Effects of lordosis-relevant neuropeptides on midbrain periaqueductal gray neuronal activity in vitro

An analgesic pathway from parvocellular oxytocin neurons to the periaqueductal gray in rats

The hypothalamic neuropeptide oxytocin (OT) exerts prominent analgesic effects via central and peripheral action. However, the precise analgesic pathways recruited by OT are largely elusive. Here we discovered a subset of OT neurons whose projections preferentially terminate on OT receptor (OTR)-expressing neurons in the ventrolateral periaqueductal gray (vlPAG). Using a newly generated line of transgenic rats (OTR-IRES-Cre), we determined that most of the vlPAG OTR expressing cells targeted by OT projections are GABAergic. Ex vivo stimulation of parvocellular OT axons in the vlPAG induced local OT release, as measured with OT sensor GRAB. In vivo, optogenetically-evoked axonal OT release in the vlPAG of as well as chemogenetic activation of OTR vlPAG neurons resulted in a long-lasting increase of vlPAG neuronal activity. This lead to an indirect suppression of sensory neuron activity in the spinal cord and strong analgesia in both female and male rats. Altogether, we describe an OT-vlPAG-spinal cord circuit that is critical for analgesia in both inflammatory and neuropathic pain models.

Mating Enhances Expression of Hormonal and Trophic Factors in the Midbrain of Female Rats

Among female rats, mating enhances neurosteroid formation in the midbrain ventral tegmental area (VTA; independent of peripheral steroid-secreting glands, ovaries, and adrenals). The sources/targets for these actions are not well understood. In Experiment 1, proestrous rats engaged in a mating paradigm, or did not, and the midbrains had been assessed via the Affymetrix rat genome microarrays. In Experiment 2, the influence of gonadal and adrenal glands on the expression of these genes was assessed in rats that were proestrous, ovariectomized (OVX), or OVX and adrenalectomized (ADX). The microarrays revealed 53 target genes that were significantly up-regulated (>2.0-fold change) in response to mating. Mating significantly enhanced the midbrain mRNA expression of genes involved in hormonal and trophic actions: Gh1, S100g, and Klk1b3 in proestrous, but not OVX and/or ADX, rats; Fshb in all but OVX/ADX rats; and lutenizing hormone β and thyroid-stimulating hormone (TSH) β in all rats. Thus, mating enhances midbrain gene expression independent and dependent of peripheral glands.

Comparing vasopressin and oxytocin fiber and receptor density patterns in the social behavior neural network: Implications for cross-system signaling

Vasopressin (AVP) and oxytocin (OXT) regulate social behavior by binding to their canonical receptors, the vasopressin V1a receptor (V1aR) and oxytocin receptor (OTR), respectively. Recent studies suggest that these neuropeptides may also signal via each other's receptors. The extent to which such cross-system signaling occurs likely depends on anatomical overlap between AVP/OXT fibers and V1aR/OTR expression. By comparing AVP/OXT fiber densities with V1aR/OTR binding densities throughout the rat social behavior neural network (SBNN), we propose the potential for cross-system signaling in four regions: the medial amygdala (MeA), bed nucleus of the stria terminalis (BNSTp), medial preoptic area, and periaqueductal grey. We also discuss possible implications of corresponding sex (higher in males versus females) and age (higher in adults versus juveniles) differences in AVP fiber and OTR binding densities in the MeA and BNSTp. Overall, this review reveals the need to unravel the consequences of potential cross-system signaling between AVP and OXT systems in the SBNN for the regulation of social behavior.

The role of oxytocin in male and female reproductive behavior

Oxytocin (OT) is a nonapeptide with an impressive variety of physiological functions. Among them, the 'prosocial' effects have been discussed in several recent reviews, but the direct effects on male and female sexual behavior did receive much less attention so far. As our contribution to honor the lifelong interest of Berend Olivier in the control mechanisms of sexual behavior, we decided to explore the role of OT in the present review. In the successive sections, some physiological mechanisms and the 'pair-bonding' effects of OT will be discussed, followed by sections about desire, female appetitive and copulatory behavior, including lordosis and orgasm. At the male side, the effects on erection and ejaculation are reviewed, followed by a section about 'premature ejaculation' and a possible role of OT in its treatment. In addition to OT, serotonin receives some attention as one of the main mechanisms controlling the effects of OT. In the succeeding sections, the importance of OT for 'the fruits of labor' is discussed, as it plays an important role in both maternal and paternal behavior. Finally, we pay attention to an intriguing brain area, the ventrolateral part of the ventromedial hypothalamic nucleus (VMHvl), apparently functioning in both sexual and aggressive behavior, which are at first view completely opposite behavioral systems.

