Does neuropeptide Y contribute to the anorectic action of amylin?

Neuropeptide Y (NPY) is a potent feeding stimulant acting at the level of the hypothalamus. Amylin, a peptide co-released with insulin from pancreatic beta cells, inhibits feeding following peripheral or central administration. However, the mechanism by which amylin exerts its anorectic effect is controversial. This study investigated the acute effect of amylin on food intake induced by NPY, and the effect of chronic amylin administration on food intake and body weight in male Sprague Dawley rats previously implanted with intracerebroventricular (icv) cannulae. Rats received 1 nmol NPY, followed by amylin (0.05, 0.1, 0.5 nmol) or 2 microl saline. Increasing doses of amylin resulted in a dose-dependent inhibition of NPY-induced feeding by 31%, 74% and 99%, respectively (P < 0.05). To determine the chronic effects of i.c.v. amylin administration on feeding, rats received 0.5 nmol amylin or saline daily, 30 min before dark phase, over 6 days. Amylin significantly reduced food intake at 1, 4, 16 and 24 hours; after 6 days, amylin-treated rats showed a significant reduction in body weight, having lost 17.3 +/- 6.1 g, while control animals gained 7.7 +/- 5.1 g (P < 0.05). Brain NPY concentrations were not elevated, despite the reduced food intake, suggesting amylin may regulate NPY production or release. Thus, amylin potently inhibits NPY-induced feeding and attenuates normal 24 hour food intake, leading to weight loss.     

Effect of systemic administration of mouse recombinant interferon-gamma on the lung tumor metastases in mice

The purpose of this study was to examine the effective anti-metastatic activity by multiple i.v. administrations of mouse recombinant interferon-gamma (IFN-gamma) against pulmonary metastases of 3LL or B16-BL6 melanoma cells after surgical excision of primary tumors. Multiple treatments with IFN-gamma reduced effectively the incidence of pulmonary tumor metastases. Repeated 4 consecutive treatment modalities with IFN-gamma showed remarkable reduction of lung tumor colonies, and also rendered alveolar macrophages (AM) cytotoxic against B16-BL6 cells. In contrast, 14 consecutive administrations of IFN-gamma at any doses (10(2) and 10(3) U/mouse) could not activate macrophages to become cytotoxic, but were effective in regressing metastases. Thus, antimetastatic activity of IFN-gamma may be due to the stimulation of host immune defense systems such as induction of tumoricidal macrophages, presumably the direct antiproliferative action to tumor cells, or both actions under the appropriate administration conditions. We found that the systemic administration of IFN-gamma under appropriate multiple treatment modalities results in the reduction of the lung metastases and can activate AM to become tumor cytotoxic at relatively low doses (10(2) U). High-dose IFN-gamma in the multiple administration schedule was also effective for the reduction of lung tumor colonies, but strongly suppressed the nonspecific immune function and could not activate tumoricidal properties of AM.     

Further evidence for a role of NMDA receptors in the locus coeruleus in the expression of withdrawal syndrome from opioids.

To examine a role of N-methyl-D-aspartate (NMDA) receptors in the locus coeruleus (LC) in the expression of the withdrawal signs from opioids, rats were continuously infused with morphine (a mu-opioid agonist, 26 nmol/microl per h) or butorphanol (a mu/delta/kappa-mixed opioid agonist, 26 nmol/microl per h) intracerebroventricularly (i.c.v.) through osmotic minipumps for 3 days. An LC injection of NMDA (0.1 and 1 nmol/5 microl) induced withdrawal signs in opioid-dependent animals. However, it did not precipitate any abnormal behaviors in saline-treated control rats. The expression of the withdrawal signs precipitated by NMDA (1 nmol/5 microl), glutamate (10 nmol/5 microl), or naloxone (an opioid antagonist, 24 nmol/5 microl) was completely blocked by pretreatment with a NMDA antagonist, MK-801 (5-methyl-10,11-dihydro-5H-dibenzo[a,d]cycloheptan-5,10-imine), 0.1 mg/kg, i.p. In animals that had been infused with opioids in the same manner, naloxone (48 nmol/5 microl, i.c.v.) precipitated withdrawal signs and increased extracellular glutamate levels in the LC of opioid-dependent rats measured by in vivo microdialysis method. Pretreatment with MK-801, however, did not affect the increases of glutamate levels in the LC. These results further demonstrate that the expression of opioid withdrawal induced by an expeditious release of glutamate in the LC region of opioid-dependent animals might be mainly mediated by the postsynaptic NMDA receptors.     

