Acrocomia aculeata oil: Beneficial effects on cyclophosphamide-induced reproductive toxicity in male rats.

This study aimed to evaluate the effects of the extracted oil of Acrocomia aculeata pulp in preventing or mitigating the reproductive toxicity induced by cyclophosphamide (CP) in male rats. Adult male rats were segregated into seven groups that received vehicle, 100 mg/kg/day of CP, or 10 mg/kg/day of ß-carotene or 3 or 30 mg/kg/day of A. aculeata oil co-administered with CP. A. aculeata oil exhibited a high content of ß-carotene. CP treatment induced reproductive toxicity in the animals, as it changed the reproductive organs weight, hormone levels, sperm counts and testicular histology. In contrast, co-administration of A. aculeata improved CP-induced alterations in these parameters. A. aculeata oil also increased the gene Ckit expression and normalised the antioxidant enzymes levels which were changed by CP. The A. aculeata oil is capable of protecting the male reproductive system from the adverse effects of CP, possibly by acting as an antioxidant and increasing the Ckit gene expression.

In vitro development of secondary follicles from pre-pubertal and adult goats cultured in two-dimensional or three-dimensional systems.

The aim of this study was to evaluate the influence of two-dimensional (2D) and three-dimensional (3D) alginate culture systems on in vitro development of pre-antral caprine follicles. In addition, the influence of the reproductive age of the ovary donor on the in vitro culture success was investigated. Pre-antral follicles from pre-pubertal or adult goats were isolated and cultured directly on a plastic surface (2D) or encapsulated in an alginate-based matrix (3D). After 18 days, the oocytes underwent in vitro maturation (IVM) and in vitro fertilization (IVF) to produce embryos. The 3D system showed higher rates of follicle survival, lower rates of oocyte extrusion, and a greater number of recovered oocytes for IVM and IVF (P < 0.05). Only pre-antral follicles from adult animals produced MII oocytes and embryos. The estradiol concentrations increased from day 2 to day 12 of culture in all groups tested (P < 0.05). Conversely, progesterone concentrations were lower in 3D-cultured follicles than in 2D-cultured follicles, with differences on days 2 and 6 of culture (P < 0.05). We provide compelling evidence that a 2D or 3D alginate in vitro culture system offers a promising approach to achieving full in vitro development of caprine pre-antral follicles to produce mature oocytes that are capable of fertilization and viable embryos.

Stress in neonatal rats with different maternal care backgrounds: monoaminergic and hormonal responses.

The first 2 weeks of life in rats are known as the stress hyporesponsive period because stress responses in pups are diminished as compared to adult animals. However, it is considered a critical period in development in which infant rats are susceptible to environmental events, such as stressful stimuli and quality of maternal care received. These early life events have long-lasting effects, shaping a variety of outcomes, such as stress responsivity. This study investigated the effects of maternal care and sex differences on the response to an aversive stimulus in rat pups from high (HL) and low licking (LL) mothers. Plasma corticosterone, oxytocin (OT), and central monoaminergic activity in 13-day-old rats submitted to cold stress were analyzed. Stress increased plasma corticosterone and marginally decreased hypothalamic dihydroxyphenylacetic acid/dopamine ratio. HL pups showed higher levels of plasma OT than LL pups. The maternal effect was also detected in the hippocampus, in which 5-hydroxyindole-3-acetic acid/serotonin ratio was increased in HL pups, independently of the sex and stress. Investigating the early life events is useful not only into understand the neurobiological and hormonal mechanisms underlying maternal and stressful influences on infant development into a healthy or psychopathological adult phenotype, but also to unveil the immediate outcomes on infancy.

Stress in Neonatal Rats with Different Maternal Care Backgrounds: Monoaminergic and Hormonal Responses.

