Acute intravenous administration of dietary constituent theanine suppresses noxious neuronal transmission of trigeminal spinal nucleus caudalis in rats.
Theanine is a non-dietary amino acid linked to the modulation of synaptic transmission in the central nervous system, although the acute effects of theanine in vivo, particularly on nociceptive transmission in the trigeminal system, remain to be determined. The present study investigated whether acute intravenous theanine administration to rats attenuates the excitability of wide dynamic range (WDR) spinal trigeminal nucleus caudalis (SpVc) neurons in response to nociceptive and non-nociceptive mechanical stimulation in vivo. Extracellular single unit recordings were made from 15 SpVc neurons in response to orofacial mechanical stimulation of pentobarbital-anesthetized rats, and responses to non-noxious and noxious mechanical stimuli were analyzed. The mean firing frequency of SpVc WDR neurons in response to all mechanical stimuli was dose-dependently inhibited by theanine (10, 50, and 100mM, i.v.) with the maximum inhibition of discharge frequency reached within 5min. These inhibitory effects were reversed after approximately 10min. The relative magnitude of theanine's inhibition of SpVc WDR neuronal discharge frequency was significantly greater for noxious than non-noxious stimulation. Iontophoretic application of l-glutamate induced the mean firing frequency of SpVc WDR neuron responding to noxious mechanical stimulation was also inhibited by intravenous administration of 100mM theanine. These results suggest that acute intravenous theanine administration suppresses glutaminergic noxious synaptic transmission in the SpVc, implicating theanine as a potential complementary and alternative therapeutic agent for the treatment of trigeminal nociceptive pain.
Laboratory of Food and Physiological Sciences, Department of Life and Food Sciences, School of Life and Environmental Sciences, Azabu University, 1-17-71, Fuchinobe, Chuo-ku, Sagamihara, Kanagawa, 252-5201, Japan.
Shiori
S
Takehana
FANCL Health Science Research Center, Research Institute, FANCL Corporation, 12-13, Kamishinano, Totsuka-ku, Yokohama, Kanagawa, 244-0806, Japan.
Yoshiko
Y
Kubota
FANCL Health Science Research Center, Research Institute, FANCL Corporation, 12-13, Kamishinano, Totsuka-ku, Yokohama, Kanagawa, 244-0806, Japan.
Nobuo
N
Uotsu
FANCL Health Science Research Center, Research Institute, FANCL Corporation, 12-13, Kamishinano, Totsuka-ku, Yokohama, Kanagawa, 244-0806, Japan.
Kei
K
Yui
Laboratory of Food and Physiological Sciences, Department of Life and Food Sciences, School of Life and Environmental Sciences, Azabu University, 1-17-71, Fuchinobe, Chuo-ku, Sagamihara, Kanagawa, 252-5201, Japan.
Yoshihito
Y
Shimazu
Laboratory of Food and Physiological Sciences, Department of Life and Food Sciences, School of Life and Environmental Sciences, Azabu University, 1-17-71, Fuchinobe, Chuo-ku, Sagamihara, Kanagawa, 252-5201, Japan. Electronic address: m-takeda@azabu-u.ac.jp.
Mamoru
M
Takeda
D000200:Action Potentials / Q000187:drug effects; D061605:Administration, Intravenous; D000818:Animals; D004594:Electrophysiology; D005971:Glutamates / Q000494:pharmacology* / Q000627:therapeutic use; D018698:Glutamic Acid / Q000494:pharmacology; D008297:Male; D009474:Neurons / Q000187:drug effects; D059226:Nociceptive Pain; D009619:Nociceptors / Q000187:drug effects; D010812:Physical Stimulation; D051381:Rats; D017208:Rats, Wistar; D009435:Synaptic Transmission; D014279:Trigeminal Nucleus, Spinal / Q000166:cytology* / Q000187:drug effects*
D005971:Glutamates; D018698:Glutamic Acid; C026166:theanine
Alternative medecinne; Nociception; Single unit recording; Spinal trigeminal nucleus caudalis; Theanine