Naive Male Mice Research Articles

Activating Lobule VI PCTH+-Med Pathway in Cerebellum Blocks the Acquisition of Methamphetamine Conditioned Place Preference in Mice.

Cerebellum has been implicated in drug addiction; however, its underlying cellular populations and neuronal circuitry remain largely unknown. In the current study, we identified a neural pathway from tyrosine hydroxylase (TH)-positive Purkinje cells (PCTH+) in cerebellar lobule VI to calcium/calmodulin-dependent protein kinase II (CaMKII)-positive glutamatergic neurons in the medial cerebellar nucleus (MedCaMKII), forming the lobule VI PCTH+-MedCaMKII pathway in male mice. In naive male mice, inhibition of PCTH+ neurons activated Med neurons. During conditioned place preference (CPP) training, exposure to methamphetamine (METH) inhibited lobule VI PCTH+ neurons while excited MedCaMKII neurons in mice. Silencing MedCaMKII using a tetanus toxin light chain (tettox) suppressed the acquisition of METH CPP in mice but resulted in motor coordination deficits in naive mice. In contrast, activating lobule VI PCTH+ terminals within Med inhibited the activity of Med neurons and subsequently blocked the acquisition of METH CPP in mice without affecting motor coordination, locomotor activity, and sucrose reinforcements in naive mice. Our findings identified a novel lobule VI PCTH+-MedCaMKII pathway within the cerebellum and explored its role in mediating the acquisition of METH-preferred behaviors.

Ketamine metabolite alleviates morphine withdrawal-induced anxiety via modulating nucleus accumbens parvalbumin neurons in male mice

Opioid withdrawal generates extremely unpleasant physical symptoms and negative affective states. A rapid relief of opioid withdrawal-induced anxiety has obvious clinical relevance but has been rarely reported. We have shown that injection of ketamine metabolite (2R,6R)-hydroxynorketamine (HNK) leads to a rapid alleviation of anxiety-like behaviors in male mice undergoing chronic morphine withdrawal. Here we investigated the contribution of nucleus accumbens shell (sNAc) parvalbumin (PV)-neurons to this process. Chronic morphine withdrawal was associated with higher intrinsic excitability of sNAc PV-neurons via reduced voltage-dependent potassium currents. Chemogenetic inhibition of sNAc PV-neurons reversed the enhanced excitability of PV-neurons and anxiety-like behaviors in these morphine withdrawal male mice, while activation of sNAc PV-neurons induced anxiety-like behaviors in naive male mice. (2R,6R)-HNK reversed the altered potassium currents and intrinsic excitability of sNAc PV-neurons. Our findings demonstrate an important contribution of sNAc PV-neurons to modulating morphine withdrawal-induced anxiety-like behaviors and rapid relief of anxiety-like behaviors by (2R,6R)-HNK, this newly identified target may have therapeutic potentials in treating opioid addiction and anxiety disorders.

Modulation of SK Channels via Calcium Buffering Tunes Intrinsic Excitability of Parvalbumin Interneurons in Neuropathic Pain: A Computational and Experimental Investigation.

