MUSCARINIC RECEPTOR PROFILES OF MOUSE-BRAIN ASTROCYTES IN CULTURE VARY WITH THEIR TISSUE OF ORIGIN BUT DIFFER FROM THOSE OF NEURONS

The two main cell populations in brain tissues are neurons and astrocytes. Cultures of both bear muscarinic acetylcholine receptors (mAChRs). Available data indicate that astrocyte mAChRs are heterogeneous, but the particular subtypes on these cells are not known, nor is there any information as to whether there is a regional variation in the mAChR profile of astrocytes. This paper describes the mAChR profiles of cultured astrocytes derived from the cerebral hemispheres, mesencephalon and medulla-pons, and is a continuation of our study on cultures of neurons from these same tissues. Pharmacological studies showed that the astrocytes accumulated small amounts of mAChRs with distinct pharmacological profiles which, for a given area, differed from those of neurons in culture. Northern blot analyses showed transcripts for m1 and m3 mAChRs only. Their concentrations differed from one cell population to another. Astrocyte cultures from the mesencephalon contained m1 mRNA amounts close to those in the tissue. Thus, at least part of the mAChR profile in vitro might be a true reflection of the cell's properties in vivo. Functional studies showed that mAChRs mediate the stimulation of phosphoinositide turnover in all three astrocyte cultures, that the amplitude of this response varies greatly with the origin of the cell, and that two pharmacological subclasses, M1 and M(1-2-), are involved in these responses, but to different extents. Thus the CNS contains discrete astrocyte populations which in culture differ in their mAChR profiles at the molecular, the pharmacological and the functional levels.