Gonadotropin-releasing hormone neurones innervate kisspeptin neurones in the female mouse brain

Kisspeptin (KP) neurones in the rostral periventricular area of the third ventricle (RP3V) and arcuate nucleus (Arc) are important elements in the neuronal circuitry regulating gonadotropin-releasing hormone (GnRH) secretion. KP and co-synthesised neuropeptides/neurotransmitters act directly on GnRH perikarya and processes. GnRH neurones not only form the final output pathway regulating the reproductive functions of the anterior pituitary gland, but also provide neuronal input to sites within the hypothalamus. The current double-label immunohistochemical studies investigated whether GnRH-immunoreactive (IR) projections to the RP3V and/or Arc establish morphological connections with KP-IR neurones at these sites. To optimise visualisation of KP immunoreactivity in, respectively, the RP3V and Arc, ovariectomised (OVX) oestrogen-treated and OVX oil-treated female mice were studied. Confocal laser microscopic analysis of immunofluorescent specimens revealed GnRH-IR axon varicosities in apposition to approximately 25% of the KP-IR neurones in the RP3V and 50% of the KP-IR neurones in the Arc. At the ultrastructural level, GnRH-IR neurones were seen to establish asymmetric synaptic contacts, which usually reflect excitatory neurotransmission, with KP-IR neurones in both the RP3V and Arc. Together with previous data, these findings indicate reciprocal connectivity between both of the KP cell populations and the GnRH neuronal system. The functional significance of the GnRH-IR input to the two separate KP cell populations requires electrophysiological investigation.

Anxiolytic-like effect of oxytocin in the simulated public speaking test

Oxytocin (OT) is known to be involved in anxiety, as well as cardiovascular and hormonal regulation. The objective of this study was to assess the acute effect of intranasally administered OT on subjective states, as well as cardiovascular and endocrine parameters, in healthy volunteers (n = 14) performing a simulated public speaking test. OT or placebo was administered intranasally 50 min before the test. Assessments were made across time during the experimental session: (1) baseline (-30 min); (2) pre-test (-15 min); (3) anticipation of the speech (50 min); (4) during the speech (1:03 h), post-test time 1 (1:26 h), and post-test time 2 (1:46 h). Subjective states were evaluated by self-assessment scales. Cortisol serum and plasma adrenocorticotropic hormone (ACTH) were measured. Additionally, heart rate, blood pressure, skin conductance, and the number of spontaneous fluctuations in skin conductance were measured. Compared with placebo, OT reduced the Visual Analogue Mood Scale (VAMS) anxiety index during the pre-test phase only, while increasing sedation at the pre-test, anticipation, and speech phases. OT also lowered the skin conductance level at the pre-test, anticipation, speech, and post-test 2 phases. Other parameters evaluated were not significantly affected by OT. The present results show that OT reduces anticipatory anxiety, but does not affect public speaking fear, suggesting that this hormone has anxiolytic properties.

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.

The regulation of brain states by neuroactive substances distributed via the cerebrospinal fluid; a review

The cerebrospinal fluid (CSF) system provides nutrients to and removes waste products from the brain. Recent findings suggest, however, that in addition, the CSF contains message molecules in the form of actively released neuroactive substances. The concentrations of these vary between locations, suggesting they are important for the changes in brain activity that underlie different brain states, and induce different sensory input and behavioral output relationships.The cranial CSF displays a rapid caudally-directed ventricular flow followed by a slower rostrally-directed subarachnoid flow (mainly towards the cribriform plate and from there into the nasal lymphatics). Thus, many brain areas are exposed to and can be influenced by substances contained in the CSF. In this review we discuss the production and flow of the CSF, including the mechanisms involved in the regulation of its composition. In addition, the available evidence for the release of neuropeptides and other neuroactive substances into the CSF is reviewed, with particular attention to the selective effects of these on distant downstream receptive brain areas. As a conclusion we suggest that (1) the flowing CSF is involved in more than just nutrient and waste control, but is also used as a broadcasting system consisting of coordinated messages to a variety of nearby and distant brain areas; (2) this special form of volume transmission underlies changes in behavioral states.

