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Postnatal alterations of GABA receptor profiles in the rat superior colliculus

2001; Elsevier BV; Volume: 104; Issue: 2 Linguagem: Inglês

10.1016/s0306-4522(01)00087-2

1873-7544

S.E. Clark, Maurice Garret, Bettina Platt,

Nicotinic Acetylcholine Receptors Study

Midbrain sections taken from Sprague–Dawley rats of varying ages within the first four postnatal weeks were used to determine, immunocytochemically, putative changes of GABAA receptor β2/3 subunits, GABAB receptor (R1a and R1b splice variants), and GABAC receptor ρ1 subunit expression and distribution in the superficial, visual layers of the superior colliculus. Immunoreactivity for the GABAA receptor β2/3 subunits was found in the superficial grey layer from birth. The labelling changed with age, with an overall continuous reduction in the number of cells labelled and a significant increase in the labelling intensity distribution (neuropil vs soma). Further analysis revealed an initial increase in the labelling intensity between postnatal days 0 and 7 in parallel with an overall reduction of labelled neurones. This was followed by a significant decrease in labelling intensity distribution between postnatal days 7 and 16, and a subsequent increase in intensity between postnatal days 16 and 28. The labelling profiles for GABAB receptors (R1a and R1b splice variants) and GABAC receptors (ρ1 subunit) showed similar patterns. Both receptors could be found in the superficial layers of the superior colliculus from birth, and the intensity and distribution of labelling remained constant during the first postnatal month. However, the cell body count showed a significant decrease between postnatal days 7 and 16. These changes may be related to the time-point of eye opening, which occurred approximately two weeks after birth. For all three receptor types, the cell body count remained constant after postnatal day 16. By four weeks of age, there was no significant difference between the cell numbers obtained for the different receptors. Both GABA itself and neurofilament labelling were also obtained in the superficial superior colliculus at birth. Neurofilament, although found at birth, showed very little ordered arrangement until 16 days after birth. When slices were double labelled for GABAC receptors and neurofilament, some overlap was observed. Double labelling for the presynaptic protein synaptophysin and GABAC receptors showed proximity in some places, indicative of a partly synaptic location of GABAC receptors. When GABAC and GABAA receptors were labelled simultaneously, some but not all neurones showed immunoreactivity for both receptor types. In conclusion, all three GABA receptor types were found to be present in the superior colliculus from birth, and all show some form of postnatal modification, with GABAA receptors demonstrating the most dramatic changes. However, GABAB and GABAC receptors are modified significantly around the onset of input-specific activity. Together, this points towards a contribution of the GABAergic system to processes of postnatal maturation in the superficial superior colliculus.