Parvalbumin-expressing interneurons (PVINs) play a crucial role within the dorsal horn of the spinal cord by preventing touch inputs from activating pain circuits. In both male and female mice, nerve injury decreases PVINs' output via mechanisms that are not fully understood. In this study, we show that PVINs from nerve-injured male mice change their firing pattern from tonic to adaptive. To examine the ionic mechanisms responsible for this decreased output, we used a reparametrized Hodgkin-Huxley type model of PVINs, which predicted (1) the firing pattern transition is because of an increased contribution of small conductance calcium-activated potassium (SK) channels, enabled by (2) impairment in intracellular calcium buffering systems. Analyzing the dynamics of the Hodgkin-Huxley type model further demonstrated that a generalized Hopf bifurcation differentiates the two types of state transitions observed in the transient firing of PVINs. Importantly, this predicted mechanism holds true when we embed the PVIN model within the neuronal circuit model of the spinal dorsal horn. To experimentally validate this hypothesized mechanism, we used pharmacological modulators of SK channels and demonstrated that (1) tonic firing PVINs from naive male mice become adaptive when exposed to an SK channel activator, and (2) adapting PVINs from nerve-injured male mice return to tonic firing on SK channel blockade. Our work provides important insights into the cellular mechanism underlying the decreased output of PVINs in the spinal dorsal horn after nerve injury and highlights potential pharmacological targets for new and effective treatment approaches to neuropathic pain.SIGNIFICANCE STATEMENT Parvalbumin-expressing interneurons (PVINs) exert crucial inhibitory control over Aβ fiber-mediated nociceptive pathways at the spinal dorsal horn. The loss of their inhibitory tone leads to neuropathic symptoms, such as mechanical allodynia, via mechanisms that are not fully understood. This study identifies the reduced intrinsic excitability of PVINs as a potential cause for their decreased inhibitory output in nerve-injured condition. Combining computational and experimental approaches, we predict a calcium-dependent mechanism that modulates PVINs' electrical activity following nerve injury: a depletion of cytosolic calcium buffer allows for the rapid accumulation of intracellular calcium through the active membranes, which in turn potentiates SK channels and impedes spike generation. Our results therefore pinpoint SK channels as potential therapeutic targets for treating neuropathic symptoms.

Disinhibition of Mesolimbic Dopamine Circuit by the Lateral Hypothalamus Regulates Pain Sensation.

Our recent study demonstrated the critical role of the mesolimbic dopamine (DA) circuit and its brain-derived neurotropic factor (BDNF) signaling in mediating neuropathic pain. The present study aims to investigate the functional role of GABAergic inputs from the lateral hypothalamus (LH) to the ventral tegmental area (VTA; LHGABA→VTA) in regulating the mesolimbic DA circuit and its BDNF signaling underlying physiological and pathologic pain. We demonstrated that optogenetic manipulation of the LHGABA→VTA projection bidirectionally regulated pain sensation in naive male mice. Optogenetic inhibition of this projection generated an analgesic effect in mice with pathologic pain induced by chronic constrictive injury (CCI) of the sciatic nerve and persistent inflammatory pain by complete Freund's adjuvant (CFA). Trans-synaptic viral tracing revealed a monosynaptic connection between LH GABAergic neurons and VTA GABAergic neurons. Functionally, in vivo calcium/neurotransmitter imaging showed an increased DA neuronal activity, decreased GABAergic neuronal activity in the VTA, and increased dopamine release in the NAc, in response to optogenetic activation of the LHGABA→VTA projection. Furthermore, repeated activation of the LHGABA→VTA projection was sufficient to increase the expression of mesolimbic BDNF protein, an effect seen in mice with neuropathic pain. Inhibition of this circuit induced a decrease in mesolimbic BDNF expression in CCI mice. Interestingly, the pain behaviors induced by activation of the LHGABA→VTA projection could be prevented by pretreatment with intra-NAc administration of ANA-12, a TrkB receptor antagonist. These results demonstrated that LHGABA→VTA projection regulated pain sensation by targeting local GABAergic interneurons to disinhibit the mesolimbic DA circuit and regulating accumbal BDNF release.SIGNIFICANCE STATEMENT The mesolimbic dopamine (DA) system and its brain-derived neurotropic factor (BDNF) signaling have been implicated in pain regulation, however, underlying mechanisms remain poorly understood. The lateral hypothalamus (LH) sends different afferent fibers into and strongly influences the function of mesolimbic DA system. Here, utilizing cell type- and projection-specific viral tracing, optogenetics, in vivo calcium and neurotransmitter imaging, our current study identified the LHGABA→VTA projection as a novel neural circuit for pain regulation, possibly by targeting the VTA GABA-ergic neurons to disinhibit mesolimbic pathway-specific DA release and BDNF signaling. This study provides a better understanding of the role of the LH and mesolimbic DA system in physiological and pathological pain.

