Morphometric analysis of Mauthner axon cytoskeletal components in adult and subadult fish.

A previous cytoskeletal analysis on trout MA during developmental stages demonstrated, during the subadult stages, neurofilaments (NF) as main components as expressed by the high values of neurofilament to microtubules (MT) ratio which was found to be of the order of 300:1. Since the MA cytoskeletal composition is not known in the adult fish, the MA cytoskeletal composition has been compared to other axons of much smaller diameter of the fasciculus longitudinalis medialis (flm) among which the MA run in the ventral spinal cord. The following parameters were measured on conventional electron microscopy in MA and flm axons cross sections micrographs by means of a computer linked graphic tablet (Apple II): axonal caliber, number of microtubules (MT), microtubular (MT/microns2) and neurofilament (NF/microns2) densities. The analysis of these parameters demonstrated that neurofilaments are the main architectural components in the adult and subadult fish MA and flm axons. However, MA cytoskeletal composition differs from the other flm axons because of its particular very high ratio of neurofilaments to microtubules. The inverse relationship of axonal caliber to microtubular density, previously found in the trout during developmental stages and suggested also for many other vertebrate species, was further confirmed for flm axons which, with calibers 10 times smaller than MA, exhibit a microtubular density 10 times larger.

A novel line of transgenic mice (RSV/LTR-bGH) expressing growth hormone in cardiac and striated muscle.

In order to further investigate the deleterious effects of GH overexpression, we generated a novel line of transgenic mice featuring stable and specific expression of bovine GH in the heart and striated muscle. A DNA construct, containing a region with promoter activity from the Long Terminal Repeat of Rous Sarcoma Virus (RSV-LTR) and the entire structural gene of bovine GH (bGH), was microinjected by standard techniques in male pronuclei of fertilized mice eggs. Transgenic mice expressed bGH mRNA in the heart and striated muscle starting at 5-6 weeks of age. They featured circulating levels of a 22 kDa form of bGH up to 700 ng/ml and enhanced growth starting at 6 weeks of age. No pathologic changes of the myocardium and striated muscle fibers, other than hypertrophy, were noticed, although severe glomerulosclerosis and liver alteration occurred in older mice. Future studies on this new line of transgenic GH mice and integration with the existing data might improve our understanding of the molecular mechanism underlying the detrimental effects of elevated GH levels on various organs and functions.

Growth hormone and insulin-like growth factor I responses to moderate submaximal acute physical exercise in man: effects of octreotide, a somatostatin analogue, administration.

We evaluated growth hormone (GH) and insulin-like growth factor I (IGF-I) response to moderate submaximal acute short-term physical exercise under basal conditions and after the administration of octreotide, a somatostatin analogue (SA), in a double-blind, counter-balanced experimental protocol. Seven untrained male volunteers performed two identical exercise tests, each on a treadmill (2.5% slope) for 30 minutes (min) at 60% of VO2max. Before starting the exercise test all the subjects received a single administration of placebo or octreotide and vice versa at two different sessions. Plasma GH, IGF-I and lactate assays were evaluated before starting, during, at the end and in the recovery phase. In the placebo-treated group GH rose significantly both during exercise and recovery whereas no significant modifications in IGF-I levels were observed. SA administration inhibited the exercise-dependent GH secretion, which showed a small rise only during exercise and returned to basal levels during recovery. In the same group, IGF-I decreased significantly after exercise compared to basal values. The results suggest that 1) in our experimental conditions acute physical exercise at aerobic threshold does not modify IGF-I concentration 2) SA is able to inhibit the exercise-dependent GH secretion and to decrease post-exercise IGF-I concentration.