Localization of α7 nicotinic receptor subunit mRNA and α‐bungarotoxin binding sites in developing mouse somatosensory thalamocortical system

Abstract

Previous studies in rat, showing a transient pattern of expression of the alpha 7 nicotinic acetylcholine receptor in the ventrobasal thalamus 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 ligand binding were employed to examine the spatiotemporal distribution of alpha 7 mRNA and alpha-bungarotoxin binding sites in the thalamocortical 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 week. Both alpha 7 mRNA and its receptor protein are observed in all cortical laminae, with the highest levels seen in the compact cortical plate, layer IV, and layer VI. When viewed in a tangential plane, alpha 7 mRNA and alpha-bungarotoxin binding sites delineate a whisker-related barrel pattern in layer IV by P3-5. Quantitative analysis reveals a dramatic decrease in the levels of expression of alpha 7 mRNA and alpha-bungarotoxin binding sites in the cortex by the end of the second postnatal week. Unlike in the rat, only low levels of alpha 7 mRNA or alpha-bungarotoxin binding sites are present in the ventrobasal complex of the mouse thalamus. The broad similarities between the thalamocortical development of rat and mouse taken together with the present results suggest that alpha 7 receptors located on cortical neurons, rather than on thalamic neurons, play a role in mediating aspects of thalamocortical development.

Acetylcholine influences growth cone motility and morphology of developing thalamic axons

“…59 Finally, there is also evidence that ACh receptors are expressed in the embryonic thalamus. 13,60,61 Taken together with the results presented here, we suggest that ACh released from cortical cells and/or cholinergic cortical projections participates to the formation of thalamocortical projections by regulating growth cone pauses at decision regions of thalamic axons.…”

Fast Synaptic Signaling by Nicotinic Acetylcholine and Serotonin 5-HT3Receptors in Developing Visual Cortex

“…Although nicotinic receptors and serotonin 5-HT 3 receptors are expressed in the neocortex (Parkinson et al, 1988;Tecott et al, 1993;Weavers et al, 1994;Bina et al, 1995;Lobron et al, 1995;Nakayama et al, 1995), and widespread cholinergic and serotonergic innervations are found in the majority of cortical areas, no indication of fast transmission mediated by these transmitters has been reported previously. However, using single-cell patch-clamp recordings of spontaneous and evoked activity, we were able to demonstrate that both nicotinic acetylcholine and ionotropic serotonin receptors contribute to fast excitatory synaptic transmission in all layers of the developing ferret visual cortex.…”

Nicotinic Acetylcholine Receptors in Sensory Cortex: Figure 1

“…These results imply an interesting species difference; however, it should be noted that the MLA dose used may block non-␣7 receptors, and the mecamylamine dose may preferentially block non-␣7 receptors (e.g., Raggenbass and Bertrand 2002). Also, the authors did not explicitly consider the rapid changes in nAChR expression that occur during the first three postnatal weeks in sensory cortex and thalamus (Fuchs 1989;Bina et al 1995;Broide et al 1995Broide et al , 1996. These changes are detailed below ("nAChRs and Sensory Cortex Development"), and it remains a possibility that different nAChR subtypes regulate thalamocortical transmission at different ages (e.g., Fig.…”