The basolateral amygdala-anterior cingulate pathway contributes to depression-like behaviors and comorbidity with chronic pain behaviors in male mice

While depression and chronic pain are frequently comorbid, underlying neuronal circuits and their psychopathological relevance remain poorly defined. Here we show in mice that hyperactivity of the neuronal pathway linking the basolateral amygdala to the anterior cingulate cortex is essential for chronic pain-induced depression. Moreover, activation of this pathway in naive male mice, in the absence of on-going pain, is sufficient to trigger depressive-like behaviors, as well as transcriptomic alterations that recapitulate core molecular features of depression in the human brain. These alterations notably impact gene modules related to myelination and the oligodendrocyte lineage. Among these, we show that Sema4a, which was significantly upregulated in both male mice and humans in the context of altered mood, is necessary for the emergence of emotional dysfunction. Overall, these results place the amygdalo-cingulate pathway at the core of pain and depression comorbidity, and unravel the role of Sema4a and impaired myelination in mood control.

Plasticity of neural connections underlying oxytocin-mediated parental behaviors of male mice

The adult brain can flexibly adapt behaviors to specific life-stage demands. For example, while sexually naive male mice are aggressive to the conspecific young, they start to provide caregiving to infants around the time when their own young are expected. How such behavioral plasticity is implemented at the level of neural connections remains poorly understood. Here, using viral-genetic approaches, we establish hypothalamic oxytocin neurons as the key regulators of the parental caregiving behaviors of male mice. We then use rabies-virus-mediated unbiased screening to identify excitatory neural connections originating from the lateral hypothalamus to the oxytocin neurons to be drastically strengthened when male mice become fathers. These connections are functionally relevant, as their activation suppresses pup-directed aggression in virgin males. These results demonstrate the life-stage associated, long-distance, and cell-type-specific plasticity of neural connections in the hypothalamus, the brain region that is classically assumed to be hard-wired.

Androgen receptor activity underlies sex differences in lung-resident ILC2 functional responses during influenza virus infection

Abstract Lung-resident group 2 innate lymphoid cells (ILC2s) produce type 2 cytokines and facilitate tissue repair in response to alarmins such as IL-33 released during respiratory virus infection, but they also may be functionally suppressed by type 1 cytokines. Lung ILC2s express notably high levels of intracellular androgen receptor (AR) compared to ILC1s, T and B cells. To test the hypothesis that females and males show differential ILC2 responses in influenza virus (IAV) infection, we analyzed the numbers and functional responses of lung ILCs in IAV infected mice. On days 3–10 post-infection, lungs of female mice contained greater numbers of ILC2s and ILC1s compared to males. However, the female ILC2s were preferentially suppressed at the peak of infection, with a dampened type 2 program manifest as attenuated proliferation, decreased IL-5 and amphiregulin production, reduced expression of GATA-3 and IL-33R and increased surface IFNGR. IFNG levels in the lung were comparable between sexes at day 7 post-infection, suggesting intrinsic differences in ILC2 responses to interferons. Indeed, naïve female ILC2s showed higher expression of IFNGR and higher phospho-STAT1 levels following stimulation by IFNG. ILC2s in naive male mice with lymphocyte-restricted AR deficiency displayed levels of IFNGR comparable to female mice, suggesting AR activity underlies sex differences in intrinsic IFNGR expression. Early life orchiectomy revealed that endogenous androgens decreased ILC2 numbers but protected males from suppression of ILC2s in IAV infection. Taken together, our data show that AR activity preserves canonical ILC2 function in males during IAV infection and may help to explain the documented human gender differences in immunity to IAV.

Dopamine Receptors Differentially Control Binge Alcohol Drinking-Mediated Synaptic Plasticity of the Core Nucleus Accumbens Direct and Indirect Pathways.