Substance P drives endocannabinoid-mediated disinhibition in a midbrain descending analgesic pathway

Substance P is thought to play an essential role in several forms of supraspinally mediated analgesia. The actions of substance P on synaptic transmission within descending analgesic pathways, however, are largely unknown. Here, we used whole-cell recordings from rat midbrain slices to examine the effects of substance P on GABAergic and glutamatergic transmission within the periaqueductal gray (PAG), a key component of a descending analgesic pathway that projects via the rostral ventromedial medulla (RVM) to the spinal cord dorsal horn. We found that substance P reversibly decreased the amplitude and increased the paired-pulse ratio of evoked IPSCs recorded from identified PAG-RVM projection neurons and from unidentified PAG neurons. Substance P had no effect on miniature IPSCs, implying an indirect mode of action. The effects of substance P were abolished by metabotropic glutamate type 5 and cannabinoid CB1 receptor antagonists, but unaltered by NMDA, GABA(B), mu,delta-opioid, adenosine A(1), and 5HT(1A) receptor antagonists. Consistent with a role for endogenous glutamate in this process, substance P increased the frequency of action potential-dependent spontaneous EPSCs. Moreover, the effect of substance P on evoked IPSCs was mimicked and occluded by a glutamate transport inhibitor. Finally, these effects were dependent on postsynaptic G-protein activation and diacylglycerol lipase activity, suggesting the requirement for retrograde signaling by the endocannabinoid 2-arachidonoylglycerol. Thus, substance P may facilitate descending analgesia in part by enhancing glutamate-mediated excitation and endocannabinoid-mediated disinhibition of PAG-RVM projection neurons.

Regulation of anxiety during the postpartum period

Healthy mother-infant interactions are critical for the physical, cognitive, and psychological development of offspring. Such interactions rely on numerous factors, including a positive maternal emotional state. However, many postpartum women experience emotional dysregulation, often involving elevated anxiety. Neuroendocrine factors contributing to the onset of postpartum anxiety symptoms are mostly unknown, but irregularities in hypothalamic-pituitary-adrenal axis function, reduced prolactin and oxytocin signaling, or parturitional withdrawal of ovarian, placental and neural steroids could contribute to anxiety in susceptible women. Although the causes of initial onset are unclear, postpartum anxiety can be mitigated by recent contact with infants. Numerous neurochemical systems, including oxytocin, prolactin, GABA, and norepinephrine mediate this anxiolytic effect of infant contact. Insight into the etiology of postpartum anxiety disorders, and how contact with infants helps counter existing anxiety dysregulation, will surely facilitate the diagnosis and treatment of postpartum women at risk for, or experiencing, an anxiety disorder.

Sex differences in the anatomical and functional organization of the periaqueductal gray-rostral ventromedial medullary pathway in the rat: a potential circuit mediating the sexually dimorphic actions of morphine

Previous studies have demonstrated that morphine, administered systemically or directly into the periaqueductal gray (PAG), produces a significantly greater degree of antinociception in males in comparison with females. Because the midbrain PAG and its descending projections to the rostral ventromedial medulla (RVM) constitute an essential neural circuit for opioid-based analgesia, the present studies were conducted to determine whether sex differences in the anatomical organization of the PAG-RVM pathway, and its activation during persistent inflammatory pain, could account for sex-based differences in opioid analgesia. In the rat, retrograde tracing was combined with Fos immunocytochemistry to investigate sexual dimorphism in the organization of the PAG-RVM circuit and its activation by persistent inflammatory pain induced by intraplantar injection of complete Freund's adjuvant (CFA). The ability of morphine to suppress the activation of the PAG-RVM circuit was also examined. Sexually dimorphic retrograde labeling was observed within the dorsomedial and lateral/ventrolateral PAG at all rostrocaudal levels, with females having significantly more PAG-RVM output neurons in comparison with males. While no sex differences were noted in the activation of the PAG by persistent inflammatory pain, significantly more PAG-RVM cells were activated in males in comparison with females. Systemic administration of morphine significantly suppressed CFA-induced Fos in the PAG in males only. The results of these studies demonstrate that both the anatomical organization and the functional activation of the PAG-RVM circuit are sexually dimorphic and may provide the anatomical substrate for sex-based differences in morphine analgesia.

