Figure 6.
The κ-OR agonist U50488 attenuates LC activation by auditory stimuli in the awake, freely moving rat. A1, Representative multiunit waveforms from different putative LC neurons extracted from a multiunit analog record by template-matching software. A2, Cluster plot of the principal component analysis for representative waveforms. Each waveform in the template is represented by a color-coded event dot in the principal component space, thereby generating its respective PC cluster. The ellipsoids around the clusters are three-dimensional representations of 1 SD from cluster centrality. The lack of overlap of the ellipsoids suggests that the clusters represent single units. A3, Below each waveform is the color-coded autocorrelogram generated by interspike intervals between events. The abscissas indicate time in milliseconds, whereas the ordinates indicate number of intervals per bin. For LC neurons, onset of relative refractory period is 3 ms, suggesting that at least 2 ms to the left of 0 and 2 ms to the right of 0 should be devoid of spike interval histograms in an autocorrelogram of a single LC unit. B, Photomicrograph showing a coronal section stained with neutral red at the level of the LC. The arrowheads indicate the location of the multiunit electrodes. The arrow points to the LC. The asterisks indicate the mesencephalic trigeminal nucleus. V, Ventricle. Scale bar, 100 μm. C, Representative PSTHs generated from trials of auditory stimulus presentations before (Pre-vehicle) and immediately after (Post-vehicle) saline administration (1 ml/kg, i.p.). The abscissas indicate time in seconds before and after an auditory stimulus, which starts at 0 s, and the ordinates indicate cumulative number of discharges (spikes) in each 8 ms bin. D, Representative PSTHs generated from a trial of auditory stimulus presentations before (Pre-U50488) and immediately after (Post-U50488) κ-OR agonist administration (5 mg/kg, i.p.). The abscissas indicate time in seconds before and after the auditory stimulus, which starts at 0 s, and the ordinates indicate cumulative number of discharges (spikes) in each 8 ms bin.