Figure 4.

Photomicrographs showing representative results after an injection of FluoroRuby (FR) into the left auditory cortex. (A) Transverse section showing part of a large deposit of FR into the left auditory cortex. The deposit site (bright red area) was confined to the cortical layers (indicated by Roman numerals); FR-labeled axons (between white arrows) are seen extending into the subcortical white matter (wm). GP724. ps, pseudosylvian sulcus. Dorsal is up; lateral is to the left. Scale bar = 1 mm. (B) FR-labeled axons in the nucleus of the brachium of the inferior colliculus (NBIC) after the injection shown in panel (A) labeled axons as well as many boutons are visible. Sagittal section. Scale bar = 20 μm. Structured illumination image stack; maximum projection image. (C,D) Structured illumination fluorescence images showing FR-labeled boutons (red) in the NBIC that are also immunoreactive for the synaptic marker synapsin 1 (imaged with AlexaFluor 647 and colorized cyan). Each row shows a single area visualized for FR (all panels), synapsin 1 (cyan, middle and right panels) and Neurotrace (a Nissl stain, colorized green, right panel). Many swellings on the FR-labeled axons were immunopositive for synapsin 1; some of these were closely apposed to labeled somas (white arrowheads), whereas other synapsin 1-positive, FR labeled boutons were located in the neuropil (yellow arrowheads), between Nissl-stained cells (presumably forming synapses with unlabeled dendrites). GP724. Sagittal sections. Scale bar = 20 μm.