LOCALIZATION OF ALPHA-7 NICOTINIC RECEPTOR SUBUNIT MESSENGER-RNA AND ALPHA-BUNGAROTOXIN BINDING-SITES IN DEVELOPING MOUSE SOMATOSENSORY THALAMOCORTICAL SYSTEM

Previous studies in rat, showing a transient pattern of expression of the alpha 7 nicotinic acetylcholine receptor in the ventrobasal thalam us and barrel cortex during the first 2 postnatal weeks, suggest that these receptors may play a role in development of the thalamocortical system. In the present study, in situ hybridization and radiolabeled l igand binding were employed to examine the spatiotemporal distribution of alpha 7 mRNA and alpha-bungarotoxin binding sites in the thalamoco rtical pathway of mouse during early postnatal development. As in the rat, high levels of alpha 7 mRNA and alpha-bungarotoxin binding sites are present in the barrel cortex of mouse during the first postnatal w eek. Both alpha 7 mRNA and its receptor protein are observed in all co rtical laminae, with the highest levels seen in the compact cortical p late, layer IV, and layer VI. When viewed in a tangential plane, alpha 7 mRNA and alpha-bungarotoxin binding sites delineate a whisker-relat ed barrel pattern in layer IV by P3-5. Quantitative analysis reveals a dramatic decrease in the levels of expression of alpha 7 mRNA and alp ha-bungarotoxin binding sites in the cortex by the end of the second p ostnatal week. Unlike in the rat, only low levels of alpha 7 mRNA or a lpha-bungarotoxin binding sites are present in the ventrobasal complex of the mouse thalamus. The broad similarities between the thalamocort ical development of rat and mouse taken together with the present resu lts suggest that alpha 7 receptors located on cortical neurons, rather than on thalamic neurons, play a role in mediating aspects of thalamo cortical development. (C) 1995 Wiley-Liss, Inc.