The first 2 weeks of life in rats are known as the stress hyporesponsive period because stress responses in pups are diminished as compared to adult animals. However, it is considered a critical period in development in which infant rats are susceptible to environmental events, such as stressful stimuli and quality of maternal care received. These early life events have long-lasting effects, shaping a variety of outcomes, such as stress responsivity. This study investigated the effects of maternal care and sex differences on the response to an aversive stimulus in rat pups from high (HL) and low licking (LL) mothers. Plasma corticosterone, oxytocin, and central monoaminergic activity in 13-day-old rats submitted to cold stress were analyzed. Stress increased plasma corticosterone and marginally decreased hypothalamic dihydroxyphenylacetic acid/dopamine (DOPAC/DA) ratio. HL pups showed higher levels of plasma oxytocin than LL pups. The maternal effect was also detected in the hippocampus, in which 5-hydroxyindole-3-acetic acid/serotonin (5-HIAA/5-HT) ratio was increased in HL pups, independently of the sex and stress. Investigating the early life events is useful not only into understand the neurobiological and hormonal mechanisms underlying maternal and stressful influences on infant development into a healthy or psychopathological adult phenotype, but also to unveil the immediate outcomes on infancy.

Role of sex steroids in progesterone and corticosterone response to acute restraint stress in rats: sex differences.

Adrenal progesterone secretion increases along with corticosterone in response to stress in male and female rats to modulate some stress responses. Here we investigated the role of sex steroids in sex differences in the progesterone response to 60 min of restraint stress in adult male and female rats. Comparisons between males and females in the progesterone response were evaluated in parallel with corticosterone responses. From day 5 to 7 after gonadectomy, female and male rats were treated with estradiol or testosterone, respectively (OVX-E and ORCH-T groups), or oil (OVX and ORCH groups). Female rats in proestrus, intact and 7 d adrenalectomized (ADX) male rats were also studied. At 10:00 h, blood samples were withdrawn via an implanted jugular cannula before (-5 min), during (15, 30, 45, 60 min) and after (90 and 120 min) restraint stress to measure plasma progesterone and corticosterone concentrations by radioimmunoassay. Intact male and proestrus female rats exhibited similar progesterone responses to stress. Gonadectomy did not alter the amount of progesterone secreted during stress in female rats but decreased secretion in male rats. Unlike corticosterone, the progesterone response to stress in females was not influenced by estradiol. In males, testosterone replacement attenuated the progesterone and corticosterone responses to stress. Basal secretion of progesterone among intact, ORCH and ADX males was similar, but ADX-stressed rats secreted little progesterone. Hence, the gonads differently modulate adrenal progesterone and corticosterone responses to stress in female and male rats. The ovaries enhance corticosterone but not progesterone secretion, while the testes stimulate progesterone but not corticosterone secretion.

Long-term effects of perinatal androgenization on reproductive parameters of male rat offspring androgenization and male rat reproduction.

It is known that during sex differentiation, fetal androgens are critical determinants of the male phenotype. Although testosterone is necessary for normal development of male sexual behavior, perinatal androgen treatment can result in disruption of normal male sexual reproduction. Pregnant Wistar rats were administered either corn oil (vehicle) or testosterone propionate at 0.2 mg/kg from gestational day 12 until the end of lactation and the reproductive function of male offspring was evaluated at 90 (adulthood) and 270 (middle age) days of age. Perinatal androgenization in the rat provoked a reduction in sperm production and reserves in adulthood that did not affect fertility and did not persist at more advanced ages, as shown by the results at post-natal day 270. If perinatal androgenization promotes similar effects in humans of reproductive age, the results of the present work can impact male reproduction health, given the less efficient spermatogenesis and lower sperm reserves in the human epididymis, compared to rodents.

Acute stress anticipates and amplifies the luteinizing hormone pre-ovulatory surge in rats: Role of noradrenergic neurons.

