Induction and maintenance of ganglionic long‐term potentiation require activation of 5‐hydroxytryptamine (5‐HT3) receptors.

Abstract

1. An extracellular recording technique was used to study the effects of 5-hydroxytryptamine (5-HT, serotonin) on the tetanus-induced long-term potentiation (LTP) of the nicotinic pathway of transmission in the superior cervical ganglion (SCG) of the rat. The postganglionic compound action potential (CAP), made submaximal by treatment with hexamethonium (0A4 mM), was used as an index of transmission in the ganglion. 2. Serotonin (10 ,M) markedly enhanced the magnitude of LTP without affecting the posttetanic potentiation (PTP). The serotonin (2-30 AM) concentration-response curve for LTP was bell shaped as no enhancement was seen with 30 /M serotonin. This may largely be due to activation of a 5-HT1 receptor subtype and not to desensitization. 7. In monoamine-depleted ganglia, tetanus preceded by superfusion with m-CPBG readily induced LTP. MDL 72222 completely blocked this LTP. However, in these ganglia tetanus failed to induce LTP when m-CPBG was given 2 min (during PTP) or 1 h after tetanus.8. Tetanic stimulation of monoamine-depleted ganglia in the presence of R4+)-DOI failed to induce LTP. 9. We conclude that tetanus-induced LTP of the SCG of the rat requires activation of 5-HT3 receptors both for induction and maintenance.Long-term potentiation (LTP) of synaptic transmission is a NMDA-dependent LTP has been so thoroughly investigated phenomenon involving use-dependent synaptic plasticity that it has somewhat eclipsed the fact that LTP at synapses found at many excitatory synapses in the central and in the peripheral nervous system and certain regions in the peripheral nervous systems. It was first described in the central nervous system is independent of NMDA activation hippocampus (Bliss & L0mo, 1973), but later shown to occur (Johnston, Williams, Jaffe & Gray, 1992

Retrograde Carbon Monoxide Is Required for Induction of Long-Term Potentiation in Rat Superior Cervical Ganglion

“…Thus, it is possible that the production of CO in ganglia is induced by activation of the Ca 2ϩ ionophore 5-HT 3 receptors. Consistent with this possibility is the finding that, in the presence of 5-HT 3 receptor antagonists that completely and irreversibly inhibit LTP (Alkadhi et al, 1996), exogenously applied CO followed by tetanic stimulation evokes a robust LTP. This indicates that CO works downstream from 5-HT 3 receptors in sympathetic ganglia.…”

“…This has been demonstrated in vivo (Alonso-deFlorida et al, 1991;, as well as in vitro (Brown and McAfee, 1982;Briggs et al, 1985Minota et al, 1991;Alkadhi et al, 1996;Alkadhi and Altememi, 1997;Altememi and Alkadhi, 1999). This LTP is independent of the activation of either cholinergic or adrenergic receptors and may be attributable to an increase in acetylcholine release as measured by biochemical assay (Briggs et al, 1985).…”

“…Recently, we have shown that activation of serotonin 5-HT 3 receptors is necessary for both induction and maintenance of tetanus-induced ganglionic LTP (Alkadhi et al, 1996). Activation of 5-HT 3 receptor, which is primarily a calcium ionophore (Loomis et al, 1994), appears to be a primary extracellular trigger for the induction of ganglionic LTP, much like the requirement for activation of NMDA receptors in hippocampal LTP.…”

Expression of gLTP in Sympathetic Ganglia from Stress-hypertensive Rats: Molecular Evidence

“…Ganglionic long-term potentiation (gLTP) is a protracted enhancement of the nicotinic pathway that has been demonstrated both in vivo (Alonso-deFlorida et al 1991; and in vitro (Brown and McAfee 1982;Briggs et al 1985;Minota et al 1991;Alkadhi et al 1996;2001a, b, 2005aAlkadhi and Altememi 1997;Gerges et al 2002). Expression of gLTP is independent of activation of cholinergic, adrenergic (Briggs et al 1985), or adenosine (Hogan et al 1998) receptors and does not involve changes in the acetylcholine (ACh) content of the ganglion (Briggs et al 1985) or in the sensitivity of nicotinic ACh receptors ).…”

Alterations in Sympathetic Ganglionic Transmission in Response to Angiotensin II in (mRen2)27 Transgenic Rats

“…A few seconds of repetitive presynaptic stimulation producing profound changes in the efficacy of chemical synaptic transmission that can last for seconds or minutes is designated PTP, whereas increased synaptic strength persisting for hours or days is termed LTP. Activitydependent LTP is dependent on activation of serotonin 5-HT 3 receptors in rat superior cervical ganglia (SCG) 1 and is independent of activation of either cholinergic or adrenergic receptors 2,3 in rats. In addition to activity-dependent mechanisms, enduring changes in the synaptic strength also occur through activity-independent mechanisms.…”