Inhibition of lactation and luteal function in postpartum rats by hypothalamic implantation of prolactin

Rat placental lactogens initiate and maintain lactation yet inhibit suckling-induced prolactin release

Mammalian reproduction is dependent on both a successful pregnancy and on the subsequent period of lactation. In the rat, ovulation occurs shortly after parturition making it possible for a dam to be simultaneously pregnant and lactating. The present studies investigate the effect of placental hormones on suckling-induced prolactin (PRL) release and the contribution of placental hormones to milk synthesis and secretion. A rat choriocarcinoma cell line, Rcho-1, which secretes placental lactogens (PLs) following transplantation in vivo, attenuated suckling-induced PRL release on both d 9 and d 14 of lactation by 43 and 58%, respectively. When PRL secretion was completely inhibited by bromocriptine, a dopamine agonist, Rcho-1-bearing dams still maintained a normal litters weight gain, demonstrating that placental lactogens can continue an established lactation. The Rcho-1 tumors also initiated milk synthesis and secretion in nulliparous rats continuously exposed to pups. Whereas none of the 11 control virgins began lactating and had an average pup weight loss of 2.07 g, the Rcho-1-bearing rats began lactating, as evidenced by a significant reduction in pup weight loss. Thirty percent of these rats became fully lactationally competent. Northern blot analysis showed that the Rcho-1 tumors expressed both PL-I and PL-II mRNA in all experimental groups. These tumors also secreted PL-I into the circulation, as shown by radioimmunoassay.

Prolactin receptor mRNA localization in the hypothalamus by in situ hybridization

Prolactin receptors may mediate the action of prolactin in the brain to influence behavior and neuroendocrine secretions. We recently demonstrated prolactin receptor gene expression in the anterior and medial basal hypothalamus and not in the cortex by the reverse transcription-polymerase chain reaction. In this paper, we localize the prolactin receptor gene expression to individual cells with in situ hybridization. Several steps in the in situ hybridization method were modified to increase sensitivity by using (i) probes complementary to the coding sequence of the extracellular binding domain common to both long and short prolactin receptor, (ii) more stringent hybridization and wash conditions to reduce background and (iii) higher specific activity, more complex and saturating amounts of probe. We detected prolactin receptor gene expression in cells of the periventricular area of the preoptic nucleus, medial preoptic nucleus, supraoptic nucleus, rostral arcuate nucleus and choroid plexus. Cortical brain tissue, which has been demonstrated previously by reverse-transcription polymerase chain reaction to be lacking in prolactin receptor mRNA, did not have any detectable signal for the receptor mRNA and was used as an indication of background levels of signal. The mean area of silver grains over labeled cells in periventricular area of the preoptic nucleus, medial preoptic nucleus, supraoptic nucleus, arcuate nucleus, lateral ventromedial nucleus was at least 10 times greater than the background in the cortex of the same brain section.

Implants containing beta-amyloid protein are not neurotoxic to young and old rat brain

Because the cellular effects of beta-amyloid protein (beta-AP) are currently unclear, we evaluated the in vivo effects of beta-AP implants in a lipid matrix to prolong tissue exposure in the brains of rats. Young 3-month-old rats and aged 18-month-old rats received implants of beta-AP prepared in a cocoa butter matrix in the dorsal hippocampus and corpus striatum on one side of the brain and implants of either prolactin or scrambled beta-AP peptide in cocoa butter on the contralateral side. The old rats also received implants of beta-AP embedded in a cholesterol matrix or cholesterol alone in the frontal cortex. The young rats were sacrificed 3-4 days after implantation, while the old rats were sacrificed 6-8 weeks after implantation. Lesion size on the beta-AP implanted side did not differ significantly from lesion size observed with control peptides. Bielschowsky silver staining revealed few argyrophilic neurites and axonal spheroids associated with either beta-AP or control implants. Alz 50 and ubiquitin immunoreactivity were not observed. None of the implant sites demonstrated cytopathology characteristic of Alzheimer's disease. The results of this study indicate that beta-AP implantation into the brains of rats produced no consistent effect beyond that seen with control peptide implants.

In vivo effects of beta-amyloid implants in rodents: lack of potentiation of damage associated with transient global forebrain ischemia

Recent studies have shown that the principal component of the senile plaque in Alzheimer's disease (AD), beta-amyloid protein (beta AP) can exert direct and indirect neurotoxicity in vitro. Because of the studies that demonstrated potentiation of excitatory amino acid toxicity by beta AP, we decided to test whether beta AP was able to potentiate damage in an in vivo model where excitotoxic damage is thought to be important. The present study evaluated the in vivo effects of beta AP implants in the brain of rats before and after being subjected to 10 min of transient global forebrain ischemia by 4-vessel occlusion (4-VO). Implants of either synthetic beta AP or prolactin (PRL), which was used as a control protein, were made into the striatum and the hippocampus of either the left (beta AP) or the right (PRL) cerebral hemisphere. The implants were made in a lipophilic, non-toxic vehicle so as to try and achieve sustained beta AP exposure. One group of animals was evaluated for direct in vivo effects within 1 week following implantation; the other group was subjected to 4-VO 3-4 days post-implantation for evaluation of potential indirect effects. This latter group was compared to the histopathology of animals subjected to 4-VO without prior implantation. In the group of animals evaluated for direct effects, no evidence of neurotoxicity was observed. Bielschowsky silver staining and immunostaining for ubiquitin were unremarkable in all lesions. beta AP was detected by immunocytochemistry in the parenchymal tissue that received beta AP implants. Marked glial activation was observed to be associated with experimental and control implants. Under the experimental conditions employed in this study, significant protection from ischemia rather than potentiation of damage was observed. These results suggest that beta AP may not be neurotoxic in rodents in vivo and that the lesions and/or trauma produced by the implantation procedure 3-4 days prior to 4-VO may have induced factors that were protective against ischemia-induced damage.