The stress experienced during rape seems to facilitate ovulation since the pregnancy rate in raped women is higher than that resulting from consensual intercourse. Adrenal progesterone, as well as central norepinephrine, is released in stressful situations. At adequate estrogenic levels, one of the main actions of progesterone is to anticipate the preovulatory LH surge through noradrenaline release. We aimed to investigate whether acute stresses that mimic those of rape (exposure to predator, restraint and cervix stimulation) applied on the proestrus morning in female rats could release progesterone, activate the noradrenergic neurons and facilitate the occurrence of the LH surge. Female rats were submitted to jugular vein cannulation immediately following acute stress: restraint (R), exposure to cat (P), uterine cervix stimulation (CS) applied individually or in association (SA). Non-stressed rats were used as control. Blood samples were collected from 11:00-18:00 h for LH, progesterone, corticosterone and estradiol measurements. Double labeling for c-Fos and tyrosine hydroxylase (TH) was examined in A1, A2 and A6 noradrenergic neurons after stresses. The SA group showed a greater stress-induced increase in progesterone compared to the other groups and the preovulatory LH surge was anticipated and amplified. This effect of SA seems to be related to the higher number of c-Fos/TH + neurons in the A1 and A2. The effect of anticipating the preovulatory surge of LH could in part elucidate why, in raped women, conception can occur in phases of the menstrual cycle other than the ovulatory phase facilitating the occurrence of pregnancies.

Photobiomodulation can improve ovarian activity in polycystic ovary syndrome-induced rats.

Follicular cystic ovary disease is a common reproductive disorder in women and females of domestic animals, characterized by anovulation and the persistence of follicle is a common cause of reproductive failure in mammalian. Polycystic ovary syndrome (PCOS) is characterized by hyperandrogenism (HA), chronic anovulation and polycystic ovaries, and it is a common reproductive endocrine disease with clinical manifestations including hirsutism, acne, infertility and obesity that can affect 5-20% of women in their reproductive age. Photobiomodulation (PBM) has been investigated and used in clinical practice, related to biomodulatory influences on cellular functions in animals and humans, both in vivo and in vitro. In this study, we include endocrine and reproductive features in a rat model for PCOS and the effects of PBM on ovarian activities. Forty-five adult female Wistar rats PCOS-induced by a single dose of the estradiol valerate (EV) were used in the study. After the EV injection for PCO induction, rats were divided into 9 groups (n = 5/group) named C30, C45 and C60 (Control group), S30, S45 and S60 (PCO group) and L30, L45 and L60 (PCO/Laser group). The rats were irradiated with laser 3 times/week. The results shown that EV PCO-induced rats had increased body mass, reduced ovary mass, and reduced GSI. The plasma levels of P4 and T were increased, and the LH plasma level was decreased by PBM stimulation. The number of ovarian follicles and corpus luteum were increased, and the number of ovarian cysts was decreased by PBM stimulation. Thus, reproductive and endocrine characteristics were modulated by PBM.

Noradrenaline release in the medial preoptic area during the rat oestrous cycle: temporal relationship with plasma secretory surges of prolactin and luteinising hormone.

During the rat oestrous cycle, the afternoon of pro-oestrous is characterised by preovulatory surges of luteinising hormone (LH) and prolactin. On the afternoon of oestrous, a secretory surge of prolactin has also been reported. Because the medial preoptic area (MPOA) is known to regulate prolactin and LH secretory surges and noradrenaline has been demonstrated to stimulate these hormones release, we evaluated whether noradrenaline release in the MPOA was temporally associated with plasma prolactin and LH surges in cycling rats. During the 4 days of oestrous cycle, noradrenaline concentrations were determined in microdialysates from the MPOA, collected at 30-min intervals from 10.30 h to 19.00 h. Plasma prolactin and LH levels were measured in blood samples withdrawn hourly from 14.00 h to 19.00 h on pro-oestrous and from 13.00 h to 18.00 h on the other days of the cycle. On the afternoons of both pro-oestrous and oestrous, noradrenaline levels increased at 14.00 h and remained elevated until 16.30 h. Conversely, they were low and constant throughout metoestrous and dioestrous. Correlating with noradrenaline release in the MPOA, plasma prolactin surges occurred during the afternoons of both pro-oestrous and oestrous. On pro-oestrous, the afternoon LH surge was also preceded by the increase in MPOA noradrenaline whereas, during oestrous, LH secretion was low and unaltered. A temporal association between noradrenaline release and prolactin secretion suggests that noradrenergic neurotransmission in the MPOA regulates prolactin surges in female rats. Moreover, our data also suggest that MPOA noradrenaline requires specific conditions to physiologically regulate LH secretion, which seems to occur during the afternoon of pro-oestrous.

