Cholecystokinin antagonist,proglumide, stimulates growth hormone release in the rat

Previous studies have revealed a stimulatory action of cholecystokinin on growth hormone release in the rat. To evaluate the physiologic significance of these effects we employed the cholecystokinin antagonist, proglumide and injected it intravenously and intraventricularly (third cerebral ventricle, 3V) to determine its actions on growth hormone. The experiments were performed in conscious, freely moving rats with indwelling cannulae in the 3V and/or external jugular vein. Intraventricular injection of 2 or 10 □g of proglumide significantly elevated plasma growth hormone concentrations in intact and castrated male rats and in ovariectomized females. Intravenous injections of 10 or 100 □g of proglumide were also effective in elevating growth hormone in a dose-related manner. Surprisingly, the response to the lower dose given intraventricularly was somewhat greater than that of the higher dose. We speculate that these stimulatory effects of proglumide given intraventricularly are due to the agonist action of proglumide at these doses since action of cholecystokinin itself is to increase plasma growth hormone following its intraventricular injection. The studies therefore do not establish a physiologically significant growth hormone-releasing action of brain cholecystokinin but provide more evidence that activation of cholecystokinin receptors in the brain can induce a stimulation of growth hormone release either by activation of the release of growth hormone-releasing hormone or by inhibition of the release of somatostatin or by a combination of these two actions.     

Effects of histamine and H1 and H2-receptor antagonists on wet-dog-shake episodes in rats induced with tranylcypromine and 5-methoxytryptamine

Intraperitoneally administered tranylcypromine and 5-methoxytryptamine induced in rats the so called wet-dogs-shake behaviour. Histamine injected intraventricularly had no effect on the number or episodes of this behaviour during the first 40 minutes of observation. On the other hand, dimaprit in doses of 5 micrograms/rat injected also intraventricularly increased the number of these episodes. Thenalidine and antazoline--antagonists of the H1-receptor, and cimetidine and ranitidine--antagonists of the H2-receptor, decreased the number of these episodes proportionally to the injected dose. Similar effects were obtained after cimetidine injection into the lateral ventricle. In the light of these observations it may be supposed that these antihistaminic agents exert an inhibitory effect not only on the histaminergic system but decrease indirectly also the activity of the serotoninergic system.     

Neostriatal administration of somatostatin:differential effect of small and large doses on behavior and motor control

The administration of small doses of somatostatin (SRIF) (0.01 and 0.1 microgram) into the neostriatal complex of unrestrained, freely moving rats induced general behavioral excitation associated with a variety of stereotyped movements, tremors, and a reduction of rapid eye movements (REM) and deep slow wave sleep (SWS). In contrast, the higher doses of SRIF (1.0 and 10.0 microgram) caused movements to be uncoordinated and frequently induced more severe difficulties in motor control such as contralateral hemiplegia-in-extension which restricted or completely prevented the expression of normal behavioral patterns. As a result, the animals appeared drowsy and inhibited. Analysis of the sleep-waking cycle revealed prolonged periods of a shallow SWS while REM sleep and deep SWS were markedly reduced; electroencephalogram recordings revealed periods of dissociation from behavior. The administration of endocrinologically inactive as well as the active analogues of SRIF failed to induce effects comparable with those observed after the administration of the same dose of the native hormone (10.0 microgram).     

The biochemical and behavioral effects of phospholipase A2 and morphine microinjections in the periaqueductal gray of the rat

In order to characterize the in vivo action of phospholipase A2 (PLA2) on opiate receptors and opiate-induced behaviors, the effects of injections of PLA2 into the periaqueductal gray region (PAG) of the rat were assessed on free fatty acid (FFA) release, opiate-binding levels, and morphine-induced behaviors. Rats received bilateral PAG injections of 2 micrograms of PLA2 while anesthetized. One hour later, regions around the cannulae tracts in PLA2-treated rats contained over 2.5 times more FFA than saline-injected controls, and 3H-dihydromorphine binding was reduced on average more than 70%. In another series of experiments, conscious rats were given 2 micrograms of PLA2 prior to 10 micrograms of morphine through cannulae chronically implanted into the PAG. PLA2 did not significantly attenuate morphine-induced analgesia as measured by the tail-flick test to radiant heat, but did prevent the explosive motor behavior observed following morphine injections alone. PLA2 by itself did not induce analgesia, but did cause explosive motor behavior 2 hr after the injections. Neither lysophosphatidylcholine nor trypsin resulted in motor seizures following PAG injections. It was concluded that the behavioral effects of PLA2 result from the unique properties of the enzyme, rather than generalized membrane damage, and that the opioid sites and mechanisms that mediate analgesia are different from those associated with explosive motor behavior.     

