Modulation of XXXX corticohippocampal synaptic activity by high pressure and extracellular calcium: single and frequency responses.

@entity308 @entity101 @entity35 @entity73 @entity141 @entity7909 @entity2848
High pressure (>1.5 MPa) induces a series of disturbances of the nervous system that are generically termed @entity7909 ( @entity7909 ). @entity7909 is characterized by motor and @entity73 . The neocortex and the hippocampus are presumably involved in this last disorder. The medial perforant path (MPP) synapse onto the granule cells of the dentate gyrus is the main connection between these structures. We have studied @entity101 ( @entity101 ) effects on single and frequency response of this synapse. Since effects of @entity101 on various synapses were mimicked by reducing [ @entity141 ]o, results under these conditions were compared. Medial perforant path-evoked field excitatory postsynaptic potentials (fEPSPs) were recorded from granule cells in @entity35 brain slices. Slices were exposed to high pressure of helium (0.1-10.1 MPa) at 30 degrees C. @entity101 depressed single fEPSPs by 35 and 55% at 5.1 and 10.1 MPa, respectively, and increased paired-pulse facilitation (PPF) at 10- to 40-ms inter-stimulus intervals. @entity308 ( @entity308 ) was enhanced by @entity101 during trains of stimuli at 50 but not at 25 Hz. @entity308 of single fEPSPs by reduction of [ @entity141 ]o from 2 mM control to 1 mM at normal pressure was equivalent to the effect of 10.1 MPa at control [ @entity141 ]o. However, this low [ @entity141 ]o induced greater enhancement of @entity2848 , and in contrast, turned @entity308 at 25-50 Hz into frequency-dependent potentiation. These results suggest that @entity101 depresses single synaptic release by reducing @entity141 entry, whereas slowing of synaptic frequency response is independent of @entity141 . These findings increase our understanding of @entity7909 experienced by deep divers.
