Sex-specific neurobehavioural outcomes and brain stimulation pattern in adult offspring paternally exposed to methamphetamine

Paternal methamphetamine (METH) exposure results in long-term behavioural deficits in the sub-generations with a sex difference. Here, we aim to investigate the sex-specific neurobehavioural outcomes in the first-generation offspring mice (F1 mice) paternally exposed to METH prior to conception and explore the underlying brain mechanisms. We found that paternal METH exposure increased anxiety-like behaviours and spatial memory deficits only in female F1 mice and caused depression-like behaviours in the offspring without sex-specific differences. In parallel, METH-sired F1 mice exhibited sex-specific brain activity pattern in response to mild stimulus (in water at room temperature for 3 min). Overall, paternal METH exposure caused a blunting phenomenon of prelimbic cortex (PrL), infralimbic cortex (IL) and nucleus accumbens (NAc) core in both male and female F1 mice, as indicated by the decreased c-Fos levels under mild stimulus. Of note, the activity of central nucleus of the amygdala (CeA) by mild stimulus was triggered in male but suppressed in female F1 mice, whereas the neurons of orbitofrontal cortex (OFC), cingulate cortex (Cg1), NAc shell, medial habenula (mHb), dorsal hippocampal CA1 (dCA1) and ventral hippocampal CA1 (vCA1) were only blunted in female F1 mice. Taken together, the distinct brain stimulation patterns between male and female F1 mice might contribute to the sex-specific behavioural outcomes by paternal METH exposure, which indicate that sex differences should be considered in the treatment of offspring paternally exposed drugs.

Brief Maternal Separation Inoculates Against the Effects of Social Stress on Depression-Like Behavior and Cocaine Reward in Mice

Exposure to intermittent repeated social defeat (IRSD) increases the vulnerability of mice to the rewarding effects of cocaine in the conditioned place preference (CPP) paradigm. According to the "inoculation of stress" hypothesis, a brief period of maternal separation (MS) can provide protection against the negative effects of IRSD. The aim of the present study was to assess whether exposure to a brief episode of MS prevents the subsequent short-term effects of IRSD on depression- and anxiety-like behaviors and to explore its long-term effects on cocaine CPP in mice. Four groups of male C57BL/6 mice were employed; two groups were separated from their mother [6 h on postnatal day (PND) 9], while the other two groups were not (controls). On PND 47, 50, 53 and 56, mice that had experienced MS were exposed to social defeat in the cage of an aggressive resident mouse (MS + IRSD group) or were allowed to explore an empty cage (MS + EXPL group). The same procedure was performed with control mice that had not experienced MS (CONTROL + IRSD and CONTROL + EXPL groups). On PND57-58, all the mice performed the elevated plus maze and the hole-board, social interaction and splash tests. Three weeks after the last episode of defeat, all the mice underwent the CPP procedure with cocaine (1 mg/kg). Irrespective of whether or not MS had taken place, a reduction in open arms measures, dips, and social interaction was observed in mice that experienced IRSD. A higher latency of grooming and acquisition of cocaine-induced CPP were observed only in mice exposed to IRSD alone (CONTROL + IRSD). These results suggest that exposure to a brief episode of stress early in life increases the subsequent resilience of animals to the effects of social stress on vulnerability to cocaine.

Roles of fibroblast growth factor 21 in the control of depression-like behaviours after social defeat stress in male rodents

Fibroblast growth factor 21 (FGF21) modulates energy metabolism and neuroendocrine stress responses. FGF21 synthesis is increased after environmental or metabolic challenges. Detailed roles of FGF21 in the control of behavioural disturbances under stressful conditions remain to be clarified. Here, we examined the roles of FGF21 in the control of behavioural changes after social defeat stress in male rodents. Central administration of FGF21 increased the number of tyrosine hydroxylase-positive catecholaminergic cells expressing c-Fos protein, an activity marker of neurones, in the nucleus tractus solitarius and area postrema. Double in situ hybridisation showed that some catecholaminergic neurones in the dorsal medulla oblongata expressed β-Klotho, an essential co-receptor for FGF21, in male mice. Social defeat stress increased FGF21 concentrations in the plasma of male mice. FGF21-deficient male mice showed social avoidance in a social avoidance test with C57BL/6J mice (background strain of FGF21-deficient mice) and augmented immobility behaviour in a forced swimming test after social defeat stress. On the other hand, overexpression of FGF21 by adeno-associated virus vectors did not significantly change behaviours either in wild-type male mice or FGF21-deficient male mice. The present data are consistent with the view that endogenous FGF21, possibly during the developmental period, has an inhibitory action on stress-induced depression-like behaviour in male rodents.

Diets rich in saturated fat and fructose induce anxiety and depression-like behaviours in the rat: is there a role for lipid peroxidation?

Epidemiological studies reveal associations between obesity/metabolic syndrome and mood disorders. We assessed behavioural changes in rats fed diets enriched in fat and fructose in different proportions and correlated the observed alterations with biochemical changes induced by the diets. Three groups of rats were used as follows: control (C) animals fed regular rat chow, rats fed high-fat diet (HF) and rats fed high-fat and high-fructose diet (HFHF). HF and HFHF animals were also given a 10% fructose solution as drinking water. Behavioural and biochemical parameters were determined. Anxiety was measured by the open-field and the social interaction test. Depression-like behaviour was evaluated by the forced swimming test. The object recognition test was utilized to assess effects on memory. Diet-exposed animals displayed signs of anxiety in the open-field (HF rats had reduced central time; HFHF rats had reduced number of central entries) and in the social interaction test (decreased time of interaction in HF group). In the forced swimming test, the immobility time was prolonged in the HFHF group. While different measures of anxiety scores correlated with visceral adiposity and dyslipidemia, results from both social interaction and forced swimming tests were significantly associated with lipid peroxidation, which in turn also correlated with the metabolic parameters. The experimental diets did not affect the object recognition memory. Both experimental diets induced metabolic derangements in rats and provoked similar anxiety- and depression-like behaviours. Lipid peroxidation seems to play a role in translating diet-induced metabolic alterations into behavioural disorders.