Effect of prostaglandin F2 alpha on temperature and behaviour of centrally sympathectomized rats

Prostaglandin F2 alpha (PG F2 alpha) in doses of 1 and 10 micrograms applied intraventricularly causes a rise in body temperature and exerts a sedative action on rat behaviour. Chemical sympathectomy of the central nervous system (CNS) induced by a twofold intraventricular administration of 250 micrograms of 6-hydroxydopamine reduces the influence of PG F2 alpha on the body temperature and behaviour. Reserpine administered to rats with chemical sympathectomy of the central nervous system reverses or prevents the PG F2 alpha action on body temperature of the animals. The results of the experiments seem to indicate that the central monoaminergic mechanisms play a role in the central action of PG F2 alpha on body temperature and behaviour.     

Behavioural effects of luteinizing hormone-releasing hormone (LHRH) in rats.

Behavioural effects of intracerebroventricularly-injected (icv) LHRH were studied in female rats. Locomotor and exploratory activities as well as irritability were determined. A pronounced inhibitory effect of 10 micrograms doses of LHRH was found. At 100 micrograms doses of LHRH, barrel behaviour was observed. We conclude that LHRH can modify the activity of central serotonergic receptors in rats.     

Comparison of central effects of noradrenaline and dopamine injected into the lateral brain ventricle in rats.

Noradrenaline and dopamine injected into the lateral brain ventricle exerted a significant effect on the behavior of rats. Both amines caused a slight rise in the basic locomotor activity which was significantly increased in the animals with inhibited monoamine oxidase activity. Besides that, they suppressed the behavior of rats in the open-field test, inhibited the conditioned avoidance response, decreased body temperature and increased amphetamine-induced motor hyperactivity. Noradrenaline, in contrast to dopamine, changed the intensity of amphetamine-induced stereotypy and prolonged the action of hypnotics. The central action of both catecholamines (in higher doses especially) seemed to have a biphasic course: in the first phase after administration depression was observed which was more pronounced after noradrenaline administration, in the second phase a stimulating effect b     

Stimulation by thyrotropin-releasing hormone of vagal outflow to the thyroid gland

An intracerebroventricular (i.c.v.) injection of TRH to the urethane anesthetized rat stimulates the activity of the superior laryngeal nerve (n.sl) which is a vagal ramus terminating at the thyroid gland and adjacent muscles. The response to TRH, a tonic increase in the n.sl outflow, was dose dependent in the 0.005-5.0 micrograms/100 g B.W. range. In contrast to this, methionine-enkephalin (ENK), neurotensin (NT) and somatostatin (SRIF) (5 micrograms/100 g, i.c.v.) all caused a transient decrease in n.sl activity. SRIF showed the highest attenuating effect when injected alone and was capable of diminishing the increased activity produced by a prior injection of TRH. ENK and NT failed to affect the TRH-induced increased activity. When injected concomitantly with TRH, SRIF blocked the response to TRH while ENK and NT both failed to affect the response to TRH. Pretreatment with triiodothyronine for 5 days strongly inhibited the response of the n.sl outflow to TRH. On the other hand, pretreatment with atropine, haloperidol, propranolol, phenoxybenzamine and p-chlorophenylalanine failed to block the stimulating effect of TRH although the response was diminished by some antagonists. It therefore seemed that TRH transmission is involved in central stimulation and SRIF is antagonistic in this regulation of n.sl outflow to the thyroid gland.     

Corticotropin-releasing factor administered intraventricularly to rhesus monkeys

Synthetic ovine corticotropin-releasing factor (CRF) administered intraventricularly (ICV) to rhesus monkeys resulted in endocrine and behavioral changes. At doses of 20 and 180 micrograms, CRF stimulated the pituitary-adrenal axis in four chair-restrained monkeys. These monkeys showed concomitant increases in arousal. To study these animals in a less restrictive setting, three of the monkeys later received CRF ICV (20 and 180 micrograms) in their home cages. At the 180-micrograms dose the monkeys exhibited a combination of huddling and lying down behavior. These behavioral effects did not seem to be due to alterations in blood pressure.     

