The V1a vasopressin receptor is necessary and sufficient for normal social recognition: a gene replacement study

Vasopressin modulates many social and nonsocial behaviors, including emotionality. We have previously reported that male mice with a null mutation in the V1a receptor (V1aR) exhibit a profound impairment in social recognition and changes in anxiety-like behavior. Using site-specific injections of a V1aR-specific antagonist, we demonstrate that the lateral septum, but not the medial amygdala, is critical for social recognition. Reexpressing V1aR in the lateral septum of V1aR knockout mice (V1aRKO) using a viral vector resulted in a complete rescue of social recognition. Furthermore, overexpression of the V1aR in the lateral septum of wild-type (wt) mice resulted in a potentiation of social recognition behavior and a mild increase in anxiety-related behavior. These results demonstrate that the V1aR in the lateral septum plays a critical role in the neural processing of social stimuli required for complex social behavior.     

Roles of α- and β-estrogen receptors in mouse social recognition memory: effects of gender and the estrous cycle

Establishing clear effects of gender and natural hormonal changes during female ovarian cycles on cognitive function has often proved difficult. Here we have investigated such effects on the formation and long-term (24 h) maintenance of social recognition memory in mice together with the respective involvement of α- and β-estrogen receptors using α- and β-estrogen receptor knockout mice and wildtype controls. Results in wildtype animals showed that while females successfully formed a memory in the context of a habituation/dishabituation paradigm at all stages of their ovarian cycle, only when learning occurred during proestrus (when estrogen levels are highest) was it retained after 24 h. In α-receptor knockout mice (which showed no ovarian cycles) both formation and maintenance of this social recognition memory were impaired, whereas β-receptor knockouts showed no significant deficits and exhibited the same proestrus-dependent retention of memory at 24 h. To investigate possible sex differences, male α- and β-estrogen receptor knockout mice were also tested and showed similar effects to females excepting that α-receptor knockouts had normal memory formation and only exhibited a 24 h retention deficit. This indicates a greater dependence in females on α-receptor expression for memory formation in this task. Since non-specific motivational and attentional aspects of the task were unaffected, our findings suggest a general α-receptor dependent facilitation of memory formation by estrogen as well as an enhanced long-term retention during proestrus. Results are discussed in terms of the differential roles of the two estrogen receptors, the neural substrates involved and putative interactions with oxytocin.     

Vasopressin 1a receptor knockout mice have a subtle olfactory deficit but normal aggression

Two receptors for vasopressin (Avp) are expressed in the brain, the Avp 1a receptor (Avpr1a) and the Avp 1b receptor (Avpr1b). To investigate the role of Avpr1a in behaviors in mice more extensively, we generated a line of mice lacking a functional Avpr1a (knockout, Avpr1a(-/-)). We first performed a baseline phenotypic screen of the Avpr1a knockouts followed by a more detailed analysis of their circadian rhythms and olfactory function. When free-running in constant darkness, the Avpr1a(-/-) mice have a longer circadian tau than the wild types. There are also subtle olfactory deficits in Avpr1a(-/-) mice as measured in an olfactory habituation/dishabituation test and in the discrimination of female urine from male urine using an operant testing paradigm. An extensive body of research has shown that manipulation of the Avpr1a alters behavior, including aggression and social recognition. Therefore, we expected profound behavioral deficits in mice lacking the Avpr1a gene. Contrary to our expectations, social aggression, anxiety-like behavior and social recognition are unaffected in this line of Avpr1a knockout mice. These data suggest either that the Avpr1a is not as critical as we thought for social behavior in mice or, more likely, that the neural circuitry underlying aggression and other social behaviors compensates for the life-long loss of the Avpr1a. However, the olfactory deficits observed in the Avpr1a(-/-) mice suggest that Avp and Avpr1a drugs may affect behavior, in part, by modulation of chemosensory systems.     

