Serotonin depresses excitatory synaptic transmission and depolarization-evoked Ca2+ influx in rat basolateral amygdala via 5-HT1A receptors.
The actions of serotonin on rat basolateral amygdala neurons were studied with conventional intracellular recording techniques and fura-2 fluorimetric recordings. Bath application of 5-hydroxytryptamine (5-HT or serotonin) reversibly suppressed the excitatory postsynaptic potential in a concentration-dependent manner without affecting the resting membrane potential and neuronal input resistance. Extracellular Ba2+ or pertussis toxin pretreatment did not affect the depressing effect of 5-HT suggesting that it is not mediated through activation of Gi/o protein-coupled K+ conductance. The sensitivity of postsynaptic neurons to glutamate receptor agonist was unaltered by the 5-HT pretreatment. In addition, the magnitude of paired-pulse facilitation was increased in the presence of 5-HT indicating a presynaptic mode of action. The effect of 5-HT was mimicked by the selective 5-HT1A agonist 8-hydroxy-dipropylaminotetralin (8-OH-DPAT) and was blocked by the selective 5-HT1A antagonist 1-(2-methoxyphenyl)-4[4-(2-phthalimido)butyl]piperazine oxadiazol-3-yl]methyl]phenyl]-methanesulphonamide. In contrast, the selective 5-HT2 receptor antagonist ketanserin failed to affect the action of 5-HT. The effects of 5-HT and 8-OH-DPAT on the high K+-induced increase in [Ca2+]i were studied in acutely dissociated basolateral amygdala neurons. High K+-induced increase in [Ca2+]i was blocked by Ca2+-free solution and Cd2+ suggesting that Ca2+ entry responsible for the depolarization-evoked increase in [Ca2+]i occurred through voltage-dependent Ca2+ channels. Application of 5-HT and 8-OH-DPAT reduced the K+-induced Ca2+ influx in a concentration-dependent manner. The effect of 5-HT was completely abolished in slices pretreated with Rp-cyclic adenosine 3',5'-monophosphothioate (Rp-cAMP), a regulatory site antagonist of protein kinase A, suggesting that 5-HT may act through a cAMP-dependent mechanism. Taken together, these results suggest that functional 5-HT1A receptors are present in the excitatory terminals and mediate the 5-HT inhibition of synaptic transmission in the amygdala.
Cheng
L L
LL
Department of Pharmacology, College of Medicine, National Cheng-Kung University, Tainan City, Taiwan.
Wang
S J
SJ
Gean
P W
PW
D000679:Amygdala / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology; D004594:Electrophysiology; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D007425:Intracellular Membranes / Q000378:metabolism; D008297:Male; D009433:Neural Inhibition / Q000502:physiology; D009994:Osmolar Concentration; D051381:Rats; D017207:Rats, Sprague-Dawley; D011985:Receptors, Serotonin / Q000502:physiology*; D012701:Serotonin / Q000494:pharmacology*; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D009435:Synaptic Transmission / Q000187:drug effects*; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000494:pharmacology
D018690:Excitatory Amino Acid Agonists; D011985:Receptors, Serotonin; D017366:Serotonin Receptor Agonists; D012701:Serotonin; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; D017868:Cyclic AMP-Dependent Protein Kinases; D002118:Calcium