Diurnal changes of arginine vasopressin-enhanced green fluorescent protein fusion transgene expression in the rat suprachiasmatic nucleus.

We have recently developed a new transgenic rat line expressing an arginine vasopressin (AVP)-enhanced green fluorescent protein (eGFP) fusion gene. The AVP-eGFP transgene is expressed in the paraventricular (PVN) and supraoptic (SON) nuclei and the suprachiasmatic nucleus (SCN) of the hypothalamus. Transgene expression in the PVN and SON showed an exaggerated response to salt loading and nociceptive stimulation. However, the expression of the AVP-eGFP transgene in the SCN did not change under these stressful conditions. Here, we examined daily profiles of the expression of the AVP-eGFP transgene in the SCN in comparison with the endogenous AVP and Period (Per1 and Per2) genes. While all of these genes elicited diurnal patterns of expression in the SCN, the rate of rhythmic change of transgene expression was significantly greater than that of the endogenous AVP gene. We also examined the effect of a light stimulus on the expression of the AVP-eGFP, AVP, Per1 and Per2 genes in the SCN of transgenic rats. Ninety minutes after a light stimulus, AVP-eGFP mRNA and AVP hnRNA levels in the SCN were significantly decreased, while Per2 mRNA levels were significantly increased. In addition, we observed the eGFP fluorescence in the SCN and recorded the electrophysiological properties of a dissociated SCN eGFP-positive neuron. The AVP-eGFP transgenic rat is a useful animal model to study the diurnal change and dynamics of the AVP system, and enables the facile identification of SCN AVP neurons both in vivo and in vitro.