Erythropoiesis and Blood Pressure Are Regulated via AT1 Receptor by Distinctive Pathways

The renin–angiotensin system (RAS) plays a central role in blood pressure regulation. Although clinical and experimental studies have suggested that inhibition of RAS is associated with progression of anemia, little evidence is available to support this claim. Here we report that knockout mice that lack angiotensin II, including angiotensinogen and renin knockout mice, exhibit anemia. The anemia of angiotensinogen knockout mice was rescued by angiotensin II infusion, and rescue was completely blocked by simultaneous administration of AT1 receptor blocker. To genetically determine the responsible receptor subtype, we examined AT1a, AT1b, and AT2 knockout mice, but did not observe anemia in any of them. To investigate whether pharmacological AT1 receptor inhibition recapitulates the anemic phenotype, we administered AT1 receptor antagonist in hypotensive AT1a receptor knockout mice to inhibit the remaining AT1b receptor. In these animals, hematocrit levels barely decreased, but blood pressure further decreased to the level observed in angiotensinogen knockout mice. We then generated AT1a and AT1b double-knockout mice to completely ablate the AT1 receptors; the mice finally exhibited the anemic phenotype. These results provide clear evidence that although erythropoiesis and blood pressure are negatively controlled through the AT1 receptor inhibition in vivo, the pathways involved are complex and distinct, because erythropoiesis is more resistant to AT1 receptor inhibition than blood pressure control.     

Genetic loss of diazepam binding inhibitor in mice impairs social interest

Neuropsychiatric disorders in which reduced social interest is a common symptom, such as autism, depression, and anxiety, are frequently associated with genetic mutations affecting γ‐aminobutyric acid (GABA)ergic transmission. Benzodiazepine treatment, acting via GABA type‐A receptors, improves social interaction in male mouse models with autism‐like features. The protein diazepam binding inhibitor (DBI) can act as an endogenous benzodiazepine, but a role for DBI in social behavior has not been described. Here, we investigated the role of DBI in the social interest and recognition behavior of mice. The responses of DBI wild‐type and knockout male and female mice to ovariectomized female wild‐type mice (a neutral social stimulus) were evaluated in a habituation/dishabituation task. Both male and female knockout mice exhibited reduced social interest, and DBI knockout mice lacked the sex difference in social interest levels observed in wild‐type mice, in which males showed higher social interest levels than females. The ability to discriminate between familiar and novel stimulus mice (social recognition) was not impaired in DBI‐deficient mice of either sex. DBI knockouts could learn a rotarod motor task, and could discriminate between social and nonsocial odors. Both sexes of DBI knockout mice showed increased repetitive grooming behavior, but not in a manner that would account for the decrease in social investigation time. Genetic loss of DBI did not alter seminal vesicle weight, indicating that the social interest phenotype of males lacking DBI is not due to reduced circulating testosterone. Together, these studies show a novel role of DBI in driving social interest and motivation.     

Neurokinin-1 receptor agonists are involved in mediating neutrophil accumulation in the inflamed, but not normal, cutaneous microvasculature: an in vivo study using neurokinin-1 receptor knockout mice

We have used tachykinin neurokinin-1 receptor (NK1 receptor) knockout mice to learn of the link between NK1 receptors and neutrophil accumulation in normal naive skin, as compared with inflamed skin. Intradermal substance P (300 pmol) induced edema formation in wild-type mice, but not in NK1 knockout mice, as expected. However, in contrast to IL-1beta (0.3 pmol), substance P did not induce neutrophil accumulation in wild-type mice. IL-1beta-induced neutrophil accumulation was similar in wild-type and knockout mice, but a significant (p < 0.05) contributory effect of added NK1 agonists, which by themselves have no effect on neutrophil accumulation in normal skin, was observed. The results support the concept that NK1 agonists such as substance P cannot act on their own to mediate neutrophil accumulation in naive skin and provide direct evidence that in inflamed skin, under certain circumstances, the NK1 receptor can play a pivotal role in modulating neutrophil accumulation during the ongoing inflammatory process. We investigated responses to two inflammatory stimuli (carrageenin and zymosan). Neutrophil accumulation was significantly attenuated (p < 0.001) in carrageenin- but not zymosan-induced inflammation in NK1 knockout mice. The carrageenin (500 microg)-induced response was inhibited (p < 0.05) by a NK1 receptor antagonist, SR140333 (480 nmol/kg i.v. at -5 min), in the wild-type group. The bradykinin B1 and B2 receptor antagonists (desArg9[Leu8]bradykinin and HOE 140) each reduced neutrophil accumulation to carrageenin in wild-type animals (p < 0.05), but did not cause further reduction of the suppressed response of knockout mice. The results provide evidence that kinin receptors participate in NK1 receptor-dependent neutrophil accumulation in inflamed mouse skin.     

