The effect of different photoperiods in circadian rhythms of per3 knockout mice.

The aim of this study was to analyse the circadian behavioural responses of mice carrying a functional knockout of the Per3 gene (Per3(-/-)) to different light : dark (L : D) cycles. Male adult wild-type (WT) and Per3(-/-) mice were kept under 12-hour light : 12-hour dark conditions (12L : 12D) and then transferred to either a short or long photoperiod and subsequently released into total darkness. All mice were exposed to both conditions, and behavioural activity data were acquired through running wheel activity and analysed for circadian characteristics during these conditions. We observed that, during the transition from 12L : 12D to 16L : 8D, Per3(-/-) mice take approximately one additional day to synchronise to the new L : D cycle compared to WT mice. Under these long photoperiod conditions, Per3(-/-) mice were more active in the light phase. Our results suggest that Per3(-/-) mice are less sensitive to light. The data presented here provides further evidence that Per3 is involved in the suppression of behavioural activity in direct response to light.

Circadian dynamics of vasopressin in mouse selection lines: translation and release in the SCN.

Arg8-vasopressin (AVP), a circadian clock-controlled gene product, is released from the hypothalamic suprachiasmatic nuclei (SCN) in mice in a circadian fashion. Previously reported differences in two mouse lines, initially selected for thermoregulatory nest-building behavior (building small nests (S-mice) or big nests (B-mice)) with different circadian organization of behavior and in number of SCN-AVP immunoreactive neurons, were further investigated. We confirmed and expanded the finding that S-mice exhibited constant high levels of SCN-AVP content with no apparent circadian rhythmicity, whereas B-mice had lower numbers of AVP positive cells which varied with time of day. We found that AVP mRNA expression levels at midnight and midday were similar in both lines, as established by in situ hybridization. When AVP transport and release were blocked by colchicine, SCN-AVP immunoreactivity was similar in both lines. This suggests that differences in SCN-AVP content depend on transport or release. Organotypic SCN cultures of B-mice showed more AVP release per neuron than cultures of S-mice. These results reveal that on a mechanistic level the mouse lines differed in transport and/or release of AVP in the SCN, rather than differential regulation of AVP gene transcription or number of AVP immunoreactive neurons.