Changes of immunoreactive somatostatin and beta-endorphin content in rat brain after amygdaloid kindling

A possible contribution of brain beta-endorphin and somatostatin to the epileptogenicity established by amygdaloid kindling was investigated in rats. Fourteen male rats were chronically implanted with electrodes placed bilaterally into the amygdala. The rats received 1 sec of electrical stimulation to the left amygdala each day. Generalized seizures were observed on average 10 days after initiation of kindling and the electrical stimulation was continued up to twenty-one days. Two months after the completion of the kindling procedure, each kindled and control rat was killed by microwave irradiation and the brains were dissected on ice into thirteen subregions. Each region was homogenized and centrifuged twice in 0.1 N acetic acid. The supernatant extracts were decanted and stored at - 20 degrees C until assay. Immunoreactive beta-endorphin and somatostatin were measured by radioimmunoassays. There were no significant differences in brain beta-endorphin contents between the two groups. In kindled rats, immunoreactive somatostatin was increased significantly in amygdala, sensorimotor, piriform, and entorhinal cortex. The results suggest that changes in somatostatin may be associated with epileptic susceptibility induced by the electrical kindling procedure.     

D-amphetamine-induced hypothermia and hypermotility in rats: Changes after systemic administration of beta-endorphin

Systemically administered beta-endorphin was tested in rats for its ability to modify the hypothermia and hypermotility induced by d-amphetamine. Colonic temperature and motor activity were measured in a cold (4°C) ambient temperature in animals given IP injections of beta-endorphin (0.1, 1.0, or 3.0 mg/kg), naloxone (10 mg/kg), or morphine (30 mg/kg). The same measurements were taken in animals given beta-endorphin (1.0 mg/kg) in combination with naloxone or saline pretreatment and d-amphetamine (15 mg/kg) or saline post-treatment. Morphine alone had a biphasic effect on thermoregulation, but did not affect d-amphetamine-induced hypothermia. Activity scores were decreased by morphine, in both d-amphetamine and saline treated animals. The thermal response of rats to beta-endorphin alone was variable, depending on dosage, but all 3 dosages partially blocked the hypothermic effect of d-amphetamine. Naloxone blocked the thermal effects of both beta-endorphin and d-amphetamine. Motor activity tended to be decreased by naloxone, regardless of amphetamine treatment, but beta-endorphin tended to increase activity in amphetamine-treated animals and reduce it in saline-treated controls. In their actions on both thermoregulation and activity, naloxone and beta-endorphin appeared to interact independently with d-amphetamine, often producing effects in the same direction, but in combination, they tended to be mutually inhibitory.     

Daily changes of GABA and taurine concentrations in various hypothalamic areas are affected by chronic hyperprolactinemia

This study was designed to characterize, in anterior, mediobasal, and posterior hypothalamic and median eminence, the 24h changes of gamma aminobutyric acid (GABA) and taurine (TAU) contents in adult male rats and to analyze whether chronic hyperprolactinemia may affect these patterns. Rats were turned hyperprolactinemic by a pituitary graft. Plasma prolactin (PRL) levels increased after pituitary grafting at all time points examined. A disruption of the circadian rhythm was observed in pituitary-grafted rats, whereas GABA and TAU content followed daily rhythms in all areas studied in controls. In the mediobasal hypothalamus, two peaks for each amino acid were found at midnight and midday. In the anterior hypothalamus, GABA and TAU showed only one peak of concentration at midnight. In the posterior hypothalamus, the values of both GABA and TAU were higher during the light as compared to the dark phase of the photoperiod. In the median eminence GABA content peaked at 20:00h, the time when TAU exhibited the lowest values. Hyperprolactinemia abolished the 24h changes of GABA in the mediobasal hypothalamus and reduced its content as compared to controls. Hyperprolactinemia advanced the diurnal peak of TAU to 12:00h in the mediobasal hypothalamus and did not modify the 24:00h peak. In the anterior hypothalamus, hyperprolactinemia increased GABA and TAU contents during the light phase while it decreased them during the dark phase of the photoperiod. In the posterior hypothalamus hyperprolactinemia did not modify GABA or TAU patterns as compared to controls. In the median eminence hyperprolactinemia increased the 20:00h peak of GABA and shift advanced the decrease in TAU content at 20:00h and its maximum at 24:00h as compared to controls. These data show that GABA and TAU content exhibit specific daily patterns in each hypothalamic region studied. PRL differentially affects the daily pattern of these amino acids in each hypothalamic region analyzed.     

