Zuclopenthixol facilitates memory retrieval in rats: possible involvement of noradrenergic and serotonergic mechanisms
Author: Khalifa AE
Source:
Pharmacology Biochemistry and Behavior, 75(4), 755-762.
Although disturbed memory function often coexists with psychosis, the cognitive
effects of antipsychotic medications with diverse pharmacodynamic properties are
rarely investigated. The neurocognitive profile of zuclopenthixol, a thioxanthene
dopaminergic antagonist and a conventional neuroleptic agent, has yet to be
investigated despite the effect of the drug on a variety of neurotransmitter
systems involved in mediation of learning and memory processes. In this study,
the effect of zuclopenthixol was tested on memory retrieval 24 h after training
using an inhibitory avoidance task in rats. Acute administration of
zuclopenthixol (0.7 and 1.4 mg/kg i.p.) before retrieval testing increased
step-through latency during the test session. The same doses of zuclopenthixol
did not affect the ambulatory activity of rats in the openfield test and
therefore the facilitatory effect of the drug on memory function could not be
confounded with any motoric properties. This study also investigated the effect
of zuclopenthixol on cortical and hippocampal monoaminergic neurotransmitters'
levels together with acetylcholinesterase enzyme (AChE) activity, both of which
are known to be important in control of cognitive function. Administration of
zuclopenthixol (0.7 and 1.4 mg/kg i.p.) neither affected dopamine (DA) level nor
AChE activity in rat cortex and hippocampus. On the other hand, the lower dose of
zuclopenthixol elevated cortical norepinephrine (NE) level, while the higher dose
elevated both cortical and hippocampal NE level together with hippocampal
serotonin (5-HT) level. These results may suggest the involvement of adrenergic
and serotonergic mechanisms in the facilitatory effect of zuclopenthixol on
retrieval memory. Zuclopenthixol may therefore be a better alternative than other
commonly used antipsychotic medications reported to impair cognitive function of
schizophrenic patients.