ABSTRACT
Previous reports suggested that a novel stimulus pattern of multi-train stimulus at low-frequency (2-Hz or 5-Hz) could induce stable long-term depression (LTD) in the CA1 area of adult rat hippocampus. In the present study, in order to determine the mechanism in LTD induced by the two novel tetanus patterns, changes in the population spikes (PS) in the hippocampal CA1 area of adult rats following the multi-train stimulus in the presence of AP5 [antagonist of N-methyl-D-aspartate receptors (NMDARs)] or MCPG [antagonist of type I/II metabotropic glutamate receptors (mGluRs)] were recorded. The results showed that both AP5 and MCPG inhibited the LTD induced by 2-Hz multi-train stimulus. The mean amplitude of population spikes (PSA) normalized to the baseline was (96.0±3.5)% after applying AP5 (n=10) and (95.7±4.1)% after applying MCPG (n=8), respectively, measured at 20 min post-tetanus. While 5-Hz multi-train tetanus failed to induce LTD in the presence of MCPG. The mean PSA was (73.6±4.4)% (n=10) and (98.2±8.9)% (n=8) in the presence of AP5 and MCPG, respectively, measured at 35 min post-tetanus. So it is suggested that LTD induced by 2-Hz multi-train tetanus involves co-activation of NMDARs and mGluRs, while LTD induced by 5-Hz multi-train tetanus is only related to activation of mGluRs.
Subject(s)
Animals , Rats , 2-Amino-5-phosphonovalerate , Pharmacology , CA1 Region, Hippocampal , Physiology , Glycine , Pharmacology , Long-Term Synaptic Depression , Receptors, Metabotropic Glutamate , Receptors, N-Methyl-D-AspartateABSTRACT
Previous reports suggested that a low-frequency stimulus (LFS) of 1~2 Hz (600~900 pulses) induced a homosynaptic long-term depression (LTD) of synaptic efficacy in the hippocampal CA1 area of young rats (< 4-week old). However, these stimulation protocols often failed to induce LTD in the adult CA1 hippocampus. In the present study, we examined the effects of two novel tetanus patterns on LTD induction in adult rat hippocampal slices. We determined that these novel stimulation protocols induced LTD in the adult hippocampus, and that the characteristics of induced LTD were parameter-specific, including latency (period from the end of tetanus to a beginning of LTD) and the amplitude of LTD. These results suggest that LFS with certain patterns can induce LTD in the CA1 area of adult rat hippocampal slices, and that the multi-trains of 2-Hz protocol provided more effective response than the 5-Hz protocol.
Subject(s)
Animals , Male , Rats , CA1 Region, Hippocampal , Physiology , Electric Stimulation , In Vitro Techniques , Long-Term Synaptic Depression , Physiology , Rats, Sprague-DawleyABSTRACT
The present study investigated the effects of prenatal exposure to the magnetic resonance imaging (MRI) magnetic fields on the synaptic ultrastructure of hippocampal formation of rats at different postnatal development stages. Pregnant rats with gestation of 12-18 days were exposed to the magnetic fields used for MRI clinical applications. When the offspring were 1, 2, or 5-month-old, the synaptic morphologic parameters were measured in female offspring. In the 2-month-old MRI group, the curvature of synaptic interface, the length of active zone and the surface density per unit volume (S(v)) of active zone in the dentate gyrus (DG) decreased significantly, and the width of synaptic cleft increased in the CA1 area. In the 5-month-old MRI group, the width of synaptic cleft increased, the thickness of postsynaptic density and the curvature of synaptic interface decreased significantly in the CA1 region, and the width of synaptic cleft increased in the DG. No significant change was observed in the 1-month-old group. These results suggest that prenatal exposure to the medical magnetic fields causes synaptic ultrastructural changes. The relationship of these changes with behavioral impairments was discussed.