Acute continuous exposure to cigarette smoke produces discrete changes in cholecystokinin and substance P levels in the hypothalamus and preoptic area of the male rat

FUXE, K., SIEGEL, R.A., ANDERSON, K., ENEROTH, P., MASCAGNI, F. & AGNATI, L.F. 1985. Acute continuous exposure to cigarette smoke produces discrete changes in cholecystokinin and substance P levels in the hypothalamus and preoptic area of the male rat. Acta Physiol Scand 125, 437–443. Received 8 January 1985, accepted 7 May 1985, TSSN 0001–6772. Department of Histology, Karolinska Institute, Stockholm, Sweden, Research and Development Laboratory, Department of Obstetrics and Gynaecology, Karolinska Hospital, Stockholm, Sweden, Deutsches Primaten Zentrum, Gottingen, FRG, and Department of Human Physiology, University of Modena, Italy. By means of a Walton Horizontal Smoking Machine, male rats were exposed to the smoke from 1–4 cigarettes burned in a continuous fashion. Cholecystokinin (CCK) and substance P levels (determined by means of radio-immunoassay) were measured in discrete hypothalamic and preoptic regions. Acute continuous exposure to cigarette smoke induced increases in CCK levels in the paraventricular hypothalamic region as well as decreases in CCK levels in the median eminence. Furthermore, this treatment resulted in decreased CCK and substance P levels in the medial preoptic region. The results have been interpreted to indicate that CCK and substance P containing neuronal systems can be regulated by cholinergic nicotine-like receptors.     

Steroid sensitive identified and unidentified neurons in the medial preoptic area of the rat

In view of the role played by the preoptic area and the glucocorticoids in adrenocortical regulation, the iontophoretic effects of cortisol on non-identified and identified preoptic neurons, which send their axons to the mediobasal hypothalamus, were investigated. More than half of the cells changed their rate or pattern of firing, as studied by autocorrelation, but few cells changed their pattern only. The iontophoretic effect persisted only few seconds beyond cessation of current. Twenty three percent of the studied cells were antidromically identified and most of them responded to the iontophoretic application of cortisol. The possible relation of these findings to the neuroendocrine regulation of adrenocortical secretion is discussed.     

Cholinergic mechanisms of the medial preoptic areas of the hypothalamus in the control of thermoregulation and the states of sleep and waking in pigeons

Cholinergic mechanisms in the medial preoptic area of the hypothalamus were found to be involved in controlling the time characteristics of the states of sleep and waking, as well as measures of thermoregulation, in pigeons. Muscarinic and nicotinic cholinergic receptors were involved in the mechanisms maintaining waking. Activation of muscarinic cholinoreceptors in the medial preoptic area was accompanied by increases in brain temperature due to increases in peripheral vasoconstriction and decreases in the level of muscle contractile activity. Activation of nicotinic cholinoreceptors in this area led to decreases in brain temperature and increases in the level of contractile muscle activity. Comparative analysis of the results of experiments and previous studies showed that changes in brain temperature in pigeons occurring on activation of cholinoreceptors depend on the type of cholinoreceptor activated but are independent of their location in the preoptic area of the hypothalamus. Translated from Rossiiskii Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 94, No. 6, pp, 681–688, June, 2008.     

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

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

GABA receptor agonists in the medial preoptic area and maternal behavior in lactating rats

We studied the effects of injecting agonists of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) muscimol (GABA-A receptor agonist) and baclofen (GABA-B receptor agonist) in the medial preoptic area (MPOA) and neighboring brain regions, the bed nucleus of the stria terminalis (BNST), and lateral preoptic area (LPO) on maternal behavior. Lactating female rats were implanted with bilateral cannulae in the MPOA/BNST on day 1 postpartum. On day 5, a maternal behavior test was conducted in the home cage after females received injections of muscimol or baclofen (0, 12.5, 50 or 200 ng per side). On day 7, after MPOA/BNST injections, a second maternal behavior test was conducted with pups placed at the end of a T-runway projecting from the home cage. Finally, after injections on day 9 maternal aggression, olfaction, and locomotor behavior were tested. The GABA receptor agonists injected in the MPOA/BNST produced dose-dependent deficits in all components of maternal behavior, including maternal aggression, except licking. Muscimol produced deficits in the active component, nest building at lower doses than baclofen, both agonists produced deficits in retrieving, while baclofen produced deficits in passive components (hovering and crouching over pups) at lower doses than muscimol. Both GABA receptor agonists increased locomotor activity and reduced olfactory responsiveness but these were only correlated with deficits in retrieving and crouching in baclofen-treated females.     