Effects of progesterone on concentrations of monoamines in hypothalamic areas and plasma prolactin levels in rats.

The role of progesterone to increase prolactin (PRL) secretion on the first estrous day in pubertal rats was compared with its role in adult cyclic rats. The first estrus was induced by the administration of pregnant mare serum gonadotrophin (5 IU) at 28 days of age. A subcutaneous administration of 2.5 or 7.5 mg of progesterone/100 g body wt significantly increased the concentration of plasma PRL in pubertal rats within 4 hr. The PRL level obtained after progesterone administration was greater than that in similarly treated adult rats. The concentration of dopamine in the arcuate nucleus-median eminence (ARC-ME) in pubertal rats significantly decreased after a lower dosage of progesterone was administered, but no change was found in the preoptic area concentration. In adult estrous rats, the concentration of dopamine in the ARC-ME showed a tendency to decrease after the administration of a larger dose of progesterone (7.5 mg/100 g body wt). No change was observed in the concentrations of indoleamines in the preoptic area and ARC-ME after the administration of progesterone in both pubertal and adult rats. The concentrations of dopamine in the preoptic area and ARC-ME were lower in pubertal rats than in adults. The concentration of 5-hydroxyindole acetic acid and the ratio of 5-hydroxyindole acetic acid to 5-hydroxytryptamine in the ARC-ME were higher in pubertal rats than in adults. These results indicate that progesterone causes a greater increase in tonic PRL secretion in pubertal rats than in adult rats and that a lower hypothalamic dopamine activity and a higher serotonin activity in pubertal rats may account for these differences.     

Reduced hypothalamic somatostatin and neuropeptide Y concentrations in the spontaneously-diabetic Chinese hamster

Hypothalamic concentrations of six regulatory peptides having central effects on appetite and/or glucoregulation were measured by radioimmunoassay in spontaneously-diabetic Chinese hamsters and in age- and sex-matched non-diabetic control animals. In the diabetic hamsters, hypothalamic concentrations of somatostatin and neuropeptide Y were significantly reduced by 25-30% below controls. None of the other four peptides examined (bombesin, galanin, neurotensin and vasoactive intestinal peptide) differed significantly between the two groups. Disturbances in neuropeptide Y (the most potent central appetite stimulant yet discovered) and in somatostatin could be related to hyperphagia, an early and possibly primary abnormality of the diabetic syndrome in the Chinese hamster.     

Effect of dopaminergic drugs on hypothalamic and pituitary immunoreactive beta-endorphin concentrations in the rat

Beta-endorphin concentrations have been evaluated in the hypothalamus, pituitary lobes and plasma after 1-and 3-week treatment with 2-Br-alpha-ergocriptine or lisuride, two potent dopaminergic drugs. Hypothalamic beta-endorphin concentrations were significantly decreased after the administration of the dopaminergic agents for 1 or 3 weeks. Similarly, beta-endorphin concentrations decreased in the neurointermediate lobe and plasma. After gel chromatography, it appeared that in the anterior pituitary, beta-lipotropin concentrations were unchanged or lightly increased concomitantly with a decrease of beta-endorphin. Our data indicate that, both in the hypothalamus and the neurointermediate pituitary lobe, beta-endorphin is under an inhibitory dopaminergic tone. The latter may also play a role in inhibiting beta-endorphin cleavage from beta-lipotropin in the anterior pituitary.     

Effect of somatostatin on beta-endorphin release in rat experimental chronic inflammation.

