A serotonergic discrimination favoring synaptic inputs that accompany robust spike firing in lateral amygdala neurons.
The amygdala and serotonergic innervations thereunto are considered to cooperatively modulate affective behaviors. By whole-cell recording, the present study examined effects of serotonin (5-HT) on synaptic transmission in the rat basolateral amygdala (BLA) complex, which is the amygdalar entrance for sensory information. Application of 5-HT-attenuated excitatory postsynaptic currents at synapses from the lateral amygdala (LA) to the BLA proper, and also at synapses from putative thalamic afferents to LA principal neurons, both depending on 5-HT(2) receptors. This reduction of synaptic responses was confirmed in the BLA under current clamp. In the LA, by contrast, synaptic potentials were not reduced, but enhanced by 5-HT. With 5-HT bath-applied, a prolonged depolarization was induced in LA neurons by strong synaptic stimulation, which appears similar to a slow after-depolarization (sADP) induced by injecting depolarizing currents. Occurrence of such current-induced sADP was confirmed in LA neurons. Both the synaptically-activated prolonged depolarization and the current-induced sADPs depended on 5-HT(2) receptor activation and postsynaptic calcium increase, suggesting that the same postsynaptic intrinsic mechanisms are involved. Reduction of potassium currents was identified as a major ionic mechanism for this sADPs. We thus revealed that 5-HT usually reduces overall synaptic transmission in the whole BLA complex, but enables sADPs to occur, thereby increasing synaptic responsiveness of LA neurons in a positive feedback manner. With this duality of 5-HT actions in operation, a weak input to the BLA complex would be usually eliminated, but could be selected were it associated with sufficiently large depolarization.
Department of Physiology, Kanazawa Medical University, Ishikawa 920-0293, Japan.
R
R
Yamamoto
Y
Y
Ueta
T
T
Sugai
N
N
Kato
D000679:Amygdala / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009924:Organ Culture Techniques; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D012701:Serotonin / Q000378:metabolism* / Q000494:pharmacology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*
D012701:Serotonin