DEVELOPMENT OF LAMINAR EXPRESSION OF THE M(2) MUSCARINIC CHOLINERGIC RECEPTOR GENE IN RAT VISUAL-CORTEX AND THE EFFECT OF MONOCULAR VISUAL DEPRIVATION

The postnatal development of laminar pattern of the m2 muscarinic acet ylcholine receptor subtype mRNA in the visual cortex of both normally raised and monocularly deprived rats (one eyelid sutured at the age of 11 days) was studied using in situ hybridization histochemistry and c omputer-assisted image analysis. In normally raised rats, on birth, th e m2 transcript was found to be more concentrated in the superficial z ones of the cortex. This laminar pattern alters to a more homogeneous distribution of the label throughout the cortex already detectable on day 7. From day 10 onwards a bimodal laminar pattern gradually develop s with increased mRNA levels in layer IV and upper layer VI. From post natal day 21 onwards the hybridization peak in layer VI decreases as c ompared to the peak level in layer IV resulting in an adult distributi on with highest labeling in layer IV, low labeling in layer I to III a nd moderate labeling in layers V and VI. Monocular deprivation results in decreased m2 mRNA levels in visual cortical layers IV-VI in both d eprived and non-deprived cortices already detectable at the age of 18 days and persisting up to the age of 21 days; but this effect disappea rs following further deprivation until adulthood. The data suggest tha t the changes in m2 receptor level from a more homogeneous distributio n to a bimodal pattern during postnatal development seem to be related to synaptogenesis and final tuning of connectional pattern within the rat visual cortex.