Oxytocin produces uterine contractions and milk ejection, functions related to parturition and nurturing. Studies were conducted to determine if this peptide, native to the brain and the posterior pituitary gland, plays a role in the induction of maternal behavior. Intact virgin female rats were given 0.4 ,g of oxytocin, 0.4 1&g of [Arg8Jvasopressin, or saline through lateral ventricular cannulae. Forty-two percent of intact rats receiving oxytocin displayed full maternal behavior towards foster pu s. None of the saline-or vasopressin-treated animals displayed full maternal behavior. Criteria in five behavioral categories had to be fulfilled by an animal within 2 hr of injection for its behavior to be considered fully maternal. When partial maternal responses were considered, oxytocin was significantly more effective than saline and marginally more effective than vasopressin. Five animals responding fully maternally after oxytocin injection were allowed to stay with pups for 10 days. All Rosenblatt (1) demonstrated that male and female rats, including intact virgin females, manifest maternal behavior after contact with foster pups for 5-7 days. Since then, several attempts have been made to shorten the latency for this phenomenon by manipulations of estrogen, progesterone, or prolactin. When these hormones were administered on selected schedules to ovariectomized, nulliparous females over either an 1 -day (2) or 27-day (3) period, latency was reduced to as little as 35 hr.Pharmacologic blockade of prolactin release has no effect on the onset of postpartum maternal behavior (3-5) or estrogen-induced maternal behavior (6). Similarly, induced elevation of prolactin in ovariectomized virgin females does not alter the onset of pup contact-induced maternal behavior (7). Progesterone has been found by most investigators to inhibit the onset of maternal behavior under various experimental conditions (8, 9), though dosage and timing of progesterone administration seem to be important (10).Of the hormones studied singly, estrogen appears most potent in inducing maternal behavior. Hysterectomy in late pregnancy, which probably causes a rapid rise in plasma estrogen (11) as judged by examination of vaginal smears, results in a high incidence of maternal behavior 48-72 hr after pup contactThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. C. §1734 solely to indicate this fact. 6661 initiated 48 hr after surgery (12-14). Ovariectomy simultaneous with hysterectomy prevents this effect. The estrogen dependence of the induction of maternal behavior is further shown by estradiol administration at the time of hysterectomy and ovariectomy in either late gestational or virginal female rats. Animals thus treated show a high rate of maternal response within 24 hr after first presentation of pups 48 hr after surgery (12,15,16).Klopfer is the only investigator who has not focused exclusively on late gestati...

Intracerebroventricular administration of oxytocin to virgin female rats that had been ovariectomized and primed with estrogen 48 hours previously induced a rapid onset of full maternal behavior. The maternal behavior persisted and its incidence was dose-related. Tocinoic acid, the ring structure of oxytocin, also rapidly induced the onset of persistent, full maternal behavior. Arginine vasopressin induced persistent maternal behavior, but this behavior had a later onset. Prostaglandin F2 alpha induced strong partial maternal behavior, which showed early onset but did not persist. Many other peptides, ovarian steroids, and prostaglandin E2 were no more effective than saline. These findings suggest that the release of oxytocin and prostaglandin F2 alpha during labor may promote maternal behavior in rats.

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It was recently demonstrated that treatment with levorotatory thyroxine (T4) plus triiodothyronine (T3) compared with treatment with T4 alone improves psychologic functioning in hypothyroid patients with thyroid cancer or autoimmune thyroiditis. In the present double-blind crossover study, we again compared the effects of combined thyroid replacement vs monotherapy on psychologic function, endocrine function, cardiovascular function, and body composition. The patients were women who were hypothyroid after thyroidectomy for Graves' disease. The substitution of 10 microg of T3 for 50 microg of T4 caused a statistically significant decrease in free T4 concentration but no significant change in T3 or thyroid-stimulating hormone concentration. Symptoms of hypothyroidism and of hyperthyroidism tended to decrease on a standard symptom scale after combined treatment. With combined hormone replacement, mental state tended to improve on some mood scales but not on cognitive tests. We found alterations in left ventricular diastolic function but no change in body composition after the combined treatment regimen. These preliminary findings in a small group of patients with Graves' disease are consistent with earlier findings that thyroid replacement with T4-T3 combination improves mental functioning.

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