Autonomic and behavioral responses of selectively bred hypercholinergic rats to oxotremorine and diisopropyl fluorophosphate

Antagonism of anticholinesterase (DFP) toxicity by donepezil plus scopolamine: a preliminary study

Studies in animals exploring the antagonism of the cholinesterase inhibitors soman and sarin have shown that pretreatment with low doses of the centrally acting cholinesterase inhibitor, physostigmine, alone or in conjunction with the centrally acting anticholinergic agent, scopolamine, is effective against their lethality and toxicity. The current study evaluated the effects of pretreatment with the oral anticholinesterase agent, donepezil (Aricept, 2.0 mg/kg), used to treat Alzheimer's disease, with and without scopolamine in decreasing the hypothermic, hypokinetic, and diarrhea-inducing effects of the irreversible long-acting cholinesterase inhibitor diisopropyl fluorophosphate (DFP, 1.0 mg/kg) in adult Flinders sensitive line (FSL) male rats. Donepezil alone and donepezil plus scopolamine (0.1 mg/kg) to a greater extent antagonized the decrease in temperature, hypoactivity, and induction of diarrhea due to DFP observed at 4 h after its administration. However, donepezil alone induced hypothermia at 1 and 2 h after treatment. Therefore, these preliminary findings are encouraging, but many additional studies are needed to establish the effectiveness of donepezil as a prophylactic agent against irreversible cholinesterase inhibition by DFP.

Contribution of cholinergic and gabaergic functions to memory processes in BALB/cANnCrlBR mice

Several lines of evidence indicate that glucose influences on memory depend on interactions between glucose, glucoregulation and hippocampal cholinergic function. We previously demonstrated that glucose and scopolamine differentially affected memory consolidation for an operant bar pressing task in two closely-related BALB/c mouse strains. Whereas glucose normally improves memory in several animal strains, memory consolidation was not effected by systemic glucose injections in BALB/cANnCrlBR mice. Moreover, these mice were relatively insensitive to the normally observed amnestic effects of scopolamine. We therefore sought to determine whether cholinergic mechanisms in the dorsal hippocampus were involved in such atypical drug effects on memory processing in that strain of mice. In Experiment 1, we examined whether post-training oxotremorine would also atypically influence memory consolidation for an appetitively reinforced operant bar pressing task following microinjection in the dorsal hippocampus. In Experiment 2, we examined the effects of intrahippocampal GABAA drugs on memory consolidation. The non-selective muscarinic agonist, oxotremorine, dose-dependently impaired memory and the GABAA antagonist, bicuculline, improved retention in BALB/cANnCrlBR mice. It was concluded that GABA-mediated influences on hippocampal pyramidal output in BALB/cANnCrlBR mice and other strains are similar; but the amnestic effects of oxotremorine from the dorsal hippocampus were opposite to facilitating effects normally observed in other animal strains. Results are discussed relative to possible altered septo-hippocampal cholinergic neurotransmission in BALB/cANnCrlBR mice.

The absence of effect of glucose on memory is associated with low susceptibility to the amnestic effects of scopolamine in a strain of mice

In this series of experiments, we examined the ability of post-training glucose injections to improve memory of the Balb/cAnNCrlBR strain of mice for a bar-pressing task. We could not replicate this effect which has been demonstrated in many other strains of mice including Balb/cbyJ, a related strain. We found that the Balb/cAnNCrlBR strain of mice is also much less sensitive to the disrupting effects produced by pre- or post-training injections of the competitive cholinergic antagonist scopolamine. This strain also shows altered glucoregulation compared to the Balb/cbyJ strain. The absence of glucose effects on memory in Balb/cAnNCrlBR mice appears to be associated with decreased sensitivity to cholinergic antagonists. These results can be contrasted with previous ones obtained in a related strain, the Balb/cbyJ, in which glucose was shown to improve memory while scopolamine could easily disrupt memory processes. Taken together, these data provide additional indirect support for the hypothesis that glucose improvement of memory is closely linked to a functional interaction with central cholinergic systems. The comparison of these two strains could be the basis for a useful animal model to investigate the relationship between age-related changes in memory and central cholinergic function.

Potential animal model of multiple chemical sensitivity with cholinergic supersensitivity

Multiple Chemical Sensitivity (MCS) is a clinical phenomenon in which individuals, after acute or intermittent exposure to one or more chemicals, commonly organophosphate pesticides (OPs), become overly sensitive to a wide variety of chemically-unrelated compounds, which can include ethanol, caffeine and other psychotropic drugs. The Flinders Sensitive Line (FSL) rats were selectively bred to be more sensitive to the OP diisopropylfluorophosphate (DFP) compared to their control counterparts, the Flinders Resistant Line (FRL) rats. The present paper will summarize evidence which indicates that the FSL rats exhibit certain similarities to individuals with MCS. In addition to their greater sensitivity to DFP, the FSL rats are more sensitive to nicotine and the muscarinic agonists arecoline and oxotremorine, suggesting that the number of cholinergic receptors may be increased, a conclusion now supported by biochemical evidence. The FSL rats have also been found to exhibit enhanced responses to a variety of other drugs, including the serotonin agonists m-chlorophenylpiperazine and 8-OH-DPAT, the dopamine antagonist raclopride, the benzodiazepine diazepam, and ethanol. MCS patients report enhanced responses to many of these drugs, indicating some parallels between FSL rats and MCS patients. The FSL rats also exhibit reduced activity and appetite and increased REM sleep relative to their FRL controls. Because these behavioral features and the enhanced cholinergic responses are also observed in human depressives, the FSL rats have been proposed as a genetic animal model of depression. It has also been reported that MCS patients have a greater incidence of depression, both before and after onset of their chemical sensitivities, so cholinergic supersensitivity may be a state predisposing individuals to depressive disorders and/or MCS. Further exploration of the commonalities and differences between MCS patients, human depressives, and FSL rats will help to elucidate the mechanisms underlying MCS and could lead to diagnostic approaches and treatments beneficial to MCS patients.