The Journal of Neuroscience, August 15, 2001, 21(16):5984-5992
Gating and Braking of Short- and Long-Term Modulatory Effects by
Interactions between Colocalized Neuromodulators
Erik
Svensson,
Sten
Grillner, and
David
Parker
Nobel Institute for Neurophysiology, Department of Neuroscience,
Karolinska Institute, S-17177, Stockholm, Sweden
Spinal locomotor networks in the lamprey are modulated by
tachykinin neuropeptides. A single 10 min application of the tachykinin substance P evokes a short-term (~1 hr) presynaptic facilitation of
glutamate release and the postsynaptic potentiation of NMDA responses.
The latter effect induces a long-term (>24 hr) protein synthesis-dependent increase in the frequency of network activity. Tachykinins are contained in a ventromedial spinal plexus into which
the medial dendrites of network neurons project. Neurons in this plexus
also contain colocalized dopamine and 5-HT. Here, dynamic plasticity
evoked by modulator interactions has been examined by investigating the
effects of 5-HT and dopamine on specific cellular, synaptic, and
network effects of substance P.
Preapplied 5-HT blocked the substance P-mediated increase in the
network burst frequency and the potentiation of NMDA-evoked cellular
responses that underlies its induction. 5-HT also blocked the
presynaptic facilitation of glutamatergic synaptic transmission by
substance P. The presynaptic, but not postsynaptic, effect of 5-HT was
reduced by the protein phosphatase 2B inhibitor cypermethrin.
Dopamine did not directly modulate the effects of substance P. However,
it reduced the presynaptic interactive effect of 5-HT and thus gated
the presynaptic potentiation of glutamatergic inputs by substance P. However, the substance P-mediated potentiation of NMDA responses was
not gated by dopamine, and thus the long-term network modulation was
not induced.
Neuromodulator effects and their interactions can thus be modulated. By
selecting components from the modulatory repertoire of substance P,
these interactions evoke dynamic changes in short- and long-term
synaptic and network plasticity.
Key words:
metamodulation; spinal cord; lamprey; neuropeptide; substance P; 5-HT; dopamine
Copyright © 2001 Society for Neuroscience 0270-6474/01/21165984-09$05.00/0