater than that of mu/galanin cells. mu/galanin co-localization was observed essentially in the anteroventral preoptic nucleus while neurons expressing kappa/galanin were present in both the anteroventral preoptic nucleus and in the periventricular hypothalamic nucleus. Co-localization of GnRH with mu or kappa could not be detected in the preoptic area. These observations showed that galaninergic neurons but not GnRH neurons of the preoptic area might be directly regulated by endogenous opioid peptides.