Daisuke Okada

Differential effects of phospholipase inhibitors in long-term potentiation in the rat hippocampal mossy fiber synapses and Schaffer/commissural synapses

Bath application of the inhibitors of phospholipases, nordihydroguaiaretic acid (NDGA) and p-bromo-phenacyl bromide (BPB), to the rat hippocampal slices suppressed long-term potentiation (LTP) in Schaffer/commissural-CA1 pyramidal synapses. On the other hand, neither of the two inhibitors suppressed LTP in mossy fiber-CA3 pyramidal cell synapses. BPB did not suppress phosphatidylinositol-specific phospholipase C (PI-PLC) activity of the slices. These results suggested that the mechanisms of LTP were quite different in the CA1 and CA3 subfields of rat hippocampus: in CA1, the involvement of an arachidonate metabolism was strongly suggested, whereas in CA3, an arachidonic acid cascade may not be necessary for LTP.

Pertussis toxin suppresses long-term potentiation of hippocampal mossy fiber synapses

The long-term potentiation (LTP) was studied using rat hippocampal slices in vitro. LTP in mossy fiber-CA3 pyramidal cell synapses was markedly suppressed in slices prepared from rats which had previously received intraventricular injection of pertussis toxin (PTX), compared with the bovine serum albumin-injected controls, suggesting the involvement of G-proteins in the mechanism of LTP in mossy fiber synapses. In contrast, LTP in Schaffer/commissural-CA1 pyramidal synapses was not affected by PTX pretreatment.

Long-term synaptic changes in rat cerebellar slices reflected in extracellular K+ activity

In rat cerebellar slices, a [K+]o increase evoked locally by molecular layer stimulation was recorded by a K(+)-sensitive microelectrode. This K+ response was reduced clearly during application of low-Ca2+ medium, kynurenate or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Sustained depression of the K+ response by about 20% was observed after simultaneously but not after alternately combined stimulation of the molecular layer and the white matter/granule cell layer. It is concluded from these results that long-term depression of parallel fiber-Purkinje cell transmission can be detected as depression of the K+ response.

Roles of Metabotropic and Ionotropic Glutamate Receptors in the Long-Term Potentiation of Hippocampal Mossy Fiber Synapses

Glutamate (Glu) is thought to be a major excitatory neurotransmitter in the central nervous system, and its receptors are believed to play important roles in brain functions such as learning and memory. For instance, Glu receptors of N-methyl-D-aspartate (NMDA) type are critically important in a certain form of synaptic long-term potentiation (LTP), which is a cellular or molecular model for memory. In other cases, however, in hippocampal mossy fiber synapses for instance, NMDA receptors may not be involved in the formation of LTP. The type of receptors involved there is not known.