Choice-based assessments outperform traditional measures for chronic depressive-like behaviors in rats after brain injury

Short-active gestational photoperiod reduces effortful choice behavior in mice, partial normalization by d-amphetamine

RATIONALE

Seasonal birth patterns consistently implicate winter gestation as a risk factor for several psychiatric conditions. We recently demonstrated that short-active (SA; 19:5 light:dark)-i.e., "winter-like"-photoperiod exposure across gestation and early life (E0-P28) induces psychiatrically relevant behavioral abnormalities in adult mice, including reduced immobility in the forced swim test (FST) and effortful amotivation. It is unknown, however, whether these effects were driven primarily by prenatal or postnatal mechanisms, and whether perinatal SA photoperiod would similarly reduce effort expenditure in a task relevant to everyday decision-making.

OBJECTIVES AND METHODS

We first tested male and female mice exposed to either gestational (E0-P0) or postnatal (E0-P28) SA photoperiod in the FST to determine whether the previously observed alteration was driven primarily by prenatal versus postnatal photoperiod. We then assessed whether SA gestational photoperiod reduces effortful choice behavior in the cross-species effort-based decision-making task (EBDMT) and whether any such deficit could be remediated by d-amphetamine (0.1 and 0.3 mg/kg, i.p.).

RESULTS

Mice exposed to prenatal, but not postnatal, SA photoperiod exhibited reduced FST immobility relative to controls and also demonstrated condition-dependently reduced preference for high-effort/high-reward versus low-effort/low-reward contingencies in the EBDMT. This effortful choice deficit was normalized by 0.1 mg/kg amphetamine.

CONCLUSIONS

These data: (1) suggest a greater contribution of gestational versus postnatal light conditions to the behavioral effects of perinatal SA photoperiod; and (2) implicate altered dopamine signaling in the behavioral phenotype of the SA-born mouse and possibly in the etiology of winter gestation-associated cases of psychiatric disease.

The interaction of the circadian and immune system: Desynchrony as a pathological outcome to traumatic brain injury

Traumatic brain injury (TBI) is a complex and costly worldwide phenomenon that can lead to many negative health outcomes including disrupted circadian function. There is a bidirectional relationship between the immune system and the circadian system, with mammalian coordination of physiological activities being controlled by the primary circadian pacemaker in the suprachiasmatic nucleus (SCN) of the hypothalamus. The SCN receives light information from the external environment and in turn synchronizes rhythms throughout the brain and body. The SCN is capable of endogenous self-sustained oscillatory activity through an intricate clock gene negative feedback loop. Following TBI, the response of the immune system can become prolonged and pathophysiological. This detrimental response not only occurs in the brain, but also within the periphery, where a leaky blood brain barrier can permit further infiltration of immune and inflammatory factors. The prolonged and pathological immune response that follows TBI can have deleterious effects on clock gene cycling and circadian function not only in the SCN, but also in other rhythmic areas throughout the body. This could bring about a state of circadian desynchrony where different rhythmic structures are no longer working together to promote optimal physiological function. There are many parallels between the negative symptomology associated with circadian desynchrony and TBI. This review discusses the significant contributions of an immune-disrupted circadian system on the negative symptomology following TBI. The implications of TBI symptomology as a disorder of circadian desynchrony are discussed.