AIMTo determine whether serotonin, a major neurotransmitter in brain, can modulate the production of secretory beta-amyloid protein precursor (sAPP) by activation of serotonin 5-HT2C receptor.

METHODSThe hippocampal slices of rats were incubated with various concentrations of serotonin, M-110, or L-107. sAPP released into the incubation medium were assayed by Western blot analysis assay with monoclonal antibody 22C11 for 2 h.

RESULTSVarious concentrations of serotonin (1.0 x 10(-2) - 1.0 x 10(3) micromol x L(-1)), M-110, a serotonin 5-HT2C agonist (1.5 x 10(-6) - 1.5 x 10(3) micromol x L(-1)), showed positive effect on the production of sAPP while L-107, a serotonin 5-HT2C antagonist (1.0 x 10(-9) - 1.0 x 10(3) micromol x L(-1)), showed negative effect on the production of sAPP over controls.

CONCLUSIONSerotonin modulates production of secretory amyloid beta-protein precursor through serotonin 5-HT2C receptor in incubated rat hippocampal slices.

Amyloid beta-Protein Precursor ; secretion ; Animals ; Hippocampus ; metabolism ; In Vitro Techniques ; Male ; Peptide Fragments ; secretion ; Rats ; Rats, Sprague-Dawley ; Receptor, Serotonin, 5-HT2C ; Serotonin ; pharmacology ; Serotonin 5-HT2 Receptor Agonists ; Serotonin 5-HT2 Receptor Antagonists

AIMTo explore the modulation of 5-HT on GABA-activated current (I(GABA)) in the membrane of rat dorsal root ganglion (DRG) neurons and its mechanism.

METHODSRat DRG neurons were isolated mechanically and enzymatically, on which whole-cell patch clamp recording and repatch technique for intracellular dialysis were performed.

RESULTSIn the majority of neurons examined (92.0%, 69/75) GABA induced a concentration-dependent inward current. In neurons sensitive to GABA preapplication of 5-HT produced potentiation effect (82.6% , 57/69) on I(GABA). Preapplication of 5-HT at concentrations of 1 x 10(-6), 1 x 10(-5), 1 x 10(-4) and 1 x 10(-3) mol x L(-1) potentiated I(GABA) by (35 +/- 8)% (n=8), (47 +/- 11)% (n=10), (65 +/- 17)% (n=9) and (75 +/- 18)% (n=11), respectively. This effect was mimicked by alpha-methyl-5-HT (1 x 10(-6) mol x L(-1)), a specific 5-HT2 receptor agonist, and reversed by cyproheptadine, a selective 5-HT2 receptor antagonist. The potentiation of I(GABA) by 5-HT was irrespective to whether the I(5-HT) presents or not in a subset of neurons. The concentration-response curves for GABA before and after pretreatment with 5-HT manifested the same threshold value and similar EC50 (2.0 x 10(-5) and 1.9 x 10(-5) mol x L(-1), respectively) , while the maximal value of I(GABA) for the latter was 33.6% higher than that for the former. Intracellular dialysis with GDP-beta-S or H-7 abolished the potentiation of I(GABA) by 5-HT, while H-9 did not.

CONCLUSION5-HT can potentiate GABA-activated current via PKC-dependent phosphorylation of GABA(A) receptor following the activation of 5-HT2 receptor.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine ; pharmacology ; Animals ; Cyproheptadine ; pharmacology ; Female ; Ganglia, Spinal ; cytology ; physiology ; Male ; Membrane Potentials ; drug effects ; Neurons ; physiology ; Patch-Clamp Techniques ; Protein Kinase C ; antagonists & inhibitors ; Rats ; Rats, Sprague-Dawley ; Receptors, Serotonin, 5-HT2 ; Serotonin ; analogs & derivatives ; pharmacology ; Serotonin 5-HT2 Receptor Agonists ; Serotonin 5-HT2 Receptor Antagonists ; Signal Transduction ; gamma-Aminobutyric Acid ; pharmacology

