Cryopreservation of Crassostrea gigas vesicular cells: viability and metabolic activity.

Cryopreservation is widely used for long-term conservation of various tissues, embryos or gametes. However, few studies have described cryopreservation of invertebrate primary cell cultures and more particularly of marine invertebrate somatic cells. This technique would however be of great interest to facilitate the study of various metabolic processes which vary seasonally. The aim of the present study was to develop a protocol for cryopreservation of Crassostrea gigas vesicular cells. Different parameters were adjusted to improve recovery of cells after freezing. The most efficient cryoprotectant agent was a mix of Me(2)SO, glycerol, and ethylene glycol (4% each). The optimal cooling rate was -1 degrees Cmin(-1) down to -70 degrees C before transfer into liquid nitrogen. In these conditions the percentage of viable cells reached 70% of the control. The glucose metabolism of thawed cells was evaluated using radioactive glucose as a tracer. Immediately after thawing, glucose uptake involving membrane transporters was greatly reduced (24% of control) whereas glucose incorporation into glycogen was less affected (68% of control).

Immediate effect of lesion of the ventromedial hypothalamic area upon glucose-induced insulin secretion in anaesthetized rats.

Insulin secretion, measured in vivo following an intravneous load of glucose to anaesthetized rats, was markedly increased ten minutes after bilateral electrolytic lesions of the ventromedial hypothalamic (VMH) area when compared to both sham-operated and unoperated controls. The successful lesioning of the VMH area was assessed by the subsequent occurrence of hyperphagia, as estimated by the increase in body weight. It is concluded that the ventromedial hypothalamic area exerts an inhibitory influence upon the secretory activity of the B-cells. Furthermore, the rapid disappearance of such inhibitory influence following lesions of the VMH suggests that this area of the brain may be of importance in the minute to minute regulation of insulin secretion. The precise anatomical location of the hypothalamic "nucleus" (or "nuclei") involved, as well as the neural or humoral nature of its inhibitory effect upon the endocrine pancreas remain to be elucidated.