The effects of staurosporine, introduced as a very potent inhibitor of protein kinase C (PKC), on evoked neurotransmitter release were investigated and compared with those of the other PKC inhibitors: 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H7) and polymyxin B (PMB). Slices of rabbit hippocampus, prelabelled with either [3H]noradrenaline, [3H]5-hydroxytryptamine or [3H]choline were superfused with physiological medium. During superfusion the slices were stimulated either electrically (3 Hz, 5 V/cm, 24 mA, 2 msec) or by high K+ (30 mM) for 2 min, respectively. Both the electrically and potassium evoked overflow were increased by the PKC activator 4 beta-phorbol 12,13-dibutyrate (PDB). The degree of the enhancement by PDB was dependent on the transmitter and the stimulation conditions used. These results may be explained by differences in the extent of activation of PKC during electrically or potassium evoked release. The PDB-induced enhancement of electrically or potassium evoked release of the 3 transmitters was counteracted by staurosporine (1 microM) in concentrations much lower than those required for H7 (100 microM) and PMB (100 microM). PMB, which has been shown to decrease electrically evoked transmitter release, similarly diminished K+-evoked release. In contrast, only the potassium evoked [3H]acetylcholine release was significantly diminished by staurosporine (1 microM) and H7 (100 microM). In conclusion, these results show again that facilitation of neurotransmitter release by phorbol esters is due to activation of PKC.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMedDate not supplied

In vivo comparative study of the seizure- and ischemia-induced synthesis of eicosanoids in the brain of gerbils.

After transient cerebral ischemia induced by bilateral ligation of carotid arteries, followed by 5 min reperfusion, concentrations of prostaglandin D2 and LTC4-like material increased with time in the gerbil brain. At least a 1 min occlusion time was necessary to elevate the eicosanoid concentrations significantly over the basal levels. Spontaneous tonic-clonic seizures of about 20 sec duration induced an increase in prostaglandin D2 and LTC4-like material comparable to the values found after a 2 min occlusion time. Following carotid artery occlusion, the eicosanoid levels were found to be elevated in midbrain, hypothalamus, striatum, hippocampus and cortex, i.e., those brain areas dependent upon the blood supply from the carotid arteries. In contrast, following spontaneous seizures, prostaglandin D2 concentrations were increased in the striatum, hippocampus and cortex only, and the LTC4-like material in the cortex. Hippocampus, striatum and cortex are brain areas which participate in the generation and propagation of seizures. It appears, therefore, unlikely that the seizure-induced eicosanoid synthesis is triggered off by a hypoxic event due to an impaired breathing caused by convulsions. The regional pattern of the eicosanoid synthesis following the seizures may rather depend on the intensity of the neuronal activity than on regional differences in the eicosanoid-synthesizing capacity.

Animals↗