Gene Expression; Hypothalamo-Hypophyseal System/metabolism; Luminescent Proteins/metabolism; Molecular Imaging/methods; Neurons/metabolism; Oxytocin/metabolism; Recombinant Fusion Proteins/metabolism; Animals; Arginine Vasopressin/blood; Arginine Vasopressin/genetics; Arginine Vasopressin/metabolism; Female; Green Fluorescent Proteins/genetics; Green Fluorescent Proteins/metabolism; Hypothalamo-Hypophyseal System/cytology; Luminescent Proteins/genetics; Male; Median Eminence/cytology; Median Eminence/metabolism; Nerve Tissue Proteins/blood; Nerve Tissue Proteins/genetics; Nerve Tissue Proteins/metabolism; Neurons/cytology; Organ Specificity; Oxytocin/blood; Oxytocin/genetics; Paraventricular Hypothalamic Nucleus/cytology; Paraventricular Hypothalamic Nucleus/metabolism; RNA, Messenger/metabolism; Rats; Rats, Transgenic; Rats, Wistar; Sex Characteristics; Sodium Chloride, Dietary/adverse effects; Supraoptic Nucleus/cytology; Supraoptic Nucleus/metabolism; Water-Electrolyte Balance; Red Fluorescent Protein