Effects of melatonin on luteinizing hormone secretion in anestrous ewes following dopamine and opiate receptor blockade

In the present investigation we have examined the ability of melatonin to modify the pulsatile LH secretion induced by treatment with a DA antagonist (sulpiride, SULP) or opioid antagonist (naloxone, NAL) in intact mid-anestrous ewes. The experimental design comprised the following treatments-in experiment 1: (1) intracerebroventricular (i.c.v.) infusion of vehicle (control I); (2) pretreatment with SULP (0.6 mg/kg subcutaneously) and then i.c.v. infusion of vehicle (SULP + veh); (3) pretreatment with SULP and then i.c.v. infusion of melatonin (SULP + MLT, 100 microg per 100 microl/h, total 400 microg). In experiment 2: (4) i.c.v. infusion of vehicle (control II); (5) i.c.v. infusion of NAL (NAL-alone, 100 microg per 100 microl/h, total 300 microg); (6) i.c.v. infusion of NAL in combination with MLT (NAL + MLT, 100 microg + 100 microg per 100 microl/h). All infusions were performed during the afternoon hours. Pretreatment with SULP induced a significant (P < 0.01) increase in LH pulse frequency, but not in mean LH concentration, compared with control I. In SULP + MLT-treated animals, the LH concentration was significantly (P < 0.01) higher during MLT infusion, but due to highly increased LH secretion in only one ewe. The significant changes in the SULP + MLT group occurred in LH pulse frequency. A few LH pulses were noted after melatonin administration compared with the number during the infusion (P < 0.05) and after vehicle infusion in the SULP + MLT group (P < 0.05). The i.c.v. infusion of NAL evoked a significant increase in the mean LH concentration (P < 0.001) and amplitude of LH pulses (P < 0.01) compared with these before the infusion. The enhanced secretion of LH was also maintained after i.c.v. infusion of NAL (P < 0.01) with a concomitant decrease in LH pulse frequency (P < 0.05). In NAL + MLT-treated ewes, mean plasma LH concentrations increased significantly during and after the infusion compared with that noted before ( P < 0.001). No difference in the amplitude of LH pulses was found in the NAL + MLT group, but this parameter was significantly higher in ewes during infusion of both drugs than during infusion of the vehicle (P < 0.01). The LH pulse frequency differed significantly (p < 0.05), increasing slightly during NAL + MLT administration and decreasing after the infusion. In conclusion, these results demonstrate that: (1) in mid-anestrous ewes EOPs, besides DA, are involved in the inhibition of the GnRH/LH axis; (2) brief administration of melatonin in long-photoperiod-inhibited ewes suppresses LH pulse frequency after the elimination of the inhibitory DA input, but seems to not affect LH release following opiate receptor blockade.     

Does vigabatrin possess an anticonvulsant action against pentylenetetrazol-induced seizures in developing rats?

Anticonvulsant action of vigabatrin (300, 600, 900 and/or 1200 mg/kg i.p.), an inhibitor of GABA-transaminase, was studied in a model of motor sezures elicited by pentylenetetrazol. Five age groups of rats (7, 12, 18, 25 and 90 days old) received a s.c. injection of pentylenetetrazol 4, 6 and/or 24 hours after vigabatrin administration. The incidence of minimal, predominantly clonic seizures was not changed in any age group, but their latencies were prolonged in 18- and 25-day-old rats. Generalized tonic-clonic seizures were influenced in a more complex manner. Incidence of these seizures was decreased in 7-day-old rat pups 24 hours after vigabatrin administration. Higher doses of vigabatrin exhibited a similar effect in adult rats at all intervals studied. Specific suppression or at least restriction of the tonic phase was observed in all groups of immature rats, the effect was more marked 24 hours after vigabatrin than at shorter intervals. The anticonvulsant action of vigabatrin, which could be demonstrated mainly against generalized tonic-clonic seizures, varies markedly during development.     

