Synchronized rhythms in chemosensitive neurons of the locus coeruleus in the absence of chemical synaptic transmission

The activity of locus coeruleus (LC) neurons was examined in the en bloc isolated brainstem–spinal cord of the neonatal rat using paired whole cell or whole cell plus extracellular recording. In artificial cerebrospinal fluid (ACSF) LC neurons were synchronized by their respiratory innervation and in some neurons showing tonic or burst patterns of discharge these patterns of discharge could also be synchronized. Replacing ACSF with low Ca²⁺-high Mg²⁺ generated synchronized rhythmic bursts which remained synchronized at high CO₂ (up to 20%). This rhythm was suppressed by TTX. Substitution of Ba²⁺ for Ca²⁺ in ACSF generated a synchronized rhythm which was TTX-insensitive. The frequency of this rhythm increased by 31±16% on raising CO₂ concentration from 2 to 10%. We conclude that the capacity of chemosensitive LC neurons to generate a synchronized rhythm depends on their electrical coupling, but not on chemical synaptic transmission.