An intrinsic oscillation in interneurons of the rat lateral geniculate nucleus

By using the whole cell patch recording technique in vitro, we examined the voltage-dependent firing patterns of 69 interneurons in the rat dorsal lat eral geniculate nucleus (LGN). When held at a hyperpolarized membrane poten tial, all interneurons responded with a burst of action potentials. In 48 i nterneurons, larger current pulses produced a bursting oscillation. When re latively depolarized, some interneurons produced a tonic train of action po tentials in response to a depolarizing current pulse. However, most interne urons produced only oscillations, regardless of polarization level. The osc illation was insensitive to the bath application of a combination of blocke rs to excitatory and inhibitory synaptic transmission, including 30 mu M 6, 7-dinitroquinoxaline2,3-dione, 100 mu M (+/-)-2-amino-5-phosphonopentanoic acid, 20 mu M bicuculline, and 2 mM saclofen, suggesting an intrinsic event . The frequency of the oscillation in interneurons was dependent on the int ensity of the injection current. Increasing current intensity increased the oscillation frequency. The maximal frequency of the oscillation was 5-15 H z for most cells, with some ambiguity caused by the difficulty of precisely defining a transition from oscillatory to regular firing behavior. In cont rast, the interneuron oscillation was Little affected by preceding depolari zing and hyperpolarizing pulses. In addition to being elicited by depolariz ing current injections, the oscillation could also be initiated by electric al stimulation of the optic tract when the interneurons were held at a depo larized membrane potential. This suggests that interneurons may be recruite d into thalamic oscillations by synaptic inputs. These results indicate tha t interneurons may play a larger role in thalamic oscillations than was pre viously thought.