Developmental Expression of Alpha 7 Neuronal Nicotinic Receptor Messenger RNA in Rat Sensory Cortex and Thalamus

Neuroscience. 1995 Jul;67(1):83-94. doi: 10.1016/0306-4522(94)00623-d.

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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acetylcholinesterase / metabolism
  • Animals
  • Autoradiography
  • Blotting, Northern
  • Bungarotoxins / metabolism
  • Cerebral Cortex / growth & development*
  • Cerebral Cortex / metabolism*
  • DNA Probes
  • Female
  • In Situ Hybridization
  • Male
  • Pregnancy
  • RNA, Messenger / biosynthesis*
  • Rats
  • Rats, Sprague-Dawley
  • Receptors, Nicotinic / biosynthesis*
  • Thalamic Nuclei / growth & development
  • Thalamic Nuclei / metabolism
  • Thalamus / growth & development*
  • Thalamus / metabolism*

Substances

  • Bungarotoxins
  • DNA Probes
  • RNA, Messenger
  • Receptors, Nicotinic
  • Acetylcholinesterase