Characterization of a [³H]glutamate binding site in rat pineal gland: Enhanced affinity following superior cervical ganglionectomy

Abstract: Glutamate, an excitatory neurotransmitter/neuromodulator involved in cell‐to‐cell communication within the central nervous system, is now believed to play a role in neuroendocrine function. In this study we describe a single, saturable, stereospecific, and temperature‐, time‐, and pH‐dependent binding site for glutamate in the pineal gland of the rat (K_d= 612 ± 23 nM, B_max= 3.17 ± 0.33 pmol/mg protein). After removal of the sympathetic innervation to the pineal gland, [³H]glutamate binding displayed a higher apparent affinity (K_d= 412 ± 28 nM) (P < 0.05) without a change in binding site number (B_max= 3.60 ± 0.24 pmol/mg protein). No difference in [³H]glutamate binding site number was observed in pineal glands obtained from animals sacrificed during the middle of the light and dark periods. These data suggest a possible modulatory role for a glutamate binding site in pineal gland function.