Chronic central infusion of growth hormone secretagogues: effects on fos expression and peptide gene expression in the rat arcuate nucleus

Growth hormone (GH) secretagogues induce GH release, in part, by direct actions upon anterior pituitary somatotropes and, in part, by actions upon the neuroendocrine circuitry that regulates GH secretion. In particular, acute systemic administration of GH secretagogues results in increased neuronal activity and Fos protein expression in the arcuate nucleus of the hypothalamus. Prolonged administration of GH secretagogues has been reported to have long-lasting effects upon GH release, promoting increased pulsatile secretion. Here, we investigated how chronic central infusion of GH secretagogues affects the response of arcuate nucleus neurons to acute systemic administration of GH secretagogues. In male rats, after central infusion of GH secretagogues for 5 days, there was no sustained expression of Fos in the arcuate nucleus, no significant induction of Fos expression in response to acute GH secretagogue challenge, and a greatly attenuated secretion of GH in response to acute GH secretagogue challenge, all reflecting loss of funtional responsiveness to GH secretagogues. In situ hybridisation revealed that, in the arcuate nucleus of GH secretagogue-infused rats, mRNA levels for GH-releasing hormone, neuropeptide Y and somatostatin were not different than in saline-infused animals. However, somatostatin mRNA levels in the periventricular nuclei of GH secretagogue-infused rats were significantly higher than those of saline-infused rats, indicating that this nucleus may play an important role in mediating the effects of chronic GH secretagogue administration.

An electrophysiological and morphological investigation of the projections of growth hormone-releasing peptide-6-responsive neurons in the rat arcuate nucleus to the median eminence and to the paraventricular nucleus

Growth hormone-releasing peptide-6 injection induces c-fos messenger RNA expression in many arcuate nucleus neurons, and sub-populations of neurons in this region project to the hypothalamic paraventricular nucleus. We examined electrophysiologically whether arcuate nucleus neurons that project to the paraventricular nucleus also project to the median eminence, and whether these neurons are activated by systemic injection of growth hormone-releasing peptide-6. Of 116 arcuate nucleus neurons tested, 43 were antidromically-identified as projecting to the paraventricular nucleus and a further 30 as projecting to the median eminence; these populations displayed distinct electrophysiological characteristics, and contrasting patterns of orthodromic response to stimulation of the median eminence and paraventricular nucleus, indicating that these two populations are functionally distinct with limited communication between them. Only one cell was antidromically-identified as projecting to both these regions. Three of 10 arcuate nucleus neurons that projected to the paraventricular nucleus were activated by injection of growth hormone-releasing peptide-6. In parallel experiments, we examined whether Fos protein expression is induced in arcuate nucleus neurons that project to the paraventricular nucleus, as identified by retrograde-labelling with FluoroGold. Immunocytochemical studies revealed that 20% of arcuate nucleus neurons that were retrogradely-labelled from the paraventricular nucleus were Fos-positive following growth hormone-releasing peptide-6 injection, although cells that were both Fos-positive and retrogradely-labelled accounted for less than 5% of the total number of Fos-positive arcuate nucleus neurons. These results confirm that there is a direct projection from the arcuate nucleus to the paraventricular nucleus and indicate that growth hormone-releasing peptide-6 activates some of these neurons.

Point of care technology: impact on people and paperwork

A systematic evaluation of a bedside computer system for nursing documentation indicates that point of care technology has a positive direct impact on the efficiency, effectiveness, and satisfaction of the nursing staff, and a positive indirect influence on other members of the health care team in their delivery of patient care.