5-hydroxytryptamine (5-HT) released in inflammatory tissues plays a pivotal role in pain hypersensitivity. However, it is not clear whether 5-HT2A receptors in the inflamed tissues mediate this effect. The present study investigated the contribution of 5-HT2A receptors in the periphery to chronic inflammatory pain. Complete Freund's adjuvant (CFA) was injected subcutaneously in the hindpaw of rats. The selective 5-HT2A receptor antagonist ketanserin was given in the inflamed site. Paw withdrawal latency responding to heat or mechanical stimuli was measured. Expression of neuropeptide Y (NPY) in the spinal dorsal horn and dorsal root ganglia (DRG) was assayed using immunohistochemistry technique. The results showed that ketanserin administered in the inflamed site inhibited thermal hyperalgesia in a dose-dependent manner (20, 40 and 80 µg) induced by the intraplantar injection of CFA. Ketanserin given once per day at a dose of 80 µg abolished heat hyperalgesia and also attenuated mechanical allodynia on the third day. CFA injection increased the expression of NPY in superficial laminae of the spinal cord, but not in the DRG. The local treatment of ketanserin completely inhibited CFA-induced increase in NPY expression in superficial laminae of the spinal cord. These results indicated that activation of 5-HT2A receptors in the inflamed tissues was involved in the pathogenesis of inflammatory pain and the blockade of 5-HT2A receptors in the periphery could relieve pain hypersensitivity and normalize the cellular disorder in the spinal dorsal horn associated with pathological pain. The present study suggests that the peripheral 5-HT2A receptors can be a promising target for pharmaceutical therapy to treat chronic inflammatory pain without central nervous system side effects.
Animals ; Freund's Adjuvant ; adverse effects ; Ganglia, Spinal ; metabolism ; Hot Temperature ; Hyperalgesia ; chemically induced ; drug therapy ; Inflammation ; drug therapy ; Ketanserin ; pharmacology ; Neuropeptide Y ; metabolism ; Pain ; drug therapy ; Pain Measurement ; Rats ; Receptor, Serotonin, 5-HT2A ; metabolism ; Serotonin ; Serotonin 5-HT2 Receptor Antagonists ; pharmacology ; Spinal Cord Dorsal Horn ; metabolism

Serotonin (5-hydroxytryptamine (5-HT)) is a neurotransmitter that regulates a variety of functions in the nervous, gastrointestinal and cardiovascular systems. Despite such importance, 5-HT signaling pathways are not entirely clear. We demonstrated previously that 4-aminopyridine (4-AP)-sensitive voltage-gated K+ (Kv) channels determine the resting membrane potential of arterial smooth muscle cells and that the Kv channels are inhibited by 5-HT, which depolarizes the membranes. Therefore, we hypothesized that 5-HT contracts arteries by inhibiting Kv channels. Here we studied 5-HT signaling and the detailed role of Kv currents in rat mesenteric arteries using patch-clamp and isometric tension measurements. Our data showed that inhibiting 4-AP-sensitive Kv channels contracted arterial rings, whereas inhibiting Ca2+-activated K+, inward rectifier K+ and ATP-sensitive K+ channels had little effect on arterial contraction, indicating a central role of Kv channels in the regulation of resting arterial tone. 5-HT-induced arterial contraction decreased significantly in the presence of high KCl or the voltage-gated Ca2+ channel (VGCC) inhibitor nifedipine, indicating that membrane depolarization and the consequent activation of VGCCs mediate the 5-HT-induced vasoconstriction. The effects of 5-HT on Kv currents and arterial contraction were markedly prevented by the 5-HT2A receptor antagonists ketanserin and spiperone. Consistently, alpha-methyl 5-HT, a 5-HT2 receptor agonist, mimicked the 5-HT action on Kv channels. Pretreatment with a Src tyrosine kinase inhibitor, 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine, prevented both the 5-HT-mediated vasoconstriction and Kv current inhibition. Our data suggest that 4-AP-sensitive Kv channels are the primary regulator of the resting tone in rat mesenteric arteries. 5-HT constricts the arteries by inhibiting Kv channels via the 5-HT2A receptor and Src tyrosine kinase pathway.
4-Aminopyridine/pharmacology ; Action Potentials ; Animals ; Calcium Channel Blockers/pharmacology ; Calcium Channels/metabolism ; Cells, Cultured ; Ketanserin/pharmacology ; Male ; Mesenteric Arteries/drug effects/*metabolism/physiology ; Muscle Contraction ; Muscle, Smooth, Vascular/cytology/drug effects/metabolism/physiology ; Myocytes, Smooth Muscle/drug effects/metabolism/physiology ; Nifedipine/pharmacology ; Potassium Channel Blockers/pharmacology ; Potassium Channels, Voltage-Gated/antagonists & inhibitors/*metabolism ; Protein Kinase Inhibitors/pharmacology ; Rats ; Rats, Sprague-Dawley ; Receptor, Serotonin, 5-HT2A/*metabolism ; Serotonin/*pharmacology ; Serotonin 5-HT2 Receptor Antagonists/pharmacology ; Spiperone/pharmacology ; *Vasoconstriction ; src-Family Kinases/antagonists & inhibitors/*metabolism