Somatostatin inhibition of growth hormone secretion in an adult bird: the domestic fowl

1. The intravenous (i.v.) infusion of somatostatin (SRIF, 1.0 microgram/kg per min) promptly (within 5 min) reduced the growth hormone (GH) concentration in the plasma of conscious adult chickens. 2. The GH concentration progressively declined throughout a 60-min period of SRIF infusion, but was dramatically increased above pre-infusion levels within 5 min of SRIF withdrawal and maintained at an elevated level for at least 30 min afterwards. 3. Sodium pentobarbitone-anaesthesia lowered the basal GH concentration to levels comparable with those in conscious birds infused with SRIF. When administered to anaesthetized birds, exogenous SRIF was unable to further reduce the GH concentration and unable to induce 'rebound' GH release. 4. While thyrotropin releasing hormone (TRH, 10 micrograms/kg) increased the GH concentration in both conscious and anaesthetized birds, only the GH response in the anaesthetized birds was diminished by SRIF infusion. 5. Rebound GH secretion following the termination of SRIF infusion was observed in both conscious and anaesthetized birds injected with TRH. 6. These results demonstrate that SRIF can inhibit basal and TRH-stimulated GH secretion in adult domestic fowl and indicate that anaesthesia disrupts the normal control of GH releases.     

Effects of MET-ENK, substance P and SRIF on the behavior of Hemichromis bimaculatus

Administration of 10 and 30 micrograms methionine-enkephalin (MET-ENK)/g bw (n = 10/dose) affected the propensity towards fighting in H. bimaculatus; 10 micrograms increased, while 30 micrograms decreased the aggressive behavior. MET-ENK also affected a number of behavior patterns displayed by the fish. Moreover, the "wet-dog-shakes" observed suggest that MET-ENK acts on opiate-receptors. Treatment with substance P (SP)/g bw (n = 10/dose) induced chafing movements in the fish slightly. It also decreased fighting and increased biting of the air stone, which is evidence that H. bimaculatus is still aggressive, directing its attacks to different objects. When 4, 8, 12 micrograms somatostatin (SRIF)/g bw (n = 10/dose) were injected, H. bimaculatus stopped fighting for several hours after the onset of treatment, depending on the dosage. Somatostatin reduces blood glucose concentration, causing a sudden stop of aggressive behavior, 0.04, 0.1, 0.6, 1.0 and 3.0 IU prolactin (PRL)/g bw (n = 5/dose) eventually decreased fighting and affected a number of behavior patterns displayed by the fish.     

Apomorphine induced biting and fighting behaviour in reserpinized rats and an approach to the mechanism of action

Various patterns of aggressive behaviour have been induced by drugs. In the present study, the biting and the fighting responses were induced in rats by apomorphine alone, and reserpine plus apomorphine combination respectively, and these could be blocked completely by a dopamine receptor blocking agent. Dopamine, norepinephrine and clonidine given intraperitoneally or intraventricularly failed to induce these responses. Chemical agents known to increase the concentration of dopamine in the brain, induced the biting, but not the fighting response, whereas these behavioural patterns were more intense due to apomorphine in the rats pretreated with reserpine and dopamine or α-methyltyrosine and reserpine combinations. In amphetamine pretreated rats, apomorphine induced intense biting after 10 min and a few bouts of fighting after 30 min. It is suggested that (i) the receptors on which apomorphine acts may be called ‘Apomorphine Receptor’ rather than ‘Dopamine Receptor’, (ii) dopamine incompletely activates these receptors which are sensitised in the absence of catecholamines and induce a higher degree of stereotyped behaviour i.e. fighting, due to apomorphine.     

Dynamic of the GRF-induced GH response in genetically obese Zucker rats: influence of central and peripheral factors

To determine the time onset of the growth hormone (GH) alteration in the genetically obese rat, we studied the in vivo and in vitro rat growth hormone releasing factor (rGRF(1-29)NH2)-induced GH secretion in 6- and 8-week-old lean and obese male Zucker rats. Under sodium pentobarbital anesthesia, rGRF(1-29)NH2 (GRF) was injected intravenously at two doses: 0.8 and 4.0 micrograms/kg b.w. Basal serum GH concentrations were similar in lean and obese age-matched animals. The GH response to both GRF doses tested was unchanged in 6-week-old obese rats as compared to their lean litter mates. In contrast, a significant decrease of the GH secretion in response to 4.0 micrograms/kg b.w. GRF was observed in the 8-week-old obese rats. The effect of GRF (1.56, 6.25 and 12.5 pM) was further studied in vitro, in a perifusion system of freshly dispersed anterior pituitary cells of lean and obese Zucker rats. Basal GH release was similar in the 6-week-old animal group. In contrast, it was significantly decreased in 8-week-old obese rats as compared to their lean litter mates. Stimulated GH response to 1.56 and 6.25 pM GRF was significantly greater in the 6-week-old obese group than in the age-matched control group. In contrast, the GH response to all GRF concentrations tested was significantly decreased in the 8-week-old obese rats as compared to their respective lean siblings. In 8-week-old obese rats, a decrease of GH pituitary content and an increase of hypothalamic somatostatin (SRIF) concentration were observed. Insulin and free fatty acid serum were significantly increased in 8-week-old obese rats. In contrast, lower insulin-like growth factor I serum levels were observed in the obese animals as compared to their lean litter mates. Finally, to further clarify the role of the periphery in the inhibition of GH secretion observed in the 8-week-old fatty rats, we exposed cultured pituitary cells of 8-week-old lean animals to 17% serum of their obese litter mates. A significant decrease of GRF-stimulated GH secretion of lean rat pituitary cells exposed to the obese serum was noted (P less than 0.05). This study demonstrates that, in the obese Zucker rat, an alteration of the GH response to GRF is evident by the 8th week of life. This defective GH secretion could be related to peripheral and central abnormalities.     