Effects of i.c.v. administration of leptin on copulatory and ingestive behavior in STZ-induced diabetic male rats.

It is well known that circulating leptin concentrations correlate with adiposity in both humans and rodents and decrease after fasting, energy restriction, or weight loss. The goal of the present study was to confirm whether the decreases of copulatory behavior and the increases of ingestive behavior in STZ-induced diabetic male rats could be reversed by i.c.v. administration of leptin. Adult male Wistar-Imamichi rats aged 9 weeks were used for the studies. Males received a single injection of STZ (60 mg/kg, i.p.) and vehicle. During the experiment, individual body weight, and food and water intake were measured. The copulatory and ingestive behaviors in STZ-induced diabetic males were observed at 2 and 4 weeks after STZ. At 6 weeks after STZ, leptin (10 microg/10 microl) or aCSF (artificial cerebrospinal fluid) was injected through a lateral ventricle cannula and the above two behaviors were observed again. The i.c.v. leptin injection to STZ-induced diabetic males resulted in a significant increase of ejaculation frequencies (3.6 +/- 0.26 vs. 2.9 +/- 0.30 times) and a significant decrease in amount of food ingested (36.2 +/- 1.93 vs. 23.2 +/- 3.76 g), compared with the aCSF-injected control (p<0.01). These findings suggest that the copulatory and ingestive behaviors in i.c.v. leptin-injected STZ diabetic males were restored to levels equivalent to those in control males.     

The effect of inhibitors of endogenous opioid degradation, bacitracin, bestatin, captopril, and D-phenylalanine, on digoxin-induced arrhythmias in guinea pigs

The purpose of this study was to investigate the effect of inhibition of endogenous opioid degradation on digitalis-induced arrhythmias, utilizing the inhibitors bacitracin, bestatin, captopril, and D-phenylalanine. Guinea pigs, anesthetized with pentobarbital, 50 mg/kg i.p., and breathing spontaneously received intracerebroventricular (i.c.v.) injection of bacitracin (6.8 mg/kg), bestatin (1 mg/kg), captopril (2 mg/kg), D-phenylalanine (1.2 mg/kg) or the diluent, saline. Digitalis arrhythmias were induced by a 50 micrograms/kg i.v. bolus of digoxin followed by 500 micrograms.kg-1.h-1 i.v. Bacitracin and bestatin, but not captopril or D-phenylalanine, significantly (p less than 0.05) altered the relationship between the digoxin dose and the first occurrence of arrhythmias, i.e., digoxin-induced ventricular arrhythmias became manifest at lower digoxin doses. The mean digoxin dose and ED50s, at which arrhythmias first occurred, were significantly (p less than 0.05) reduced by bacitracin and bestatin. The findings were similar for fatal arrhythmias, although D-phenylalanine appeared to decrease the digoxin dose at the development of fatal arrhythmias. The opioid antagonist naloxone, in a 50 micrograms/kg bolus and 50 micrograms.kg-1.h-1 i.c.v., completely prevented these effects of bacitracin and reduced the effect of bestatin. The relationship to arrhythmias could not be ascribed to an effect on blood pressure, as the blood pressure response to digoxin was the same in bestatin, D-phenylalanine, and control groups. To examine whether systemic administration of an inhibitor of opioid degradation had similar effects, a second protocol was selected with systemic administration of bacitracin because it altered the dose effect relationship after i.c.v. administration and systemic concentrations could be readily attained. Bacitracin, in a 13.5 mg/kg i.v. bolus and 135 mg.kg-1.h-1 i.v., was followed by 100 micrograms/kg digoxin i.v. every 15 min.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of intracerebroventricularly injected glucagon-like peptide-1 on cardiovascular parameters; role of central cholinergic system and vasopressin

