Postnatal development of serotonin-accumulating neurones in the rabbit retina and an immunohistochemical analysis of the uptake and release of serotonin.

The serotonin-accumulating neurones in the rabbit and bovine retina were studied with the use of immunohistochemistry to localize serotonin. It was established that a subpopulation of amacrine cells in both tissues has the ability to take up and store serotonin. The uptake process is very specific; known serotonergic uptake blockers, viz. chlorimipramine and Lilly 110140, abolish transport, while benztropine, a dopamine-uptake blocker, is ineffectual. The serotonin accumulated by the serotonergic neurones can be released by potassium depolarization in a calcium-dependent manner. All these results form a strong case for serotonin being a likely transmitter in the mammalian retina. The subpopulation of serotonin-accumulating neurones in the rabbit retina appears to be determined prenatally, as they can be observed immediately after birth. On the basis of the serotonin content in retinas from animals of different ages, it is suggested that the serotonin-accumulating cells mature around the 24th postnatal day. The same maturation period has been proposed for the rabbit retinal dopamine cells (Lam et al., 1981).