Medial preoptic and anterior hypothalamic lesions: influences on aggressive behavior in female hamsters.

Bilateral radio-frequency lesions in the medial preoptic area (MPOA) were found to reduce aggressiveness and to increase the incidence of submissive responding in female hamsters that were paired against other females. The reduced aggressiveness of females with MPOA lesions appeared to be relatively independent of their hormonal state, since ovariectomy and subsequent replacement therapy with 200 μg a day of testosterone propionate (TP) had no influence on the low levels of aggression exhibited by these females. In contrast to females with lesions in the MPOA, females with lesions in anterior hypothalamus (AHA) exhibited increased aggressiveness in the postoperative tests preceding ovariectomy. Ovariectomy reduced the frequency with which AHA-lesioned females exhibited fights, attack-chase sequences, and low intensity aggressive acts, and TP injections failed to reinstate precastration levels of these behaviors.     

Characteristics of estradiol receptor system of the anterior hypothalamus and adenohypophysis in guinea pigs

The presence of a specific estradiol-receptor system (E₂-R) with limited capacity and with a high degree of strength of formation of the E₂-R complex was demonstrated in the cytosol of the adenohypophysis, and anterior hypothalamus of guinea pigs in experiments in vivo and in vitro. The physicochemical properties of the E₂-R system of the adenohypophysis and anterior hypothalamus differ in certain parameters. The E₂-R complexes of the cytosols of the adenohypophysis and anterior hypothalamus formed at different temperatures are not identical.Laboratory of Endocrinology, All-Union Research Institute of Obstetrics and Gynecology, Ministry of Health of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR L. S. Persianinov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 85, No. 1, pp. 70–73, January, 1978.     

Direct projections from the sacral spinal cord to the medial preoptic area in cat and guinea pig

The medial preoptic area (MPO) plays an important role in many behavioral, autonomic and endocrine functions, including micturition and genital responses. Although afferents of the MPO have been studied extensively, it is unknown whether direct lumbosacral-MPO projections exist that could convey afferent information from the pelvic organs. We hypothesized that, if such direct projections exist, MPO projecting cells would be located in the lateral part of the sacral cord, where primary afferents from pelvic and pudendal nerves terminate. We used retro- and anterograde tracing techniques in cat and guinea pig to study this. In cats, injections in the MPO resulted in labeled cells throughout the spinal cord, but with the highest density in the S1–S2 segments. In guinea pigs, labeled cells were found exclusively in the S1–S3 segments after MPO injections. Labeled cells in the sacral segments were not located in the lateral parts of the gray matter, but were found in the medial laminae VI–VII and dorsal lamina VIII in cats, and mainly in lamina X in guinea pigs. Anterograde tracing results after injections in the sacral cord in cats or guinea pigs showed labeled fibers in the MPO, just ventral to the anterior commissure. The central location of the cells of origin within the sacral cord, together with the termination pattern of the spino-MPO projections, strongly suggest a role for the spino-MPO pathway in the sensory relay of pelvic viscera, important for micturition and genital responses.     

Preoptic area estradiol-concentrating neurons project to the hypothalamus in female rats

Summary Estradiol (E₂)-concentrating neurons afferent to the ventromedial nucleus of the hypothalamus (VMH) were identified by combining fluorescent retrograde tracing with steroid hormone autoradiography. The majority of E₂-concentrating neurons that projected to the VMH were located in the medial preoptic area. In the entire medial preoptic area, 10.0% of the E₂-sensitive neurons sent axons that terminated in the VMH. Twenty percent of the E₂-concentrating neurons located in the periventricular preoptic area projected to the VMH. Of the E₂-concentrating neurons found in the medial preoptic nucleus, 8.0% sent axons directly to the VMH. The bed nucleus of the stria terminalis, septum, and medial amygdala contained very few E₂-receptive neurons that projected to the VMH. Preoptic area E₂-concentrating neurons that project to the VMH may be part of a neural circuit that influences reproduction.Abbreviations ac Anterior commisure - ARH Arcuate nucleus - AVPv Anteroventral periventricular nucleus - BST Bed nucleus of the stria terminalis - fx Fornix - LPO Lateral preoptic area - ME Median eminence - MPN Medial preoptic nucleus - mt Mammilothalamic tract - och Optic chiasm - sm Stria medullaris - VMH Ventromedial nucleus of the hypothalamus     

Effects of estradiol,sex, and season on estrogen receptor alpha mRNA expression and forebrain morphology in adult green anole lizards

