Effects of intraventricular injections of 6-hydroxydopamine on anterior pituitary cell proliferation

Third Ventricular Injection of CCL2 in Rat Embryo Stimulates CCL2/CCR2 Neuroimmune System in Neuroepithelial Radial Glia Progenitor Cells: Relation to Sexually Dimorphic, Stimulatory Effects on Peptide Neurons in Lateral Hypothalamus

Clinical and animal studies show maternal alcohol consumption during pregnancy causes in offspring persistent alterations in neuroimmune and neurochemical systems known to increase alcohol drinking and related behaviors. Studies in lateral hypothalamus (LH) demonstrate in adolescent offspring that maternal oral administration of ethanol stimulates the neuropeptide, melanin-concentrating hormone (MCH), together with the inflammatory chemokine C-C motif ligand 2 (CCL2) and its receptor CCR2 which are increased in most MCH neurons. These effects, consistently stronger in females than males, are detected in embryos, not only in LH but hypothalamic neuroepithelium (NEP) along the third ventricle where neurons are born and CCL2 is stimulated within radial glia progenitor cells and their laterally projecting processes that facilitate MCH neuronal migration toward LH. With ethanol's effects similarly produced by maternal peripheral CCL2 administration and blocked by CCR2 antagonist, we tested here using in utero intracerebroventricular (ICV) injections whether CCL2 acts locally within the embryonic NEP. After ICV injection of CCL2 (0.1 µg/µl) on embryonic day 14 (E14) when neurogenesis peaks, we observed in embryos just before birth (E19) a significant increase in endogenous CCL2 within radial glia cells and their processes in NEP. These auto-regulatory effects, evident only in female embryos, were accompanied by increased density of CCL2 and MCH neurons in LH, more strongly in females than males. These results support involvement of embryonic CCL2/CCR2 neuroimmune system in radial glia progenitor cells in mediating sexually dimorphic effects of maternal challenges such as ethanol on LH MCH neurons that colocalize CCL2 and CCR2.

Pituitary phenotypes of mice lacking the notch signalling ligand delta-like 1 homologue

The Notch signalling pathway ligand delta-like 1 homologue (Dlk1, also named Pref1) is expressed throughout the developing pituitary and becomes restricted to mostly growth hormone (GH) cells within the adult gland. We have investigated the role of Dlk1 in pituitary development and function from late embryogenesis to adulthood using a mouse model completely lacking the expression of Dlk1. We confirm that Dlk1-null mice are shorter and weigh less than wild-type littermates from late gestation, at parturition and in adulthood. A loss of Dlk1 leads to significant reduction in GH content throughout life, whereas other pituitary hormones are reduced to varying degrees depending on sex and age. Both the size of the pituitary and the proportion of hormone-producing cell populations are unchanged, suggesting that there is a reduction in hormone content per cell. In vivo challenge of mutant and wild-type littermates with growth hormone-releasing hormone and growth hormone-releasing hexapeptide shows that reduced GH secretion is unlikely to account for the reduced growth of Dlk1 knockout animals. These data suggest that loss of Dlk1 gives rise to minor pituitary defects manifesting as an age- and sex-dependent reduction in pituitary hormone contents. However, Dlk1 expression in other tissue is most likely responsible for the weight and length differences observed in mutant animals.

Endocrine/paracrine control of pituitary cell proliferation and its involvement in pituitary tumorigenesis

The paper concisely reviews the data on the humoral factors which regulate the anterior pituitary cell proliferation in endocrine and/or paracrine manner. Their relevance for pituitary tumorigenesis is also discussed. The role of estrogens, growth factors, neuropeptides, dopamine, interleukins and angiotensins is presented.

In situ analysis of adenohypophysis proliferative activity in beagle dogs. Preliminary results

In order to establish control data on adenohypophysis cell cycle in beagle dogs, two different approaches were used. In the first approach, the adenohypophysis mitotic index (percentage of cells in mitosis: MI) was determined using pituitary glands from 50 control beagle dogs, 10 to 25 months old, from retrospective regulatory safety assessment studies. We found that the MI in males was 0.024 +/- 0.007% and in females 0.068 +/- 0.019%. The second approach involved the determination of the adenohypophysis cell fraction in S phase by means of bromodeoxyuridine (BrdU) anti-BrdU method in 16 control beagle dogs, 8 to 20 months old, from ongoing safety assessment studies. We found that the BrdU labeling index (percentage of BrdU-positive cells per total number of cells: BrdU LI) was 0.053 +/- 0.009% in males and 0.059 +/- 0.015% in females. Analysis of our data indicated that the results obtained from the BrdU LI were more reliable (coefficient of variation [CV] less than 0.07) compared to those obtained from the MI (CV greater than 1.4). No clear difference was found between male and female beagle dogs, regarding adenohypophysis cell proliferation. In both studies, adenohypophysis cell proliferation was found to be age-dependent, with the highest value in immature dogs. No correlation between estrus cycle in females and adenohypophysis cell proliferation was noted.

Growth factors and pituitary tumors

Growth within the anterior pituitary gland is probably controlled by several interacting extracellular messenger molecules, including hypothalamic peptides, target gland hormones, and several growth factors acting in autocrine or paracrine fashion. Adenoma formation may result from abnormal production of such factors or their specific cellular receptors, loss of local inhibitory influences, activation of the intracellular secondary message pathways conveying the mitogenic signal to the nucleus, or deregulation of the nuclear processes controlling mitosis.

Effect of intracerebroventricular injection of prostaglandin E2 on anterior pituitary cell proliferation

The influence of an intracerebroventricular (i.c.v.) injection of prostaglandin E2 (PGE2) on the mitotic activity of the rat anterior pituitary was investigated. It was found that i.c.v. PGE2 (3 micrograms/20 microliters) resulted in a significant decrease of the mitotic activity in the anterior pituitary. This drop involved mainly chromophobic cells. No mitoses were found in acidophilic cells either in controls or in PGE2-treated rats. It is suggested that PGE2 may release an unidentified hypothalamic factor which inhibits the cell proliferation of the anterior pituitary.