Assessment of early postpartum reproductive performance in two high producing Estonian dairy herds.

Early postpartum (6 weeks) ovarian activity, hormonal profiles, uterine involution, uterine infections, serum electrolytes, glucose, milk acetoacetate and blood urea nitrogen (BUN) levels were studied in 2 Estonian high producing dairy herd with annual milk production of 7688 (Farm A) and 9425 (Farm B). From each farm 10 cows, with normal calving performance were used. Blood samples for the hormonal (PGF2alpha-metabolite, progesterone) analyses were withdrawn. On day 25 PP blood serum samples were taken for the evaluation of metabolic/electrolyte status. On the same day estimation of milk acetoacetate values was done. The ultrasound (US) was started on day 7 PP and was performed every 3rd day until the end of experiment. Uterine content, follicular activity and sizes of the largest follicle and corpus luteum were monitored and measured. Vaginal discharge and uterine tone were recorded during the rectal palpation. Each animal in the study was sampled for bacteriological examination using endometrial biopsies once a week. Two types of PGF2alpha-metabolite patterns were detected: elevated levels during 14 days PP, then decline to the basal level and then a second small elevation at the time of final elimination of the bacteria from the uterus: or elevated levels during first 7 days PP, then decline to the basal level and a second small elevation before the final elimination of bacteria. Endometritis was diagnosed in 5 cows in farm A and in 3 cows in farm B respectively. In farm A, 5 cows out of 10 ovulated during experimental period and in 1 cow cystic ovaries were found. In farm B, 3 cows out of 10 ovulated. In 3 cows cystic ovaries were found. Altogether 40% of cows had their first ovulation during the experimental period. Three cows in farm A and 5 cows in farm B were totally bacteria negative during the experimental period. The most frequent bacteria found were A. pyogenes, Streptococcus spp., E. coli., F. necrophorum and Bacteroides spp. The highest incidence of bacteriological species was found during the first 3 weeks in both farms. All animals were free from bacteria after 5th week PP in farm A and after 4th week in farm B respectively. Serum electrolytes and glucose levels were found to be within the reference limits for the cows in both farms. No significant difference was found between farms (p > 0.05). Low phosphorus levels were found in both farms. Significant difference (p < 0.05) was found in BUN levels between farms. In both farms milk acetoacetate values were staying within the reference range given for the used test (< 100 micromol/l). The uterine involution and bacterial elimination in the investigated cows could consider as normal but more profound metabolic studies could be needed to find reasons for later resumption of ovarian activity. Some recommendations to changing feeding regimes and strategies should also be given.

Factors influencing behavior of group-housed male rats in the social interaction test: focus on cohort removal.

The rat social interaction (SI) test is used widely to measure anxiety-like behavior, yet the influence of various factors such as testing time, pre-experimental manipulations (transport stress), and testing of animals from the same cage (cohort removal, CR) on SI has not been systematically studied. We measured SI behavior of male triad-housed Wistar rats in a novel dimly lit arena (low light unfamiliar, LU) and found that SI time is higher in the beginning of the activity (dark) phase when compared with SI time in first half of the light phase. Furthermore, SI time is significantly increased by habituation of animals to the testing room during light phase, but this intervention has no effect in early dark phase when SI behavior is already maximal. Sequential removal of rats from the home cage led to the stress-like behavioral and physiological consequences. Rats removed in the last position had shorter SI time and higher body temperature. These data demonstrate that SI is higher during early dark vs. early light phase and confirm that CR has anxiogenic-like effects in rats. We conclude that the usage of sequentially removed group-housed rats in behavioral tests can be a source for considerable variation due to anxiety that develops in animals remaining in the cage. On the other hand, CR may be a useful method to study behavioral/neurochemical mechanisms of psychogenic stress in rats.

Neuropeptide Y Y1 receptor-mediated anxiolysis in the dorsocaudal lateral septum: functional antagonism of corticotropin-releasing hormone-induced anxiety.

