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The nerve growth factor (NGF) participates in cell survival and glucose-stimulated insulin secretion (GSIS) processes in rat adult beta cells. GSIS is a complex process in which metabolic events and ionic channel activity are finely coupled. GLUT2 and glucokinase (GK) play central roles in GSIS by regulating the rate of the glycolytic pathway. The biphasic release of insulin upon glucose stimulation characterizes mature adult beta cells. On the other hand, beta cells obtained from neonatal, suckling, and weaning rats are considered immature because they secrete low levels of insulin and do not increase insulin secretion in response to high glucose. The weaning of rats (at postnatal day 20 in laboratory conditions) involves a dietary transition from maternal milk to standard chow. It is characterized by increased basal plasma glucose levels and insulin levels, which we consider physiological insulin resistance. On the other hand, we have observed that incubating rat beta cells with NGF increases GSIS by increasing calcium currents in neonatal cells. In this work, we studied the effects of NGF on the regulation of cellular distribution and activity of GLUT2 and GK to explore its potential role in the maturation of GSIS in beta cells from P20 rats. Pancreatic islet cells from both adult and P20 rats were isolated and incubated with 5.6 mM or 15.6 mM glucose with and without NGF for 4 hours. Specific immunofluorescence assays were conducted following the incubation period to detect insulin and GLUT2. Additionally, we measured glucose uptake, glucokinase activity, and insulin secretion assays at 5.6 mM or 15.6 mM glucose concentrations. We observed an age-dependent variation in the distribution of GLUT2 in pancreatic beta cells and found that glucose plays a regulatory role in GLUT2 distribution independently of age. Moreover, NGF increases GLUT2 abundance, glucose uptake, and GSIS in P20 beta cells and GK activity in adult beta cells. Our results suggest that besides increasing calcium currents, NGF regulates metabolic components of the GSIS, thereby contributing to the maturation process of pancreatic beta cells. [ABSTRACT FROM AUTHOR]

The volcano mouse, Neotomodon alstoni, was studied in order to describe basic circadian behavior during free running and entrainment to parametric and non-parametric photoperiods. Responses to short and long days were also tested to ascertain any potential photoperiodic response. This species is endemic to the high grasslands of central Mexico. Its breeding peaks during summer, indicating a possible circannual regulation of reproduction. Our results indicate that locomotor activity in Neotomodon alstoni is typical of a nocturnal rodent when studied using running wheels, however, when activity was observed in freely moving recordings with no running wheel, locomotor activity shifts to a semidiurnal architecture when exposed to long day photoperiods. When gonadal activity was studied in males exposed to short and long days, significant differences were observed in testis size, nevertheless levels of testosterone and seminiferous tubuli indicated that day length does not inhibit sexual maturity in this species. The results indicated that N. alstoni may not be photoperiodic with regard to gonadal activity, however it does display photoperiodic differences with regard to behavior, body weight and testis size. [ABSTRACT FROM AUTHOR]