Studies on the role of brain cholinergic systems in the therapeutic mechanisms and adverse effects of ECT and lithium

Proactive and retroactive effects of repeated electroconvulsive shock on passive avoidance retention in rats

In spite of technical modifications, the therapeutic administration of electroconvulsive shock (ECS) to humans is still associated with significant memory impairment. Studies aimed at elucidating the neurobiologic basis of this impairment and developing appropriate treatment approaches have been limited by the absence of an appropriate animal model. We report here that ECS administered daily for 1-7 days to male albino rats (ECS X 1-ECS X 7) cumulatively impaired retention of passive avoidance when animals were trained 24 hours after the last ECS and tested 24 hours after training. Retention was directly proportional to the interval between training and testing; animals trained 24 hours after ECS X 7 and tested 1 hour later showed no deficit while animals tested after 24 hours showed maximal impairment. Retention was significantly improved by 10 days following the last of ECS X 7 and intact by 21 days. These findings parallel the effects of ECS on memory function in humans. The retrograde effects of ECS also paralleled those demonstrated in humans; while retention of a passive avoidance task learned 24 hours before ECS X 7 was grossly impaired, retention was intact if learning took place 7 days before the ECS course. The application of these findings as an animal model of ECS-induced memory impairment in humans, is discussed.

Prospective strategies for cholinergic interventions in Alzheimer's disease

The cholinergic hypothesis of memory dysfunction has guided most of the recent proposals for treating the primary symptoms of AD. The efficacy of these treatments has been severely limited. This review examines two major lines of evidence which suggest that the cholinergic hypothesis may have to be expanded and revised. The cholinergic hypothesis focuses on pre-synaptic defects. It assumes cholinoceptive neurons would function normally with adequate stimulation. Evidence is not sufficient to support this assumption. In addition, dissociations have been demonstrated between muscarinic receptor number and functional response of cholinoceptive neurons. Various measures are proposed to investigate the functional integrity of muscarinic receptors in AD patients. AD often has been characterized as a disorder produced by generalized cholinergic hypoactivity. Evidence for cortisol hypersecretion, abnormal dexamethasone suppression, and the occurrence of depressive symptoms, motoric dysfunction and sleep abnormalities in AD patients is more consistent with regional cholinergic hyperactivity than generalized hypoactivity. Resolution of these discrepancies could shed new light on the pathophysiology and treatment strategies for AD. Cholinoceptive neurons could be hypersensitive, subsensitive or have unaltered responsivity. These options would have very different treatment implications. New developments in outcome assessment which are capable of discriminating varieties of differential response to treatment can spur treatment development and improve quality of care for patients with complex disorders such as AD.