Effects of long-term estrogen replacement on social investigation and social memory in ovariectomized C57BL/6 mice

Estrogen has been shown to play a role in modulating social recognition memory. However, the literature regarding the influence of estrogen on social memory is sparse and only covers two experimental manipulations: acute injections and receptor knockout. Long-term effects of estrogen replacement on social investigation and social recognition are unknown. Furthermore, existing social recognition protocols focus on memory of very short durations (<2 h). In the present study, we examined long-term effects of estrogen replacement on both short- (<30 min) and long-term (24 h) social recognition in ovariectomized female C57BL/6 mice by implanting 60-day time-release pellets containing physiological doses of estradiol (0, 0.18, or 0.72 mg of 17beta-estradiol). After 55 days of treatment, evidence of social recognition memory, measured by 24-h habituation, was found only in mice receiving the 0.72-mg pellet. This result is remarkable as previous reports indicate that individually-housed untreated rats and mice do not show habituation beyond 2 h. Our study further revealed that estrogen also increased frequencies of baseline social investigation without affecting general activity levels and decreased delayed post-swim-stress serum corticosterone concentration. Thus, these results suggest that long-term estrogen replacement increased the interest in social interaction as well as decreased stress responses. It is likely that the 24-h habituation observed in the estrogen replacement group is mediated jointly by the non-mnemonic effects of estrogen on the behavior displayed during the stage of memory encoding as well as mnemonic effects during the stage of memory consolidation.     

Deletion of Glutamate Delta-1 Receptor in Mouse Leads to Enhanced Working Memory and Deficit in Fear Conditioning

Glutamate delta-1 (GluD1) receptors are expressed throughout the forebrain during development with high levels in the hippocampus during adulthood. We have recently shown that deletion of GluD1 receptor results in aberrant emotional and social behaviors such as hyperaggression and depression-like behaviors and social interaction deficits. Additionally, abnormal expression of synaptic proteins was observed in amygdala and prefrontal cortex of GluD1 knockout mice (GluD1 KO). However the role of GluD1 in learning and memory paradigms remains unknown. In the present study we evaluated GluD1 KO in learning and memory tests. In the eight-arm radial maze GluD1 KO mice committed fewer working memory errors compared to wildtype mice but had normal reference memory. Enhanced working memory in GluD1 KO was also evident by greater percent alternation in the spontaneous Y-maze test. No difference was observed in object recognition memory in the GluD1 KO mice. In the Morris water maze test GluD1 KO mice showed no difference in acquisition but had longer latency to find the platform in the reversal learning task. GluD1 KO mice showed a deficit in contextual and cue fear conditioning but had normal latent inhibition. The deficit in contextual fear conditioning was reversed by D-Cycloserine (DCS) treatment. GluD1 KO mice were also found to be more sensitive to foot-shock compared to wildtype. We further studied molecular changes in the hippocampus, where we found lower levels of GluA1, GluA2 and GluK2 subunits while a contrasting higher level of GluN2B in GluD1 KO. Additionally, we found higher postsynaptic density protein 95 (PSD95) and lower glutamate decarboxylase 67 (GAD67) expression in GluD1 KO. We propose that GluD1 is crucial for normal functioning of synapses and absence of GluD1 leads to specific abnormalities in learning and memory. These findings provide novel insights into the role of GluD1 receptors in the central nervous system.     