Neuropeptide Y and corticotropin-releasing hormone are involved in the regulation of various physiological functions including the expression of anxiety and fear. The anxiogenic effects of corticotropin-releasing hormone can be modulated by neuropeptide Y, yet the brain regions involved in this interaction are only partly understood. By utilizing antibodies raised against neuropeptide Y and the Y1 receptor protein we identified a densely labeled cell group in the dorsal zone of caudal part of the rat lateral septum. Bilateral microinjections of neuropeptide Y into the dorsocaudal lateral septum but not into the intramedial septum dose-dependently decreased anxiety in the social interaction test of rats, whereas the effects of corticotropin-releasing hormone were opposite. The anxiogenic-like effect of corticotropin-releasing hormone was reversed by neuropeptide Y pretreatment. Local microinjection of the neuropeptide Y receptor selective antagonists revealed that neither Y1 receptor nor Y2 receptor selective antagonists had effects on experimental anxiety on their own suggesting that neuropeptide Y-induced anxiolysis is not tonic. The Y1 receptor antagonist blocked the anxiolytic-like effect of neuropeptide Y, while the Y2 receptor antagonist was ineffective.We conclude that neuropeptide Y in the dorsocaudal lateral septum may act as an endogenous anxiolytic and antagonize corticotropin-releasing hormone (stress)-induced anxiety. This functional antagonism probably shapes behavior under aversive conditions, as neuropeptide Y-induced anxiolysis is not tonic in nature. An imbalance between these two neuropeptide systems in the septum may lead to a maladaptive expression of anxiety after stress exposure.

Chronic variable stress and partial 5-HT denervation by parachloroamphetamine treatment in the rat: effects on behavior and monoamine neurochemistry.

Chronic variable stress (CVS) and manipulations of 5-HT-ergic neurotransmission are increasingly used as animal models of depression. In the present study, CVS for 2 weeks and a partial lesion of 5-HT projections by a small dose of parachloroamphetamine (PCA, 2 mg/kg) were applied independently or in combination. CVS reduced significantly the gain in body weight and increased the number of defecations in the open field test. PCA reduced body weight only within the first 24 h after its administration. Consumption of sucrose solution and its preference to water in non-deprived rats were significantly higher in PCA-pretreated rats 2 weeks after CVS compared to control animals. In the forced swimming test, both PCA and CVS treatments reduced immobility on the first but not the second session. Both treatments reduced significantly the time rats spent in social interaction. CVS also elicited an increase in the weight of the right adrenal, but this effect was not present in the PCA-pretreated group. PCA reduced 5-HT and 5-HIAA levels in the frontal cortex, hippocampus, and septum by approximately 20%. CVS increased HVA levels in the frontal cortex. Applied together, PCA pretreatment and CVS increased dopamine turnover in the frontal cortex. Conclusively, this study has provided evidence that chronic variable stress, which elicited expected physiological and neurochemical changes, does not reduce sucrose intake or preference in non-deprived animals, but, instead, may increase it after partial 5-HT-ergic denervation; and that partial 5-HT-ergic denervation by a low dose PCA treatment has a long-lasting effect on forced swimming and social behavior similar to chronic stress.

Neuropeptide Y Y(5) receptor antagonist CGP71683A: the effects on food intake and anxiety-related behavior in the rat.

The effects of neuropeptide Y Y(5) receptor antagonist (trans-naphtalene-1-sulphonic acid [4-[(4-amino-quinazolin-2-ylamino)-methyl]-cyclohexylmethyl]-amide hydrochloride; CGP71683A), on food intake, anxiety and locomotor activity were studied. CGP71683A (1-10 mg/kg, i.p.) dose-dependently decreased nocturnal and fasting-induced food intake. CGP71683A did not have an anxiogenic-like effect in the rat social interaction test. In the elevated plus-maze test, where novel neuropeptide Y Y(1) receptor antagonist (2R)-5-([amino(imino)methyl)amino)-2-[(2.2-diphenylacetyl)-amino]-N-[(1R)-1-(4-hydroxyphenyl)ethyl-pentanamide (H 409/22) had anxiogenic-like effect, CGP71683A was inactive. In the open-field test, carried out immediately after the elevated plus-maze test, CGP71683A inhibited horizontal and vertical activity. CGP71683A did modify the habituation of locomotor response in novel environment. These data show that the inhibition of food intake induced by CGP71683A could not be explained by increased fearfulness, a state that is induced by neuropeptide Y Y(1) receptor antagonists. Thus, our data, obtained with first neuropeptide Y Y(5) receptor antagonist CGP71683A, suggest that in contrast to the neuropeptide Y Y(1) receptor, Y(5) receptor is not involved in tonic neuropeptide Y-induced anxiolysis.

