Joseph Terkel

Participation of serotonin-containing neurons in the suckling-induced rise in plasma prolactin levels in lactating rats.

Plasma prolactin levels were measured by radioimmuno-assay in free-moving lactating rats bearing heart cannulas. Litters adjusted to 6 pups were returned to the mothers after a separation of 8–12 h fr

Effects of small medial preoptic area lesions on maternal behavior: Retreiving and nest building in the rat

Previous studies in rats have demonstrated that large lesions in the medial preoptic area (MPOA) disrupt all aspects of maternal behavior. In the present study, small bilateral electrolyte lesions in the MPOA of lactating females abolished nest building and retrieving components of maternal behavior while crouching and nursing were unaffected. Animals which failed to show retrieval and nest building behaviors tended to have a greater area of lesion within the more dorsal part of the MPOA. Although the dorsal MPOA may play a role in the maintenance of the active components of maternal behavior, i.e. nest building and retrieving, another critical factor in determining which components of maternal behavior are disrupted may be the size of the lesion. As one increases the area of damaged tissue there is also an accompanying increase in the components of maternal behavior which are disrupted. No correlation was found between damage to the Sexually Dimorphic Nucleus of the preoptic area and retrieving and nest building.

Effects of transecting lateral neural connections of the medial preoptic area on maternal behavior in the rat : nest building, pup retrieval and prolactin secretion

In lactating female rats bilateral parasagittal cuts transecting the dorsolateral neural connections of the medial preoptic area (MPOA) abolished nest building and retrieving components of maternal behavior, while crouching and nursing were unaffected. While few animals with these cuts were suckled when presented with pups the prolactin secretion response was undiminished when suckling did occur. Whereas previous studies have demonstrated that extensive surgical separation of the medial preoptic area-anterior hypothalamic continuum from the lateral preoptic area-lateral hypothalamus disrupts all aspects of maternal behavior, the present study has determined more specifically the zone of fibers essential for the active components of maternal behavior, i.e., nest building and retrieving. These fibers appear to enter/leave MPO dorsolaterally beneath the crossing of the anterior commissure in the region of the bed nucleus of the stria terminalis. These neural connections are not the same as those that regulate prolactin secretion in the lactating rat.

Ultrasonic cries from infant rats stimulate prolactin release in lactating mothers.

Abstract Lactating female rats, separated from their litters for 6 hr, showed a dramatic elevation in plasma prolactin following a 15-min playback of ultrasonic vocalizations recorded from 7-day-old pups. Virgin females exhibited a smaller but still significant prolactin response to recorded pup calls. Control recordings of either background noise or adult ultrasonic vocalizations (22–26 kHz) had no effect on prolactin secretion even in lactating females. These results demonstrate that infant vocalizations can act as a stimulus for prolactin release and suggest that such communications may play a role in the maintenance of normal lactation.

Male copulatory behavior triggers nightly prolactin surges resulting in successful pregnancy in rats.

Abstract A positive correlation between the number of preejaculatory intromissions that a female receives during copulation and the probability of successful pregnancy has been demonstrated previously. In the present investigation the nocturnal secretion of prolactin (PRL) was followed for 4 days after mating in female rats receiving either 3–5 intromissions before ejaculation (low intromission group) or 15–18 intromissions (high intromission group). Nightly PRL surges occurred in most of the females ( 9 12 ) in the high intromission group and the same 9 females became pregnant. Only 2 9 females in the low intromission group exhibited nightly PRL surges and again only these 2 females became pregnant. This study demonstrates that the stimulation which the female receives from multiple intromissions during mating is effective in setting off nightly PRL surges. We propose that the so-called pregnancy-inducing neuroendocrine reflex which is triggered in this manner is expressed in a characteristic pattern of nightly surges of prolactin, the hormone known to be essential for the activation of the corpora lutea and their secretion of progesterone.

Changes in serum luteinizing hormone folowing intraventricular and intravenous injections of luteinizing hormone-releasing hormone in the rat.

A comparison was made of the effects of administering luteinizing hormone-releasing hormone (LH-RH) by the intravenous (i.v.) vs. intraventricular routes to ovariectomized estrogenprimed rats. LH-RH w

Pup survival and prolactin levels in nicotine-treated lactating rats.

Summary Administration of 0.5 and 1 mg nicotine tartrate twice daily to female rats through pregnancy and lactation affected neither duration of pregnancy nor litter size at birth. However, pups born to females given the higher dose of nicotine were lighter in weight at birth than pups in the two other groups, and most of them died of starvation before weaning because the mothers mammary glands contained so little milk. Blood was collected via a chronic intra-atrial cannula, and radioimmunoassay of prolactin was performed. Plasma prolactin levels of the group receiving the high dose of nicotine were much lower than in the low dose nicotine and saline groups. It is suggested that failure of prolactin release following chronic nicotine administration was responsible for low milk production and starvation of the pups. The mechanism by which nicotine affects prolactin levels may involve effects on brain catecholamines. We thank Mrs. Sylvia Barr for the drawing of the figure and Mrs. Frances Smith for secretarial aid.

Effect of Adrenalectomy on a Diurnal (Circadian) Rhythm in Hypothalamic Multiple Unit Activity in the Female Rat

In freely-moving female rats multiple unit activity(MUA) was recorded from medial hypothalamic and septal structures for 4–7 days throughout the estrous cycle. A consistent elevation of MUA during par

Technique for Recording Multiple-Unit Activity from the Brain of the Freely-Moving Rat

The development and improvement of electrodes for the chronic recording of multiple-unit activity in the freely-moving rat is described. The problems of long-term recording from localized subcortical

Thyroid Stimulating Hormone and Prolactin Secretion: Reduced Sensitivity to TRH-Stimulated Prolactin Release after Midpregnancy in Rats

Abstract Prolactin (PRL) and thyroid stimulating hormone (TSH) plasma concentrations were measured during the latter part of the dark period in early and mid-late pregnancy in the rat. On Days 4-5 and 7-8 of pregnancy, plasma PRL concentrations surged between 22:00 and 06:00 hr and TSH values increased between 22:00 and 02:00 hr. While the TSH pattern was maintained during the second-half of pregnancy, surges in PRL release ceased and PRL levels remained at <10 ng/ml. The effects of thyrotropin releasing hormone (TRH) administration on PRL and TSH secretion were then measured to determine whether the second-half of pregnancy is associated with a decrease in sensitivity to an agent that can stimulate PRL release. Injection (iv) of cannulated pregnant rats with a low dosage (20 ng) of TRH stimulated a twofold increase in plasma TSH during both early (Days 5-9) and later (Days 14-18) pregnancy but did not change plasma PRL levels. Treatment with a high dosage (2 μg) of TRH induced a sixfold rise in plasma TSH during both phases of gestation. The higher dose of TRH also stimulated elevations in plasma PRL during early and mid-late pregnancy; however, both the absolute increase in the amount of PRL in plasma and the percentage increase over baseline levels were greater from Days 5-9 than from Days 14-16 of gestation. These data indicate that the neuroendocrine sensitivity to factors that stimulate PRL secretion changes as pregnancy progresses, and suggest that nocturnal secretion of PRL and TSH during pregnancy may be regulated, in part, by a common trophic factor.