S. B. Abbott and R. Kanbar contributed equally to this work.
C1 neurons excite locus coeruleus and A5 noradrenergic neurons along with sympathetic outflow in rats
Article first published online: 23 MAY 2012
© 2012 The Authors. The Journal of Physiology © 2012 The Physiological Society
The Journal of Physiology
Volume 590, Issue 12, pages 2897–2915, June 2012
How to Cite
Abbott, S. B., Kanbar, R., Bochorishvili, G., Coates, M. B., Stornetta, R. L. and Guyenet, P. G. (2012), C1 neurons excite locus coeruleus and A5 noradrenergic neurons along with sympathetic outflow in rats. The Journal of Physiology, 590: 2897–2915. doi: 10.1113/jphysiol.2012.232157
- Issue published online: 14 JUN 2012
- Article first published online: 23 MAY 2012
- Accepted manuscript online: 1 MAY 2012 05:25AM EST
- (Resubmitted 12 March 2012; accepted after revision 20 April 2012; first published online 23 April 2012)
- • C1 neurons activate sympathetic tone and stimulate the hypothalamic–pituitary–adrenal axis in circumstances such as pain, hypoxia or hypotension.
- • C1 neurons innervate pontine noradrenergic cell groups, including the locus coeruleus (LC) and A5.
- • In this study, using an optogenetic approach in anaesthetized rats, we show that C1 neurons form excitatory synapses with LC neurons and that selective stimulation of C1 neurons activates LC and A5 neurons.
- • These results show that the C1 neurons activate pontine noradrenergic neurons through the release of glutamate. This effect may be important in the arousal-promoting effects of hypoxia and pain.
Abstract C1 neurons activate sympathetic tone and stimulate the hypothalamic– pituitary–adrenal axis in circumstances such as pain, hypoxia or hypotension. They also innervate pontine noradrenergic cell groups, including the locus coeruleus (LC) and A5. Activation of C1 neurons reportedly inhibits LC neurons; however, because these neurons are glutamatergic and have excitatory effects elsewhere, we re-examined the effect of C1 activation on pontine noradrenergic neurons (LC and A5) using a more selective method. Using a lentivirus that expresses channelrhodopsin2 (ChR2) under the control of the artificial promoter PRSx8, we restricted ChR2 expression to C1 neurons (67%), retrotrapezoid nucleus neurons (20%) and cholinergic neurons (13%). The LC contained ChR2-positive terminals that formed asymmetric synapses and were immunoreactive for vesicular glutamate transporter type 2. Low-frequency photostimulation of ChR2-expressing neurons activated LC (38 of 65; 58%) and A5 neurons (11 of 16; 69%) and sympathetic nerve discharge. Locus coeruleus and A5 inhibition was not seen unless preceded by excitation. Locus coeruleus activation was eliminated by intracerebroventricular kynurenic acid. Stimulation of ChR2-expressing neurons at 20 Hz produced modest increases in LC and A5 neuronal discharge. In additional rats, the retrotrapezoid nucleus region was destroyed with substance P–saporin prior to lentivirus injection into the rostral ventrolateral medulla, increasing the proportion of C1 ChR2-expressing neurons (83%). Photostimulation in these rats activated the same proportion of LC and A5 neurons as in control rats but produced no effect on sympathetic nerve discharge owing to the destruction of bulbospinal C1 neurons. In conclusion, low-frequency stimulation of C1 neurons activates pontine noradrenergic neurons and sympathetic nerve discharge, possibly via the release of glutamate from monosynaptic C1 inputs.