Toshio Ishikawa

Studies on long-term potentiation of the population spike component of hippocampal field potential by the tetanic stimulation of the perforant path in rats: effects of a dopamine agonist, SKF-38393

Long-term potentiation of the field potentials recorded in the dentate gyrus of the hippocampus was observed in freely-moving rats by delivering a brief tetanic stimulation to the perforant path, and the effects of the D1 agonist, SKF-38393, on it was investigated. The field potential was divided into two components; excitatory postsynaptic potential (EPSP) and population spike. In Expt. I, synaptic stimulus-response (S-R) relationship, spike S-R relationship, and EPSP-spike (E-S) relationship were plotted. The estimated slope of the regression line in the spike S-R relationship was enhanced after delivery of the tetanic stimulation (10 pulse at 400 Hz), where that in synaptic S-R relationship was not enhanced. The estimated slope of the regression line in the E-S relationship was also enhanced by the tetanic stimulation. In Expt. II, time-dependent change of the field potential after tetanic stimulation was investigated. The population spike was enhanced significantly for about 2 h following tetanic stimulation, while pEPSP did not change significantly. These changes following tetanic stimulation in Expt. I and II were significantly inhibited by previous administration of SKF-38393 (10 mg/kg, i.p.), and the effect of this drug was dose-dependently antagonized by the D1 antagonist, SCH-23390 (0.1, 0.2 and 0.5 mg/kg, i.p.). These results suggest that a brief tetanic stimulation of the perforant path induces long-term potentiation of the population spike without potentiating the synaptic input in the perforant path-dentate synapses, and that potentiation of the population spike is inhibited by the dopaminergic D1 mechanism.

The effects of apomorphine on the hippocampal field potential in freely moving rats: Pharmacological evidence of the involvement of D2 receptors

The effects of apomorphine on the hippocampal field potential of dentate granule cells were investigated in freely-moving male Sprague-Dawley rats. Five sequential field potentials were recorded from the dentate gyrus of the dorsal hippocampus, by stimulating the perforant path in the entorhinal cortex at 30 sec intervals. The slope of the population excitatory postsynaptic potential (EPSP) slope and the amplitude of the population spike of these field potentials were analyzed and averaged with a computer. The effects of apomorphine were observed at intervals of 15 min over 2 hr. Although the slope of the population EPSP showed no significant change after the administration of apomorphine (1.0 mg/kg, i.p.), the amplitude of the population spike was enhanced by about 30%. This enhancement continued for about 90 min. These results suggest that the apomorphine does not change the synaptic input from the perforant path to the granule cells but enhances the excitability of the hippocampal dentate granule cells. This effect of apomorphine on the amplitude of the population spike was decreased by sulpiride (20 mg/kg, i.p.) but was not affected by SCH-23390 (0.1 mg/kg, i.p.). These results lead to the conclusion that the enhancement of the excitability of the dentate granule cells by apomorphine is caused by the activation of the postsynaptic D2 receptors.

Hippocampal after-discharge and the mode of action of psychotropic drugs.

Publisher Summary This chapter describes hippocampal after-discharge and the mode of action of psychotropic drugs. As a result of many studies on the effects of psychotropic drugs, it is recognized that these drugs have both facilitatory and inhibitory effects on the central nervous system, and also that they have some effects on the limbic system. High amplitude and polymorphic types of after-discharge were generally produced by electrical stimulation of the hippocampus. The discharge usually propagated to the opposite hippocampus and many cortical and subcortical structures. Propagation to the neocortex was more readily found in the parieto-temporal and occipital areas. Propagation of after-discharge was also recorded from some subcortical structures such as fornix, mammillary body, anterior thalamic nuclei and hypothalamus. It is found that when the reticular formation was stimulated electrically immediately before, after and during stimulation of the hippocampus, no change in hippocampal after-discharge was observed. The mode of action of psychotropic drugs is characterized by the absence of a depressing action on the hippocampal after-discharge.

Usefulness of SDS-Minislab Method in Electrophoretic Analyses of Photographic Gelatin

AbstractIn SDS-electrophoretic analysis of gelatin, much shorter running time and better resolution compared with the standard system have been obtained by using a minislab system. The electrophoretic patterns have clearly shown the characteristics of each gelatin type. In particular, ratios of α-band intensities, αl/α2 of several lime processed gelatins have been examined. The ratios for hide gelatins were larger than 1.5 whereas those for bone gelatins were smaller than 1.1. It is assumed that the deviations from the theoretical ratio for type I collagen could be due to preferential extraction of α2 chains from raw materials.