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 astrocy tes. 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 an y information as to whether there is a regional variation in the mAChR profile of astrocytes. This paper describes the mAChR profiles of cul tured astrocytes derived from the cerebral hemispheres, mesencephalon and medulla-pons, and is a continuation of our study on cultures of ne urons from these same tissues. Pharmacological studies showed that the astrocytes accumulated small amounts of mAChRs with distinct pharmaco logical profiles which, for a given area, differed from those of neuro ns in culture. Northern blot analyses showed transcripts for m1 and m3 mAChRs only. Their concentrations differed from one cell population t o another. Astrocyte cultures from the mesencephalon contained m1 mRNA amounts close to those in the tissue. Thus, at least part of the mACh R profile in vitro might be a true reflection of the cell's properties in vivo. Functional studies showed that mAChRs mediate the stimulatio n of phosphoinositide turnover in all three astrocyte cultures, that t he amplitude of this response varies greatly with the origin of the ce ll, and that two pharmacological subclasses, M1 and M(1-2-), are invol ved in these responses, but to different extents. Thus the CNS contain s discrete astrocyte populations which in culture differ in their mACh R profiles at the molecular, the pharmacological and the functional le vels.