Development of the mammalian pineal gland

The literature concerning the morphological, biochemical, and pharmacological development of the mammalian pineal gland is reviewed with an emphasis on the ontogeny of pineal innervation by noradrenergic neurons. Mature pineal responses to various pharmacological manipulations and the well-characterized rhythms in pineal biochemistry appear only after postnatal axogenesis of sympathetic neurons, synaptogenesis between sympathetic nerve terminals and pineal adrenergic receptors, and pineal nerve terminal synthesis, storage, and inactivation of catecholamine neurotransmitter. Since postsynaptic biochemical capacities for pineal enzymatic and endocrine function appear at a relatively early age, it is proposed that development of presynaptic inputs to the pineal is rate-limiting in the maturation of the pineal gland as a circadian neuroendocrine transducer. Because of this, the pineal gland is an excellent model for the functional development of noradrenergic inputs to selective target organs.