Sex-dependent control of murine emotional-affective behaviour in health and colitis by peptide YY and neuropeptide Y

BACKGROUND AND PURPOSE

Peptide YY (PYY) and neuropeptide Y (NPY) are involved in regulating gut and brain function. Because gastrointestinal inflammation is known to enhance anxiety, we explored whether experimental colitis interacts with genetic deletion (knockout) of PYY and NPY to alter emotional-affective behaviour.

EXPERIMENTAL APPROACH

Male and female wild-type, NPY (NPY(-/-) ), PYY (PYY(-/-) ) and NPY(-/-) ; PYY(-/-) double knockout mice were studied in the absence and presence of mild colitis induced by ingestion of dextran sulphate sodium (2%) in drinking water. Anxiety-like behaviour was tested on the elevated plus maze and open field, and depression-like behaviour assessed by the forced swim test.

KEY RESULTS

In the absence of colitis, anxiety-like behaviour was increased by deletion of NPY but not PYY in a test- and sex-dependent manner, while depression-like behaviour was enhanced in NPY(-/-) and PYY(-/-) mice of either sex. The severity of DSS-induced colitis, assessed by colonic myeloperoxidase content, was attenuated in NPY(-/-) but not PYY(-/-) mice. Colitis modified anxiety- and depression-related behaviour in a sex-, genotype- and test-related manner, and knockout experiments indicated that NPY and PYY were involved in some of these behavioural effects of colitis.

CONCLUSIONS AND IMPLICATIONS

These data demonstrate sex-dependent roles of NPY and PYY in regulation of anxiety- and depression-like behaviour in the absence and presence of colitis. Like NPY, the gut hormone PYY has the potential to attenuate depression-like behaviour but does not share the ability of NPY to reduce anxiety-like behaviour.

Delayed stress-induced differences in locomotor and depression-related behaviour in female neuropeptide-Y Y1 receptor knockout mice

Neuropeptide-Y acting through Y1 receptors reduces anxiety and stress sensitivity in rodents. In Y1 receptor knockout (Y1⁻/⁻) mice, however, anxiety-related behaviour is altered only in a context-dependent manner. Here, we investigated whether stress causes a delayed change in the emotional-affective behaviour of female Y1⁻/⁻ mice. Locomotor and anxiety-related behaviour was assessed with the elevated plus-maze (EPM) test and depression-like behaviour with the forced swim test (FST). These behavioural tests were also used as experimental stress paradigms. Locomotion and anxiety-like behaviour did not differ between naïve control and Y1⁻/⁻ mice. One week after the FST, locomotion was reduced in control animals but unchanged in Y1⁻/⁻ mice, whereas anxiety-like behaviour remained unaltered in both genotypes. Depression-like behaviour (immobility) was identical in naïve control and Y1⁻/⁻ mice but, 1 week after the EPM test, was attenuated in Y1⁻/⁻ mice relative to control animals. Our data show that naïve female Y1⁻/⁻ mice do not grossly differ from female control animals in their locomotor and depression-like behaviour. Exposure to the stress associated with behavioural testing, however, leads to delayed genotype-dependent differences in locomotion and depression-like behaviour. These findings attest to a role of Y1 receptor signalling in the control of stress coping and/or adaptation.

Evidence from knockout mice that neuropeptide-Y Y2 and Y4 receptor signalling prevents long-term depression-like behaviour caused by immune challenge

Neuropeptide Y participates in the acute behavioural responses to immune challenge, since Y2 receptor knockout (Y2⁻/⁻) mice are particularly sensitive to the short-term anxiogenic-like effect of bacterial lipopolysaccharide. The present exploratory study addressed the involvement of Y2 and Y4 receptors in the long-term behavioural responses to immune challenge. A single intraperitoneal injection of lipopolysaccharide (0.83 mg/kg) to control mice did not affect open field behaviour 3 h post-treatment but enhanced anxiety-like behaviour in Y2⁻/⁻ as well as Y4⁻/⁻ mice. Four weeks post-treatment this behavioural effect of lipopolysaccharide persisted in Y4⁻/⁻ mice but had gone in Y2⁻/⁻ mice. Depression-related behaviour in the forced swim test was enhanced 1 day post-lipopolysaccharide in control and Y2⁻/⁻ mice, but not in Y4⁻/⁻ mice. Four weeks post-treatment, the depressogenic-like effect of lipopolysaccharide had waned in control mice, persisted in Y2⁻/⁻ mice and was first observed in Y4⁻/⁻ mice. In summary, knockout of Y2 and/or Y4 receptors unmasks the ability of a single lipopolysaccharide injection to cause a delayed and prolonged increase in anxiety- and/or depression-like behaviour. These findings suggest that neuropeptide Y acting via Y2 and Y4 receptors prevents the development of long-term anxiety- and depression-like behaviour caused by acute immune challenge.