Reproductive experience modifies dopaminergic function, serum levels of prolactin, and macrophage activity in female rats.

Reproductive experience (RE), i.e. pregnancy and lactation, induces physiological changes in mammals. Recent data show that neuroimmune interactions are modulated by a diversity of events involving neurotransmitters and neuropeptides. These molecules, particularly dopamine (DA), were reported to mediate the relevant cross talk between immune and neuroendocrine systems. Moreover, DA-mediated regulation of leukocyte function is a reasonable approach to investigate the DA-operated regulatory switch for immune-competent cells, such as macrophages. Therefore, the goals of the present study were to determine the effects of RE on: (1) dopaminergic function through hypothalamic levels of DA, dihydroxyphenylacetic acid (DOPAC), homovanilic acid (HVA), serotonin (5-HT), and 5-hydroxyindole acetic acid (5-HIAA); (2) basal levels of circulating prolactin (PRL); and (3) activity of peritoneal macrophage (phagocytosis and oxidative burst). A total of 16 adult (200-250 g) female Wistar rats were used, divided in two groups: nulliparous and primiparous. Approximately 2-3 weeks after weaning pups from the primiparous group, both groups of rats were tested. The findings indicate that: (1) DOPAC concentrations, DOPAC/DA and HVA+DOPAC/DA ratios decreased in primiparous rats as compared to virgin rats, (2) primiparous rats showed significantly lower serum PRL levels, and (3) phorbol miristate acetate (PMA)-induced oxidative burst was decreased in peritoneal macrophage from primiparous rats as compared to virgin rats. To test the possible positive correlation between serum levels of PRL and the intensity of oxidative burst by peritoneal macrophage, an extra experiment was done with adult virgin female rats treated with domperidone, an antagonist of DA receptors. Domperidone-treated animals showed increased serum levels of PRL and simultaneous increase in peritoneal macrophage oxidative burst. Thus, suggesting an indirect participation of hyperprolactinemia, induced by this treatment in peritoneal macrophage activity of female rats. These results suggest that a previous RE can modulate the activity of dopaminergic hypothalamic systems, while decreasing PRL serum levels and the oxidative burst of peritoneal macrophage. The neurochemical and hormonal RE-induced changes correlate with the immune alterations.

Neuroprotective effect of ketamine/xylazine on two rat models of Parkinson's disease.

There is a great concern in the literature for the development of neuroprotectant drugs to treat Parkinson's disease. Since anesthetic drugs have hyperpolarizing properties, they can possibly act as neuroprotectants. In the present study, we have investigated the neuroprotective effect of a mixture of ketamine (85 mg/kg) and xylazine (3 mg/kg) (K/X) on the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or 6-hydroxydopamine (6-OHDA) rat models of Parkinson's disease. The bilateral infusion of MPTP (100 microg/side) or 6-OHDA (10 microg/side) into the substantia nigra pars compacta of adult male Wistar rats under thiopental anesthesia caused a modest (~67%) or severe (~91%) loss of tyrosine hydroxylase-immunostained cells, respectively. On the other hand, an apparent neuroprotective effect was observed when the rats were anesthetized with K/X, infused 5 min before surgery. This treatment caused loss of only 33% of the nigral tyrosine hydroxylase-immunostained cells due to the MPTP infusion and 51% due to the 6-OHDA infusion. This neuroprotective effect of K/X was also suggested by a less severe reduction of striatal dopamine levels in animals treated with these neurotoxins. In the working memory version of the Morris water maze task, both MPTP- and 6-OHDA-lesioned animals spent nearly 10 s longer to find the hidden platform in the groups where the neurotoxins were infused under thiopental anesthesia, compared to control animals. This amnestic effect was not observed in rats infused with the neurotoxins under K/X anesthesia. These results suggest that drugs with a pharmacological profile similar to that of K/X may be useful to delay the progression of Parkinson's disease.