The aim of the present study was to investigate the effect of somatostatin administration in arthritic rats. Inflammation was induced by daily interplantar injection of 100 microl of Freund's complete adjuvant into the left hind paw of the rat. Arthritis developed 20 days following the first injection and was stable in the inoculate paw. Arthritic rats were treated interplantarly with somatostatin (5 or 10 microg) or with indomethacin (100 microg) daily for 14 days. Inflammatory response was studied at 12 h, 7 and 14 days following drug administration. The effect of somatostatin was determined by local (into popliteal lymph nodes) and systemic production of beta-endorphin. Our results showed that somatostatin treatment significantly increased beta-endorphin levels in the blood and lymphocytes from popliteal lymph nodes. Greater efficiency was seen when 5 microg instead of 10 microg of somatostatin was used. A significant decrease of absolute leukocytosis was observed at the 14th day following somatostatin administration. Moreover, a significant reduction of plasmatic beta-globulins at 12 h and the 7th day and of plasmatic alpha2-globulins at the 14th day was observed after the beginning of somatostatin treatment.     

Centrally applied somatostatin inhibits the estrogen-induced luteinizing hormone surge via hypothalamic gonadotropin-releasing hormone cell activation in female rats

Overexpression of growth hormone (GH) as well as GH-deficiency dramatically impairs reproductive function. Decreased reproductive function as a result of altered GH release is, at least partially, due to changes at the hypothalamic-pituitary level. We hypothesize that hypothalamic somatostatin (SOM), the inhibiting factor of GH release from the pituitary, may play a central role in the "crosstalk" between the somatotropic and gonadotropic axes. In the present study we investigated the possible effects of a centrally applied SOM analog on the LH surge and the concurrent activation of hypothalamic GnRH neurons in female rats. To this end, female rats were treated with estradiol 2 wk after ovariectomy and were given a single central injection with either the SOM analog, octreotide, or saline just prior to surge onset, after which hourly blood samples were taken to measure LH. Two weeks later, the experimental setup was randomly repeated to collect brains during the anticipated ascending phase of the LH surge. Vibratome sections were subsequently double-stained for GnRH and cFos peptide. Following octreotide treatment, LH surges were significantly attenuated compared to those in saline-treated control females. Also, octreotide treatment significantly decreased the activation of hypothalamic GnRH neurons. These results clearly demonstrate that SOM is able to inhibit LH release, at least in part by decreasing the activation of GnRH neurons. Based on these results, we hypothesize that hypothalamic SOM may be critically involved in the physiological regulation of the proestrus LH surge.     

Relationship between plasma concentrations of immunoreactive beta-endorphin and food intake in rats

Periods of increased food intake in male rats were characterized by significant elevations in the plasma concentrations of immunoreactive beta-endorphin (beta-ep). Administration of 2-deoxy-D-glucose (400 mg/kg) produced rapid and concurrent increases in both food intake and plasma beta-ep. Administration of insulin (10 units/kg) produced large delayed increases in food intake but only modest delayed increases in plasma beta-ep. Spontaneous nocturnal feeding was associated with increased plasma beta-ep. Increases in daytime food intake in rats subjected to 24 hr of food deprivation were also characterized by elevated plasma beta-ep. In all cases examined, those feeding behaviors in male rats which were subject to inhibition by naloxone were characterized by elevated concentration of plasma beta-ep.     

Thyroid hormone concentrations in rats after chronic nicotine metabolite administration

In an attempt to evaluate the observed relationship of chronic cigarette smoking and reduced thyroid hormone activity, the major urinary metabolites of nicotine were administered to rats for 78 weeks. The animals were divided equally into one control (n = 33) and three treatment groups. Treatment group 1 received 0.1% (w/v continine, group 2 received 0.02% pure trans-nicotine-N'-oxide, and group 3 received 0.02% of a trans/cis mixture (64/36%) of nicotine-N'-oxide. Plasma and urinary nicotine and cotinine concentrations were determined as well as a variety of thyroid hormone parameters. Pure trans-nicotine-N'-oxide was more extensively metabolized to its cotinine end product, relative to the diasteromeric N'-oxides, mixture. Serum triiodothyronine (T3) was markedly reduced in animals receiving nicotine-N'-oxides, but was not different in the cotinine treatment group when compared to control values. A reduction in serum thyroxine (T4) values was noted only among those rats receiving the pure trans-nicotine-N'-oxide. The T3/T4 ratio, free T3 index, T3 uptake, and rT3 were altered in animals receiving nicotine-N'-oxides. These findings indicate that specific nicotine metabolites alter thyroid hormone concentrations after chronic low-dose administration and possibly do so through back conversion to the parent compound, nicotine.     

