Long-term, homologous prolactin, administered through ectopic pituitary grafts, induces hypothalamic dopamine neuron differentiation in adult Snell dwarf mice

Experimental Models for Aging and their Potential for Novel Drug Discovery

Background:

An interesting area of scientific research is the development of potential antiaging drugs. In order to pursue this goal, it is necessary to gather the specific knowledge about the adequate preclinical models that are available to evaluate the beneficial effects of new potential drugs. This review is focused on invertebrate and vertebrate preclinical models used to evaluate the efficacy of antiaging compounds, with the objective to extend life span and health span.

Methods:

Research and online content related to aging, antiaging drugs, experimental aging models is reviewed. Moreover, in this review, the main experimental preclinical models of organisms that have contributed to the research in the pharmacol-ogy of lifespan extension and the understanding of the aging process are discussed.

Results:

Dietary restriction (DR) constitutes a common experimental process to extend life span in all organisms. Besides, classical antiaging drugs such as resveratrol, rapamycin and metformin denominated as DR mimetics are also discussed. Likewise, the main therapeutic targets of these drugs include sirtuins, IGF-1, and mTOR, all of them being modulated by DR.

Conclusion:

Advances in molecular biology have uncovered the potential molecular pathways involved in the aging process. Due to their characteristics, invertebrate models are mainly used for drug screening. The National Institute on Aging (NIA) developed the Interventions Testing Program (ITP). At the pre-clinical level, the ITP uses Heterogeneous mouse model (HET) which is probably the most suitable rodent model to study potential drugs against aging prevention. The accelerated-senescence mouse P8 is also a mammalian rodent model for aging research. However, when evaluating the effect of drugs on a preclinical level, the evaluation must be done in non-human primates since it is the mammalian specie closest to humans. Research is needed to investigate the impact of new potential drugs for the increase of human quality of

The progesterone and estrogen modify the uterine prolactin and prolactin receptor expression of hyperprolactinemic mice

The aim of this study was to evaluate the effects of metoclopramide-induced hyperprolactinemia on the prolactin (PRL) and PRL receptor's expression in the uterus of mice. For this purpose, 49 Swiss mice were divided into the following groups: GrSS (non-ovariectomized mice given vehicle); GrMET (non-ovariectomized mice treated with metoclopramide); OvSS (ovariectomized mice given vehicle); OvMET (ovariectomized mice treated with metoclopramide); OvMET+17βE (ovariectomized mice treated with metoclopramide and 17β estradiol); OvMET+MP (ovariectomized mice treated with metoclopramide and micronized progesterone); OvMET+17βE+MP (ovariectomized mice treated with metoclopramide and a solution of 17β estradiol and micronized progesterone). Immunohistochemical analyzes were evaluated semi-quantitatively. Our results showed that GrMET, OvMET+MP, and OvMET+17βE+MP presented strong PRL expression. OvMET and OvMET+17βE presented mild reaction, while GrSS and OvSS presented weak reaction. Concerning PRL receptor, OvMET+MP and OvMET+17βE+MP showed strong reaction; GrMET, OvSS, and OvMET+17βE showed mild reaction; and GrSS and OvMET showed weak reaction. These findings suggest that progesterone alone or in combination with estrogen may increase the expression of uterine PRL and PRL receptor.

Changes in vasoactive intestinal peptide and tyrosine hydroxylase immunoreactivity in the brain of nest-deprived native Thai hen

Hyperprolactinemia is associated with incubation behavior and ovarian regression in birds. To investigate the association of prolactin (PRL), vasoactive intestinal peptide (VIP), and dopamine (DA) with the neuroendocrine regulation of incubation behavior, changes in the number of visible VIP-immunoreactive (VIP-ir) neurons in the nucleus inferioris hypothalami (IH) and nucleus infundibuli hypothalami (IN) and tyrosine hydroxylase-immunoreactive (TH-ir) neurons in the nucleus intramedialis (nI) and nucleus mamillaris lateralis (ML) of incubating native Thai hens were compared with those of nest-deprived hens. TH was used as a marker for dopaminergic (DAergic) neurons. Blood samples were collected to determine PRL levels. The localization and the number of visible VIP-ir and TH-ir neurons were determined by immunohistochemistry. Disruption of incubation behavior was accompanied by a precipitous decline in plasma PRL levels. The number of visible VIP-ir neurons in the IH-IN and TH-ir neurons in the nI and ML were high during incubation and decreased when hens were deprived of their nests. This study indicated an association between VIP neurons in the IH-IN and DA neurons in the nI and ML with the degree of hyperprolactinemia, suggesting that the expression of incubation behavior in birds might be, in part, regulated by the DAergic input from the nI and ML to VIP neurons in the IH-IN and subsequent PRL release.

