Transcriptomic analyses of limbic structures across photoperiodic phenotypes in the Siberian hamster and Japanese quail brains.

Seasonal morphological brain plasticity plays a key role in driving adaptive behavioural responses. Structural changes in the brain including the hippocampus and amygdala (nucleus taeniae in birds), across photoperiods are thought to underlie seasonal shifts in emotional state. For humans, this includes manifestations of short photoperiod seasonal affective disorder (SAD). While morphological brain changes are well documented, the associated transcriptomic dynamics remain poorly understood. Here, we examined the transcriptomes of the hippocampus and amygdala or nucleus taeniae in two highly photoperiodic species, the Siberian hamster (Phodopus sungorus) and the Japanese quail (Coturnix japonica), to identify transcriptomic changes which could underpin seasonal shifts in emotional state. Hamsters and quail exhibited robust physiological changes between long and short photoperiod treatment. Under short photoperiod, hamsters displayed anxiety-like behaviour (increased grooming) in the open field test. Transcriptomic analysis of the amygdala in hamsters identified 76 significantly differentially expressed (DE) transcripts (including transthyretin, TTR) and prolactin receptor, PRLR as differentially expressed, but not significantly. In the quail nucleus taeniae, we found 54 DE transcripts (including tenascin-C, TNC). In the hamster hippocampus, 14 DE transcripts were found, including mahogunin ring finger-1 (MGRN1), and 31 in the quail hippocampus, including eyes absent-2 (Eya2). These findings provide novel insights into the transcriptomic mechanisms underpinning seasonal affective states and suggest potential conserved roles for prolactin and thyroid hormone signalling in mediating seasonal changes in physiology and affective behaviour, particularly in the Siberian hamster.