Effects of stress on parental care are sexually dimorphic in prairie voles

The effects of stress on parental care are poorly understood, especially in biparental species where males also display care. Data from previous studies in prairie voles, as well as parallels with pair-bonding behavior, suggest the hypothesis that a stressful experience might facilitate parental care in males but not in females. In the present study, male and female prairie voles were exposed to either a 3-min swim stressor or no stressor; 45 min later each animal was tested in a parental care paradigm. Following the parental care test, blood samples were collected and assayed for corticosterone (CORT). After the stressor males, but not females, showed significant changes in parental behavior including significantly more time in kyphosis (arched-back huddling), and a tendency to spend more time licking and grooming pups. In males, CORT levels measured following the parental care test were inversely related to licking and grooming but positively correlated with retrievals. These findings support earlier studies suggesting that the neuroendocrine substrates of parental behavior, as well as the effects of stressors, are sexually dimorphic in this species.

Postsynaptic actions of substance P on rat periaqueductal grey neurons in vitro

The postsynaptic actions of substance P on rat midbrain periaqueductal grey (PAG) neurons were examined using whole-cell patch-clamp recordings in brain slices. Substance P produced an inward current in a subpopulation (60%) of PAG neurons. The substance P induced current was concentration dependent (EC50=27 nM) and was reduced by the NK1, NK2 and NK3 antagonists L-732,138 (20 microM), GR 159897 (3 microM) and SB 218795 (3 microM). The selective NK1, NK2 and NK3 agonists [Sar9,Met(O2)11]-Substance P (100 nM), GR 64349 (300-500 nM) and senktide (300 nM) also produced inward currents in subpopulations of neurons. A greater proportion of substance P-sensitive neurons (70%) than substance P-insensitive neurons (31%) responded to the mu/delta opioid agonist met-enkephalin (10 microM). Substance P reduced the outward current produced by met-enkephalin. The reversal potential of the substance P induced current varied from -5 mV to below -140 mV in the absence of met-enkephalin, and was -105 mV in the presence of met-enkephalin. These results indicate that substance P acts via NK1, NK2 and NK3 receptors to excite subpopulations of opioid-sensitive and insensitive PAG neurons by increasing a non-selective cation conductance and by reducing a K+ current. In addition, substance P has anti-opioid actions that are largely mediated by a reduction in the opioid induced K+ current.

Blockade effect of mu and kappa opioid antagonists on the anti-nociception induced by intra-periaqueductal grey injection of oxytocin in rats

Intra-periaqueductal grey (PAG) injection of 1 nmol of oxytocin induced significant increases in hindpaw withdrawal latency (HWL) to thermal and mechanical stimulation in rats. The anti-nociceptive effect of oxytocin was attenuated significantly by subsequent intra-PAG injection of the mu opioid antagonist beta-funaltrexamine (beta-FNA) and the kappa opioid antagonist nor-binaltorphimine (nor-BNI), but not by the delta antagonist naltrindole. The results demonstrated that mu and kappa opioid receptors, not delta receptors, were involved in the oxytocin-induced anti-nociception in PAG of rats.