Cocaine and amphetamine-regulated transcript peptide (CART(62-76))-induced changes in regional monoamine levels in ratbrain.

Cocaine- and amphetamine-regulated transcript (CART) is a novel neuropeptide with neurotransmitter-like effects. In the present study we examined the influence of CART peptide fragment, CART(62-76), on the levels of catecholamines (dopamine and norepinephrine), serotonin and their metabolites in five regions of the rat brain. CART(62-76) was administered at 0.5 or 5.0 microg dose intracerebroventricularly. A high-pressure liquid chromatograph coupled to electrochemical array detector was used to analyse the tissue homogenates. In the frontal cortex, CART(62-76) increased the levels of 5-hydroxyindoleacetic acid (5-HIAA), a metabolite of serotonin (5-HT). In the striatum, CART(62-76) decreased the levels of noradrenaline and 5-HT. In the hypothalamus, CART(62-76) increased the levels of 5-HIAA. CART(62-76) had no significant effect in the hippocampus and cerebellum. Our data suggest that CART(62-76) peptide has no major effect on dopaminergic pathways, but it modulates the activity of striatal noradrenergic and corticostriatal and hypothalamic serotoninergic system in the rat brain. These regionally selective neurochemical changes may explain the effects of CART peptides on appetitive, emotional and locomotor behaviour.

Inhibition of amphetamine- and apomorphine-induced behavioural effects by neuropeptide Y Y(1) receptor antagonist BIBO 3304.

Neuropeptide Y (NPY) has an important role in the regulation of stress responses and feeding behaviour. There is evidence that some effects elicited by NPY occur due to modulation of action of regular neurotransmitters. The main objective of the present study was to test behavioural effects of the novel neuropeptide Y (NPY) Y(1) receptor antagonist (R)-N-[[4-(aminocarbonylaminomethyl)-phenyl]methyl]-N(2)-(diphe nylacetyl)-argininamide trifluoroacetate (BIBO 3304) on dopamine-dependent behaviour. Intracerebroventricular administration of BIBO 3304 (1, 10, 50 nmol) had no effect on locomotor activity as measured by number of rearings and number of squares visited in an open field test in rats, but at 50 nmol dose defecation was significantly increased. BIBO 3304 (10 nmol) reduced amphetamine-induced increases in horizontal and vertical activity whereas its S-configurated enantiomer BIBO 3457 was inactive. In an open field test BIBO 3304 (10 nmol) inhibited purposeless running in rats sensitized to direct dopaminergic agonist apomorphine (0.5 mg/kg, s.c.). BIBO 3304 (10 nmol but not 1 nmol, i.c.v.) reduced fighting in apomorphine-induced aggression paradigm. Apomorphine-induced aggression was reduced by another, structurally similar, but less potent NPY Y(1) receptor antagonist BIBP 3226 (10 nmol, i.c.v.). A lower dose of BIBP 3226 (1 nmol, i.c.v.) was inactive. Concomitant administration of BIBO 3304 (10 nmol) with low doses of apomorphine (0.5 mg/kg s.c.) over the course of 10 days failed to prevent the development of apomorphine-induced aggressiveness. These data demonstrate that behavioural response to indirectly (amphetamine) and directly (apomorphine) acting dopaminergic stimulants is inhibited by NPY Y(1) receptor antagonists and suggest that NPY Y(1) receptor activation might be important in pathophysiology of disorders associated with hyperactivity of dopaminergic pathways, such as psychosis, schizophrenia and drug abuse. We propose that the effects of BIBO 3304 on amphetamine/apomorphine-induced locomotion and apomorphine-induced aggressiveness are due to modulation of postsynaptic dopaminergic responses rather than direct effects of NPY Y(1) receptor antagonists on dopamine or NPY release.