Postnatal handling reverses social anxiety in serotonin receptor 1A knockout mice

Mice lacking the serotonin receptor 1A (Htr1a knockout, Htr1a ^KO ) show increased innate and conditioned anxiety. This phenotype depends on functional receptor activity during the third through fifth weeks of life and thus appears to be the result of long-term changes in brain function as a consequence of an early deficit in serotonin signaling. To evaluate whether this phenotype can be influenced by early environmental factors, we subjected Htr1a knockout mice to postnatal handling, a procedure known to reduce anxiety-like behavior and stress responses in adulthood. Offspring of heterozygous Htr1a knockout mice were separated from their mother and exposed 15 min each day from postnatal day 1 (PD1) to PD14 to clean bedding. Control animals were left undisturbed. Maternal behavior was observed during the first 13 days of life. Adult male offspring were tested in the open field, social approach and resident–intruder tests and assessed for corticosterone response to restraint stress. Knockout mice showed increased anxiety in the open field and in the social approach test as well as an enhanced corticosterone response to stress. However, while no effect of postnatal handling was seen in wild-type mice, handling reduced anxiety-like behavior in the social interaction test and the corticosterone response to stress in knockout mice. These findings extend the anxiety phenotype of Htr1a ^KO mice to include social anxiety and demonstrate that this phenotype can be moderated by early environmental factors.     

Social dominance in male vasopressin 1b receptor knockout mice

We have previously reported that mice with a targeted disruption of their vasopressin 1b receptor gene, Avpr1b, have mild impairments in social recognition and reduced aggression. The reductions in aggression are limited to social forms of aggression, i.e., maternal and inter-male aggression, while predatory aggression remains unaffected. To further clarify the role of the Avpr1b in the regulation of social behavior we first examined anxiety-like and depression-like behaviors in Avpr1b knockout (Avpr1b −/−) mice. We then went on to test the ability of Avpr1b −/− mice to form dominance hierarchies. No major differences were found between Avpr1b −/− and wildtype mice in anxiety-like behaviors, as measured using an elevated plus maze and an open field test, or depression-like behaviors, as measured using a forced swim test. In the social dominance study we found that Avpr1b −/− mice are able to form dominance hierarchies, though in early hierarchy formation dominant Avpr1b −/− mice display significantly more mounting behavior on Day 1 of testing compared to wildtype controls. Further, non-socially dominant Avpr1b −/− mice spend less time engaged in attack behavior than wildtype controls. These findings suggest that while Avpr1b −/− mice may be able to form dominance hierarchies they appear to employ alternate strategies.     

Introduction of the human AVPR1A gene substantially alters brain receptor expression patterns and enhances aspects of social behavior in transgenic mice

Central arginine vasopressin receptor 1A (AVPR1A) modulates a wide range of behaviors, including stress management and territorial aggression, as well as social bonding and recognition. Inter- and intra-species variations in the expression pattern of AVPR1A in the brain and downstream differential behavioral phenotypes have been attributed to differences in the non-coding regions of the AVPR1A gene, including polymorphic elements within upstream regulatory areas. Gene association studies have suggested a link between AVPR1A polymorphisms and autism, and AVPR1A has emerged as a potential pharmacological target for treatment of social cognitive impairments and mood and anxiety disorders. To further investigate the genetic mechanism giving rise to species differences in AVPR1A expression patterns and associated social behaviors, and to create a preclinical mouse model useful for screening drugs targeting AVPR1A, we engineered and extensively characterized bacterial artificial chromosome (BAC) transgenic mice harboring the entire human AVPR1A locus with the surrounding regulatory elements. Compared with wild-type animals, the humanized mice displayed a more widely distributed ligand-AVPR1A binding pattern, which overlapped with that of primates. Furthermore, humanized AVPR1A mice displayed increased reciprocal social interactions compared with wild-type animals, but no differences in social approach and preference for social novelty were observed. Aspects of learning and memory, specifically novel object recognition and spatial relocation recognition, were unaffected. The biological alterations in humanized AVPR1A mice resulted in the rescue of the prepulse inhibition impairments that were observed in knockout mice, indicating conserved functionality. Although further behavioral paradigms and additional cohorts need to be examined in humanized AVPR1A mice, the results demonstrate that species-specific variations in the genomic content of regulatory regions surrounding the AVPR1A locus are responsible for differential receptor protein expression patterns across species and that they are likely to contribute to species-specific behavioral variation. The humanized AVPR1A mouse is a potential preclinical model for further understanding the regulation of receptor gene expression and the impact of variation in receptor expression on behaviors, and should be useful for screening drugs targeting human AVPR1A, taking advantage of the expression of human AVPR1A in human-relevant brain regions.KEY WORDS: AVPR1A, Humanized mouse, Social behavior, Species-specific, Microsatellite, Autism     

The initiation of B cell clonal expansion occurs independently of pre-B cell receptor formation.