Early postnatal administration of growth hormone increases tuberoinfundibular dopaminergic neuron numbers in Ames dwarf mice

Hypothalamic tuberoinfundibular dopaminergic (TIDA) neurons secrete dopamine, which inhibits pituitary prolactin (PRL) secretion. PRL has demonstrated neurotrophic effects on TIDA neuron development in PRL-, GH-, and TSH-deficient Ames (df/df) and Snell (dw/dw) dwarf mice. However, both PRL and PRL receptor knockout mice exhibit normal-sized TIDA neuron numbers, implying GH and/or TSH influence TIDA neuron development. The current study investigated the effect of porcine (p) GH on TIDA neuron development in Ames dwarf hypothalamus. Normal (DF/df) and dwarf mice were treated daily with pGH or saline beginning at 3 d of age for a period of 42 d. After treatment, brains were analyzed using catecholamine histofluorescence, tyrosine hydroxylase immunocytochemistry, and bromodeoxyuridine (BrdU) immunocytochemistry to detect BrdU incorporation. DF/df males and df/df treated with pGH experienced increased (P </= 0.01) weight gain compared with those treated with saline. DF/df had greater (P </= 0.01) TIDA neuron numbers than df/df, regardless of treatment. TIDA neuron number in pGH-treated df/df was greater (P </= 0.01) than in saline-treated df/df. Zona incerta and periventricular dopamine neurons were not affected by treatment or genotype. There was no effect of genotype or treatment on BrdU incorporation in the arcuate nucleus, median eminence, or periventricular region surrounding the third ventricle. Saline-treated df/df experienced decreased (P </= 0.05) dentate gyrus BrdU incorporation compared with saline-treated DF/df. In the lateral ventricle, pGH-treated males had greater BrdU immunoreactivity than pGH-treated females. The results show an effect of pGH on TIDA neuron development, although this effect is less potent than that of PRL, and likely GH-induced preservation of TIDA neurons rather than generation of new TIDA neurons via neurogenesis.

Prolactin induces tuberoinfundibular dopaminergic neurone differentiation in Snell dwarf mice if administered beginning at 3 days of age

The hypothalamic tuberoinfundibular dopaminergic (TIDA) neurones secrete dopamine, which inhibits prolactin secretion. TIDA neurone numbers are deficient in Ames (df/df) and Snell (dw/dw) dwarf mice, which lack prolactin, growth hormone and thyroid-stimulating hormone. Prolactin therapy initiated before 21 days maintains normal-sized TIDA neurone numbers in df/df mice and, when initiated as early as 7 days, maintains the maximum TIDA neurone numbers observed in dw/dw development, which are decreased compared to those in normal mice. The present study investigated the effect of prolactin dose and species on TIDA neurone development. Snell dwarf and normal mice were treated with saline, 5 microg of ovine prolactin (oPRL), 50 microg of oPRL, or 50 microg of recombinant mouse prolactin (rmPRL) beginning at 3 days of age. Brains were analysed at 45 days using catecholamine histofluorescence, and immunohistochemistry for tyrosine hydroxylase or bromodeoxyuridine. Normal mice had greater (P <or= 0.01) TIDA neurones than dw/dw, regardless of treatment. TIDA neurones in 50 microg oPRL-treated dw/dw mice were greater (P <or= 0.05) than those in 5 microg oPRL- and rmPRL-treated dw/dw mice, which were greater (P <or= 0.01) than those in saline-treated dw/dw mice. Fifty microgram oPRL-treated dw/dw mice also had greater (P < 0.01) TIDA neurone numbers than the maximum numbers observed in untreated dw/dw mice development. Among saline, 5 microg oPRL and 50 microg oPRL treatments, but not rmPRL, A14 neurone numbers were higher (P <or= 0.01) in normal compared to in dw/dw mice. The mechanism of TIDA neurone recruitment was investigated using bromodeoxyuridine (BrdU) treatment at intervals after 21 days. Mice treated with rmPRL, but not oPRL, had increased BrdU incorporation in the periventricular area surrounding the third ventricle and median eminence and in the arcuate nucleus. The data obtained in the present study indicate that oPRL, but not rmPRL, when given at a high enough dose, induces TIDA neurone differentiation in dw/dw mice. This supports neurotrophic effects of prolactin on TIDA neurones in early postnatal development that extends beyond maintenance of the cell population.