Related Experiment Videos
Muramyl dipeptide, amphetamine, and physostigmine: effects on sleep of rabbits
S Shoham1, D Davenne, J M Krueger
1Department of Physiology and Biophysics, University of Tennessee, Memphis 38163.
Abstract:
Muramyl peptides (MPs) are constituents of bacterial cell walls and mammalian tissue. Some MPs have the capacity to enhance slow-wave sleep (SWS). In rabbits, it was unknown whether MPs enhanced SWS by prolonging SWS episodes or by increasing the number of SWS episodes. In rabbits, there is a frequent alternation between sleep and waking; thus, demonstration of induction of new SWS episodes is difficult unless pharmacologic manipulations are used. We injected amphetamine subcutaneously to reduce duration of sleep (from about 45% to 20%) for a period of two hours; it reduced the number of SWS episodes. Muramyl dipeptide (MDP: NAM-L-ala-D-isogln) injected into a lateral ventricle one hour before amphetamine significantly increased the number of SWS episodes. Physostigmine, a cholinergic agonist, was also used. By itself, physostigmine greatly reduced SWS and rapid eye movement sleep. Pretreatment of animals with MDP two hours before physostigmine injection failed to reverse subsequent physostigmine-induced wakefulness. We conclude that MDP has the ability to induce SWS episodes but does not act directly on the thalamocortical cholinergic mechanisms of EEG phenomena. Our results, together with earlier evidence on anatomical levels of action of amphetamine and physostigmine, suggest that the somnogenic mechanisms of MPs likely involve the midbrain.
Insights
Muramyl peptides (MPs) can increase slow-wave sleep (SWS) episodes in rabbits. This study shows muramyl dipeptide (MDP) induces SWS episodes, suggesting midbrain involvement in sleep regulation.
Area of Science:
- Neuroscience
- Sleep Science
- Pharmacology
Background:
- Muramyl peptides (MPs), found in bacterial cell walls and mammalian tissues, are known to influence slow-wave sleep (SWS).
- The precise mechanism by which MPs enhance SWS, specifically whether they prolong existing episodes or increase their frequency, remained unclear in rabbits.
Purpose of the Study:
- To investigate whether muramyl peptides (MPs) enhance slow-wave sleep (SWS) by increasing the number of SWS episodes in rabbits.
- To explore the potential involvement of midbrain mechanisms in the somnogenic effects of MPs.
Main Methods:
- Rabbits were administered amphetamine to reduce sleep duration and the number of SWS episodes.
- Muramyl dipeptide (MDP), a specific MP, was injected intracerebroventricularly before amphetamine administration.
- Physostigmine, a cholinergic agonist, was used to assess MDP's interaction with cholinergic pathways.
Main Results:
- Intracerebroventricular injection of muramyl dipeptide (MDP) significantly increased the number of SWS episodes, even when sleep was pharmacologically suppressed by amphetamine.
- MDP pretreatment did not reverse the wakefulness induced by physostigmine, indicating it does not directly act on thalamocortical cholinergic mechanisms.
- The findings suggest that MDP's somnogenic effects are mediated through pathways likely involving the midbrain.
Conclusions:
- Muramyl dipeptide (MDP) possesses the ability to induce the occurrence of slow-wave sleep (SWS) episodes.
- The somnogenic mechanisms of muramyl peptides (MPs) appear to involve the midbrain, rather than directly targeting thalamocortical cholinergic systems.