Current models of B cell development posit that clonal expansion occurs as a direct result of Ig H chain expression. To test this hypothesis, we isolated a population of early B cells in which H chain recombination is initiated and assessed V(H)DJ(H) rearrangements in both cycling and noncycling cells. We found that actively dividing cells within this population are enriched for H chain rearrangements that are productive when compared with their counterparts in G(0)/G(1), apparently supporting a role for H chain expression in initiating early B cell division; entrance into the cell cycle was accompanied by V(H) gene-dependent H chain selection. However, we also identified a phenotypically identical population of actively cycling early B cells in the absence of H chain expression in recombination activating gene knockout mice. In addition, actively cycling early B cells could be detected in pre-B cell receptor (pBCR)-negative lambda5 knockout mice, but we found no evidence for V(H)-dependent H chain selection in this population. Given these results, we suggest that the initiation of clonal expansion, at this early stage in B cell development, occurs independently of H chain expression. Although the cycling cell pool is enriched for pBCR-positive cells in mice expressing surrogate L chain, pBCR formation is not required for the initiation of cell division.     

T cell regulation of polyclonal B cell responsiveness. II. Evidence for a deficit in T cell function in mice with an X-linked B lymphocyte defect.

In addition to the x-linked B cell maturation deficit previously reported in CBA/N mice, a functional T cell defect has now been observed. T lymphocyte regulation of the polyclonal PFC response was studied within the context of this x-linked immunodeficiency model. The ability of 1) B cells from (CBA X CBA/CaJ)F1, male mice to respond to nonspecific T cell helper signals and 2) T cells from NCF1 male mice to provide such signals was investigated under in vitro conditions by using bacterial lipopolysaccharide (LPS) as the polyclonal activator. B lymphocytes from both male and female NCF1 mice were receptive to T cell help rendered by NCF1 female T cells. Male T cells. however, were unable to augment polyclonal B cell responses of either NCF1 male or female B cells to LPS. Treatment with ATS + C reduced the polyclonal response of female but not male spleen cells to LPS. This deficit could not be overcome by the use of greater numbers of NCF1 male T cells. The observation that this deficiency in T cell regulation is not due to active suppression suggests that the results may be attributable to an intrinsic T cell defect.     

Enhanced proliferation of astrocytes from beta(2)-adrenergic receptor knockout mice is influenced by the IGF system

In the present study, we investigated the IGF system in neonatal astrocytes derived from mice with a targeted disruption of the beta-2 adrenergic receptor (β₂AR). β₂AR knockout astrocytes demonstrated higher proliferation rates and increased expression of the astrogliotic marker GFAP, as compared with wild-type cells. β₂AR deletion also regulated molecules of the IGF system. Although IGF-1 levels remained unaltered, IGF-2 and type 1 IGF receptor expression was increased in β₂AR knockout cells. Furthermore, conditioned medium from knockout astrocytes contained lower levels of IGF binding protein-2 and -4. Our data suggest a deficit of β₂AR on astrocytes, as previously reported in multiple sclerosis, may have implications on proliferative status of astrocytes, a feature that might be attributed to regulation of IGF mitogenic actions.     

Very low density lipoprotein (VLDL) receptor-deficient mice have reduced lipoprotein lipase activity. Possible causes of hypertriglyceridemia and reduced body mass with VLDL receptor deficiency.

