Hypothalamic vasopressin response to stress and various physiological stimuli: visualization in transgenic animal models

Arginine vasopressin (AVP) is involved in the homeostatic responses numerous life-threatening conditions, for example, the promotion of water conservation during periods of dehydration, and the activation of the hypothalamo-pituitary adrenal axis by emotional stress. Recently, we generated new transgenic animals that faithfully express an AVP-enhanced green fluorescent protein (eGFP) fusion gene in the paraventricular nucleus (PVN), the supraoptic nucleus (SON) and the suprachiasmatic nucleus (SCN) of the hypothalamus. In these transgenic rats, marked increases in eGFP fluorescence and fusion gene expression were observed in the magnocellular division of the PVN and the SON, but not the SCN, after osmotic challenges, such as dehydration and salt loading, and both acute and chronic nociceptive stimuli. In the parvocellular division of the PVN, eGFP expression was increased after acute and chronic pain, bilateral adrenalectomy, endotoxin shock and restraint stress. In the extra-hypothalamic areas of the brain, eGFP expression was induced in the locus coeruleus after the intracerebroventricular administration of colchicine. Next, we generated another transgenic rat that expresses a fusion gene comprised of c-fos promoter-enhancer sequences driving the expression of monomeric red fluorescent protein 1 (mRFP1). In these transgenic rats, abundant nuclear fluorescence of mRFP1 was observed in the PVN, the SON and other osmosensitive areas after acute osmotic stimulation. Finally, we generated a double transgenic rat that expresses both the AVP-eGFP and c-fos-mRFP1 fusion genes. In this double transgenic rat, we have observed nuclear mRFP1 fluorescence in eGFP-positive neurons after acute osmotic stimulation. These unique transgenic rats provide an exciting new tool to examine neuroendocrine responses to physiological and stressful stimuli in both in vivo and in vitro preparations.