Differential effects of beta-carbolines and antidepressants on rat exploratory activity in the elevated zero-maze.

Present experiments were designed to compare the effects of antidepressants desipramine (10 and 20 mg/kg IP) and fluoxetine (5 and 10 mg/kg IP) with anxiogenic beta-carboline DMCM (0.5 and 1.0 mg/kg IP) in the elevated zero-maze test in rats. The second aim of this study was to assess the effects of pinoline (6-methoxy-1,2,3, 4-tetrahydro-beta-carboline) in the rat elevated zero-maze test in comparison with structurally unrelated beta-carboline DMCM and antidepressants. The time spent in the open part of the elevated zero-maze was not significantly affected by antidepressants, but was decreased by beta-carbolines pinoline and DMCM. The number of line crossings in the open parts and the number of head dips were also decreased more by beta-carbolines in comparison with antidepressants. Latency to enter the open part was statistically significantly increased only by DMCM. Measurement of locomotor activity in a separate experiment indicated that activity of the rats' time moving, distance traveled, and number of rearings were reduced by all four drugs studied. These results demonstrate that the effects of antidepressants in the elevated zero-maze test differ from the effects of the reference anxiogenic compound DMCM. The effects of pinoline and DMCM in the zero-maze test were similar, which suggests the involvement of mechanisms other than serotoninergic in the action of pinoline.

Differential effects of melanocortin peptides on ingestive behaviour in rats: evidence against the involvement of MC(3) receptor in the regulation of food intake.

The pro-opiomelanocortin-derived peptides decrease food intake possibly via MC4 receptor. In this study we compared the effects of alpha-melanocyte-stimulating hormone (MSH), beta-MSH and gamma(1)-MSH (0.2, 1.0 and 5.0 microg, i.c.v.) on food intake. alpha-MSH and beta-MSH inhibited spontaneous food intake in a dose dependent manner, whereas the gamma(1)-MSH did not. alpha-MSH and beta-MSH but not gamma(1)-MSH (all 5.0 microg, i.c.v.) inhibited fasting-induced food intake about 50%. None of the three peptides inhibited fluid consumption in water-deprived (24 h) rats. It is suggested that MC(3) receptor, activated selectively by gamma(1)-MSH, is not involved in the regulation of food intake.

Orexigenic effect of the melanocortin MC4 receptor antagonist HS014 is inhibited only partially by neuropeptide Y Y1 receptor selective antagonists.

Neuropeptide Y (NPY) and melanocortin (MC) peptides have opposite effects on food intake: NPY-like peptides and MC receptor antagonists stimulate feeding and increase body weight, whereas melanocortins and NPY antagonists inhibit food intake. In this study we tested whether the orexigenic effect of the selective MC4 receptor antagonist HS014 (1 nmol) could be inhibited by three different NPY antagonists, (R)-N2-(diphenylacetyl)-N-[(4-hydroxy-phenyl)methyl]D-argininam ide (BIBP3226), (R)-N-[[4-(aminocarbonylaminomethyl)-phenyl]methyl]-N2(diphenyl acetyl)-argininamidetrifluoroacetate (BIBO3304), and decapeptide [D-Tyr(27,36)D-Thr32]NPY(27-36), after icv administration in freely feeding male rats. All three NPY receptor antagonists inhibited the orexigenic effects of HS014 partially and with markedly different potency. [D-Tyr(27,36)D-Thr32]NPY(27-36) was active only in subconvulsive dose. The NPY Y1 selective antagonist BIBP3226 was more effective in inhibiting the effect of HS014 than BIBO3304 despite in vitro data indicating that BIBP3226 is about 10 times less potent than BIBO3304 at NPY Y1 receptor. An enantiomer of BIBO3304, BIBO3457, failed to inhibit HS014-induced feeding, indicating that the effects of BIBO3304 were stereoselective. These results suggest that stimulation of food intake caused by weakening of melanocortinergic tone at the MC4 receptor is partially but not exclusively related to NPY Y1 receptor activation.

