title: Two types of neurotransmitter release patterns in isolectin B4-positive and negative trigeminal ganglion neurons.
abstract: Mammalian nociceptors have been classified into subclasses based on differential neurotrophin sensitivity and binding of the plant isolectin B4 (IB4). Most of the nerve growth factor-responsive IB4-negative (IB4 (-)) nociceptors contain neuropeptides such as substance P and calcitonin gene-related peptide, whereas the glial-derived neurotrophic factor-responsive IB4-positive (IB4 (+)) neurons predominantly lack such neuropeptides. We hypothesized that the differences in neuropeptide content between IB4 (+) and (-) neurons might be reflected in differences in stimulated exocytosis and/or endocytosis. To address this, we monitored the secretory activity of acutely dissociated neurons from adult rat trigeminal ganglia (TRG) using cell membrane capacitance (Cm) measurements and the fluorescent membrane-uptake marker N-(3-triethylammoniumpropyl)-4-(6-(4-(diethylamino)phenyl)hexatrienyl)pyridinium dibromide (FM4-64). Cm measurements were performed under whole-cell voltage clamp and neurons were depolarized from -75 mV to +10 mV to elicit exocytosis. Both types of TRG neurons showed similarly-sized, calcium-dependent increases in Cm, demonstrating that both IB4 (+) and (-) TRG neurons are capable of stimulated exocytosis. However, the peak Cm of IB4 (+) neurons decayed faster toward baseline than that of IB4 (-) neurons. Also, IB4 (+) neurons had stable Cm responses to repeated stimuli whereas IB4 (-) neurons loss their secretory response during repeated stimulation. These data suggested that the IB4 (+) neurons possess a faster rate of endocytosis and vesicle replenishment than IB4 (-) neurons. To test this, we measured vesicle trafficking with the fluorescent membrane dye FM4-64. FM4-64 staining showed that IB4 (-) neurons exhibit a larger pool of endocytosed vesicles than IB4 (+) neurons because the peak fluorescence increases in IB4 (-) neurons were larger but slower than in IB4 (+) neurons. However, the recycled vesicles were released faster in IB4 (+) compared with IB4 (-) neurons. Taken together these data suggest that the IB4 (+) TRG neurons have faster exocytosis and endocytosis than the IB4 (-) neurons.
authors.affiliation: Division of Oral Biology and Medicine, UCLA School of Dentistry, 63-078 CHS, Los Angeles, CA 90095-1668, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Matsuka
authors.forename: B
authors.initials: B
authors.lastname: Edmonds
authors.forename: S
authors.initials: S
authors.lastname: Mitrirattanakul
authors.forename: F E
authors.initials: FE
authors.lastname: Schweizer
authors.forename: I
authors.initials: I
authors.lastname: Spigelman
mesh_terms: D000818:Animals; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods; D037102:Lectins / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D009474:Neurons / Q000145:classification* / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D018377:Neurotransmitter Agents / Q000378:metabolism*; D018408:Patch-Clamp Techniques / Q000379:methods; D011189:Potassium Chloride / Q000494:pharmacology; D011726:Pyridinium Compounds / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D051381:Rats; D013997:Time Factors; D012668:Trigeminal Ganglion / Q000166:cytology*
chemical_list: C092350:FM 4-64; D037102:Lectins; D018377:Neurotransmitter Agents; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D011189:Potassium Chloride