Although very low density lipoprotein (VLDL) receptor (VLDLr) knockout mice have been reported to have no lipoprotein abnormalities, they develop less adipose tissue than control mice when fed a high calorie diet. Mice that are deficient in adipose tissue expression of lipoprotein lipase (LpL) also have less fat, but only when crossed with ob/ob mice. We hypothesized that the VLDLr, a protein that will bind and transport LpL, is required for optimal LpL actions in vivo and that hypertriglyceridemia due to VLDLr deficiency is exacerbated by either LpL deficiency or VLDL overproduction. Fasted VLDLr knockout (VLDLr0) mice were more hypertriglyceridemic than controls (2-fold greater triglyceride levels). The hypertriglyceridemia due to VLDLr0 was even more evident when VLDLr0 mice were crossed with heterozygous LpL-deficient (LpL1) and human apolipoprotein B (apoB) transgenic mice. This was due to an increase in apoB48-containing VLDL. [(3)H]VLDL turnover studies showed that VLDL-triglyceride clearance in VLDLr0/LpL1 mice was impaired by 50% compared with LpL1 mice. VLDLr0/LpL1 mice had less LpL activity in postheparin plasma, heart, and skeletal muscle. Infection of mice with an adenovirus-expressing receptor-associated protein, an inhibitor of the VLDLr, reduced LpL activity in wild type but not VLDLr0 mice. Therefore, the VLDLr is required for normal LpL regulation in vivo, and the disruption of VLDLr results in hypertriglyceridemia associated with decreased LpL activity.     

Overexpression of the NR2A subunit in the forebrain impairs long‐term social recognition and non‐social olfactory memory

Animals must recognize and remember conspecifics and potential mates, and distinguish these animals from potential heterospecific competitors and predators. Despite its necessity, aged animals are known to exhibit impaired social recognition memory. As the brain ages, the ratio of NR2A:NR2B in the brain increases over time and has been postulated to underlie the cognitive decline observed during the aging process. Here, we test the hypothesis that an increased NR2A:NR2B subunit ratio underlies long‐term social recognition memory. Using transgenic overexpression of NR2A in the forebrain regions, we investigated the ability of these mice to learn and remember male and female conspecifics, mice of another strain and animals of another rodent species, the rat. Furthermore, due to the importance of olfaction in social recognition, we tested the olfactory memory in the NR2A transgenic mice. Our series of behavioral experiments revealed significant impairments in the NR2A transgenic mice in long‐term social memory of both male and female conspecifics. Additionally, the NR2A transgenic mice are unable to recognize mice of another strain or rats. The NR2A transgenic mice also exhibited long‐term memory impairments in the olfactory recognition task. Taken together, our results provide evidence that an increased NR2A:NR2B ratio in the forebrain leads to reduced long‐term memory function, including the ethologically important memories such as social recognition and olfactory memory .     

genetic overexpression of NR2B subunit enhances social recognition memory for different strains and species

The ability to learn and remember conspecifics is essential for the establishment and maintenance of social groups. Many animals, including humans, primates and rodents, depend on stable social relationships for survival. Social learning and social recognition have become emerging areas of interest for neuroscientists but are still not well understood. It has been established that several hormones play a role in the modulation of social recognition including estrogen, oxytocin and arginine vasopression. Relatively few studies have investigated how social recognition might be improved or enhanced. In this study, we investigate the role of the NMDA receptor in social recognition memory, specifically the consequences of altering the ratio of the NR2B:NR2A subunits in the forebrain regions in social behavior. We produced transgenic mice in which the NR2B subunit of the NMDA receptor was overexpressed postnatally in the excitatory neurons of the forebrain areas including the cortex, amygdala and hippocampus. We investigated the ability of both our transgenic animals and their wild-type littermate to learn and remember juvenile conspecifics using both 1-hr and 24-hr memory tests. Our experiments show that the wild-type animals and NR2B transgenic mice preformed similarly in the 1-hr test. However, transgenic mice showed better performances in 24-hr tests of recognizing animals of a different strain or animals of a different species. We conclude that NR2B overexpression in the forebrain enhances social recognition memory for different strains and animal species.     