We aimed to investigate the effects of intracerebroventricularly (i.c.v.) injected glucagon-like peptide-1 (GLP-1) on blood pressure and heart rate, and whether central cholinergic system and vasopressinergic system play roles in these effects. Male Wistar albino rats were used throughout the experiments. Blood pressures and heart rates were observed before and for 30 min following drug injections. i.c.v. GLP-1 (100, 500 and 1000 ng/10 microl) caused a dose-dependent increase in both blood pressure and heart rate. Nicotinic receptor antagonist mecamylamine (25 microg/10 microl, i.c.v.) and muscarinic receptor antagonist atropine (5 microg/10 microl, i.c.v.) prevented the stimulating effect of GLP-1 on blood pressure. The effect of GLP-1 on heart rate was blocked only by mecamylamine. The V1 receptor antagonist of vasopressin (B-mercapto B, B-cyclopentamethylenepropionyl, O-Me-Tyr,Arg)-vasopressin (10 microg/kg), that was applied intraarterially, only prevented the effect of GLP-1 on blood pressure, but did not show any effect on heart rate. Our data indicate that i.c.v. GLP-1 increases blood pressure and heart rate, and stimulation of central nicotinic and partially muscarinic receptors and vasopressinergic system play a role in the effects of i.c.v. GLP-1 on blood pressure. The effect of GLP-1 on heart rate may be partially due to stimulation of central nicotinic receptors.     

Aging and photoperiod affect the daily rhythm pattern of atrial natriuretic peptide in the rat atrium

This study investigates the release characteristics of atrial natriuretic peptide (ANP) from young (10 weeks) and old (22 months) rat atrium. Levels of ANP release from samples of atrium were studied by organ perifusion. Rats were exposed to light:dark (LD) cycles of 12:12 or 18:6 and sacrificed at different zeitgeber time (ZT) points: ZT0, ZT6, ZT8, ZT12, ZT16, and ZT19 for LD 12:12 or ZT0, ZT9, ZT16, ZT18, ZT20, and ZT 21.5 for LD 18:6. The heart was collected, and the right atrium was removed, weighed, and perifused with Krebs-bicarbonate buffer for 100 min, including a period of 50 min for stabilization of secretion rate. ANP concentrations released by atrium did not differ between the two age groups either under LD 12:12 or under LD 18:6, except at the light:dark transition under LD 12:12 conditions where ANP levels were significantly (P < 0.05) lower in young compared to old rats. ANP exhibited daily variations in concentrations under LD 12:12, with a peak during the beginning of photophase (ZT0) in young rats and a peak at the beginning of scotophase (ZT12) in old animals. These variations were strongly modified under LD 18:6, where the pattern of the release exhibited a peak during the light phase at ZT16 in both young and old rats. This strongly suggests that the atrial ANP rhythm is dependent on the environmental light:dark cycle. Moreover, the total ANP levels released by atria in old rats were significantly increased under LD 18:6 compared to standard LD 12:12. This observation strongly suggests that old animals are more sensitive to a photoperiodic change. In conclusion, our results show that ANP concentrations in the rat atrium exhibit daily variations which are significantly affected by the daylength (photoperiod) change in aged rats.     

Protective effect of recombinant tumor necrosis factor-alpha in murine salmonellosis

The enhancement of resistance by i.p. administration of murine rTNF-alpha into mice against i.p. challenge with virulent Salmonella typhimurium was studied. Administration of TNF-alpha (5 x 10(4) U/mouse) into mice at 6 or 12 h before the challenge with S. typhimurium organisms enhanced the bactericidal capacity in the peritoneal cavities of the mice. The diminution of the infecting organism in the peritoneal cavities of the TNF-alpha-treated mice was not due to the systemic spread of the organism inasmuch as few organism were recovered from other areas such as the spleen and liver. The TNF-alpha treatment effected a slight increase of neutrophils in the peritoneal cavity, but did not effect an increase of macrophages, including Ia-bearing macrophages. The survival rate of mice infected with Salmonella was improved by the i.p. injection of TNF-alpha before infection. Co-administration of smaller doses of TNF-alpha (5 x 10(3) U) and murine rIFN-gamma (10(2) U) at 6 h before the challenge also effectively enhanced bactericidal activity and protectivity. The cooperative effect of TNF-alpha and IFN-gamma was only seen when these recombinant cytokines were injected together at the proper time before the challenge. Injection of rabbit anti-TNF-alpha serum abolished the effects of TNF-alpha and the cooperative effect of TNF-alpha and IFN-gamma. Furthermore, the serum could abolish the cooperative effect of IFN-gamma and LPS on bactericidal activity, suggesting participation of LPS-induced TNF-alpha in the cooperation.     