Ovarian steroids but not the locus coeruleus regulate stress-induced prolactin secretion in female rats.

Stress has been proposed to stimulate prolactin release if its prestress levels are low, or to inhibit it if they are elevated, but the role of ovarian-steroid fluctuations in the prolactin stress response is not yet clearly understood. Because the noradrenergic nucleus locus coeruleus has been implicated in stress responses and generation of prolactin surges in female rats, the present study aimed to evaluate stress-induced prolactin secretion under different hormonal conditions, determining the effect of locus coeruleus lesion on each response. Blood samples were withdrawn from a jugular vein catheter 5 and 2 min before and 2, 5, 10, 15 and 30 min after ether stress in male rats, female rats during the oestrous cycle and ovariectomised rats treated with oil (OVX), oestradiol (OVE) or oestradiol plus progesterone (OVEP). Increased Fos immunoreactivity demonstrated locus coeruleus activation following ether stress. Ether stress increased both low (at 16.00 h in males, in OVX and on dioestrous and at 11.00 h on pro-oestrous and oestrous) and high plasma prolactin (at 16.00 h on oestrous and in OVE), but it decreased elevated prolactin levels during the afternoon on pro-oestrous and in OVEP. Locus coeruleus lesion prevented prolactin surges during the afternoon on pro-oestrous, oestrous, OVE and OVEP but did not modify either pattern (i.e. increase or decrease) or degree of prolactin stress response under any condition studied. The present data therefore suggest that oestradiol and progesterone modulate stress-induced prolactin secretion, regardless of its prestress levels. Moreover, the locus coeruleus is probably not involved in prolactin response to stress and most likely has a specific role in prolactin surges induced by ovarian steroids.

Neuropeptide Y in the medial basal hypothalamus and medial preoptic area during the induction of LH surge may be controlled by locus coeruleus.

The multiple control of gonadotropin releasing hormone (GnRH)/luteinizing hormone (LH) secretion involves locus coeruleus (LC) and neuropeptide Y (NPY). The objective of the present study was to analyze the possible contribution of the LC to the control of NPY activity in the medial basal hypothalamus (MBH) and medial preoptic area (MPOA) during the LH surge induced by estrogen (E(2)) and progesterone (P(4)). Ovariectomized adult Wistar rats were submitted to the hormone replacement and to the LC bilateral lesion (lesioned groups) or sham surgery (control groups). On the day of the experiment the rats were decapitated at 11:00, 13:00, 15:00 and 17:00 h for plasma and brain collection. Plasma LH was determined by radioimmunoassay. MBH and MPOA were microdissected for the measurement of NPY by enzyme immunoassay. NPY mRNA levels in MBH were assessed by the ribonuclease protection assay. The results showed that LC lesion: decreased the plasma LH; increased the content of NPY in the MBH and reduced the increase of NPY content in the MPOA during afternoon in which LH surge was induced. The increased NPY content in MBH was not associated with an increase of the respective mRNA content, suggesting the action of postranscriptional and/or postranslational mechanisms. In conclusion, the NPY activity in the MPOA on LH surge induced by estrogen and progesterone could be controlled by LC through two ways, at least: one direct way, by the release of NPY from LC neurons terminals that innervate the MPOA and they release NA and NPY; one indirect way, by the control of release but not synthesis of NPY from neurons in the MBH which innervate the MPOA.

Neonatal handling and reproductive function in female rats.

