Different glutamate receptor mechanisms in long-term depression induced by different stimulus patterns in the CA1 area of adult rat hippocampus.

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.

[Impact of fetal growth restriction on spatial learning and memory abilities of the offspring of rats].

OBJECTIVE: To test the impact of fetal growth restriction (FGR) on the spatial learning and memory abilities of the offspring of rats. METHODS: FGR Model of Sprague-Dawley rats was constructed according to the method of passive smoking. The offspring of the rats were divided into male FGR group, male control group, female FGR group and female control group. Within each group, the rats were randomly divided into three subgroups to be tested at 1, 2, and 4 months of age, respectively (n =10 for each subgroup). Morris water maze task was performed to assess the spatial learning and memory abilities of the rats. RESULTS: The escape latencies to find the platform were shortened with increased training times for all of the rats. At the age of 1 and 2 months, both male and female rats in the FGR group spent more time in finding the platform than their counterparts in the control group (P < 0.05). At the age of 4 months, significant prolonged latency was only found in the female rats. The rats in the FGR group, except the 4 months old male rats, were more likely to use non-effective strategies (random or marginal strategies) to find the platform than the efficient strategies (tendency or straight strategies). The rats in the FGR group stayed in the platform shorter than those in the control groups (P < 0.05). CONCLUSION: FGR can cause gender- and age-specific impairment of spatial learning and memory abilities to the offspring.

The tetanus patterns for the induction of long-term depression in the adult rat hippocampus.

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.

Gender- and age-specific impairment of rat performance in the Morris water maze following prenatal exposure to an MRI magnetic field.

We examined the effects of prenatal exposure (40 min/day, gestation days 12-18) of rats to a magnetic resonance imaging (MRI) magnetic field (MF) on their performance in the Morris water maze. At 2 months of age, female rats showed impaired performance. The animals spent longer time swimming and used inefficient strategies. However, no significant effects on maze performance were observed at 1 and 5 months of age. No evident maze performance deficit was detected in male rats prenatally exposed to the magnetic field. Thus, we conclude that prenatal exposure to MRI magnetic field induces cognitive/behavioral deficits in female rats at a specific age.

Morphological alteration of the hippocampal synapses in rats prenatally exposed to magnetic resonance imaging magnetic fields.

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.

Prolonged reversal of long-term potentiation that is N-methyl-D-aspartate receptor independent: implications for memory formation.

Reversal of long-term potentiation (LTP) by low-frequency stimulation (LFS) is often referred to as depotentiation (DP), a phenomenon that is time-dependent. The present study aimed to determine whether LTP could still be reversed when the stimulation was applied beyond the optimal time window in hippocampal slices from adult rats. Field excitatory postsynaptic potentials (fEPSPs) were recorded from the strata radiatum in CA1, following stimulation of Schaffer collaterals. Theta-burst stimulation (TBS) induced LTP that could be reversed by repeated paired-pulse LFS (PP-LFS) after almost 3 h post-TBS. Only when synapse strength reached a plateau did application of PP-LFS trigger DP. In addition, it was surprising to observe that PP-LFS, which generally induces LTD in adult rats, evoked an LTP-like further strengthening in previously potentiationed synapses, even in the presence of APV, a competitive antagonist of N-methyl-D-aspartate receptors (NMDA-Rs). Our results suggest that LTP can be reversed NMDAR-independently more than 2 h after TBS by PP-LFS in adult hippocampus and that saturation of LTP is effective to promote this process.