Endogenous ghrelin is an orexigenic peptide acting in the arcuate nucleus in response to fasting

Ghrelin, a circulating growth-hormone releasing peptide derived from stomach, stimulates food intake through neuropeptide Y (NPY) neurons of the arcuate nucleus in the hypothalamus (ARC). We examined the effect of ghrelin microinjected into the ARC and the influence of intracerebroventricular (i.c.v.) pretreatment with a GHRH or NPY receptor antagonist on ghrelin-induced food intake in free-feeding male rats. Ghrelin (0.1-1 microg) stimulated food intake in a dose-dependent manner, and this effect was reduced by 55-60% by the Y(5) NPY receptor antagonist (10 microg i.c.v.), but not by the GHRH receptor antagonist MZ-4-71 (10 microg i.c.v.). We also evaluated the effects of passive ghrelin immunoneutralization by the microinjection of anti-ghrelin immunoglobulins (IgGs) intracerebroventricularly or directly into the ARC on food intake in free-feeding and fasted male rats. i.c.v. administration of anti-ghrelin IgGs decreased cumulative food intake over 24 h, whereas microinfusion of anti-ghrelin IgGs into the ARC induced only a short-lived (2 and 6 h) effect. Collectively, these data would indicate that centrally derived ghrelin has a major role in the control of food intake in rats and, in this context, blood-born ghrelin would be effective only in relation to its ability to reach the ARC, which is devoid of blood-brain barrier.     

Circadian rhythm of autophagy proteins in hippocampus is blunted by sleep fragmentation

Autophagy is essential for normal cellular survival and activity. Circadian rhythms of autophagy have been studied in several peripheral organs but not yet reported in the brain. Here, we measured the circadian rhythm of autophagy-related proteins in mouse hippocampus and tested the effect of sleep fragmentation (SF). Expressions of the autophagy-related proteins microtubule‐associated protein 1 light chain 3 (LC3) and beclin were determined by western blotting and immunohistochemistry. Both the hippocampal LC3 signal and the ratio of its lipid-conjugated form LC3-II to its cytosolic form LC3-I showed a 24 h rhythm. The peak was seen at ZT6 (1 pm) and the nadir at ZT16 (1 am). The LC3 immunoreactivity in hippocampal CA1 pyramidal neurons also distributed differently, with more diffuse cytoplasmic appearance at ZT16. Chronic SF had a mild effect to disrupt the 24 h rhythm of LC3 and beclin expression. Interestingly, a greater effect of SF was seen after 24 h of recovery sleep when LC3-II expression was attenuated at both the peak and trough of circadian activities. Overall, the results show for the first time that the hippocampus has a distinct rhythm of autophagy that can be altered by SF.     

Hypnotic activity of N3-benzylthymidine on mice

The pharmacological effect in mice of N3-benzylthymidine (N3-ByTd) was examined by two routes of administration; intravenous (i.v.) and intracerebroventricular (i.c.v.), and compared with the effect of administration of N3-benzyluridine (N3-ByUd) previously reported. Hypnotic activity, pentobarbital (PB)-induced sleeping time, motor incoordination and spontaneous activity were used as indices of pharmacological effects. N3-ByTd (0.5-2.0 mumol/mouse, i.c.v.) and N3-ByUd (1.5-3.0 mumol/mouse, i.c.v.) were found to possess dose-dependent hypnotic activity, and N3-ByTd had more potent hypnotic activity than N3-ByUd. Both N3-ByTd and N3-ByUd (0.5 and 1.0 mumol/mouse, i.c.v., respectively) showed a synergistic effect on PB-induced sleep, although their parent compounds, thymidine (Td) and uridine (Ud), did not potentiate the activity at each dose. In motor incoordination, the effect of N3-ByTd (0.5 mumol/mouse) continued for 6 hr after i.c.v. injection. All compounds decreased the spontaneous activity of mice by i.c.v. administration. Furthermore, both N3-ByTd and N3-ByUd decreased the activity, when they were administered by i.v. These results reveal that both N3-benzylpyrimidine nucleosides have more direct depressant effects on the central nervous system (CNS) than the parent compounds. Among the pyrimidine nucleoside derivatives tested, N3-ByTd was found to be the most potent hypnotic substance.     

