RESUMEN
The hypothalamic suprachiasmatic nuclei (SCN) comprise the main site in the brain involved in the control of the homeostatic mechanism which respond to environmental daily light changes. The sympathetic nervous system and hypothalamic releasing or inhibiting factors mediate the SCN control of a number of peripheral organs and tissues. In this work we analyzed the involvement of two environmental light conditions, constant light (LL) and constant dark (DD) for 20 days, on the expression of mRNAs for catecholamines biosynthetic enzymes and neuropeptide Y (NPY) genes in rat superior cervical ganglia (SCG) and adrenal gland. The results of Northern blot analysis show that LL exposure reduces mRNA levels for tyrosine hydroxylase (TH) the rate limiting catecholamine biosynthetic enzyme and also of dopamine beta-hydroxylase (DBH) as well as for NPY in SCG to about half the levels in control animals. In contrast, exposure of the rats to DD did not elicit any change in the SCG. In the adrenal gland, both, LL and DD conditions increased the TH, DBH as well as phenylethanolamine N-methyltransferase (PNMT) mRNA levels. Under the same conditions, adrenal NPY mRNA levels were decreased by either LL or DD. The results show, for the first time, that prolonged changes in environmental light can alter the gene expression of catecholamine biosynthetic enzymes and of NPY. There was differential response in SCG and adrenal gland.
Asunto(s)
Glándulas Suprarrenales/metabolismo , Catecolaminas/biosíntesis , Ritmo Circadiano/genética , Luz , Neuropéptido Y/biosíntesis , Ganglio Cervical Superior/metabolismo , Adaptación Fisiológica/genética , Glándulas Suprarrenales/citología , Animales , Catecol O-Metiltransferasa/genética , Oscuridad , Dopamina beta-Hidroxilasa/genética , Regulación hacia Abajo/genética , Regulación hacia Abajo/efectos de la radiación , Ambiente Controlado , Masculino , Neuropéptido Y/genética , Estimulación Luminosa , ARN Mensajero/metabolismo , ARN Mensajero/efectos de la radiación , Ratas , Ratas Wistar , Ganglio Cervical Superior/citología , Tirosina 3-Monooxigenasa/genética , Regulación hacia Arriba/genética , Regulación hacia Arriba/efectos de la radiaciónRESUMEN
The aim of this work was to analyse the parasympathetic control of submandibular saliva secretory response to cholinergic and peptidergic agonists in rats chronically exposed to constant light or repeated immobilization. Thirty two adult male Wistar rats were used: LL (8 rats exposed to constant light for 20 days), IMO (8 rats submitted to 14:10 h light: dark cycle and immobilized 2 hours daily for 7 days), and control (16 rats not exposed to stress and submitted to 14:10 hours light:dark cycle). Saliva was collected under anesthesia from the salivary ducts of submandibular glands under increasing doses of methacholine and substance P. Secretory responses (µg/saliva/mg dry weight gland) to methacholine were significantly higher in LL and IMO groups compared to control for the following doses (µg/kg body weight): 3 (153±9 versus 46±3, p<0.001 and 76±3 versus 40±3, p<0.001), 10 (379±23 versus 277±8, p<0.001 and 275±19 versus 250±10, p<0.01) and 30 (729±25 versus 695±19, p<0.05 and 1008±39 versus 640±20, p<0.001). Also, responses to substance P were significantly increased in LL and IMO groups compared to control for the following doses: 0.2 (80±3 versus 30±3, p<0.01 and 94±16 versus 31±3, p<0.001), 0.5 (328±20 versus 231±16, p<0.01 and 531±31 versus 219±25,p<0.001), 1 (681±35 versus 547±30, p<0.01 and 1031±63 versus 563±53, p<0.001), and 5 (2222±88 versus 1868±59, p<0.01 and 3230±145 versus 1921±218, p<0.001). In conclusion, supersensitivity of secretory response to both agonists suggests that chronic exposure of rats to stressors capable of activating the sympathetic adrenal system promotes inhibition of the parasympathetic control of salivary secretion.