Binge alcohol drinking, a behavior characterized by rapid repeated alcohol intake, is most prevalent in young adults and is a risk factor for excessive alcohol consumption and alcohol dependence. Although the alteration of synaptic plasticity is thought to contribute to this behavior, there is currently little evidence that this is the case. We used drinking in the dark (DID) as a model of binge alcohol drinking to assess its effects on spike timing-dependent plasticity (STDP) in medium spiny neurons (MSNs) of the core nucleus accumbens (NAc) by combining patch-clamp recordings with calcium imaging and optogenetics. After 2 weeks of daily alcohol binges, synaptic plasticity was profoundly altered. STDP in MSNs expressing dopamine D1 receptors shifted from spike-timing-dependent long-term depression (tLTD), the predominant form of plasticity in naive male mice, to spike-timing-dependent long-term potentiation (tLTP) in DID mice, an effect that was totally reversed in the presence of 4 μm SCH23390, a dopamine D1 receptor antagonist. In MSNs presumably expressing dopamine D2 receptors, tLTP, the main form of plasticity in naive mice, was inhibited in DID mice. Interestingly, 1 μm sulpiride, a D2 receptor antagonist, restored tLTP. Although we observed no alterations of AMPA and NMDA receptor properties, we found that the AMPA/NMDA ratio increased at cortical and amygdaloid inputs but not at hippocampal inputs. Also, DID effects on STDP were accompanied by lower dendritic calcium transients. These data suggest that the role of dopamine in mediating the effects of binge alcohol drinking on synaptic plasticity of NAc MSNs differs markedly whether these neurons belong to the direct or indirect pathways.SIGNIFICANCE STATEMENT We examined the relationship between binge alcohol drinking and spike timing-dependent plasticity in nucleus accumbens (NAc) neurons. We found that repeated drinking bouts modulate differently synaptic plasticity in medium spiny neurons of the accumbens direct and indirect pathways. While timing-dependent long-term depression switches to long-term potentiation (LTP) in the former, timing-dependent LTP is inhibited in the latter. These effects are not accompanied by changes in AMPA and NMDA receptor properties at cortical, amygdaloid, and hippocampal synapses. Interestingly, dopamine D1 and D2 receptor antagonists have opposite effects on plasticity. Our data show that whether core NAc medium spiny neurons belong to the direct or indirect pathways determines the form of spike timing-dependent plasticity (STDP), the manner by which STDP responds to binge alcohol drinking, and its sensitivity to dopamine receptor antagonists.

311. AAV8 Vexosome Vectors Enhance Cell Transduction In Vitro and Outperform Conventional AAV8 Vectors in Liver-Transduction In Vivo in the Presence of Anti-AAV Neutralizing Antibodies

