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Basic Sleep Research

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Figure 1. Representative, color-coded autoradiographic images of 3 adjacent, coronal sections of cat brain stem assayed to reveal M1, M2, and M3 mAChR subtypes in pons. Color scale provides quantitative index of total mAChR binding in fmol/mg tissue equivalent.

The forum for this month focuses on a discussion of the strengths and limitations of receptor autoradiography, immunocytochemistry, and in situ hybridization for elucidating structure-function relationships relative to sleep. The following are the specific questions that we would like to discuss:
  1. Which of these techniques might be used to determine whether a particular subtype is related to the mediation of muscle atonia?
  2. Are disfacilitation and active inhibition mediated by different receptors or receptor subtypes?
  3. What about other traits (PGO waves, EEG desynchrony, respiratory depression) comprising active sleep?

Abstract

Cholinergic mechanisms are known to play a key role in the regulation of breathing, but the distribution of muscarinic receptor (mAChR) subtypes has not been localized within brain stem respiratory nuclei. This study examined the hypothesis that mAChR subtypes are heterogeneously distributed across brain stem nuclei that control breathing. With the use of in vitro receptor autoradiography, the results provide the first selective labeling and quantitative mapping of M1, M2, and M3 mAChR subtypes in cat brain stem regions known to regulate breathing. Among brain stem nuclei known to contain respiratory-related neurons, the greatest amount of mAChR binding was measured in the lateral and medial parabrachial nuclei and the lateral nucleus of the solitary tract. Fewer mAChRs were localized in nuclei comprising the ventral respiratory group (nucleus ambiguus, retrofacial nucleus) and ventral medulla (retrotrapezoid nucleus and ventrolateral medulla). The data provide an essential first step for future studies aiming to specific the regulatory role of mAChR subtypes within brain stem respiratory nuclei.

From: Muscarinic receptor subtypes are differentially distributed across brain stem respiratory nuclei.
By: Vasiliki J. Mallios, Ralph Lydic, and Helen A Baghdoyan, Department of Anesthesia, College of Medicine, Pennsylvania State University, Hershey, Pennsylvania 17033
In:Am. J. Physiol. 268 (Lung Cell. Mol. Physiol. 12):L941-L949, 1995.
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