The primary afferent depolarizing action of kainate in the rat

Abstract

1 Dorsal roots (L3-L7) isolated from immature (1-9 day old) rats were depolarized selectively by kainate (I-1I00 M). L-Glutamate (25-1000 pM), but not L-aspartate, mimicked the action of kainate. N-methylaspartate had no activity on these preparations and quisqualate was thirty times less active than kainate.2 Depolarizations evoked by L-glutamate (100-1OO0pM) faded rapidly in the presence of Lglutamate. Depolarizations evoked by kainate were depressed during the fade induced by L-glutamate. 3 Certain electrically evoked C-fibre volleys in dorsal roots or leg nerves of rats at any age were selectively depressed or abolished in the presence of kainate. The effect of kainate was more selective than that of y-aminobutyric acid or capsaicin.

Novel kainate derivatives: potent depolarizing actions on spinal motoneurones and dorsal root fibres in newborn rats

“…Some excitatory amino acids, however, that are not related structurally to kainate, including 5-bromowillardiine (Agrawal & Evans, 1986) and some derivatives of 2-(carboxycyclopropyl)glycine (CCG) , also cause considerable depolarization of the dorsal root fibre, and 5-bromowillardiine is much more potent than kainate in causing depolarization of the dorsal root fibre. Therefore, they have been regarded as kainate-type agonists (Watkins et al, 1990a;Ishida et al, 1991 (Agrawal & Evans, 1986) and the dorsal root ganglion (Huettner, 1990) while it did not occur in the spinal motoneurone. Therefore, the difference in degree of development of receptor desensitization between both preparations may play a key role for a difference in the rank order of the depolarizing activity, but the existence of different types of kainate receptors is also strongly suggested.…”

“…On the other hand, CNQX was quite effective in reducing kainoid-induced depolarization (Figure 6), but there were some differences in the (Watkins et al, 1990a). The difference in depolarizing activities between dorsal root C fibres and motoneurones of the newborn rat would provide some useful information for elucidating the mechanism of activation of kainate receptors (Agrawal & Evans, 1986;Evans et al, 1987;Shinozaki, 1991). Dorsal root fibres of the newborn rat are depolarized selectively by kainate and its derivatives (Agrawal & Evans, 1986;Shinozaki, 1991).…”

“…The difference in depolarizing activities between dorsal root C fibres and motoneurones of the newborn rat would provide some useful information for elucidating the mechanism of activation of kainate receptors (Agrawal & Evans, 1986;Evans et al, 1987;Shinozaki, 1991). Dorsal root fibres of the newborn rat are depolarized selectively by kainate and its derivatives (Agrawal & Evans, 1986;Shinozaki, 1991). Some excitatory amino acids, however, that are not related structurally to kainate, including 5-bromowillardiine (Agrawal & Evans, 1986) and some derivatives of 2-(carboxycyclopropyl)glycine (CCG) , also cause considerable depolarization of the dorsal root fibre, and 5-bromowillardiine is much more potent than kainate in causing depolarization of the dorsal root fibre.…”

“…Dorsal root fibres of the newborn rat are depolarized selectively by kainate and its derivatives (Agrawal & Evans, 1986;Shinozaki, 1991). Some excitatory amino acids, however, that are not related structurally to kainate, including 5-bromowillardiine (Agrawal & Evans, 1986) and some derivatives of 2-(carboxycyclopropyl)glycine (CCG) , also cause considerable depolarization of the dorsal root fibre, and 5-bromowillardiine is much more potent than kainate in causing depolarization of the dorsal root fibre. Therefore, they have been regarded as kainate-type agonists (Watkins et al, 1990a;Ishida et al, 1991 (Agrawal & Evans, 1986) and the dorsal root ganglion (Huettner, 1990) while it did not occur in the spinal motoneurone.…”

“…At present, highly specific antagonists for kainate receptors are not yet available, therefore, it is difficult to classify electrophysiologically these derivatives as pure kainate agonists, but it has been reported that dorsal root C fibres of immature rats are directly depolarized by kainic acid, whereas quisqualate and (± )-2-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) are much less active than kainate, and Nmethyl-D-aspartate (NMDA) does not cause depolarization of the dorsal root even at higher concentrations (Davies et al, 1979;Agrawal & Evans, 1986;Huettner, 1990), although the pharmacological properties of the dorsal root C fibre depolarization have been reported to be not always identical to those of spinal motoneurones (Evans et al, 1987;Shinozaki, 1991). Therefore, we have compared the neuropharmacological properties of depolarizations induced by kainoids in spinal motoneurones and dorsal root fibres of the newborn rat.…”