Neonatal handling induces anovulatory estrous cycles and decreases sexual receptivity in female rats. The synchronous secretion of hormones from the gonads (estradiol (E2) and progesterone (P)), pituitary (luteinizing (LH) and follicle-stimulating (FSH) hormones) and hypothalamus (LH-releasing hormone (LHRH)) are essential for the reproductive functions in female rats. The present study aimed to describe the plasma levels of E2 and P throughout the estrous cycle and LH, FSH and prolactin (PRL) in the afternoon of the proestrus, and the LHRH content in the medial preoptic area (MPOA), median eminence (ME) and medial septal area (MSA) in the proestrus, in the neonatal handled rats. Wistar pup rats were handled for 1 min during the first 10 days after delivery (neonatal handled group) or left undisturbed (nonhandled group). When they reached adulthood, blood samples were collected through a jugular cannula and the MPOA, ME and MSA were microdissected. Plasma levels of the hormones and the content of LHRH were determined by RIA. The number of oocytes counted in the morning of the estrus day in the handled rats was significantly lower than in the nonhandled ones. Neonatal handling reduces E2 levels only on the proestrus day while P levels decreased in metestrus and estrus. Handled females also showed reduced plasma levels of LH, FSH and PRL in the afternoon of the proestrus. The LHRH content in the MPOA was significantly higher than in the nonhandled group. The reduced secretion of E2, LH, FSH and LHRH on the proestrus day may explain the anovulatory estrous cycle in neonatal handled rats. The reduced secretion of PRL in the proestrus may be related to the decreased sexual receptiveness in handled females. In conclusion, early-life environmental stimulation can induce long-lasting effects on the hypothalamus-pituitary-gonad axis.

Locus coeruleus norepinephrine regulates the surge of prolactin during oestrus.

A secondary surge of prolactin has been recently characterised on the afternoon of oestrus. Because the noradrenergic nucleus locus coeruleus participates in the genesis of the pro-oestrous and steroid-induced surges of prolactin, the aim of the present study was to investigate the importance of locus coeruleus norepinephrine in the generation of the prolactin surge of oestrus. For this purpose, we initially re-evaluated the profile of prolactin secretion during the oestrous cycle to verify whether this surge of prolactin was physiological and specific to the day of oestrus. Thereafter, the following were evaluated: (i) the effect of locus coeruleus lesion on the secondary surge of prolactin and on norepinephrine concentration in the medial preoptic area (MPOA), medial basal hypothalamus (MBH) and paraventricular nucleus (PVN) during the day of oestrus and (ii) locus coeruleus neurones activity during the same day by Fos immunoreactivity. Locus coeruleus lesion completely blocked the prolactin surge of oestrus in all rats studied and also significantly reduced norepinephrine concentration in the MPOA, MBH and PVN during the day of oestrus. The number of double-labelled tyrosine hydroxylase/Fos immunoreactive neurones in locus coeruleus was significantly higher at 14.00 h of oestrus, suggesting an increase in its activity preceding the prolactin surge that generally occurs at 15.00 h. Therefore, the increase in locus coeruleus activity on the afternoon of oestrus supports the data obtained with bilateral lesion of this nucleus, suggesting a stimulatory role of locus coeruleus norepinephrine in the genesis of the secondary surge of prolactin.

Kisspeptin regulates tuberoinfundibular dopaminergic neurones and prolactin secretion in an oestradiol-dependent manner in male and female rats.

