title: Developmental expression of alpha 7 neuronal nicotinic receptor messenger RNA in rat sensory cortex and thalamus.
abstract: The distribution of alpha 7 messenger RNA expression was characterized in developing rat cortex and thalamus. Northern blot analysis of neonatal and adult cortex revealed a single messenger RNA transcript of 5.7 kb. Using in situ hybridization with both full length and short 35S-labeled alpha 7 riboprobes, a distinct transient expression of messenger RNA within sensory cortex and thalamus, during early postnatal development, was observed. alpha 7 transcripts were expressed in low levels as early as embryonic day 13 in the ventricular zone of the neocortex, and as early as embryonic day 15 in the thalamic neuroepithelium. A marked increase in messenger RNA levels was observed during the late prenatal period in both sensory and non-sensory regions of the cortex and thalamus. Moderate to high levels of messenger RNA were maintained into the first postnatal week, followed by a decline into adulthood. alpha 7 messenger RNA expression was significantly higher in the anterodorsal, lateral dorsal, ventral posterior medial and ventral posterior lateral thalamic nuclei of postnatal day 7 pups than in adult brains. Expression of messenger RNA within dorsal lateral geniculate, ventral lateral geniculate and medial geniculate did not show a significant reduction with age. Within the developing cortex, messenger RNA expression delineated the primary somatosensory, auditory and visual cortices in a unique laminar pattern that was consistently and significantly higher than in the adult in superficial layer VI. Higher levels of expression were also observed in retrosplenial cortex at postnatal day 7 than in the adult. Tangential sections through postnatal day 7 cortex revealed low levels of alpha 7 messenger RNA expression delineating the primary sensory areas in layer IV, corresponding to acetylcholinesterase-labeled thalamocortical afferents. However, these sensory areas exhibited higher levels of alpha 7 messenger RNA expression and were more clearly defined in layer VI, but not by acetylcholinesterase staining. The distribution of alpha 7 messenger RNA within the developing thalamocortical system parallels the distribution of alpha-bungarotoxin binding sites and suggests that the receptor is localized on both thalamic cells and their cortical target neurons. This transient and distinct pattern of distribution of the alpha 7 neuronal nicotinic receptor, which coincides with the major phase of thalamocortical development, suggests that it may play a functional role in the development of cortical circuitry.
mesh_terms: D000110:Acetylcholinesterase / Q000378:metabolism; D000818:Animals; D001345:Autoradiography; D015152:Blotting, Northern; D002038:Bungarotoxins / Q000378:metabolism; D002540:Cerebral Cortex / Q000254:growth & development* / Q000378:metabolism*; D015342:DNA Probes; D005260:Female; D017403:In Situ Hybridization; D008297:Male; D011247:Pregnancy; D012333:RNA, Messenger / Q000096:biosynthesis*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011978:Receptors, Nicotinic / Q000096:biosynthesis*; D013787:Thalamic Nuclei / Q000254:growth & development / Q000378:metabolism; D013788:Thalamus / Q000254:growth & development* / Q000378:metabolism*
chemical_list: D002038:Bungarotoxins; D015342:DNA Probes; D012333:RNA, Messenger; D011978:Receptors, Nicotinic; D000110:Acetylcholinesterase