Noradrenaline modulates GABA-mediated synaptic transmission in neurones of the mediolateral part of the guinea pig lateral septum via local circuits.
The response to bath-applied noradrenaline (NA, 50 microM) was tested with conventional intracellular recordings in neurones of the mediolateral part of the lateral septum (LSml) by using guinea-pig brain slices. NA elicited direct hyperpolarizations and depolarizations and affected the frequency of tetrodotoxin (TTX)- and bicuculline-sensitive inhibitory post-synaptic potentials (IPSPs). Decrease or increase in IPSPs frequency was observed in 37.6 and 18.2% neurones respectively. Frequency of bicuculline-sensitive miniature IPSPs recorded under TTX was unchanged. Increase in IPSPs frequency was blocked by TTX and was observed during iontophoretic application of NA in the LSml. Taken together, these data suggest that NA hyperpolarizes or depolarizes local presynaptic GABAergic neurones to cause alterations in action potential-dependent transmitter release. NA-induced decrease or increase in IPSPs frequency were respectively mimicked by clonidine and L-phenylephrine and blocked by yohimbine and prazosin, indicating that NA modifies release of GABA by activation of alpha(2) and alpha(1) adrenoceptors at the somato-dendritic region of presynaptic GABAergic neurones. These findings show that, in addition to their direct input from NA afferents, LSml neurones receive a indirect input by way of GABAergic interneurones. These interneurones may serve as inhibitory relays for noradrenergic afferents originating from the locus coeruleus and may be involved in the NA control of LSml functions.
Carette
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INSERM U 422, 1 Place de Verdun, 59045 Lille Cedex, France.
Poulain
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Beauvillain
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JC
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D006168:Guinea Pigs; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D009638:Norepinephrine / Q000494:pharmacology*; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects* / Q000502:physiology; D012686:Septal Nuclei / Q000187:drug effects* / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects* / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000187:drug effects / Q000378:metabolism
D000316:Adrenergic alpha-Agonists; D018341:Receptors, Adrenergic, alpha-2; D005680:gamma-Aminobutyric Acid; D009638:Norepinephrine