Fig. 2. Localization of iontophoresis sites. (A) The precommand nucleus (PCN). (B) The dorsal posterior nucleus (DP). (C) The ventroposterior nucleus (VP). The first column shows photomicrographs of transverse sections with retrogradely labeled neurons against a background of cresyl violet counterstain, taken from the anatomical study by Carlson (2002b). In A and B, the label results from an injection of neurobiotin into the command nucleus (CN), while in C it results from an injection of neurobiotin into PCN. The second column shows photomicrographs of transverse sections with alcian blue staining against a background of neutral red counterstain, at the same approximate rostro-caudal locations as the first column. The small blue dots provide a precise marker of electrode location, which was always accurately placed into one of the three nuclei. In the third column, continuous voltage traces of electromotor neuron (EMN) activity are shown, with each spike corresponding to a single EMN volley. Iontophoretic injections of L-glutamate (L-Glu; 500 ms pulses of –500 nA) occurred during the times represented by horizontal green lines below each series of traces. Each example is taken from the site shown in the second column, with 0 µm corresponding to the exact location of the alcian blue marker. The effects of L-Glu iontophoresis at 50 µm and 100 µm dorsal and ventral to these sites are also shown. CP, central posterior nucleus of the thalamus; FR, fasciculus retroflexus; Hyp, hypothalamus; IL, inferior lobe of the hypothalamus; L, lateral nucleus of the torus semicircularis; ll, lateral lemniscus; MV, medioventral nucleus of the torus semicircularis; nLR, nucleus of the lateral recess; pc, posterior commissure; PGc, caudal subdivision of the preglomerular nucleus; PGm, medial subdivision of the preglomerular nucleus; tc, tectocerebellar tract; tt, toro-praeeminential tract; v, ventricle. Scale bars, 200 µm in A, 50 µm in B and 200 µm in C.