Anorexigenic cocaine- and amphetamine-regulated transcript peptide intensifies fear reactions in rats.

An increasing number of appetite-regulating peptides are being discovered. The list of regulators inhibiting food intake is considerably longer than that of appetite stimulators. In many cases, the peptides inhibiting food intake facilitate fear reactions, whereas the majority of the agents reducing anxiety responses stimulate appetite. Cocaine- and amphetamine-regulated transcript (CART) cDNA was isolated from hypothalamic libraries and CART was reported to inhibit food intake and to mediate the anorectic effects of leptin. Here, we show that the active core fragment of CART (CART(89-103), 0.04-5.0 nmol) injected into lateral cerebral ventricle not only inhibits food intake, but also causes a dose-dependent increase in anxiety-like reactions in elevated plus-maze test. Intracerebroventricular administration of CART(82-103) (0.04-5.0 nmol) did not inhibit water intake and did not affect spontaneous locomotor activity in the open field test ruling out unspecific effects of the peptide. Our results suggest that CART could be an endogenous factor in the brain mediating the effects of stress on appetite.

Neuropeptide Y attenuates the effect of locus coeruleus denervation by DSP-4 treatment on social behaviour in the rat.

Noradrenaline (NA) has been implicated in both increase and reduction of anxiety. Selective destruction of nerve endings of the locus coeruleus projections by DSP-4 has been shown to reduce active behaviour in novel situations by enhancing anxiety. In the present study, DSP-4 (50 mg/kg) treatment reduced locomotor activity and time spent in social interaction in rats placed into a novel environment together with an unfamiliar rat, indicating an anxiogenic-like effect. The effect of DSP-4 on time spent in social interaction was completely antagonized by intracerebroventricular administration of neuropeptide Y (NPY) (1 microg) which had no effect of its own on this measure. The present study thus supports the idea that DSP-4 pretreatment is anxiogenic in novel situations and suggests a functional relationship of NA- and NPY-using neural mechanisms in the regulation of social behaviour.

Tonic inhibition of food intake during inactive phase is reversed by the injection of the melanocortin receptor antagonist into the paraventricular nucleus of the hypothalamus and central amygdala of the rat.

Melanocortins inhibit food intake and melanocortin 4 receptor (MC(4)R) antagonists stimulate feeding behaviour. These effects may occur due to stimulation or blockade of MC(4) receptors in the hypothalamus. To test the validity of this hypothesis, a cyclic peptide, the MC(4)R selective antagonist HS014 (20, 100 and 500 pmol), or vehicle, was injected unilaterally into the paraventricular nucleus of the hypothalamus (PVN). As MC receptors are expressed also in extrahypothalamic sites involved in the regulation of feeding behaviour, HS014 was injected bilaterally into the vicinity of the central nucleus of the amygdala (CA) and the nucleus accumbens region (Acc). All doses of HS014 induced a dose-dependent increase in food intake when injected into the PVN. Intra-amygdalar injections of HS014 (50 and 250 pmol/side) also stimulated food intake, whereas a 10-pmol dose was inactive. Local microinjections of HS014 into the Acc failed to stimulate feeding. These data suggest that endogenous melanocortin receptor agonists exert a tonic inhibitory influence on food consumption by stimulating MC(4) receptors in the hypothalamus and amygdala.

Neuropeptide Y Y1 receptor antagonist BIBP3226 produces conditioned place aversion in rats.

1. Previous studies have shown that the blockade of the neuropeptide Y (NPY) Y1 receptors with N2-(diphenylacetyl)-N-[(4-hydroxy-phenyl)methyl]-D-arginine amide (BIBP3226) induces anxiogenic-like reaction in rats tested in elevated plus-maze test. 2. The present study examined whether such a treatment is aversive using place conditioning in a two-compartment apparatus. Locomotor activity was measured in open field test. 3. Pairings with potentially anxiogenic dose of BIBP3226 (5 micrograms/6.5 microliters, i.c.v.) produced a conditioned aversion for the drug-associated place, whereas the locomotor activity in the open field test was not affected by this dose of BIBP3226. 4. These data suggest that the blockade of central NPY Y1 receptors is aversive and provide additional evidence to the hypothesis that the NPY Y1 receptors are involved in the regulation of affective states.