Distribution of luteinizing hormone-releasing hormone in the upper brainstem and diencephalon of the cat: an immunocytochemical study

The distribution of luteinizing hormone-releasing hormone (LH-RH)-immunostained cell bodies and fibres was studied in the brainstem and diencephalon of the cat using an indirect immunoperoxidase technique. The brainstem and the thalamus were devoid of immunostained cell bodies, whereas in the hypothalamus immunopositive perikarya were observed in the supraoptic nucleus, the anterior hypothalamus, the preoptic region and in the arcuate nucleus. Our findings also showed that the hypothalamus is richer in immunostained fibres, and that in this region such fibres are more widely distributed than in the thalamus and upper brainstem. No immunopositive fibres were observed in the lower brainstem. Our results point to a more widespread distribution of LH-RH-immunostained perikarya in the cat hypothalamus than that previously reported in the cat; a similar distribution to that found in the rat, and a more restricted distribution than in primates. Additionally, our study shows a more widespread distribution of immunostained fibres in the cat brainstem and diencephalon than that previously described for other mammals. In this context, our results describe for the first time in the mammals central nervous system fibres containing LH-RH located in the stria medullaris of the thalamus, the supramammillary decussation, the laterodorsal and lateroposterior thalamic nuclei, the nucleus reuniens, the supraoptic nucleus, and the optic chiasm. Thus, our findings reveal that LH-RH-immunostained structures are widely distributed in the upper brainstem and in the diencephalon of the cat, suggesting that the peptide may be involved in several physiological functions.

Mapping of neural and signal transduction pathways for lordosis in the search for estrogen actions on the central nervous system

Estrogen can act on the brain to regulate various biological functions and behavior. In attempts to elucidate the estrogen action, the rodent female reproductive behavior, lordosis, was used as a model. Lordosis is an estrogen-dependent reflexive behavior and, hence, is mediated by discrete neural pathways that are modulated by estrogen. Therefore, a strategy of mapping the pathways, both neural and biochemical, and examining them for estrogen effect was used to localize and subsequently analyze the central action of estrogen. Using various experimental approaches, an 'inverted Y-shaped' neural pathway both sufficient and essential for mediating lordosis was defined. The top portion is a descending pathway conveying the permissive estrogen influence which originated from hypothalamic ventromedial nucleus relayed via midbrain periaqueductal grey down to medullary reticular formation, the top of the spino-bulbo-spinal reflex arc at the bottom. This estrogen influence alters the input-output relationship, shifting the output toward more excitation. With this shift in output, estrogen can enable the otherwise ineffective lordosis-triggering sensory stimuli to elicit lordosis. In the ventromedial nucleus, the origin of the estrogen influence, a multidisciplinary approach was used to map intracellular signaling pathways. A phosphoinositide pathway involving a specific G protein and the activation of protein kinase C was found to be involved in the mediation of lordosis as well as a probable target of the permissive estrogen action. The action of estrogen on this signal transduction pathway, a potentiation, is consistent with and, hence, may be an underlying mechanism for the estrogen influenced shift toward excitation. Thus, further investigation on this specific signal transduction pathway should be helpful in elucidating the action of estrogen on the brain.

Multiple peptides infrequently coexist in progesterone receptor-containing neurons in the ventrolateral hypothalamic nucleus of the guinea-pig: an immunocytochemical triple-label analysis of somatostatin, neurotensin and substance P

Progesterone plays an important role in regulating reproductive behaviour in guinea-pigs through actions exerted at the ventrolateral nucleus (VL), an area of the brain that contains progesterone receptors (PR) and neuroactive peptides, somatostatin (SOM), neurotensin (NT) and substance P (SP). Previous double-label analyses provided evidence that a substantial proportion of these neuropeptidergic cells contain PR. By means of triple-label immunofluorescence histochemistry, we examined whether PR are colocalized with two neuropeptides (SOM + NT or SP + SOM or SP + NT) within the same neurons in the VL. Ovariectomized guinea-pigs were primed with estradiol to induce PR immunoreactivity, and treated with colchicine to visualize immunoreactive (IR) neuropeptidergic cells. Both monoclonal mouse PR and polyclonal rabbit neuropeptide antibodies were used in double staining and in elution-restaining experiments. In the whole VL, the proportion of each coexisting peptide with PR obtained after double immunofluorescence appeared in decreasing order as: SOM (34%)>NT (25%)>SP (20%). Occasional colocalization was seen between PR and two neuropeptides throughout the rostrocaudal extent of the VL. Combining our various quantitative observations, we found that, of the total population of PR-IR neurons containing any combination of SOM, NT and SP, only about 1.5% contained SOM and NT, 2% contained SP and SOM and 1.6% contained SP and NT. These results indicate that while many PR-IR neurons also contain SOM or NT or SP in the guinea-pig VL, there may be very few PR-IR neurons that express more than one of these three peptides.