Regulation of the rat brain endothelin system by endogenous beta-endorphin

Several lines of evidence indicate that the central endogenous opioid and endothelin (ET) system regulate each other. To explore this idea further, we determined the effect of intracerebroventricular (i.c.v.) administration of anti-beta-endorphin IgG (rabbit) on the expression level of the opioid, corticotropin-releasing hormone and endothelin receptors, and tissue concentration of ET-1. Three days after implanting cannula into the lateral ventricle, male Sprague-Dawley rats were administered 10 microl (i.c.v.) of either control rabbit IgG (2.5 microg/microl) or anti-beta-endorphin IgG (2.5 microg/microl) on days 1, 3 and 5. On day 6, animals were euthanized and caudate, cortex and hippocampus collected for Western blot analysis. Anti-beta-endorphin IgG down-regulated ET-A receptor protein expression in the caudate (51%), but had no effect on the expression of mu, delta, kappa opioid, ET-B, CRH-1 and CRH-2 receptors in any brain region. Anti-beta-endorphin IgG increased tissue ET-1 levels in the caudate by 30.3%. [35S]GTP-gamma-S binding assays demonstrated that anti-beta-endorphin IgG increased the efficacy of [D-Ala2-MePhe4, Gly-ol5]enkephalin without altering its potency in caudate. Control experiments showed that there was no detectable rabbit IgG in caudate, cortex and hippocampus samples. These results suggest that beta-endorphin in the CSF coordinately regulates ET-1 levels and the ET-A receptor in rat caudate. These findings support the hypothesis that CSF neuropeptides have regulatory effects and further demonstrate a link between opioid and ET system.     

ANP(1-28), BNP(1-32) and CNP(1-22) increase the severity of picrotoxin-kindled seizure syndrome in rats

The administration of rANP(1-28) in doses of 1.0 and 2.0 nmol (but not 0.2 nmol) into the lateral cerebral ventricle (i.c.v) of rats preliminarily kindled with picrotoxin resulted in an increase of the severity of picrotoxin-kindled convulsions 24 hrs after injection of the peptide. I.c.v. injection of pBNP(1-32) also resulted in a proepileptic effect when it was applied in the same doses with a similar time course; the increased seizure severity was observed 48 hrs after injection of pBNP in a dose of 2 nmol. I.c.v. administration of CNP(1-22) in a dose of 2 nmol induced an increase in the severity of picrotoxin-kindled convulsions 24 and 48 hrs after application of the peptide. None of the peptides influenced the seizure syndrome immediately after the injections. It is presumed that the delayed proepileptic properties of the three natriuretic peptides could be caused by some of their stable fragments which accumulate during their metabolism.     

Central noradrenergic neurons and the hypertensive effects of intracerebroventricularly administered prostaglandin E2 in anaesthetized rabbits

The participation of central noradrenergic neurons in the pressor responses to intracerebroventricular (i.c.v.) administration of prostaglandin (PG) E2 was studied in anaesthetized rabbits. The hypertensive effect induced by i.c.v. injection of PGE2 was inhibited by i.c.v. pretreatment with 6-hydroxydopamine and phentolamine, but not propranolol. These findings suggest that the cerebral noradrenergic neurons may be involved in the development of hypertensive effect of PGE2 through the adrenergic alpha-receptors.     

Dimethyl Sulfoxide and Ebselen Prevent Convulsions Induced by 5-Aminolevulinic Acid

We investigated whether intrastriatal (i.s.) administration of 5-aminolevulinic acid (ALA) induces oxidative damage and whether behavioral alterations induced by i.s. administration of ALA could be affected by antioxidants. Unilateral injection of ALA (6 micromol/striatum) increased (approximately 30%) thiobarbituric acid-reactive substances (TBARS), but did not affect striatal content of total thiol groups. ALA-induced body asymmetry was not prevented by pretreatment with ascorbic acid (100 mg/kg, s.c.), dimethyl sulfoxide (DMSO, 0.5 microl/striatum, i.s.) or ebselen (10 nmol/striatum, i.s.). ALA-induced convulsions were not prevented by ascorbic acid, but were partially prevented by DMSO and completely prevented by ebselen. Ebselen completely prevented the increase of striatal TBARS induced by ALA. Results obtained suggest the involvement of reactive species in ALA-induced convulsions and may be of value in understanding the physiopathology of neurological dysfunctions associated to ALA overload.     

