Effects of 5‐HT receptor agonists on depolarization‐induced [³H]‐noradrenaline release in rabbit hippocampus and human neocortex

Abstract

1 The present study attempted to determine whether noradrenaline (NA) NA release were investigated. 3 In rabbit hippocampus, 5-HT, 5-carboxamidotryptamine (5-CT; 32 pM) and 2-CH3-5-HT (32 pM) increased [3H]-NA release elicited with 360 pulses/3 Hz. Facilitation of transmitter release was not influenced by the 5-HT3 receptor antagonist, tropisetron but was prevented by the a2-adrenoceptor antagonist, rauwolscine. When autoinhibition was avoided by stimulating the tissue with 4 pulses/100 Hz (pseudo-one pulse-(POP) stimulation), 2-CH3-5-HT decreased evoked transmitter release, whereas 5-HT and 5-CT had no effect. Inhibition caused by 2-CH3-5-HT was not affected by tropisetron but counteracted by the x2-adrenoceptor ligands, clonidine and rauwolscine. Inhibition caused by clonidine was diminished in the presence of 5-CT or 2-CH3-5-HT.4 In human neocortex, [3H]-NA release elicited with 360 pulses/3 Hz was increased by 10 pM 5-HT and 32 pM 5-CT, whereas 2-CH3-5-HT was ineffective.[31H]-NA release evoked with a modified POP stimulation (2 bursts of 4 pulses/100 Hz, 3.5 min apart) was not affected by 2-CH3-5-HT or 5-CT. 5 The present results indicate that 5-HT, 2-CH3-5-HT and 5-CT can act on presynaptic a2-autoreceptors as partial agonists (2-CH3-5-HT; in rabbit hippocampal tissue) or antagonists (5-HT and 5-CT; in tissue of rabbit hippocampus and human neocortex). Furthermore the existence of autoinhibition dictates whether these drugs cause facilitation of release, inhibition or have no effect.

Effect of 5‐hydroxytryptamine on neurogenic vasoconstriction in the isolated, autoperfused hindquarters of the rat

“…Different studies have reported the occurrence of an interaction between adrenergic and serotonergic mechanisms in the central nervous system, 19,20 and also at the periphery. [21][22][23] Previous studies performed in our laboratory have revealed the existence of different serotonergic mechanisms that increase or inhibit sympathetic vascular and cardiac neurotransmission.…”

Cholinergic enhancement of episodic memory in healthy young adults

“…In this context, a continual decline of cortical Ach concentration has been reported, which parallels the declining learning rate with aging (Feuerstein et al 1992). In contrast, no such age-related decline is known for norepinephrine (Allgaier et al 1995).…”

Impaired Autofeedback Regulation of Hypothalamic Norepinephrine Release in Experimental Uremia

“…19,20). For autoinhibition-free electrical stimulation, the stimulation must not exceed 60 to 80 ms, because after this time, autoinhibition via ␣ 2 -autoreceptors begins (19).…”

“…Four stimulation periods were applied (S 1 to S 4 ); they began 75, 110, 145, and 180 min after start of superfusion. For evoking NE release free of autoinhibition, each stimulation period consisted of three trains of six pulses per 100 Hz, with a train interval of 1 min (pseudo-one-pulse conditions; see references 19,20). For autoinhibition-free electrical stimulation, the stimulation must not exceed 60 to 80 ms, because after this time, autoinhibition via ␣ 2 -autoreceptors begins (19).…”