Adeno-associated virus vectors based on serotype 8 (AAV8) have demonstrated superior efficiency of transduction of hepatocytes in vivo in animal models and in humans. Recently, we described extracellular vesicle (exosomes) -associated AAV vectors termed vexosomes (vAAV). We tested vAAV1, 2, and 9 and found them to enhance transduction and antibody evasion capabilities compared to conventional AAV vectors.With the goal of developing an enhanced vector for liver gene therapy, we sought to characterize the in vitro and in vivo transduction, biodistribution, and immunogenicity profile of vAAV8 vectors compared to conventional AAV8 vectors purified from the same preparation.Several cell lines were transduced with conventional AAV8 or vAAV8 vectors expressing luciferase, at multiplicity of infection (MOI) ranging from 250 to 25000, and luciferase expression was measured after an overnight incubation. In HeLa and HEK293 cells, levels of luciferase up to 1 log higher were observed with vAAV8 compared with AAV8 vectors, with detectable levels of luciferase at MOIs as low as 250. In hepatocyte cell lines, the magnitude of enhancement was about 3-fold, with lower max relative light unit signal measured compared to the other cell lines. Notably, although at low levels, transduction with vAAV8 vectors was also observed in a Jurkat T cell line, in which no transduction was observed with conventional AAV8 vectors.We then evaluated the efficiency of liver targeting in vivo with this vector system using the secreted factor IX (F.IX) transgene. Conventional or vAAV8 vectors expressing human F.IX under the control of a liver-specific promoter were administered i.v. to C57BL/6J male mice at 5×1010 vg/mouse. In naive animals, no difference in F.IX transgene expression levels was observed between the two vector types; similarly, vector genome were found at similar levels in liver, spleen, muscle, lungs, heart, and kidneys. In these animals, i.v. vector administration also resulted in identical levels of anti-AAV antibody formation. We next evaluated the effect of vAAV8 on liver transduction in the presence of antibodies. Animals were passively immunized with IVIg intraperitoneally (0.5, 5.0, and 15 mg/mouse) followed by administration of vector (5×1010 vg) intravenously 24 hours later. At a neutralizing antibody titer of~1:10 (0.5mg IVIg), vAAV8 vector-injected mice had levels of expression identical to those in naive animals. At higher titers (>1:100, 5.0 mg), low levels of residual expression of F.IX were measure with vAAV8 vectors and no expression was measured with conventional AAV. No expression was detected with either AAV8 or vAAV8 vectors in animals immunized with the highest dose of IVIg.In conclusion, vAAV8 vectors have unique transduction characteristics that may be exploited in vitro to transduce various cell types. In vivo, these vectors showed identical levels of liver transduction in naive male mice and provided some level of protection from antibody-mediated vector neutralization.

Behavioral Transition from Attack to Parenting in Male Mice: A Crucial Role of the Vomeronasal System

Sexually naive male mice show robust aggressive behavior toward pups. However, the proportion of male mice exhibiting pup-directed aggression declines after cohabitation with a pregnant female for 2 weeks after mating. Subsequently, on becoming fathers, they show parental behavior toward pups, similar to maternal behavior by mothers. To elucidate the neural mechanisms underlying this behavioral transition, we examined brain regions differentially activated in sexually naive males and fathers after exposure to pups, using c-Fos expression as a neuronal activation marker. We found that, after pup exposure, subsets of neurons along the vomeronasal neural pathway-including the vomeronasal sensory neurons, the accessory olfactory bulb, the posterior medial amygdala, the medioposterior division of the bed nucleus of stria terminalis, and the anterior hypothalamic area-were more strongly activated in sexually naive males than in fathers. Notably, c-Fos induction was not observed in the vomeronasal sensory neurons of fathers after pup exposure. Surgical ablation of the vomeronasal organ in sexually naive males resulted in the abrogation of pup-directed aggression and simultaneous induction of parental behavior. These results suggest that chemical cues evoking pup-directed aggression are received by the vomeronasal sensory neurons and activate the vomeronasal neural pathway in sexually naive male mice but not in fathers. Thus, the downregulation of pup pheromone-induced activation of the vomeronasal system might be important for the behavioral transition from attack to parenting in male mice.

Either main or accessory olfactory system signaling can mediate the rewarding effects of estrous female chemosignals in sexually naive male mice.

A long-held view has been that interest of male mice in female body odors reflects an activation of reward circuits in the male brain following their detection by the vomeronasal organ (VNO) and processing via the accessory olfactory system. We found that adult, sexually naive male mice acquired a conditioned place preference (CPP) after repeatedly receiving estrous female urine on the nose and being placed in an initially nonpreferred chamber with soiled estrous bedding on the floor. CPP was not acquired in control mice that received saline on the nose before being placed in a nonpreferred chamber with clean bedding. Robust acquisition of a CPP using estrous female odors as the reward persisted in separate groups of mice in which VNO-accessory olfactory function was disrupted by bilateral lesioning of the accessory olfactory bulb (AOB) or in which main olfactory function was disrupted by zinc sulfate lesions of the main olfactory epithelium (MOE). By contrast, no CPP was acquired for estrous odors in males that received combined AOB and MOE lesions. Either the main or the accessory olfactory system suffices to mediate the rewarding effects of estrous female odors in the male mouse, even in the absence of prior mating experience. The main olfactory system is part of the circuitry that responds to chemosignals involved in motivated behavior, a role that may be particularly important for humans who lack a functional accessory olfactory system.