Role of postnatal androgens in sexual differentiation of the lordosis-inhibiting effect of central injections of cholecystokinin

The neuropeptide cholecystokinin (CCK) inhibits lordosis behavior when infused into the ventromedial nucleus of the hypothalamus (VMN) of female rats and has no effect when infused into the VMN of male rats. To test whether this sex difference develops under the control of perinatal steroids, male rats were castrated or given sham surgeries within 3 h of birth and female rats were injected with either 0 or 100 micrograms testosterone propionate on postnatal day 5. As adults, these rats were castrated as necessary, implanted with unilateral cannulae directed at the VMN, and tested for their ability to display female sexual behavior and to respond to CCK. Neonatal castration of males prevented defeminization of this response. When treated with 5 micrograms estradiol benzoate (EB), neonatally castrated males showed both lordosis behavior and a profound inhibition of that behavior after infusions of CCK. Neonatally castrated males did not display lordosis behavior when treated with 2 micrograms EB. Control males showed no lordosis behavior and, therefore, no response to CCK. Both doses of EB induced lordosis behavior in neonatally androgenized females. Significantly, these neonatally androgenized females were less responsive to CCK's inhibition of lordosis and were also anovulatory. These results imply that androgens alter the development of CCK responsive circuits as well as defeminize cyclic gonadotropin release. Levels of 125I-sCCK-8 binding in the VMN were correlated closely with an individual's ability to respond to sCCK-8. In summary, the inhibition of female sexual behavior caused by exogenously administered CCK in normal adult female rats appears to be controlled at least partially by levels of CCK receptors in the VMN and to differentiate under the control of perinatally present testosterone.     

Inhibition of copulatory behavior in male rats by D-ALA2-Met-Enkephalinamide

D-Ala²-Met-Enkephalinamide (DALA), a synthetic analog of met-enkephaline resistant to enzymatic degradation, was injected intraventricularly to sexually experienced male rats paired with receptive females. A dose of DALA of 6 μg which did not influence spontaneous motor activity, completely suppressed the copulatory behavior of all animals tested. A dose of 3 μg significantly increase mounting and intromission latencies, but did not influence other measures of the copulatory behavior. The effect of DALA was prevented by naloxone (1 mg/Kg), a specific inhibitor of opioid receptors. The results suggest that enkephalins may play a role in the regulation of copulatory behavior.     

Nerve growth factor increases stimulus-evoked metabolic activity in acetylcholine-depleted barrel cortex

Lesions of the basal forebrain deplete the neocortex of cholinergic fibers. Acetylcholine depletion in the somatosensory cortex of rats results in reduced stimulus-evoked activity in response to whisker stimulation. Previous studies demonstrate that embryonic basal forebrain transplants improve functional activity toward normal. It is not clear if the activity increase is due to cholinergic replacement or other factors present in the graft. In this study, we examined the possibility that nerve growth factor (NGF), a neurotrophin known as a survival factor and a specific protectant for cholinergic basal forebrain neurons, can preserve basal forebrain cells after a lesion and restore functional activity in the somatosensory cortex. We report that NGF alone is capable of restoring functional activity in the barrel cortex of animals with basal forebrain lesions, while vehicle injections of saline do not alter activity. Both high (10 mug) and low (5 mug) doses of NGF unilaterally injected into the lateral ventricle improved stimulus-evoked functional activity during bilateral whisker stimulation. The mechanism of NGF action is not clear since the restoration of functional activity in cortex was not accompanied by increased cholinergic activity as detected by acetylcholinesterase fiber staining. NGF may act directly on cortical neurons, although its site of action is not well defined.     

