Control of postganglionic neurone phenotype by the rat pineal gland.

As neurones develop they are faced with choices as to which genes to express, to match their final phenotype to their role in the nervous system. A number of processes can guide these decisions. Within the autonomic and sensory nervous systems, there are a handful of examples that suggest that one mechanism that may match phenotype to function is the presence of target-derived differentiation factors. We tested whether the rat pineal gland controls the expression of a neuropeptide (neuropeptide Y) and a calcium-binding protein (calbindin) in sympathetic postganglionic neurones that innervate it. We first showed that the chemical phenotype of sympathetic neurones innervating the rat pineal includes the expression of both neuropeptide Y and the calcium-binding protein, calbindin. After transplanting the pineal gland of neonatal rats into the submandibular salivary gland of neonatal hosts, it was innervated by sympathetic axons from the surrounding salivary gland tissue, which do not normally express neuropeptide Y and calbindin. The presence of the pineal gland led to the appearance of neuropeptide Y and calbindin in many of the postganglionic neurones that innervated the graft. From these findings we suggest that, like the rodent sweat gland, the pineal gland generates a signal that can direct the neurochemical phenotype of innervating sympathetic neurones.