The paternally expressed gene Peg3 regulates sexual experience-dependent preferences for estrous odors.

Sexual experience has marked and long-lasting effects on male behavior in mammals, regulating traits such as the anticipation and display of sexual behavior, aggression, and olfaction. The authors conducted urine preference, habituation-dishabituation, and partner choice tests with sexually experienced and naive male mice and found that wild-type males acquire adaptively significant preferences for the odors of receptive, estrous females with sexual experience, and that these preferences are matched by changes in main olfactory system responses involving the piriform cortex, as indicated by c-Fos expression. The authors also report that these experiential effects are disrupted in male mice carrying a knockout of the imprinted gene Peg3. This paternally expressed gene regulates maternal care and offspring development, but the authors here report that Peg3 mutant males suffer a complex olfactory deficit that affects estrous odor preferences and the responses of the main olfactory system to such odors. Peg3 appears to have evolved to regulate the experience-dependent preference for receptive females, an adaptive trait that would enhance male reproductive success and so potentially increase paternal transmission of this paternally expressed gene.

Gender-dependent IL-12 secretion by APC is regulated by IL-10.

Female SJL mice preferentially mount Th1-immune responses and are susceptible to the active induction of experimental allergic encephalomyelitis. By contrast, young adult male SJL are resistant to experimental allergic encephalomyelitis due to an APC-dependent induction of Th2 cells. The basis for this gender-dependent differential T cell induction was examined by analysis of macrophage APC cytokine secretion during T cell activation. APC derived from females secrete IL-12, but not IL-10, during T cell activation. By contrast, APC derived from males secrete IL-10, but not IL-12, during T cell activation. Activation of T cells with APC derived from the opposite sex demonstrated that these cytokines were derived from the respective APC populations. Furthermore, inhibition of IL-10, but not TGF-beta, during T cell activation resulted in the secretion of IL-12 by male-derived APC. APC from naive male mice, in which IL-10 was reduced in vivo before isolation, also secrete IL-12, demonstrating altered APC cytokine secretion was due to an environment high in IL-10 before Ag encounter. Finally, APC derived from castrated male mice preferentially secrete IL-12 during T cell activation. These data demonstrate a link between gonadal hormones and APC activity and suggest that these hormones alter the APC, thereby influencing cytokine secretion during initial T cell activation.

Enhancement of Sexual Motivation in Sexually Naive Male Mice by Eurycoma longifolia

Eurycoma longifolia was preliminary investigated for aphrodisiac property on sexually naive male mice using both the modified runway-choice and open field methods. The animals were conditioned to seek, either an estrous female, a measure of right choice for sexual motivation or a male mouse, a measure of wrong choice, within two minutes. However, male mice which failed to response within the stipulated period were considered as having no choice. Oral administration of 0.5 g/kg daily of different fractions of E. longifolia viz., chloroform, methanol, water and butanol resulted in an enhancement of the sexual motivation of the animals after three days post-treatment and the effect was more prominent after eight days post-treatment.