Steroid hormones, especially estradiol, facilitate reproductive behaviors in male and female rodents and birds. In green anole lizards estradiol facilitates receptivity in females but, unlike in some other species, is not the activating hormone for courtship and copulatory behavior in males. Instead, testicular androgens directly facilitate male courtship and copulation. Yet, activity of the estradiol synthesizing enzyme aromatase is higher in the brain of male than female green anoles, and it is increased during the breeding compared to the non-breeding season. The functional relevance of these differences in local estradiol production is unknown. They might prime the male forebrain to facilitate production of appropriate sexual behaviors, perhaps by modifying morphology of relevant brain regions. In addition, we recently reported increased expression of estrogen receptor alpha (ERα) in selected brain regions in females compared to males [Beck LA, Wade J (2009b) Sexually dimorphic estrogen receptor α mRNA expression in the preoptic area and ventromedial hypothalamus of green anole lizards. 55:398–403]. Thus, it is possible that the hormone serves to downregulate its receptor in males to inhibit the expression of estradiol-dependent receptive behaviors. To begin to address these ideas, the present study examines the effects of estradiol treatment, sex, and season on forebrain morphology and ERα mRNA abundance in three regions important for anole reproductive behavior—the preoptic area, ventromedial amygdala, and ventromedial hypothalamus. While a number of effects of sex and season on forebrain morphology were detected, direct effects of estradiol treatment on these measures were minimal. ERα expression was greatest in the ventromedial hypothalamus, and a large female-biased sex difference was detected in this area alone; it resulted from estradiol-treated animals. These results indicate a sex- and region-specific mechanism by which estradiol can modify ERα expression in the green anole and could impact the expression of female-typical receptivity.     

Endothelin B receptor-like immunoreactivity is associated with LHRH-immunoreactive fibers in the rat hypothalamus

Antisera were raised against amino-acid residues 425–439 of the rat endothelin B (ET_B) receptor. Massive ET_B receptor immunoreactive fibers were observed in the median eminence and organum vasculosum lamina terminalis of rats. Double labeling studies with anti-luteinizing hormone-releasing hormone (LHRH) antiserum revealed that ET_B receptor-like immunoreactivity associated with LHRH-immunoreactive fibers in these areas. However, ET_B receptor-like immunoreactivity was not detected in LHRH-immunoreactive somata. This result suggests that endothelin affects the LHRH neuronal systems via ET_B receptors on the axon at the terminal field.     

Role of the cholinergic mechanisms of the ventrolateral preoptic area of the hypothalamus in regulating the state of sleep and waking in pigeons

Maintenance of waking in pigeons was found to be linked with the mechanisms of activation of muscarinic (M-) cholinergic receptors of the ventrolateral preoptic area of the hypothalamus. “Muscarinic” waking was characterized by an increase in the power of the EEG spectrum at 0.75–12 Hz and an increase in brain temperature. Activation of nicotinic (N-) cholinergic receptors in this area was associated with an increase in the duration of slow sleep, a decrease in the spectral EEG power at 0.75–7 Hz, and a decrease in brain temperature in this state; hyperactivation of these receptors led to the development of waking, where waking episodes were associated with significant decreases in brain temperature. Blockade of M-and N-cholinergic receptors resulted in changes in the sleep-waking cycle and thermoregulation which were oppose to those seen on receptor activation. It is suggested that M-and N-cholinergic receptors of the ventrolateral preoptic area of the pigeon hypothalamus are involved in regulating sleep and waking, their effects being associated with influences on the GABAergic system of this area. __________ Translated from Rossiiskii Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 93, No. 2, pp. 189–200, February, 2007.     

Efferent projections from the median preoptic nucleus to sleep- and arousal-regulatory nuclei in the rat brain

The median preoptic nucleus (MnPO) has been implicated in the regulation of hydromineral balance and cardiovascular regulation. The MnPO also contains neurons that are active during sleep and in response to increasing homeostatic pressure for sleep. The potential role of these neurons in the regulation of arousal prompted an analysis of the efferent projections from the MnPO. Anterograde and retrograde neuroanatomical tracers were utilized to characterize the neural connectivity from the MnPO to several functionally important sleep- and arousal-regulatory neuronal systems in the rat brain. Anterograde terminal labeling from the MnPO was confirmed within the core and extended ventrolateral preoptic nucleus. Within the lateral hypothalamus, labeled axons were observed in close apposition to proximal and distal dendrites of hypocretin/orexin immunoreactive (IR) cells. Projections from the MnPO to the locus coeruleus were observed within and surrounding the tyrosine hydroxylase-IR cell cluster. Labeled axons from the MnPO were mostly observed within the lateral division of the dorsal raphé nucleus and heavily within the ventrolateral periaqueductal gray. Few anterogradely labeled appositions were present juxtaposed to choline acetyltransferase-IR somata within the magnocellular preoptic area. The use of retrogradely transported neuroanatomical tracers placed within the prospective efferent terminal fields supported and confirmed findings from the anterograde tracer experiments. These anatomical findings support the hypothesis that MnPO neurons function to promote sleep by inhibition of orexinergic and monoaminergic arousal systems and disinhibition of sleep regulatory neurons in the ventrolateral preoptic area.     

