Immunocytochemical demonstration of glucose transporters in epiphyseal growth plate chondrocytes of young rats in correlation with autoradiographic distribution of 2-deoxyglucose in chondrocytes of mice.

The epiphyseal growth plate, where chondrocytes proliferate and differentiate, is the major site for longitudinal bone growth, matrix synthesis and mineralization. Glucose is an important energy source for the metabolism and growth of chondrocytes. The family of facilitative glucose transporters (GLUTs) mediates glucose transport across the plasma membrane in mammalian cells. We used immunocytochemical methods with anti-GLUT antibodies to investigate the localization of GLUTs in chondrocytes of the epiphyseal growth plate in 3 age groups of rats (3, 7, and 28 days after birth). Intense immunoreactivity of GLUT isoforms 1-5 was detected in chondrocytes of 3-day and 7-day old rats, and all GLUTs were localized in the maturation zone of the hypertrophic zone. On postnatal day 28, chondrocytes in the maturation zone showed intense GLUT1, 4 and 5 immunoreactivity, and weak GLUT2 and 3 immunoreactivity. In addition to chondrocytes in the maturation zone, those in the degenerative zone and in the zone of provisional calcification showed strong GLUT4 and 5 immunoreactivity. Autoradiography of bone sections from 4-week old mice injected with 14C-2-deoxyglucose showed high silver grain density within matrix tissue in the reserve and proliferative zones but not around chondrocytes. However, in the hypertrophic zone, silver grain density was high in matrix and chondrocytes. These data indicate that chondrocytes in the hypertrophic zones use glucose as energy source. High levels of GLUT4 expression imply that glucose use in chondrocytes is regulated by insulin. Expression of GLUT5 in chondrocytes suggests that fructose is also used as an energy source.

Autoradiographic distribution of radioactivity from (14)C-GABA in the mouse.

We investigated the distribution of radioactivity from (14)C-labeled gamma-aminobutyric acid (GABA) in the mouse by in vivo autoradiography to clarify the tissues that show GABA uptake and/or GABA binding. Male mice were injected intravenously with (14)C-GABA in both the absence and presence of an excess of unlabeled GABA, baclofen and isoguvacine. Whole-body autoradiography of (3)H-baclofen, a GABA(B) receptor agonist was also performed. At short intervals after (14)C-GABA injection ( 3 and 6 minutes), very high radioactivity was detected in the kidney cortex, liver, pineal gland, hypophysis, median eminence of the hypothalamus, and cervical ganglion. The hyaline cartilage and glandular part of the stomach showed moderate radioactivity. In the presence of an excess amount of unlabeled GABA, radioactivity in most of tissues decreased significantly, but no significant difference in radioactivity was observed in the presence of baclofen and isoguvacine, agonists of GABA(A) and GABA(B) receptors, respectively. Autoradiography of (3)H-baclofen showed that the kidney had high level of radioactivity, whereas the activity in other tissues and organs was similar or lower than in the blood except for the content of the urinary bladder and the pancreas at 15 minutes after injection. These data indicate that radioactivity from incorporated (14)C-GABA into a variety of cells is much higher than that from bound (14)C-GABA to the receptor sites. Our results suggest that GABA can be quickly localized in many organs of the mouse body after 3 minutes following injection, and GABA may serve multiple functions in those organs.

Histologic distribution of insulin and glucagon receptors.

Insulin and glucagon are the hormonal polypeptides secreted by the B and A cells of the endocrine pancreas, respectively. Their major physiologic effects are regulation of carbohydrate metabolism, but they have opposite effects. Insulin and glucagon have various physiologic roles, in addition to the regulation of carbohydrate metabolism. The physiologic effects of insulin and glucagon on the cell are initiated by the binding of each hormone to receptors on the target cells. Morphologic studies may be useful for relating biochemical, physiologic, and pharmacologic information on the receptors to an anatomic background. Receptor radioautography techniques using radioligands to label specific insulin and glucagon receptors have been successfully applied to many tissues and organs. In this review, current knowledge of the histologic distribution of insulin and glucagon receptors is presented with a brief description of receptor radioautography techniques.

Forelimb muscle contraction induced by cerebral cortical stimulation after callosotomy: a myographic study in the mouse.

The effect of callosotomy upon motor control by the cerebral cortex on the forelimb was examined in the mouse. On the 10th day after callosotomy in the rostral or caudal part of the corpus callosum, the forelimb area of the cerebral motor cortex was stimulated intracortically with a microelectrode and muscle contraction of the forelimb was recorded by electromyography. Muscle contraction was observed in the contralateral forelimb in the mice of which callosal fibers were cut in the caudal part of the corpus callosum including the splenium corporis callosi as well as in the normal mice. On the other hand, muscle contraction was observed in the ipsilateral forelimb in the mice of which callosal fibers were incised in the rostral part of the corpus callosum including the genu, rostrum and trunk. The latency of the muscle contraction was about 0.5 msec in the both groups of the callosotomized mice, as well as in the normal mice.