Effects of arginine vasotocin on levels of plasma gonadotropins and prolactin in ovariectomized conscious rats

Arginine vasotocin was injected into the third ventricle or intravenously in conscious, ovariectomized rats and its effect on gonadotropin and prolactin release evaluated. The peptide lowered plasma levels of both LH and prolactin in doses of 40 or 100 ng given intraventricularly. The higher dose was slightly more effective than the lower dose. Intravenous injection of a 1-microgram dose of vasotocin failed to alter plasma LH in the ovariectomized animals; however, a 5-micrograms dose induced a slight depression apparent at only 60 min following injection. Intravenous injection of 1 microgram produced a significant lowering of plasma prolactin, whereas a dramatic lowering followed the injection of the higher dose. Plasma FSH was unaffected in these experiments. Incubation of dispersed anterior pituitary cells from ovariectomized rats with various doses of vasotocin revealed no effect of the peptide on the release of FSH, LH, or prolactin. It also did not alter the response to LHRH, but it partially blocked the action of dopamine to inhibit prolactin release. The data indicate that quite low doses of arginine vasotocin act within the brain to inhibit LH and prolactin secretion in ovariectomized, conscious animals.     

Mechanism of corticotropin action on adrenal protein synthesis. The effects of inhibitors of protein synthesis and calcium chelators

We have recently shown that beside a general stimulation of most adrenal proteins, corticotropin induces a marked increase in a specific adrenal cytosolic protein, protein E, in intact and hypophysectomized rats. To further clarify the mechanisms by which corticotropin exerts its trophic action we have investigated the effects of cycloheximide, calcium and calcium chelator administration on intact and hypophysectomized animals. These substances were injected in rats with or without corticotropin, and slices of adrenal glands from control and treated animals were removed 5 h later, incubated with [14C]- or [3H]-leucine for 2 h, and cytosolic proteins analyzed by polyacrylamide gel electrophoresis using a dual labelling technique. When high doses of cycloheximide (higher than 500 micrograms) were injected in rats, incorporation of labelled leucine in adrenal slices of control and corticotropin-treated animals was inhibited. With 500 micrograms cycloheximide per rat, incorporation of labelled leucine in adrenal slices of control animals was normal, but the corticotropin stimulation of both protein E and total protein synthesis was inhibited. Lower doses of cycloheximide (100 micrograms per rat) completely inhibited the stimulatory effect of corticotropin on total protein synthesis but did not affect protein E synthesis, while after 50 micrograms per rat both stimulatory effects were preserved. The two higher doses of cycloheximide (500 and 100 micrograms per rat) could not completely block the steroidogenic effect of the hormone. The effects of calcium and calcium chelators were studied in 1-day hypophysectomized rats. Calcium alone or injected simultaneously with corticotropin has no effect. Calcium chelators injected simultaneously with corticotropin partially inhibited the stimulatory effects of corticotropin on steroidogenesis but totally inhibited stimulation of total protein synthesis, while the stimulation of protein E persisted. Our results show that after corticotropin, stimulation of protein E synthesis correlates better with steroidogenesis than with total protein synthesis.     

Somatostatin and intestinal calcium transport in the rat

In intact rats we studied the influence of low doses of intravenously (i.v.) administered somatostatin (SRIF) on the net absorption and the bidirectional fluxes (lumen-to-plasma, LP; plasma-to-lumen, PL) of calcium in the duodenum, jejunum, ileum and caecum. In the duodenum SRIF inhibited the LP-flux and the net absorption of Ca significantly at infusion rates of 0.75 and 1.0 microgram SRIF . kg-1 . h-1. The PL-flux was not altered by any of the SRIF doses administered. In the other gut segments studied (jejunum, ileum, caecum) neither the net absorption nor the bidirectional Ca fluxes were changed by i.v. SRIF. It is concluded that SRIF in the plasma levels achieved in this study has an influence on the duodenal calcium absorption (CaA) of the rat; questions regarding the mechanisms of this action as well as the physiological significance of our findings are as yet unresolved.     

Caerulein, a cholecystokinin-related peptide, depresses somatic function via the vagal afferent system

Intravenous doses of 0.5-8 micrograms/kg (0.3-4.9 nmol/kg) of caerulein, a cholecystokinin-related peptide, depressed the crossed extensor reflex response of chloralose-anesthetized rats in a dose-dependent manner. Intraventricularly administered caerulein was effective only at high doses (1-2 micrograms/animal, i.e., 0.6-1.2 nmol/animal). Cervical vagotomy completely abolished the inhibitory effect of peripherally injected caerulein. Electrical stimulation of vagal afferent nerves could simulate the caerulein effect to some extent. These results suggest that the primary site of action of peripherally administered caerulein is located in the gastrointestinal tract and thus the generated afferent vagal impulses mediate the reflex depression via the nucleus tractus solitarius and other as yet unclarified brain stem structures.