RESUMO
States of increased metabolic demand such as fasting modulate hypothalamic neuropeptide gene expression and decrease circulating leptin levels. This study tested the hypotheses that fasting stimulates gene induction mediated by cAMP response element (CRE)-dependent increases in gene transcription and that fasting-induced decreases in leptin can regulate this CRE-mediated gene induction. Using C57BL/6J mice transgenic for a CRE-lacZ construct, an immunocytochemical study showed that fasting activated reporter gene expression in the hypothalamic arcuate nucleus (Arc) in a small subset of neurons and increased phosphorylation of CRE binding protein. The increase of beta-galactosidase expression caused by fasting was inhibited by a protein kinase A inhibitor, Rp-8-Br-cAMPS, when the compound was microinjected into the medial basal hypothalamus, and enhanced by intraperitoneal injection of selective phosphodiesterase inhibitors. In situ hybridization studies showed that neuropeptide Y (NPY) mRNA levels increased in the Arc during fasting, whereas proopiomelanocortin (POMC) mRNA levels decreased. Double labeling of mRNA and beta-galactosidase immunoreactivity in the fasted brain indicated that the subpopulation of the neurons expressing beta-galactosidase all produced NPY but not POMC. To study the possible involvement of decreased circulating leptin during starvation on CRE-mediated gene induction, leptin was administered intraperitoneally to fasted mice. Leptin significantly attenuated both beta-galactosidase expression and NPY gene expression stimulated by fasting, suggesting that leptin inhibits fasting-stimulated NPY gene expression at least in part through downregulation of CRE-mediated gene induction in the Arc. Leptin-induced modification of CRE-mediated gene induction in the Arc may play an essential role in the central regulation of feeding behavior and energy expenditure.
Assuntos
Núcleo Arqueado do Hipotálamo/metabolismo , Jejum/metabolismo , Regulação da Expressão Gênica/fisiologia , Leptina/metabolismo , Neurônios/metabolismo , Animais , Núcleo Arqueado do Hipotálamo/citologia , Núcleo Arqueado do Hipotálamo/efeitos dos fármacos , Proteína de Ligação ao Elemento de Resposta ao AMP Cíclico/genética , Proteína de Ligação ao Elemento de Resposta ao AMP Cíclico/metabolismo , Proteínas Quinases Dependentes de AMP Cíclico/antagonistas & inibidores , Regulação para Baixo/efeitos dos fármacos , Regulação para Baixo/fisiologia , Inibidores Enzimáticos/farmacologia , Regulação da Expressão Gênica/efeitos dos fármacos , Genes Reporter , Leptina/farmacologia , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Neurônios/efeitos dos fármacos , Neuropeptídeo Y/genética , Neuropeptídeo Y/metabolismo , Inibidores de Fosfodiesterase/farmacologia , Fosforilação , Pró-Opiomelanocortina/genética , Pró-Opiomelanocortina/metabolismo , RNA Mensageiro/metabolismo , Sequências Reguladoras de Ácido Nucleico/fisiologia , Ativação Transcricional , beta-Galactosidase/biossíntese , beta-Galactosidase/genéticaRESUMO
Our objective was to investigate ejaculation and transport of sperm in the reproductive tract of male rats treated with an alpha-adrenergic receptor antagonist. Males were dosed (s.c.) with vehicle or 1.4 mg/kg prazosin. Sperm recovered in utero and ex vivo from the vas deferens and cauda epididymis were evaluated. Mating behavior and sperm motility were unaffected by prazosin. Prazosin treated males ejaculated fewer sperm (12.58 +/- 8.12 vs. 110.5 +/- 29.15 million), and the distal vas deferens contained fewer sperm (2.72 +/- 0.84 vs. 24.42 +/- 3.25 million) relative to controls. Prazosin-treated males had more sperm in the cauda epididymis relative to controls indicating inhibition of sperm transport to the vas deferens. These data demonstrate that inhibition of sperm transport from the cauda epididymis to the distal vas deferens is related to low ejaculate sperm counts in prazosin treated rats.
Assuntos
Antagonistas Adrenérgicos alfa/toxicidade , Prazosina/toxicidade , Motilidade dos Espermatozoides/efeitos dos fármacos , Animais , Ejaculação/efeitos dos fármacos , Feminino , Masculino , Ratos , Ratos Sprague-Dawley , Contagem de EspermatozoidesRESUMO
Decreased daily sperm production (DSP) and cauda epididymal sperm number (CESN) are some of the most sensitive effects of in utero and lactational 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure. The reduction in CESN cannot be fully accounted for by decreased spermatogenesis. To explain the decrease in CESN it was hypothesized that TCDD exposure increases the rate of sperm transit through the excurrent duct system, thereby decreasing the number of sperm in the system at any given time. Pregnant Holtzman rats were administered a single dose of TCDD (1.0 microgram/ kg,po) or vehicle on gestation day 15 and offspring were weaned on postnatal day (PND) 21. On PND 50, testicular sperm were labeled in five males per litter, from 30 control and 26 TCDD-exposed litters, by injecting 15 microCi [3H]thymidine into each testis, under general anesthesia. Sperm movement through the excurrent duct system was monitored daily 35-64 days post [3H]thymidine injection. On PNDs 92-93, TCDD exposure significantly decreased DSP/testis, corpus and cauda epididymis sperm numbers, vas deferens sperm number, and ejaculated sperm number by 28, 30, 36, 39, and 46%, respectively. The decreases in sperm number in the distal excurrent duct system were greater than the decrease in DSP, consistent with the hypothesis that TCDD exposure causes an effect other than decreased DSP that reduced epididymal and ejaculated sperm numbers. However, in utero and lactational TCDD exposure did not alter radiolabeled sperm transit time through the whole epididymis (15 days). With TCDD exposure causing no obvious alteration in sperm transit rate, a plausible explanation for the sperm loss is an increase in sperm phagocytosis in the excurrent duct system.