Social and sexual incentive properties of estrogen receptor alpha, estrogen receptor beta, or oxytocin knockout mice

Social and sexual incentive motivation, defined as the intensity of approach to a social and a sexual incentive, respectively, were studied in female Swiss Webster mice. In the first experiment, the social incentive was a castrated mouse of the same strain as the females, whereas the sexual incentive was an intact male mouse of the same strain. Ovariectomized females were first tested after oil treatment and then after administration of estradiol benzoate + progesterone in doses sufficient to induce full receptivity. The hormones increased sexual incentive motivation while leaving social incentive motivation unaffected. This suggests that sexual incentive motivation in the female mouse is dependent on ovarian hormones. In the next experiment, ovariectomized females were tested with an intact, male estrogen receptor α knockout and its wild type as incentives, first without hormones and then when fully receptive. There were no differences in incentive properties between the wild type and the knockout. In a similar experiment, we used an intact male estrogen receptor β knockout and its corresponding wild type as incentives. The wild type turned out to be a more attractive social incentive than the knockout, while they were equivalent as sexual incentives. Finally, an intact male oxytocin knockout and its wild type were used as incentives. The knockout turned out to be a superior incentive, particularly a superior sexual incentive. The fact that the estrogen receptor β and oxytocin knockouts have incentive properties different from their wild types may be important to consider in studies of these knockouts' sociosexual behaviors.     

Interaction of nitric oxide and serotonin in aggressive behavior

Nitric oxide (NO) modulates many behavioral and neuroendocrine responses. Genetic or pharmacological inhibition of the synthetic enzyme that produces NO in neurons evokes elevated and sustained aggression in male mice. Recently, the excessive aggressive and impulsive traits of neuronal NO synthase knockout (nNOS-/-) mice were shown to be caused by reductions in serotonin (5-HT) turnover and deficient 5-HT1A and 5-HT1B receptor function in brain regions regulating emotion. The consistently high levels of aggression observed in nNOS-/- mice could be reversed by 5-HT precursors and by treatment with specific 5-HT1A and 5-HT1B receptor agonists. The expression of the aggressive phenotype of nNOS-/- knockout mice requires isolated housing prior to testing. The effects of social factors such as housing condition and maternal care can affect 5-HT and aggression, but the interaction among extrinsic factors, 5-HT, NO, and aggression remains unspecified. Taken together, NO appears to play an important role in normal brain 5-HT function and may have significant implications for the treatment of psychiatric disorders characterized by aggressive and impulsive behaviors.     

NR2B‐deficient mice are more sensitive to the locomotor stimulant and depressant effects of ethanol

The NR2B subunit of N‐methyl d ‐aspartate glutamate receptors influences pharmacological properties and confers greater sensitivity to the modulatory effects of ethanol. This study examined behavioral responses to acute ethanol in a conditional knockout mouse model that allowed for a delayed genetic deletion of the NR2B subunit to avoid mouse lethality. Mice lacking the NR2B gene (knockout) were produced by mating NR2B[f/f] mice with CAMKIIa‐driven tTA transgenic mice and the tetO‐CRE transgenic mice. Adult male and female offspring representing each of the resultant genotypes (knockout, CAM, CRE and wildtype mice) were tested for open‐field locomotor activity following acute low‐ and high‐dose ethanol challenge as well as loss of righting reflex. Findings indicate that male and female mice lacking the NR2B subunit exhibited greater overall activity in comparison to other genotypes during the baseline locomotor activity test. NR2B knockout mice exhibited an exaggerated stimulant response to 1.5 g/kg (i.p.) and an exaggerated depressant response to 3.0 g/kg (i.p.) ethanol challenge. In addition, NR2B knockout mice slept longer following a high dose of ethanol (4.0 g/kg, i.p.). To evaluate pharmacokinetics, clearance rates of ethanol (1.5, 4.0 g/kg, i.p.) were measured and showed that female NR2B knockouts had a faster rate of metabolism only at the higher ethanol dose. Western blot analyses confirmed significant reduction in NR2B expression in the forebrain of knockout mice. Collectively, these data indicate that the NR2B subunit of the N‐methyl d ‐aspartate glutamate receptor is involved in regulating low‐dose stimulant effects of ethanol and the depressant/hypnotic effects of ethanol.