The actions of serotonin on frog primary afferent terminals and cell bodies

Abstract

Abstract1. The actions of serotonin (5-HT) were studied in the isolated frog spinal cord and dorsal root ganglion preparations. 2.In the spinal cord, 5-HT increased the spontaneous activity recorded from dorsal roots, facilitated evoked spinal reflexes and produced fast and slow primary afferent depolarization (PAD). 3.A direct action of 5-HT on primary afferent terminals is likely since 5-HT induced PAD remained in the presence of 1 µM tetrodotoxin and 2 mM Mn 2+ . 4.The direct action of 5-HT on primary afferent terminals was blocked by methysergide and attenuated by concentrations of Mn 2+ in excess of that required to block transmitter release. 5.Cell bodies of the dorsal root ganglion were also depolarized by 5-HT. A slow hyperpolarization occasionally followed the initial depolarization. The depolarizing action of 5-HT in the dorsal root ganglion was also attenuated by treatment with Mn 2+ .6. It is concluded that 5-HT acts directly on frog primary afferents and that this influence may involve a calcium sensitive process. The dorsal root ganglion response to 5-HT appears to be a suitable model of the afferent terminal response.

Serotonin depolarizes type A and C primary afferents: an intracellular study in bullfrog dorsal root ganglion

“…Some of the actions of 5-HT reported here resemble 5-HT responses recorded extracellularly from the dorsal roots of isolated spinal cord preparations 15 . These dorsal root recordings of polarization changes in the central terminations of primary afferents demonstrated fast and slow 5-HT depolarizations due, in part, to serotonin's direct action on afferent nerve endings.…”

“…These actions of 5-HT on sensory nerve endings underlie serotonin's peripheral algesic action 5,19 . Studies employing isolated nerve and spinal cord preparations have also demonstrated that 5-HT depolarizes and excites the axons 26 and central (spinal) terminations of primary afferents 15,29,35 . This is of particular interest in view of the possibility that endogenously released 5-HT may affect primary afferent transmission in the spinal cord through a direct action on the central terminations of sensory neurons.…”

“…As an alternative to intracellular recording, Holz and Anderson 15 employed the sucrose gap technique to obtain extracellular recordings of 5-HT depolarizations of primary afferent cell bodies and central terminations in isolated frog DRG and spinal cord preparations. The similarity of 5-HT responses recorded from DRG and spinal cord preparations suggested that DRG cells may serve as a suitable model of the sensory nerve terminals when studying serotonin's mechanism of action on primary afferents.…”

Effects of sciatic nerve transection on ultrastructure, NADPH-diaphorase reaction and serotonin-, tyrosine hydroxylase-, c-Fos-, glucose transporter 1- and 3-like immunoreactivities in frog dorsal root ganglion

“…In this ganglion some neurons show reactivity to nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-diaphorase) (3, 4), which is considered to be equivalent to nitric oxide (NO) synthase, the enzyme responsible for NO synthesis (5). DRG cells also respond to application of serotonin (6, 7) and catecholamine (8). …”

Light-Activated Serotonin for Exploring Its Action in Biological Systems

“…Previous studies have shown that 5-HT elicits depolarizing responses in small-diameter trigeminal ganglion neurons in mammals and type A and C primary afferent neurons in the dorsal root ganglia (DRG) of mammals and frogs (Holz and Anderson, 1984; Holz, et al, 1985; Todorovic and Anderson, 1990; Tsutsui, et al, 2008). 5-HT is also known to increase a hyperpolarization-activated cation current in type Aα and Aβ DRG neurons (Cardenas, et al, 1999; Harper and Lawson, 1985a; Harper and Lawson, 1985b; Scroggs, et al, 1994; Villière and McLachlan, 1996).…”