“School of Cognitive Sciences”
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| Paper IPM / Cognitive Sciences / 11300 |
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| Abstract: | |||||||||||||
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The present study evaluated the possible role of a-adrenergic receptors of the dorsal hippocampus on
scopolamine-induced amnesia and scopolamine state-dependent memory in adult male Wistar rats.
The animals were bilaterally implanted with chronic cannulae in the CA1 regions of the dorsal hippocampus,
trained in a step-through type inhibitory avoidance task, and tested 24 h after training to measure
step-through latency. Results indicate that post-training or pre-test intra-CA1 administration of scopolamine
(1 and 2 lg/rat) dose-dependently reduced the step-through latency, showing an amnestic
response. Amnesia produced by post-training scopolamine (2 lg/rat) was reversed by pre-test administration
of the scopolamine that is due to a state-dependent effect. Interestingly, pre-test intra-CA1 microinjection
of a1-adrenergic agonist, phenylephrine (1 and 2 lg/rat) or a2-adrenergic agonist, clonidine
improved post-training scopolamine (2 lg/rat)-induced retrieval impairment. Furthermore, pre-test
intra-CA1 microinjection of phenylephrine (0.25, 0.5 and 1 lg/rat) or clonidine (0.25, 0.5 and 1 lg/rat)
with an ineffective dose of scopolamine (0.25 lg/rat), synergistically improved memory performance
impaired by post-training scopolamine. On the other hand, pre-test injection of a1-receptors antagonist
prazosin (1 and 2 lg/rat) or a2-receptors antagonist yohimbine (1 and 2 lg/rat) prevented the restoration
of memory by pre-test scopolamine. It is important to note that pre-test intra-CA1 administration
of the same doses of prazosin or yohimbine, alone did not affect memory retrieval. These results suggest
that a1- and a2-adrenergic receptors of the dorsal hippocampal CA1 regions may play an important role
in scopolamine-induced amnesia and scopolamine state-dependent memory.
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