Paternal Care in Biparental Rodents: Intra- and Inter-individual Variation

Parental care by fathers, although rare among mmmals, can be essential for the survival and normal development of offspring in biparental species. A growing body of research on biparental rodents has identified several developmental and experiential influences on paternal responsiveness. Some of these factors, such as pubertal maturation, interactions with pups, and cues from a pregnant mate, contribute to pronounced changes in paternal responsiveness across the course of the lifetime in individual males. Others, particularly intrauterine position during gestation and parental care received during postnatal development, can have long-term effects on paternal behavior and contribute to stable differences among individuals within a species. Focusing on five well-studied, biparental rodent species, we review the developmental and experiential factors that have been shown to influence paternal responsiveness, and consider their roles in generating both intra- and inter-individual variation. We also review hormones and neuropeptides that have been shown to modulate paternal care and discuss their potential contributions to behavioral differences within and between males. Finally, we discuss the possibility that vasopressinergic and possibly oxytocinergic signaling within the brain, modulated by gonadal steroid hormones, may represent the "final common pathway" mediating effects of developmental and experiential variables on intra- and inter-individual variation in paternal care

Individual differences in circadian locomotor parameters correlate with anxiety- and depression-like behavior

Disrupted circadian rhythms are a core feature of mood and anxiety disorders. Circadian rhythms are coordinated by a light-entrainable master clock located in the suprachiasmatic nucleus. Animal models of mood and anxiety disorders often exhibit blunted rhythms in locomotor activity and clock gene expression. Interestingly, the changes in circadian rhythms correlate with mood-related behaviours. Although animal models of depression and anxiety exhibit aberrant circadian rhythms in physiology and behavior, it is possible that the methodology being used to induce the behavioral phenotype (e.g., brain lesions, chronic stress, global gene deletion) affect behavior independently of circadian system. This study investigates the relationship between individual differences in circadian locomotor parameters and mood-related behaviors in healthy rats. The circadian phenotype of male Lewis rats was characterized by analyzing wheel running behavior under standard 12h:12h LD conditions, constant dark, constant light, and rate of re-entrainment to a phase advance. Rats were then tested on a battery of behavioral tests: activity box, restricted feeding, elevated plus maze, forced swim test, and fear conditioning. Under 12h:12h LD conditions, percent of daily activity in the light phase and variability in activity onset were associated with longer latency to immobility in the forced swim test. Variability in onset also correlated positively with anxiety-like behavior in the elevated plus maze. Rate of re-entrainment correlated positively with measures of anxiety in the activity box and elevated plus maze. Lastly, we found that free running period under constant dark was associated with anxiety-like behaviors in the activity box and elevated plus maze. Our results provide a previously uncharacterized relationship between circadian locomotor parameters and mood-related behaviors in healthy rats and provide a basis for future examination into circadian clock functioning and mood