Exp. 1992,52: 48. Ontogenesis of muscarinic cholinergic receptor binding in the barrel cortex of mice. J. Skangiel-Kramska, S. Glaiewski, E. Siucinska and M.
Rapid communication
Acta Neurobiol. Exp. 1992,52: 48
Ontogenesis of muscarinic cholinergic receptor binding in the barrel cortex of mice J. Skangiel-Kramska, S. Glaiewski, E. Siucinska and M. Kossut Department of Neurophysiology, Nencki Institute of Experimental Biology, 3 Pasteur St., Warsaw, Poland
INTRODUCTION AND METHODS. Acetylcholine modulates neuronal excitability and is an important factor in the mechanisms of synaptic plasticity and neuronal development. The cholinergic transmission in the cortex occurs mainly via the muscarinic receptors (MChRs). The aim of this study was to examine the development of MChRs in the barrel field (1) of somatosensory cortex of mice during the first postnatal month, i.e. in the critical period for morphological plasticity of the barrels (2) and around the time when first manifestations of functional plasticity of the barrel cortex could be observed (3). Mice aged 3, 5, 8, 12, 21 and 28 days were used. Quantitative in vitro binding autoradiography using [3H]quinuclidynyl benzilate (QNB) as a ligand was performed on coronal sections of the brains as described previously (4). The results were quantified with computer controlled image analyzer. RESULTS AND DISCUSSION. The [3H]QNB binding increased four-fold during the first postnatal month. The binding values were low during the first postnatal week and then rose rapidly between day 8 and day 12. Later on, they declined slightly in cortical layers I-IV and VI, on day 21 and showed a 20% increase by day 28. [3H]QNB binding in layer V reached a plateau at day 12 (Fig.1). The labelling of the cortex was uniform at days 3 and 5. Heavier labelling in layer IV appeared at day 8. Starting from day 12 the typical pattern of binding was seen, with heavy labelling over layers 11-IV and VI, and lower binding intensity in layer V; this differences in labelling density between the cortical layers were more pronounced at later ages. The site of the heaviest labelling changed from layer IV at day 8 to layer 11-111 at later examined ages (Fig.2). Our study provides quantitative data of the time-course of MChRs binding sites in the barrel cortex of mice. The course of developmental changes of [3H]QNB binding is similar to that described previously in qualitative experiments using [3H]PrBCM as a ligand (5, 6), except for the first postnatal week where no significant increase of binding values were found in the present study. During the critical period for morphological plasticity (day 1 to 5) the [3H]QNB binding values are low; they rise rapidly in the second week of life, before the onset of functional plasticity. Our results point to differential pattern of maturation of MChRs in different cortical layers.
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Fig. 1. Development of binding of [3H]QNB in the barrel cortex of mice.
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Fig.2. Optical density scans across the cortical layers; the development of laminar pattern of [3H]QNB binding.
1. Woolsey T.A., Van der Loos H.(1970) Brain Res. 17: 205-242. 2. Weller W.L. Johnson J.I.(1975) Brain Res. 83: 504-508. 3. Kossut M.(1992) Prog. Neurobiol. (in press) 4. Glaiewski S., Kossut M., Siucinska E., Skangiel-Krarnska J. (1990) Acta Neurobiol. Exp. 50: 69-78. 5. Hohmann C.F., Pert C.C., Ebner F.F.(1985) Dev.Brain Res.23: 243-253. 6. Rotter A., Field P.M., Raisman G.(1979) Brain Res. Rev.1: 185-205.
Accepted 20 February 1992