Chronic hyperprolactinemia depletes hypothalamic dopamine concentrations in male rats

The tuberoinfundibular dopamine (TIDA) system appears to tonically inhibit pituitary prolactin secretion while moderate elevations in serum prolactin levels, in turn, augment the turnover rate of dopamine (DA) without affecting the steady state concentrations of DA in the TIDA neurons (1–5). The present study demonstrates that chronic elevations in serum prolactin, to greater than 2,000 ng/ml, induced by the prolactin secreting MtTW15 tumor, decreased DA concentrations by 47% in the median eminence-arcuate nucleus (ME-ARC) region, by 43% in the medial basal hypothalamus (MBH) and 14% in the preoptic area-anterior hypothalamic region (POA-AH) without influencing the norepinephrine levels in these regions. Thus, chronic stimulation of hypothalamic DA neurons by prolactin may lead to depletion of DA concentrations and this may be an important factor in the reduced DA levels observed in hyperprolactinemia of senescent rats or that produced by chronic estrogen treatment.     

Time-dependent effects of starvation on serum, pituitary and hypothalamic leptin levels in rats

Leptin is produced by white adipose tissue and other cell types and is involved in both short- and long-term appetite control. Here we studied effects of starvation on serum, pituitary and hypothalamic levels of leptin during 72 h period. Each of the starved groups was sacrificed simultaneously with the group of ad libitum fed animals. The progression of the discrete starvation response phases was monitored by testing the blood glucose, free fatty acid, urea and corticosterone levels. Starvation caused biphasic increase in corticosterone and free fatty acid levels, and significant but transient decrease in urea and glucose levels. Starvation also abolished diurnal rhythm of changes in leptin concentrations in serum and hypothalamic and pituitary tissues. Only 6 h starving period was sufficient to lock serum leptin at low levels, whereas 12 h were needed to silence leptin production/secretion in hypothalamus for the whole examined period. In contrast, leptin production by pituitary tissues of starved animals required 24 h to reach minimum, followed by full recovery by the end of starvation period. These results indicate the tissue specific pattern of leptin release and suggest that the locally produced leptin could activate its receptor in pituitary cells independently of serum levels of this hormone.     

Changes in hypothalamic and extra-hypothalamic vasopressin content of water-deprived rats

A correlative radioimmunoassay (RIA) and immunocytochemical (ICC) study was carried out on vasopressin (VP) distribution and content in brains of normal and 3-day water-deprived rats. By RIA there were statistically significant differences in brain VP per pg/mg between normal and osmotically stressed specimens in hypothalamus (338.4 versus 134.4), thalamus (4.8 versus 0.9), septum (18.0 versus 3.4), striatum (1.6 versus 0.7) and amygdala (17.3 versus 1.3), but not in other brain regions measured. Pituitary VP decreased from 71.1 to 8.7 ng/mg, and plasma VP rose from 3.6 to 19.3 pg/ml during water deprivation. Application of the peroxidase-anti-peroxidase ICC method of Sternberger to vibratome sections showed that VP-immunoreactivity in dehydrated specimens decreased in perikarya of paraventricular nucleus and suprachiasmatic nucleus, while intrahypothalamic immunoreactive magnocellular fibers appeared more conspicuous due to proliferation of large Herring bodies. In extrahypothalamic sites VP-immunoreactivity in water-deprived rats was visibly reduced in periventricular thalamus and septum. Thus it is apparent that both intra- and extrahypothalamic VP are affected by osmotic stress, and these results are discussed within the context of current ideas relating to co-activation of neurosecretory cells that project to different sites.     

