Noradrenergic modulation of intrinsic and synaptic properties of lumbar motoneurons in the neonatal rat spinal cord.
Front. Neural Circuits. 2010-01-01; :
DOI: 10.3389/neuro.04.004.2010
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Although it is known that noradrenaline (NA) powerfully controls spinal motor
networks, few data are available regarding the noradrenergic (NAergic) modulation
of intrinsic and synaptic properties of neurons in motor networks. Our work
explores the cellular basis of NAergic modulation in the rat motor spinal cord.
We first show that lumbar motoneurons express the three classes of adrenergic
receptors at birth. Using patch-clamp recordings in the newborn rat spinal cord
preparation, we characterized the effects of NA and of specific agonists of the
three classes of adrenoreceptors on motoneuron membrane properties. NA increases
the motoneuron excitability partly via the inhibition of a K(IR) like current.
Methoxamine (alpha(1)), clonidine (alpha(2)) and isoproterenol (beta)
differentially modulate the motoneuron membrane potential but also increase
motoneuron excitability, these effects being respectively inhibited by the
antagonists prazosin (alpha(1)), yohimbine (alpha(2)) and propranolol (beta). We
show that the glutamatergic synaptic drive arising from the T13-L2 network is
enhanced in motoneurons by NA, methoxamine and isoproterenol. On the other hand,
NA, isoproterenol and clonidine inhibit both the frequency and amplitude of
miniature glutamatergic EPSCs while methoxamine increases their frequency. The
T13-L2 synaptic drive is thereby differentially modulated from the other
glutamatergic synapses converging onto motoneurons and enhanced by presynaptic
alpha(1) and beta receptor activation. Our data thus show that the NAergic system
exerts a powerful and complex neuromodulation of lumbar motor networks in the
neonatal rat spinal cord.