Hormonal and neurotransmitter regulation of GnRH gene expression and related reproductive behaviors

Gonadotropin-releasing hormone (GnRH), having a highly conserved structure across mammalian species, plays a pivotal role in the control of the neuroendocrine events and the inherent sexual behaviors essential for reproductive function. Recent advances in molecular genetic technology have contributed greatly to the investigation of several aspects of GnRH physiology, particularly steroid hormone and neurotransmitter regulation of GnRH gene expression. Behavioral studies have focused on the actions of GnRH in steroid-sensitive brain regions to understand better its role in the facilitation of mating behavior. To date, however, there are no published reports which directly correlate GnRH gene expression and reproductive behavior. The intent of this article is to review the current understanding of the way in which changes in GnRH gene expression, and modifications of GnRH neuronal activity, may ultimately influence reproductive behavior.

In vitro electrophysiological characterization of midbrain periaqueductal gray neurons in female rats: responses to GABA- and Met-enkephalin-related agents

Met-Enkephalin, which can be induced by estrogen in the ventromedial nucleus of hypothalamus (VMH), has been proposed to help mediate estrogenic action on lordosis behavior by acting on midbrain periaqueductal gray (PAG) neurons. Also, in the PAG, GABA may locally regulate the levels of lordosis behavior through GABAA receptors. Therefore, we examined the effects of both Met-enkephalin and GABA-related agents on neuronal activity of PAG neurons in slices. Overall, 72.6% of the PAG neurons were inhibited by GABA and 60.9% of GABA-responsive neurons were also excited by the GABAA receptor antagonist, bicuculline methiodide (BMI), suggesting that many of GABA-responsive PAG neurons are tonically inhibited by GABAergic neurons through GABAA receptors. Dorsal PAG neurons were more responsive to BMI than ventral PAG neurons. Moreover, in the middle part of the dorsal PAG, where prominent inhibitory behavioral effects of BMI have been reported, BMI excited 94% of GABA-responsive PAG neurons from estrogen-treated animals, significantly more than observed in ovariectomized control (50%). The most frequent action of Met-enkephalin on PAG neurons was inhibitory (38 out of 149 recorded neurons) although it excited 12 neurons. A dose-dependent increase of inhibitory action of enkephalin was found in the estrogen-primed group but not in the ovariectomized control group while higher doses of enkephalin failed to excite any more neurons in both groups. Most frequently (90%), enkephalin inhibited the same neurons as those on which GABA had the inhibitory effects. Conversely, these neurons composed about 50% of the entire GABA-responsive PAG neurons. Moreover, 76% of neurons inhibited by enkephalin were found to be tonically inhibited by endogenous GABA through GABAA receptors. It is argued, therefore, that increased enkephalinergic influences from the VMH to the PAG in estrogen-treated females could participate in the PAG neuronal control of lordosis by acting on the same neurons as are innervated by intrinsic GABAergic neurons. Since GABAA agonists actually facilitate lordosis in the PAG, these PAG neurons inhibited by both GABA and enkephalin may themselves facilitate behaviors which are antagonistic to lordosis, such as defensive behaviors.

Activation of protein kinase C in the hypothalamic ventromedial nucleus or the midbrain central gray facilitates lordosis