Long-term administration of MC4 receptor antagonist HS014 causes hyperphagia and obesity in rats.

In this study we investigated the long term effects of a potent and selective melanocortin 4 (MC4) receptor antagonist (HS014) on food intake, body weight, body composition and blood glucose levels in adult rats. HS014 was injected i.c.v. either by twice-daily injections (2 x 1 nmol) for 6 days or administered by continuous infusion with osmotic minipumps (0.16 nmol/h) for 2 weeks. The results show a considerable increase in food intake and body weight after both of the treatments without any signs of tachyphylaxis. After 2 weeks of treatment with osmotic pumps, the HS014-treated rats (average weight 425g) had 20% higher body weight than the controls rats (average 360 g). When i.c.v. injections were terminated, the body weight of the twice-daily HS014-treated rats returned to the levels of control group, whereas the rats treated with continuous infusion of HS014 remained hyperphagic and still gained weight. Blood glucose levels in the rats treated with HS014 infusion were significantly increased. Analysis of body composition in HS014-infused rats indicated that body weight was increased due to fat deposits. These data show for the first time that chronic administration of exogenous MC4 receptor antagonist causes hyperphagia and severe obesity in rats. These data also indicate that the melanocortic control of food intake is very robust and suggest that changes induced by such treatment overcome negative feedback signals.

Dose-dependent effects of noradrenergic denervation by DSP-4 treatment on forced swimming and beta-adrenoceptor binding in the rat.

DSP-4 is a neurotoxin highly selective for the noradrenergic nerve terminals originating from the locus coeruleus. Preliminary data suggested that its effect in a typical screening test for antidepressant drugs, the forced swimming test, is biphasic dependent on the dose. In the present study, DSP-4 was administered in four doses (5, 10, 30 and 50mg/kg) to male Wistar rats. Administration of the neurotoxin had a dose-dependent biphasic effect on immobility time in the forced swimming test 8 and 9 days later. Thus, DSP-4 at the dose of 10mg/kg increased immobility, but higher doses reduced this measure. The reduction of noradrenaline concentration in the frontal cortex and hippocampus was dose-dependent starting from the dose 10mg/kg. Cortical beta-adrenoceptor binding was increased by DSP-4 treatment at the doses 30mg/kg and 50mg/kg. These results suggest that the increase in immobility time in the forced swimming test is associated with presynaptic changes in noradrenaline availability, whereas the decrease in immobility observed after more complete denervation is associated with postsynaptic receptor supersensitivity.

Evidence for involvement of the melanocortin MC4 receptor in the effects of leptin on food intake and body weight.

The hypothesis that the melanocortin MC4 receptor mediates the homeostatic effects of leptin was tested. Leptin (0.3 nmol, i.c.v.) lowered food intake at 4 and 24 h and body weight at 24 h. This effect was inhibited by pretreatment with an analogue of melanocyte stimulating hormone (MSH), the selective melanocortin MC4 receptor antagonist HS014 (cyclic [AcCys11,D-Nal14,Cys18,Asp-NH2(22)]-beta-MSH11-2 2, 0.3 nmol, i.c.v.). HS014 alone at this dose did not modify food intake or body weight. At a higher dose (1.0 nmol, i.c.v.) HS014 stimulated food intake and this orexigenic effect of HS014 was attenuated by leptin pretreatment (0.3 nmol, i.c.v.). These results confirm earlier findings that leptin inhibits food intake and lowers body weight via the melanocortin system and suggest that leptin affects signalling at the melanocortin MC4 receptor.

Discovery of a novel superpotent and selective melanocortin-4 receptor antagonist (HS024): evaluation in vitro and in vivo.

