Abstract
Mammalian pinealocytes are neuroendocrine cells that synthesize and secrete melatonin, these processes being positively controlled by norepinephrine derived from innervating sympathetic neurons. Previously, we showed that pinealocytes contain a large number of microvesicles (MVs) that specifically accumulate L-glutamate through a vesicular glutamate transporter and contain proteins for exocytosis such as synaptobrevin 2 (VAMP2). These findings suggested that the MVs are counterparts of synaptic vesicles and are involved in paracrine-like chemical transduction in the pineal gland. Here, we show that pinealocytes actually secrete glutamate upon stimulation by KCl in the presence of Ca2+ at 37°C. The ability of glutamate secretion disappeared when the cells were incubated at below 20°C. Loss of the activity was also observed on successive stimulation, but it was recovered after 12 hr incubation. A low concentration of cadmium chloride or ω-conotoxin GVIA inhibited the secretion. Botulinum neurotoxin E cleaved synaptic vesicle-associated protein 25 (SNAP-25) and thus inhibited the secretion. The released L-glutamate stimulated pinealocytes themselves via glutamate receptor(s) and inhibited norepinephrine-stimulated melatonin secretion. These results strongly suggest that pinealocytes are glutaminergic paraneurons, and that the glutaminergic system regulates negatively the synthesis and secretion of melatonin. The MV-mediated paracrine-like chemical transduction seems to be a novel mechanism that regulates hormonal secretion by neuroendocrine cells.
Original language | English |
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Pages (from-to) | 175-191 |
Number of pages | 17 |
Journal | Journal of Pineal Research |
Volume | 21 |
Issue number | 3 |
DOIs | |
Publication status | Published - Oct 1996 |
Externally published | Yes |
Keywords
- Chemical transaction
- Glutamate receptors
- L-glutamate
- Melatonin
- Microvestcles
- Paracrine
- Paraneuron
- Pineal gland
ASJC Scopus subject areas
- Endocrinology