Chronic administration of fluoxetine alters locomotor behavior, but does not potentiate the locomotor stimulating effects of CRH in juvenile Chinook salmon (Oncorhynchus tshawytscha)

The present study investigated: 1) the behavioral effects of chronic administration of a serotonin uptake inhibitor (fluoxetine) in juvenile Chinook salmon, Oncorhynchus tshawytscha and, 2) whether chronic administration of fluoxetine alters the behavioral effects of corticotropin-releasing hormone (CRH). Chronic (20 day) treatment with fluoxetine decreased locomotor activity when compared to fish given long-term injections of saline. An intracerebroventricular (i.c.v.) injection of CRH had no effect on locomotor activity following a 20 day intraperitoneal treatment with either saline or fluoxetine. Chronic treatment with fluoxetine also increased the amount of time fish spent near the center of the tank. A similar increase was seen in fish given a chronic intraperitoneal (i.p.) series of saline followed by an acute i.c.v. injection of CRH. However, the effect was not additive when fish were given chronic i.p. injections of fluoxetine followed by an acute i.c.v. injection of CRH. These results provide evidence to support the hypothesis that the serotonergic system is involved in mediating locomotor activity and habitat choice in teleosts.     

Intracerebroventricular administration of calcitonin enhances glucose-stimulated release of insulin

Intracerebroventricular (i.c.v.) administration of salmon calcitonin (500 ng) augmented glucose-stimulated release of insulin in rats. Vagotomy increased this enhancement effect of i.c.v. calcitonin significantly, whereas peripheral atropine treatment did not change it. Adrenal catecholamines did not participate in the centrally mediated insulinotropic effect of calcitonin since acute adrenalectomy did not modify the enhancement effect of i.c.v. calcitonin. Destruction of the sympathetic ganglia by neonatal treatment with 6-hydroxydopamine abolished the enhancement effect of i.c.v. calcitonin, which suggests that the sympathetic nervous system participates in the central action of calcitonin to enhance glucose-stimulated release of insulin.     

Differential antagonism of endomorphin-1 and endomorphin-2 supraspinal antinociception by naloxonazine and 3-methylnaltrexone

To determine if different subtypes of mu-opioid receptors were involved in antinociception induced by endomorphin-1 and endomorphin-2, the effect of pretreatment with various mu-opioid receptor antagonists beta-funaltrexamine, naloxonazine and 3-methylnaltrexone on the inhibition of the paw-withdrawal induced by endomorphin-1 and endomorphin-2 given intracerebroventricularly (i.c.v.) were studied in ddY male mice. The inhibition of the paw-withdrawal induced by i.c.v. administration of endomorphin-1, endomorphin-2 or DAMGO was completely blocked by the pretreatment with a selective mu-opioid receptor antagonist beta-funaltrexamine (40 mg/kg), indicating that the antinociception induced by all these peptides are mediated by the stimulation of mu-opioid receptors. However, naloxonazine, a mu1-opioid receptor antagonist pretreated s.c. for 24h was more effective in blocking the antinociception induced by endomorphin-2, than by endomorphin-1 or DAMGO given i.c.v. Pretreatment with a selective morphine-6 beta-glucuronide blocker 3-methylnaltrexone 0.25mg/kg given s.c. for 25 min or co-administration of 3-methylnaltrexone 2.5 ng given i.c.v. effectively attenuated the antinociception induced by endomorphin-2 given i.c.v. and co-administration of 3-methylnaltrexone shifted the dose-response curves for endomorphin-2 induced antinociception to the right by 4-fold. The administration of 3-methylnaltrexone did not affect the antinociception induced by endomorphin-1 or DAMGO given i.c.v. Our results indicate that the antinociception induced by endomorphin-2 is mediated by the stimulation of subtypes of mu-opioid receptor, which is different from that of mu-opioid receptor subtype stimulation by endomorphin-1 and DAMGO.