Absence of progestin receptors alters distribution of vasopressin fibers but not sexual differentiation of vasopressin system in mice

Perinatal estrogens increase the number of vasopressin-expressing cells and the density of vasopressin-immunoreactive fibers observed in adult male rodents. The mechanism of action of estrogens on sexual differentiation of the extra-hypothalamic vasopressin system is unknown. We hypothesized that the sexually dimorphic expression of progestin receptors (PRs) during development would masculinize vasopressin expression in mice. We compared the number of vasopressin-expressing cells in the bed nucleus of the stria terminalis (BNST) and medial amygdala and the density of vasopressin-immunoreactive fibers in several brain regions of male and female wild type and PRKO mice using in situ hybridization and immunohistochemistry. As expected, sex differences in vasopressin cell number were observed in the BNST and medial amygdaloid nucleus. Vasopressin-immunoreactive fiber density was sexually dimorphic in the lateral septum, lateral habenular nucleus, medial amygdaloid nucleus, and mediodorsal thalamus. Sex differences were also observed in the principal nucleus of the BNST and medial preoptic area but not in the dorsomedial hypothalamus, which are thought to receive vasopressin innervation from the suprachiasmatic nucleus. Deletion of PRs did not alter the sex difference in vasopressin mRNA expression and vasopressin fiber immunoreactivity in any area examined. However, deletion of PRs increased the density of vasopressin fiber immunoreactivity in the lateral habenular nucleus. Our data suggest that PRs modulate vasopressin levels, but not sexual differentiation of vasopressin innervation in mice.     

Immunocytochemical colocalization of GABA-B receptor subunits in gonadotropin-releasing hormone neurons of the sheep

GABA has been shown to play an important role in the control of gonadotropin-releasing hormone (GnRH) and luteinizing hormone secretion in many mammals. In sheep, seasonal differences in the ability of GABA-B receptor antagonists to alter pulsatile luteinizing hormone secretion have led to the hypothesis that this receptor subtype mediates the increased inhibitory effects of estradiol on GnRH and luteinizing hormone pulse frequency seen during the non-breeding season (anestrus). The aim of the present study was to use multiple-label immunocytochemistry to determine if ovine GnRH neurons contain the GABA-B receptor subunits R1 and/or R2, and to determine whether there are seasonal differences in the colocalization of these subunits in GnRH neurons. A majority of GnRH cells in the preoptic area, anterior hypothalamic area, and medial basal hypothalamus of both breeding season and anestrous ewes contained either GABA-B R1 or R2 subunits; a subset of GnRH neurons in breeding season (42%) and anestrous ewes (60%) contained both subunits. In contrast to colocalization within cell bodies, GnRH fibers in the median eminence did not colocalize GABA-B receptor subunits. Although the percentage of GnRH neurons expressing GABA-B receptor subunits tended to be higher in anestrus than in the breeding season, there were no significant seasonal differences in R1 and R2 subunit colocalization in GnRH cell bodies. Thus, while GABA may act directly on GnRH cell bodies via GABA-B receptors in the sheep, any role that GABA-B receptors may play in seasonal reproductive changes is likely mediated by other neurons afferent to GnRH cells.     

Effects of RU486 in the expression of progesterone receptor isoforms in the hypothalamus and the preoptic area of the rat during postpartum estrus

In several mammalian species females undergo postpartum estrus, a brief period of ovulation and sexual receptivity that in rats usually occurs during the first 24 h following parturition. The maximal lordotic expression occurs at 12 h after the initiation of parturition and depends on intracellular progesterone receptor (PR). We studied the regulation of PR expression by its antagonist, RU486 in the hypothalamus and the preoptic area of the rat during postpartum estrus by Western blot. Adult female rats were treated with RU486 (1.25 and 5 mg) 3 h after parturition, and Western blot was performed to assess the expression of PR-A and PR-B at 12 h postpartum. RU486 (1.25 and 5 mg) reduced the expression of PR-A (63% and 95%) and that of PR-B (75% and 99%), respectively in the preoptic area whereas it had no effects in the hypothalamus. These results suggest a differential regulation of PR expression in the rat brain during postpartum estrus.     

Dopamine, the medial preoptic area, and male sexual behavior

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