| Budget Amount *help |
¥2,900,000 (Direct Cost: ¥2,900,000)
Fiscal Year 2006: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2005: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 2004: ¥1,100,000 (Direct Cost: ¥1,100,000)
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| Research Abstract |
The hippocampal-medial prefrontal cortex (mPFC) pathway provides highly convergent input to the mPFC in rats and shows two types of short-term plasticity in terms of paired-pulse facilitation (PPF) of the field potential under urethane anesthesia. We now report that stimulating either the dorsal or ventral subregions of the posterior hippocampus elicited PPF (by about 335 and 120 %, respectively) of field potentials recorded in the mPFC at 100 ms interpulse interval. This PPF-like interaction occurred when projections were stimulated in the ventral-dorsal order (by about 200% of the single-pulsed response), but not vice versa. When weak long-term potentiation (LTP) of the dorsal projection was evoked simultaneously with strong LTP of the ventral projection, an associative effect was revealed (about +55 %), although the magnitudes of LTP in each projection were not correlated. Even when the impermutable PPF-like facilitation was further enhanced (by about +120 %), the enhancement was no
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t correlated with either form of LTP, but exhibited the interaction of changes in the dorsal PPF, rather than in the heterotopic priming effect through the ventral projection. Moreover, this change was correlated with the associated LTP ratio of dorsal to ventral projection LTP (i.e., LTP associativity). Larger increases in LTP associativity correlated with greater impermutable PPF-like facilitation; in addition, there was hardly attenuation of the response to the dorsal projection by subsequent electrolytic lesions of the ventral subregion. // After conditioning rats to a 1-min auditory tone paired with pulsed footshock, an intensity of 1.0 mA caused more consolidated and inextinguishable freezing in response to both context and tone on consecutive test days 7-8 when the co-monitored activities were lower, than those on days 1-2 of another version (incubation effect). The two indexes showed a mutual negative correlation at 0.5 but not at 1.0 mA regardless of test retention days (resource-loss of activity). Ibotenate lesions of the bilateral amygdala on the post-conditioning day reduced freezing and restored the hypoactivity evident on days 7-8 (0-35 and 150-300 % of sham, respectively) to a greater extent than lesions of the hippocampus, unlike lesions of the medial prefrontal cortex. Unexpectedly, three disconnection versions to intrahemispheric interactions among these, one unilateral and another contralateral lesions out of three regions, reproduced freezing reduction consistent with bilateral amygdala lesions, whereas consistent restoration of hypoactivity appeared in the amygdala-hippocampal rather than the amygdala-or hippocampal-prefrontal version. Less
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