Prolactin (PRL) secretion is inhibited by hypothalamic dopamine. Kisspeptin controls luteinising hormone (LH) secretion and is also involved in PRL regulation. We further investigated the effect of kisspeptin-10 (Kp-10) on the activity of tuberoinfundibular dopaminergic (TIDA) neurones and the role of oestradiol (E2 ) in this mechanism. Female and male rats were injected with i.c.v. Kp-10 and evaluated for PRL release and the activity of dopamine terminals in the median eminence (ME) and neurointermediate lobe of the pituitary (NIL). Kp-10 at the doses of 0.6 and 3 nmol increased plasma PRL and decreased 4-dihydroxyphenylacetic acid (DOPAC) levels in the ME and NIL of ovariectomised (OVX), E2 -treated rats but had no effect in OVX. In gonad-intact males, 3 nmol Kp-10 increased PRL secretion and decreased DOPAC levels in the ME but not in the NIL. Castrated males treated with either testosterone or E2 also displayed increased PRL secretion and reduced ME DOPAC in response to Kp-10, whereas castrated rats receiving oil or dihydrotestosterone were unresponsive. By contrast, the LH response to Kp-10 was not E2 -dependent in either females or males. Additionally, immunohistochemical double-labelling demonstrated that TIDA neurones of male rats contain oestrogen receptor (ER)-α, with a higher proportion of neurones expressing ERα than in dioestrous females. The dopaminergic neurones of periventricular hypothalamic nucleus displayed much lower ERα expression. Thus, TIDA neurones express ERα in male and female rats, and kisspeptin increases PRL secretion through inhibition of TIDA neurones in an E2 -dependent manner in both sexes. These findings provide new evidence about the role of kisspeptin in the regulation of dopamine and PRL.

Role of nitric oxide in rat locus coeruleus in hypoxia-induced hyperventilation and hypothermia.

The locus coeruleus modulates the ventilatory and thermoregulatory response to hypoxia and contains nitric oxide synthase. Therefore, we examined the effects of L-NAME unilaterally microinjected into the locus coeruleus on hypoxic hyperventilation and hypothermia. Ventilation and body temperature were measured before and after microinjection of L-NAME (100 nmol/0.5 microl) into the locus coeruleus, followed by hypoxia. Control rats received microinjection of D-NAME (an inactive enantiomer of L-NAME). Under normoxia, L-NAME treatment did not affect ventilation or body temperature. D-NAME did not affect hypoxia-induced hyperventilation and hypothermia. L-NAME treatment reduced the ventilatory response to hypoxia but did not affect hypoxia-induced hypothermia. These data suggest that nitric oxide in the locus coeruleus is involved in the ventilatory response to hypoxia, exercising an inhibitory modulation on the locus coeruleus neurons, but plays no role in hypoxia-induced hypothermia.

Angiotensinergic neurons physiologically inhibit prolactin, growth hormone, and thyroid-stimulating hormone, but not adrenocorticoptropic hormone, release in ovariectomized rats.

Angiotensin II (AII)-containing neurons with cell bodies in the rostral medial hypothalamus and axons project to the external layer of the median eminence, so that AII maybe released into the hypophyseal portal vessels for actions on the pituitary gland. Indeed, intrahypothalamic actions of the peptide on the release of hypothalamic hormones and direct actions on the pituitary have been reported. To determine the role of endogenously released AII in hypothalamic-pituitary hormone release, we have determined the effects of central immunoneutralization of AII upon the plasma concentrations of prolactin (PRL), growth hormone (GH), thyroid-stimulating hormone (TSH), and adrenocorticotropic hormone (ACTH). Specific antiserum directed against AII (AB-AII) or normal rabbit serum (NRS), as a control, was microinjected into third ventricular (3 V) cannulae of conscious, ovariectomized (OVX) rats. Immediately before and at various intervals after this procedure, blood samples were withdrawn through previously implanted external jugular catheters. Three hours after injection of the AB-AII, plasma PRL levels diverged from those of the NRS-injected animals and progressively increased from 4 to 24 h after administration of the antiserum. Results were similar with respect to plasma GH, except that the increase in the AB-AII animals above that in the NRS-injected controls from 4 to 6 h was not significant, but was highly significant on measurement 24 h after injection, at which time plasma GH was three times higher than in control rats. Similarly, following injection of AB-AII, plasma TSH values did not diverge significantly from those of the NRS-injected controls until 3 h after injection. From 3 to 5 h they remained constant and significantly elevated above values in the NRS-injected controls with a further nonsignificant increase at 6 h. At 24 h, there was no longer a difference between the values in both groups. In contrast to the significant elevations in plasma hormone levels observed with respect to PRL, GH, and TSH following injection of the antiserum, there was no change in plasma ACTH between the AB-AII-injected and NRS-injected animals throughout the same period of observation. Previous results by others have shown that intraventricular injection of AII has a suppressive action on the release of PRL, GH, and TSH. Consequently, we believe that the antiserum is acting intrahypothalamically to block the action of AII within the hypothalamus, resulting in the elevation of the three hormones mentioned. Therefore, the AII neurons appear to have a physiologically significant suppressive action on the release of hypothalamic neurohormones controlling the release of PRL, GH, and TSH. In contrast, there apparently is no effect of intrahypothalamically released AII on the secretion of corticotropin-releasing factors under these nonstress conditions. We cannot rule out an action of the antiserum at the pituitary level; however, in view of the fact that the actions of AII directly on the gland are to stimulate PRL, GH, TSH, and ACTH release, it appears that the antiserum was acting at the hypothalamic level.