Involvement of hypothalamic somatostatin in glucagon-induced suppression of growth hormone secretion in conscious rats

The role of central glucagon in regulating GH secretion was studied in conscious male rats with chronic indwelling intra-atrial and intracerebro-ventricular (ICV) cannulae. Repeated blood sampling every 20 min from 1000 hr to 1700 hr showed two major GH bursts occurring at regular intervals (3.6±0.1 hr) around 1200 hr and 1540 hr. The ICV (lateral ventricle) injection of glucagon (10 μg/rat) at 1100 hr inhibited spontaneous GH secretion, and the mean (±SE) plasma GH levels from 1120 hr to 1700 hr were lower than those in controls injected ICV with the vehicle solution only (31.9±7.8 ng/ml vs. 157.1±13.4 ng/ml, p<0.01). The GH bursts did not appear until 5 hr after the injection. The intravenous (IV) injection of glucagon (10 μg/rat) did not change plasma GH levels or the occurrence of spontaneous GH bursts. The glucagon-induced suppression of GH release was attenuated when anti-somatostatin serum (ASS), but not normal rabbit serum (NRS), was given IV in a volume of 0.25 ml immediately before the ICV injection of glucagon (10 μg/rat) (mean GH levels at 1120–1700 hr: ASS+glucagon, 133.6±26.7 ng/ml vs. NRS+glucagon, 30.5±7.4 ng/ml, p<0.01). These findings suggest that central glucagon may play an inhibitory role in regulating GH secretion by stimulating SRIF release from the hypothalamus in the rat.     

Neonatal exposure to estradiol decreases hypothalamic allopregnanolone concentrations and alters agonistic and sexual but not affective behavior in adult female rats

Exposure of developing female rats to estradiol during the perinatal period induced long-lasting dysregulation of gonadal axis and decreased cerebrocortical and plasma concentrations of allopregnanolone. We have now examined the effects of neonatal estradiol administration in female rats on hypothalamic allopregnanolone concentrations and on exploratory, affective, agonistic and sexual behaviors as well as social learning. A single administration of β-estradiol 3-benzoate (EB, 10 μg) on the day of birth resulted in a delay of vaginal opening, acyclicity and ovarian failure. These alterations were associated with a significant decrease in the concentrations of allopregnanolone in the hypothalamus at 21 and 60 days, but not at 7 days, after birth. Neonatal administration of EB also increased agonistic behaviors in adult rats, such as dominant behaviors and following of an ovariectomized intruder, while living attacks unaffected. EB-treated rats showed also an increase in anogenital investigation, associated with a drastic reduction in spontaneous and induced female sexual behaviors (receptivity and proceptivity). In contrast, neonatal administration of EB did not affect locomotor activity, anxiety- and mood-related behaviors, the social transmission of flavor preferences, and seizures sensitivity. These effects of estradiol suggest that it plays a major role in regulation of both the abundance of allopregnanolone and the expression of agonistic and sexual behaviors, while failing to influence affective behaviors and social learning. Thus, the pronounced and persistent decrease in hypothalamic allopregnanolone concentration may be related to the manifestation of agonistic and sexual behaviors.     

Mediation by gonadal steroids of plasma beta-endorphin and LH in castrated female and male rats

Immunoreactive beta-endorphin (IR-BE) was significantly decreased and luteinizing hormone (LH) significantly increased in female rats castrated for four weeks. Forty eight hours after a single injection of estradiol benzoate (EB), IR-BE levels increased, and LH levels were reduced. On the afternoon following the administration of a second injection of EB given six hours earlier, IR-BE levels were reduced below control values, whereas LH levels were significantly elevated. There was no change in IR-BE levels during the remainder of that afternoon whereas LH levels decreased over time. Similar to female rats, IR-BE was diminished and LH increased in castrated male rats. IR-BE was increased significantly above those values observed in intact animals 24 hr after a single injection of TP and returned to control levels by 48 hr after administration of TP. Injection of TP reduced LH to levels observed prior to castration. These findings suggest that gonadal steroids exert a feedback on the release of IR-BE from the pituitary of female and male rats opposite to their feedback effect on the release of pituitary gonadotropins.