Many neurotransmitters and neuropeptides can act through the hypothalamic ventromedial nucleus (VMN) or midbrain central gray (MCG) to facilitate lordosis. Since these lordosis-facilitating agents can also stimulate the phosphoinositide (PI) second-messenger pathway, it was hypothesized that direct activation of this pathway can also potentiate the behavior. To evaluate this possibility, a phorbol ester, TPA (12-O-tetradecanoyl phorbol 13-acetate), was used to activate a key enzyme, protein kinase C (PKC), of the PI pathway in ovariectomized (OVX) rats either primed or not primed with estrogen. These female rats were paired with males for mating tests before and after an intracerebral infusion of TPA, and both the lordosis quotient (LQ) and the lordosis strength (LS) were measured. Bilateral infusion of TPA (5 micrograms/0.5 microliter or 0.2 microgram/0.2 microliter, but not 0.1 microgram/0.2 microliter/side) into the VMN or MCG of estrogen-primed subjects facilitated both LQ and LS in 30 min, peaked at 60-90 min, and the facilitation lasted for more than 180 min. This facilitatory effect of TPA was: (1) not observed in OVX rats not primed with estrogen; (2) not observed if the infused TPA did not reach both sides of the VMN or MCG; (3) not mimicked by 4 alpha-phorbol 12,13-didecanoate, which does not activate PKC; (4) blocked by PKC inhibitors (H7 10 mM or staurosporine 1 microM, 0.2 microliter/side), which by themselves did not facilitate lordosis; and (5) was not affected by pretreatment of the progestin antagonist RU486.(ABSTRACT TRUNCATED AT 250 WORDS)

Roles of second-messenger systems and neuronal activity in the regulation of lordosis by neurotransmitters, neuropeptides, and estrogen: a review

Many neurotransmitters and neuropeptides can affect the rodent feminine sexual behavior, lordosis, when administered in the ventromedial hypothalamus (VMH), midbrain central gray (MCG), or other brain regions. A survey of the electrophysiological and biochemical actions of these neural agents revealed that there is a very consistent association between lordosis facilitation with both the activation of the phosphoinositide (PI) pathway and the excitation of VMH and MCG neurons. In contrast, lordosis inhibition is associated, less consistently, with alterations of the adenylate cyclase (AC) system and the inhibition of neuronal activity. The findings that lordosis could be facilitated by going beyond membrane receptors and directly activating the PI pathway, suggest that this second-messenger pathway is a common mediator for the lordosis-facilitating agents. Furthermore, as in the case of stimulating membrane receptors, direct activation of this common mediator also requires estrogen priming for lordosis facilitation. Therefore, it is likely that the PI pathway is modulated by estrogen in the permissive action of estrogen priming. Indeed, a literature review shows that estrogen can affect selective isozymes of key enzyme families of the PI pathway at various levels. Such selective modulations, at several levels, could easily alter the course of a PI cascade; thence, the eventual functional outcome. These findings prompt us to propose that estrogen enables lordosis to be facilitated by a selective modulation of the PI pathway.

Projections from ventrolateral hypothalamic neurons containing progestin receptor- and substance P-immunoreactivity to specific forebrain and midbrain areas in female guinea pigs

Many neurons within the ventrolateral hypothalamus in guinea pigs contain estrogen-induced progestin receptors as well as substance P. Retrograde tracing combined with immunocytochemistry was used to determine the specific projections of this subset of steroid-sensitive cells. Unilateral Fluoro-Gold injections into the dorsal midbrain, including the central gray, labeled a large proportion of the ventrolateral hypothalamic neurons immunoreactive for both progestin receptors and substance P (approximately 30%); substantially fewer of these neurons were labeled by unilateral Fluoro-Gold injections into the preoptic area (approximately 6%), medial amygdala (approximately 10%), or the bed nucleus of the stria terminalis (approximately 11%). The projections of progestin receptor-immunoreactive neurons in the ventrolateral hypothalamus were similar to those of progestin receptor/substance P double-labeled neurons, while a slightly lower percentage of the ventrolateral hypothalamic, substance P-immunoreactive neurons tended to project to each of these areas. These pathways may prove to be components of the neural circuitry underlying a variety of functions influenced by gonadal steroid hormones and substance P, such as female sexual behavior, salt intake, nociception and aggression.

CNS effects of peptides: a cross-listing of peptides and their central actions published in the journal Peptides, 1986-1993

The centrally mediated effects of peptides as published in the journal Peptides from 1986 to 1993 are tabulated in two ways. In one table, the peptides are listed alphabetically. In another table, the effects are arranged alphabetically. Most of the effects observed after administration of peptides are grouped, wherever possible, into categories such as cardiovascular and gastrointestinal. The species used in most cases has been rats; where other animals were used, the species is noted. The route of administration of peptides and source of information also are included in the tables, with a complete listing provided at the end. Many peptides have been shown to exert a large number of centrally mediated effects.