Similar localization of immunoreactive glutamate and aspartate in the pineal organ and retina of various nonmammalian vertebrates.

The localization of immunoreactive glutamate and aspartate was compared in the pineal organ and retina of various vertebrates (Raja clavata, Carassius auratus, Salvelinus alpinus, Triturus vulgaris, Triturus cristatus, Lacerta muralis, Lacerta agilis, Lacerta viridis, Columbia livia and white leghorn chicken) by postembedding immunoelectron microscopy. Immunoreaction of both excitatory amino acids was detected in the pinealocytes in a localization similar to that of retinal photoreceptors. The reaction was intense in the axonal processes of pinealocytes as well as retinal rods and cones, further in their terminals on secondary pineal and retinal neurons. Subsequent immunoreaction on the same section showed a colocalization of glutamate and aspartate. The accumulation of these amino acids in the presynaptic part of pinealocytes suggests that they act as synaptic mediators in the neural efferentation of the pineal organ. In reptiles and birds where the hormonal efferentation of the pineal is well developed, glutamate and aspartate was also found to be accumulated in neuroendocrine terminals of pinealocytes. Therefore, glutamate and aspartate may have a role in both the hormonal and neural efferentation of the pineal organ.