Withdrawal of collaterals of sympathetic axons to the rat eye during postnatal development: the role of function.

Neurones in the superior cervical ganglion (SCG) of the rat can be retrogradely labelled by injection of Fast blue (FB) into the anterior eye chamber with the maximum number being labelled during the second postnatal week. In adult rats, however, many fewer neurones can be so labelled. In the present study, we have investigated whether this reduction may be due to the withdrawal of collaterals of neurones which project to the posterior eye compartments. For these experiments, we have used either one (FB) or two (FB and horseradish peroxidase (HRP)) retrogradely transported markers injected with a micropipette into the anterior or posterior (vitreous) parts of the eye in rats aged 14, 31 and greater than 50 days. Using FB, we have shown that in 14-day-old rats, 40% of the neurones which project to the eye have collaterals in anterior and posterior compartments while only 1% of neurones maintain dual projections in animals aged more than 7 weeks. Furthermore, there is a reduction in the total number of neurones projecting to the eye between 14 and 31 days postbirth. The presence of significantly greater numbers of cells with collaterals to both eye compartments in the young versus the adult rats has been confirmed using both FB and HRP as retrograde markers. The importance of function on the rearrangement of these projections was investigated by either rearing animals in the dark from the time of birth, or by sectioning the preganglionic nerve trunk to the SCG, soon after birth.(ABSTRACT TRUNCATED AT 250 WORDS)