Several novel cyclic MSH analogs were synthesized, and their binding properties were tested on cells transiently expressing the human melanocortin-1 (MC1), MC3, MC4, and MC5 receptors. We discovered a novel substance (HS024) that showed about 20-fold selectivity and very high affinity (Ki = 0.29 nM) for the MC4 receptor. HS024 (cyclic [AcCys3,Nle4,Arg5,D-Nal7,Cys-NH2(11)]alpha-MSH-(3-11)) has a 29-membered atom ring structure that includes an Arg in position 5. HS024 was found to antagonize an alphaMSH-induced cAMP response in cells expressing the human MC1, MC3, MC4, and MC5 receptor DNAs. HS024 also caused a dose-dependent increase in food intake, with a maximum response (4-fold increase) at a 1-nmol dose injected intracerebroventricularly in free feeding rats. We also tested SHU9119, a previously described nonselective MC receptor antagonist, and found HS024 and SHU9119 to have similar potencies for increasing food intake, although SHU9119 appeared to induce more serious side-effects. HS024 increased the food intake of free feeding rats to levels comparable to those in food-deprived rats, indicating that blockade of the MC4 receptor is a highly effective way to increase feeding. Moreover, we tested the effects of intracerebroventricular injections of HS024 in elevated plus-maze and open-field experiments on rats. In these tests, HS024 did not appear to affect emotionality or locomotor activity, suggesting that the MC4 receptor does not mediate the anxiogenic-like and locomotor effects related to the melanocortic peptides.

Anxiogenic-like effect of the NPY Y1 receptor antagonist BIBP3226 administered into the dorsal periaqueductal gray matter in rats.

Exogenous neuropeptide Y (NPY) administered intracerebroventricularly or into the central nucleus of amygdala has anxiolytic-like effects in animal models of anxiety. These effects are probably mediated by the NPY Y1 receptor. The role of the NPY Y1 receptor activation by endogenous NPY in this and other brain areas has not been fully elucidated. The selective NPY Y1 receptor antagonist (R)-N2-(diphenylacetyl)-N-[(4-hydroxy-phenyl)methyl]-D-arginine amide (BIBP3226) was microinjected into various brain sites implicated in the regulation of anxiety-related behaviour and resultant behavioural changes were assessed using the elevated plus-maze (EPM) and open-field test in rats. Intracerebroventricular application of BIBP3226 (5.0 microg) which caused an anxiogenic-like effect in the EPM did not affect exploratory activity in the open-field test. A decrease in EPM exploration was observed also when BIBP3226 (0.5 microg) was microinjected into the dorsal periaqueductal gray matter (DPAG). Intra-DPAG BIBP3226 did not change open-field behaviour suggesting that the effects of BIBP3226 in the EPM test were not related to changes in locomotor activity in general. Bilateral application of BIBP3226 into the central nucleus of amygdala (0.5 and 2.5 microg/side) and unilateral injections into the locus coeruleus and the paraventricular nucleus of the hypothalamus (both 0.5 microg) were ineffective in modifying the plus-maze exploration. These data suggest that endogenous NPY may regulate anxiety-related behaviour in rats by acting via the NPY Y1 receptors in DPAG.

NPY Y1 receptors in the dorsal periaqueductal gray matter regulate anxiety in the social interaction test.

We have reported previously that the NPY Y1 receptor antagonist BIBP3226 applied into the dorsal periaqueductal gray matter (DPAG) has an anxiogenic-like effect in the elevated plus-maze test in rats. In the present study the effects of neuropeptide Y (NPY) Y1 receptor antagonists BIBP3226 (500 pmol) and 1229U91 (formerly also GR231118, GW1229 and EXBP68, 100 and 500 pmol) administered into the DPAG were investigated in the social interaction test in rats. BIBP3226 and 1229U91 (both 500 pmol) significantly decreased the time spent in active social interaction. These results provide additional evidence that NPY-ergic neurotransmission in the DPAG may be involved in the modulation of anxiety-related behaviour and suggest that endogenous NPY, released under stressful conditions in the DPAG, relieves anxiety via the NPY Y1 receptors. This is the first report demonstrating the effect of NPY receptor active agent on social behaviour.