[ effect of reversible inactivation of locus coeruleus on long-term potentiation in the dentate gyrus of rat hippocampus]

Introduction: The nucleus locus coeruleus [LC] is located next to the fourth ventricle of the brain. Behavioral and electrophysiological studies have revealed the importance of LC noradrenergic projections in processes such as attention, learning and memory. Long-term potentiation [LTP] in hippocampal neurons is believed to be neural basis of learning and memory. The effects of LC on hippocampal electrophysiology have been investigated since many years ago, but have had different and conflicted results

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Objective: In this study the effect of reversible inactivation of LC on induction and maintenance of LTP in hippocampal dentate gyrus [DG] of male anesthetized rats was investigated

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Materials and Methods: This is an expelimental study. Inactivation of LC was conducted through bilateral injection of 0.5microl lidocaine [4%]. For producing LTP, two high frequency stimulations [HFS], 5 minutes apart were given to perforant pathway [PP] neurons. The amplitude of population spikes [PS] and the slope of population excitatory post synaptic potentials [PEPSP] were recorded before and 5, 10, 20, 40, 60 and 120 minutes after tetanic stimulations in DG

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Results: The findings of this study showed that inactivation of LC had no effect on DG granule cells baseline activity. Also, LC inactivation 5 minutes before HFS had no effect on LTP induction. However, PS amplitude was decreased significantly [P<0.05, P<0.01 respectively] in comparison with control group, 60 and 120 minutes after tetanization. Lidocaine injection after HFS had no effect on induced LTP

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Conclusion: According to results, we can conclude that, LC inactivation has no effect on LTP production in DG area, but probably LC neurons regulate part of events that occurs during tetanic stimulations in granular cells and are necessary for maintenance of LTP in PS amplitude