Stress increases oxytocin release within the hypothalamic paraventricular nucleus.

Evidence indicates that the hypothalamic paraventricular nucleus (PVN) and oxytocin (OT) neurons in particular play a role in the physiological response to stress. Microdialysis (MD) experiments were performed to determine whether OT is released into the PVN during shaker stress. Male rats were prepared with venous catheters and PVN guide cannulae. OT and vasopressin (VP) release into PVN and peripheral blood were measured under basal conditions and during and after shaker stress (10 min at 110 cycles/min). Stress produced a specific increase in PVN and plasma OT. Dialysate OT levels were 0.3+/-0.1, 2.8+/-1.2 and 1.3+/-0.6 pg/sample (control, stress and recovery, respectively). Plasma OT was significantly increased during stress (3.7+/-1.2 vs. 11.7+/-2.3 pg/ml, basal vs. stress, respectively). When MD probes were located outside the PVN, there was no increase in OT release, demonstrating site specificity. Stress produced no change in VP levels, either in dialysate or plasma. These results show that OT, but not VP, is released into the PVN and peripheral blood in response to shaker stress. The data raise the possibility that local release of OT into the PVN plays a role in the neuroendocrine stress cascade.

Locus ceruleus lesions block pulsatile LH release in ovariectomized rats.

Luteinizing hormone (LH) secretion during the reproductive cycle and in ovariectomized (OVX) rats is pulsatile and this pattern of secretion is determined by intermittent discharges of LH-releasing hormone (LHRH) into the hypophysial portal vessels. LHRH secretion is probably controlled by prior pulsatile norepinephrine (NE) release. The locus ceruleus (LC) is an important source of NE to the LHRH neurons. We have shown previously that LC lesions block the preovulatory LH surge and ovulation and also cause a decrease in plasma LH concentrations in OVX rats. The possible role of the LC in regulating pulsatile LH release has not been explored. Therefore, the aim of this work was to investigate, in OVX rats, the effects of LC lesions on pulsatile LH secretion. LC lesions were produced in adult female rats three weeks after OVX. On the next morning, the jugular vein was catheterized and, on the afternoon of the same day, blood samples (0.3 ml) were withdrawn every 5 min, during 90 min, from conscious freely moving rats. Plasma LH was measured by radioimmunoassay. LC lesions greatly suppressed pulsatile LH secretion by decreasing both LH pulse frequency and amplitude. The basal as well as total secretion of LH were also decreased. This inhibitory effect of the lesions was observed only when at least 50% of the nucleus was destroyed. Data from sham-operated animals as well as those with less than 50% destruction of the LC did not differ from those of the control rats without brain lesions. Since LC lesions induce a decrease in NE content in the preoptic area and median eminence, the inhibition of pulsatile LH release in ovariectomized rats with LC lesions occurs presumably as result of decreased pulsatile NE release into these areas of the brain that decreases both the frequency and the amount of LHRH released per pulse.