Spinal cord interneurones labelled transneuronally from the adrenal gland by a GFP-herpes virus construct contain the potassium channel subunit Kv3.1b.

Interneurones in the spinal cord are likely to play an important role in the generation of activity in sympathetic preganglionic neurones (SPNs) and, therefore, sympathetic outflow. Although the properties of these interneurones have rarely been studied directly, here we show that neurones antecedent to SPNs contain the voltage-gated potassium channel subunit Kv3.1b, while SPNs do not. SPNs and interneurones were labelled by injection of a green fluorescent protein expressing herpes simplex virus (HSV-GFP) into the adrenal gland. SPNs identified by concomitant tracing with Fluorogold did not contain Kv3.1b immunoreactivity. Significantly, neurones that did not contain Fluorogold and which were unlikely to be SPNs were double labelled for Kv3.1b and GFP. This indicates that spinal cord intemeurones antecedent to SPNs contain Kv3.1b. To test the role of Kv3.1b whole cell patch clamp recordings were made from SPNs and interneurones in spinal cord slices. Selective blockade of Kv3.1b containing channels with 30 microM 4-amino-pyridine (4-AP) or 500 microM tetraethylammonium chloride (TEA) revealed that this Kv subunit contributes to fast repolarisation and fast firing frequencies of interneurones in the vicinity of the IML, allowing them to fire action potentials at much higher frequencies than SPNs. This is the first time that transneuronal labelling with this viral construct has been combined with immunohistochemical detection of ion channels. In conjunction with our electrophysiological data, this highlights a role for the Kv3.1b subunit in shaping the activity of intemeurones involved in sympathetic control.