Johns Hopkins University School of Medicine

About: Johns Hopkins University School of Medicine is a healthcare organization based out in Baltimore, Maryland, United States. It is known for research contribution in the topics: Population & Medicine. The organization has 44277 authors who have published 79222 publications receiving 4788882 citations.

Primate motor cortex and free arm movements to visual targets in three-dimensional space. II. Coding of the direction of movement by a neuronal population.

Abstract: We describe a code by which a population of motor cortical neurons could determine uniquely the direction of reaching movements in three- dimensional space. The population consisted of 475 directionally tuned cells whose functional properties are described in the preceding paper (Schwartz et al., 1988). Each cell discharged at the highest rate with movements in its “preferred direction” and at progressively lower rates with movements in directions away from the preferred one. The neuronal population code assumes that for a particular movement direction each cell makes a vectorial contribution (“votes”) with direction in the cell9s preferred direction and magnitude proportional to the change in the cell9s discharge rate associated with the particular direction of movement. The vector sum of these contributions is the outcome of the population code (the “neuronal population vector”) and points in the direction of movement in space well before the movement begins.

Human Growth Hormone and Human Aging

Abstract: In humans, both aging and GH deficiency are associated with reduced protein synthesis, decreased lean body and bone mass, and increased percent body fat. In healthy individuals, spontaneous and stimulated GH secretion, as well as circulating IGF-I and IGFBP-3 levels, are significantly decreased with advancing age. The extent to which these age-related changes in GH and IGF-I contribute to alterations in body composition and function remains to be elucidated. GH treatment of GH-deficient adults or old men with reduced IGF-I levels with exogenous GH increases plasma IGF-I, nitrogen retention, and lean body mass, decreases percent body fat, and exerts little effect on bone mineral density. Short-term adverse effects of GH therapy have been minimized by using low-dose regimens, but it is still uncertain whether long-term GH supplementation in adult life increases the risk of metabolic abnormalities or malignancy. Administration of GHRH, which has been shown to maintain the pattern of pulsatile GH secretion in old men, may represent another possible physiological approach to therapy. It may be justifiable initially to limit use of GH to certain elderly patients such as those suffering from catabolic illnesses, malnourishment, burns, cachexia, etc. A great deal more research will be necessary to determine whether normalization of GH and IGF-I levels in healthy older persons will lead to improvements in their physical and psychological functional capacity and quality of life.

The nuclear lamina is a meshwork of intermediate-type filaments.

Abstract: The nuclear lamina, a protein meshwork lining the nucleoplasmic surface of the inner nuclear membrane, is thought to provide a framework for organizing nuclear envelope structure and an anchoring site at the nuclear periphery for interphase chromatin. In several higher eukaryotic cells, the lamina appears to be a polymer comprised mainly of one to three immunologically related polypeptides of relative molecular mass (Mr) 60,000-75,000 (60-70K) termed lamins. Three lamins (A, B, and C) are typically present in mammalian somatic cells. Previous studies on nuclear envelopes of rat liver and Xenopus oocytes suggested that the lamina has a fibrillar or filamentous substructure. Interestingly, protein sequences recently deduced for human lamins A and C from complementary DNA clones indicate that both of these polypeptides contain a region of approximately 350 amino acids very similar in sequence to the coiled-coil alpha-helical rod domain that characterizes all intermediate-type filament (IF) proteins. Here we analyse the supramolecular organization of the native nuclear lamina and the structure and assembly properties of purified lamins, and show that the lamins constitute a previously unrecognized class of IF polypeptides.