Fig. 4.

Histamine application to the PGN is able to block or reduce both evoked and spontaneous spindle waves. (A) Local application of HA to this PGN neuron results in a hyperpolarizing response, an increase in membrane conductance, inhibition of rebound burst firing, and a reduction of spindle waves. The cell was injected with hyperpolarizing constant-current pulses (0.2 nA) once every second (see B and C for expansion). After the application of HA, the electrotonic response to the hyperpolarizing current pulse is reduced, and the burst firing is inhibited that is normally triggered by the spindle-wave EPSPs and in response to the hyperpolarizing current pulses. (D) Local application of glutamate (50 μM) to thalamocortical neurons of the A1 lamina with multiunit (MU) extracellular and intracellular recording electrodes placed in the PGN area immediately rostral to the glutamate application site. Activation of the A1 lamina resulted in a barrage of EPSPs followed by a spindle wave in the intracellularly recorded PGN neuron. (E) After local application of HA in the PGN, glutamate activation of lamina A1 still evoked a barrage of EPSPs but not a spindle wave. (F) Overlay of the postsynaptic potentials evoked in the PGN cell by glutamate application in the LGNd before and after application of HA in the PGN. Note that HA does not reduce the evoked EPSPs but abolishes the generation of spindle waves. (G) Illustration of the arrangement of the recording and drug-applying electrodes for the experiment in D-F.