Search

The spatial and temporal distribution of cerebral metabolites and pHi were examined in the cortex during spreading depression. Acidification and marked depression in the energy status of the tissue was evident at the wavefront of spreading depression. In its aftermath, the residual activation of glycolysis and accumulation of cGMP persisted for minutes after a relatively rapid restoration of high-energy phosphates and pHi.

The distribution of the cyclic nucleotides was examined in layers of the mouse cerebellum following decapitation. Cyclic AMP increased and cyclic GMP decreased in all three layers of the cerebellum examined. The increase in cyclic AMP in the granular layer was far greater than in either the molecular or white layers. In the cerebellum from control mice, the cyclic GMP concentration was highest in the molecular layer and lowest in the white layer. Even after decapitation, this cyclic GMP gradient in the cerebellum was maintained.

Of the secondary messengers, cyclic quanosine monophosphate, but not cyclic adenosine monophosphate, was reduced by 80% in the cervical spinal cord and by 56% in the cerebellum of clinically affected homozygote "wobbler" mice compared to sex- and age-matched litter-mate clinically unaffected control mice. A neurotransmitter, gamma aminobutyric acid, and high-energy intermediates, adenosine triphosphate and phosphocreatine, were not significantly different in affected or unaffected mice.

A simple method for the rapid removal and freezing of mouse cardiac and pulmonary tissues is described. Samples thus obtained were judged to be suitable for valid estimation of in vivo levels of cyclic AMP and cyclic GMP based on the following findings: (a) the samples could be obtained and frozen in the very short time period of a few seconds; (b) no indication of adverse effects of the collection procedure was found upon examination of chemical indicators of energy metabolism; (c) the apparent rates of change of cyclic AMP and cyclic GMP levels during the first seconds after tissue isolation could produce small, but acceptable errors; and (d) dose-dependent elevations of pulmonary cAMP levels consistent with known effects in vitro were found after in vivo administration of isoproternol.

We tested the ability of the following putative vasoactive agents to stimulate guanylate cyclase activity in isolated rat cerebral microvessels: angiotensin II, arginine vasopressin, atrial natriuretic peptide, bradykinin, carbachol and thrombin; at concentrations ranging between 10(-3) and 10(-9) M. The ability of cerebral microvessels to increase their cyclic GMP generation was ascertained in the presence of sodium nitroprusside. Of all the agents tested, only atrial natriuretic peptide stimulated cyclic GMP generation in isolated rat cerebral microvessels. Such stimulation was dose-dependent, reaching its maximum at 1 microM concentration. These results are consistent with the finding of atrial natriuretic peptide receptors in brain microvessels, and suggest that this peptide has an important role in modulating the function of brain capillaries, which constitute the blood-brain barrier. If receptors for the other vasoactive agents exist in brain microvessels, their action does not seem to be mediated by cyclic GMP as a second messenger.