LAMINAR EXPRESSION OF M1-MUSCARINIC, M3-MUSCARINIC AND M4-MUSCARINIC CHOLINERGIC RECEPTOR GENES IN THE DEVELOPING RAT VISUAL-CORTEX USING IN-SITU HYBRIDIZATION HISTOCHEMISTRY - EFFECT OF MONOCULAR VISUAL DEPRIVATION

The postnatal development of laminar pattern of m1-, m3- and m4-mRNA-m uscarinic acetylcholine receptor subtypes 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 histochemi stry and computer-assisted image analysis. From birth until day 15 the level of m1-receptor transcript in layer II/III increases markedly as compared to deeper layers. From day 15 up to day 18 a transient bimod al pattern develops with peaks in layers II/III and VI. Already on day 35 a more homogeneous distribution of m1-receptor mRNA level is detec table persisting until adulthood. In contrast, the M3-receptor mRNA sh ows already at birth a bimodal distribution with peaks in layers II/II I and VI. Further development until adulthood results in transient cha nges in the ratio of the mRNA levels in these layers. In the adult vis ual cortex a similar laminar pattern as at birth is observed. From day 1 up to day 10 a relative increase in the mRNA level of the m4-recept or in layers II to IV is observed. From day 10 until day 15 a bimodal distribution of receptor mRNA develops with peaks in layers III and VI which is similar to the adult stage. However, between days 18 and 35 a shift in the laminar receptor mRNA distribution occurs resulting in peaks in layers IV and VI. The labeling of the m5-receptor transcript in rat visual cortex was very weak and did not show any alteration wit h age. Unilateral eyelid closure from postnatal day 11 resulted in tra nsient changes in the laminar distribution of m3- and m4-receptor mRNA between postnatal days 18 and 25, whereas the development of the lami nar pattern of the m1-receptor mRNA was not affected regardless of the length of visual deprivation. The distinct laminar developmental patt ern of mRNA muscarinic receptor subtypes in rat visual cortex suggests specific roles of the muscarinic receptor subtypes during the first w eeks of postnatal maturation of visual function.