Saline drinking and naloxone: Lightcycle dependent effects on social behaviour in male mice

Social approach behaviors are similar on conventional versus reverse lighting cycles, and in replications across cohorts, in BTBR T+ tf/J, C57BL/6J, and vasopressin receptor 1B mutant mice

Mice are a nocturnal species, whose social behaviors occur primarily during the dark phase of the circadian cycle. However, laboratory rodents are frequently tested during their light phase, for practical reasons. We investigated the question of whether light phase testing presents a methodological pitfall for investigating mouse social approach behaviors. Three lines of mice were systematically compared. One cohort of each line was raised in a conventional lighting schedule and tested during the light phase, under white light illumination; another cohort was raised in a reverse lighting schedule and tested during their dark phase, under dim red light. Male C57BL/6J (B6) displayed high levels of sociability in our three-chambered automated social approach task when tested in either phase. BTBR T+ tf/J (BTBR) displayed low levels of sociability in either phase. Five cohorts of vasopressin receptor subtype 1b (Avpr1b) null mutants, heterozygotes, and wildtype littermate controls were tested in the same social approach paradigm: three in the dark phase and two in the light phase. All three genotypes displayed normal sociability in four out of the five replications. In the juvenile play test, testing phase had no effect on play soliciting behaviors in Avpr1b mice, but had modest effects on nose sniff and huddling. Taken together, these findings indicate that testing phase is not a crucial factor for studying some forms of social approach in juvenile and adult mice.

The dark phase improves genetic discrimination for some high throughput mouse behavioral phenotyping

Dark-phase testing has previously been shown by others to improve the outcome of some 'classical' behavior test situations. However, the importance of such ethological correctness and the effect of the light/dark cycle on high throughput behavioral testing situations such as 'mutant vs. wild type' and 'screening', are less or unknown, respectively. These testing situations differ from the 'classical' in that they are designed primarily to discriminate between genetically different mice rather than provide a detailed assessment of ability or psychosocial state. Here we test the hypotheses that dark-phase testing affects the outcome of high throughput behavioral tests and that dark-phase testing improves discrimination between genetically distinct mice (C57BL/6J, 129S1/SvImJ and B6129F1) using high throughput behavioral tests. Our results demonstrate that, although all successful tests showed some effect of phase, only the SHIRPA primary screen, open-field test and motor learning on the rotarod showed improved strain discrimination in the dark phase. Surprisingly, the social interaction test did not show a clear benefit to either phase, and interestingly, the tail-flick test discriminated strains better in the light phase. However, since the preponderance of our data shows that dark-phase testing improves, or does not affect, strain discrimination, we conclude that for these strains and tests, dark-phase testing provided superior outcomes. If discrimination is not achieved in the dark phase, then light phase-testing would be undertaken.

Social behaviour in pairs of C57BL/6 mice of both sexes in the open field: effects of saline drinking and of naloxone

We have previously found that saline drinking increases fighting in male pairs and decided to test this treatment (0.9% NaCl for 24 hours before test day 1; SAL) on social behaviour of both males and females. Paired C57BL/6 mice (same-sex pairs) were observed in the open field in daily sessions for three days. One member of each pair (test mouse) was given either SAL treatment, a control injection of saline (SI), an injection of naloxone (1 mg/kg IP; NLX) or a combination of both treatments (NLX + SAL). NLX alone had previously been found to increase aggression in resident/intruder tests at the dose used. Open field testing is not associated with aggressive encounters in our experience. SAL had little effect on (unaggressive) social behaviour in males, but increased social contact seeking in females. The NLX and NLX + SAL treatments had essentially the same effects, irrespective of sex; the treated animals showed behavioural inhibition (reduced social and ambulatory behaviour), while their untreated partners showed significantly more than normal interest in the naloxone treated mice. The results are discussed in terms of opioid involvement in social behaviour.

Endogenous opiates: 1984

This paper is the seventh in an annual series of reviews of research involving the endogenous opiate peptides, each installment being restricted to work published during the previous year. As in the past three years, the review this year is limited to non-analgesic and behavioral studies of the opiate peptides. The specific topics this year include: stress, tolerance and dependence, consummatory responses, gastric and renal activity, alcohol, mental illness, learning and memory, cardiovascular responses, respiratory effects, thermoregulation, seizures and neurological disorders, activity, and miscellaneous other topics.

Stimulation of aggression in male mice by alpha-MSH and its relation to light phase and to saline intake effects

The resident/intruder test was used to examine the social approach and aggressive behaviour of male albino mice. Digging, self-grooming and rearing were also recorded, as was the post-test response to hot-plate exposure. The resident mice were given either a single acute injection of MSH (MSH); 0.9% NaCl to drink (for 48 h prior to testing; SAL); a combination of both treatments (MSH + SAL) or an injection of 0.9% physiological saline (control group; CON). Testing was carried out at the midpoints of the light and dark phases of the 12:12 light cycle. Data on plasma ion levels and hypothalamic cAMP levels were collected after the hot-plate test. MSH stimulated fighting both in the light and dark, and SAL in the light. MSH + SAL reversed the effects of the single treatments in that fighting declined below CON levels in both light and dark. Social contact and other behaviours were much less affected by treatments. Pain responding and plasma ion levels were not changed. Effects on cAMP were largely inconclusive, but intruders had significantly lower levels than the aggressive resident animals.