Differential effects of bromocriptine treatment on LH release and copulatory behavior in hyperprolactinemic male rats

Hyperprolactinemia (hyperPRL) induced by grafting four pituitary glands under the kidney capsule suppresses copulatory behavior in male rats and sexually naive male mice. In mice sexual experience attenuates the suppressive effects of hyperPRL on mating behavior, thus a comparison of the behavioral consequences of inducing hyperPRL in sexually naive and experienced male rats was undertaken. Hyperprolactinemia had a significant suppressive effect on mating behavior in both groups of animals. Experienced animals showed deficits in all parameters studied except mount frequency and postejaculatory interval, while naive animals differed from respective controls only in mount latency, intromission latency, and intromission frequency. To determine if the inhibition of chronically elevated prolactin (PRL) levels would reverse the suppression of gonadotropin secretion and copulatory behavior in hyperprolactinemic animals, the effects of bromocriptine (CB-154) administration on plasma hormone levels and mating behavior were examined in pituitary-grafted and control rats. Bromocriptine treatment (1 mg/day for 14 days) led to increases in sexual activity in both the sham-operated and grafted animals. In the grafted animals, plasma PRL was reduced and plasma LH significantly increased in the CB-154-treated animals when compared to oil-treated controls. In sham-operated animals, CB-154 produced no significant changes in plasma LH or FSH despite the suppressed PRL levels. These results indicate that (1) hyperPRL induced by pituitary grafts can cause deficits in mating behavior in male rats despite previous sexual experience, and (2) while CB-154 may be acting through other mechanisms to stimulate copulatory behavior, the reduction of chronically elevated PRL levels due to CB-154 treatment is responsible for reversal of the suppressive effects of hyperPRL on LH secretion.

Effects of lithium chloride injections on rank-related fighting, maternal aggression and locust-killing responses in naive and experienced ‘TO’ strain mice

Three experiments investigated lithium chloride's (LiCl) effects on three forms of aggression in male ‘TO’ strain mice. Models of aggression investigated, included attack by preisolated males on male conspecifics (rank-related or intermale fighting), attack by lactating females on male intruders (matermal aggression) and the locust-killing response (a form of predatory aggression?) In the first study, injections of naive male mice with 0.2 and 0.4 mEq of LiCl resulted in marked declines in rank-related fighting. The effects of this treatment on locust killing could not be assessed, as this activity was already at a low incidence in controls. In a second experiment, LiCl injection had little influence on the locust-killing response in selected, experienced male killer mice. As in Experiment 1, rank-related fighting was suppressed by this treatment. The third experiment revealed that LiCl injections did not influence either maternal aggression or locust killing in naive females and predatory aggression in experienced-killer females. These results provide further support for the contention that these three behaviors have very different physiological bases. The data suggests that one should be cautious when extrapolating between different models of aggression even within the same species.

Sexual behavior of the naive male mouse as affected by the presence of a male and a female performing mating behavior

Sexually naive male mice allowed to observe conspecifics engaged in copulation later exhibited a preference ( p<0.01) for the odor of estrous females over that of diestrous females. They also mounted estrous females more frequently than diestrous females ( p<0.001). Naive males observing noncopulating pairs or isolated females exhibited a preference ( p<0.01) for the odor of diestrous females over that of estrous females but showed no difference in mounting behavior in the presence of estrous versus diestrous females.

Changes in the aggressiveness of mice resulting from selective breeding, learning and social isolation.

LAGERSPETZ, K. M. J. &amp; LAGERSPETZ, K. Y. H. Changes in the aggressiveness of mice resulting from selective breeding, learning and social isolation. Scand. J. Psychol. 1971, 12, 241–248.–Selective breeding for aggressiveness and non‐aggressiveness in mice has now been going on for 19 generations. The aggressiveness score distributions of the males have not changed since the 7th generation. Socially naive male mice which had been living in isolation, had five encounters with submissive males, and five with receptive females. Learning of aggressive and sexual behaviour occurred in males of both the aggressive and the non‐aggessive strain. When living in groups, the males of both strains show no aggressiveness towards a submissive opponent. Social isolation for 1–2 weeks greatly increases the aggressiveness level of the animals of the aggressive strain. The effects of grouping is interpreted as social learning of non‐aggressive behaviour, the effect of isolation as return of the inter‐individually variable aggressiveness level, determined by genetic variation and early experience. Some neurochemical findings are in agreement with the observed behavioural effects.