HRP Labelling of Bulb and Mucosa. A-C. Photomicrographs of HRP labelling (TMB substrate) and Fast Red counterstaining in a horizontal section through cortical frontal pole and olfactory bulbs of unilaterally bulbectomized mouse (Mouse S in Fig. 2). A. Arrows mark HRP foci in glomerular layer of preserved bulb. B. Higher magnification view on side ipsilateral to bulbectomy showing bulb stump rostral to cortical frontal pole (see region of interest in A, right). Note lack of HRP positive axonal ingrowth to bulb vestige. C. Higher magnification view of mediocaudal region of preserved bulb (see region of interest in A, left). Note HRP positive axonal ingrowth to glomerular region. D. Coronal view of fixed but undecalcified portion (see ragged borders) of caudal nasal cavity with HRP labelling. HRP had been infused into right naris 48 hrs prior to labelling. Note HRP in presumptive olfactory receptor neurons of both nasal fossa (arrows) but label is limited on the left side to ventral turbinates. ect = ectoturbinate; ent = endoturbinate; lfp = left frontal pole; lnc = left nasal cavity; lob = left olfactory bulb; rnc = right nasal cavity; rfp = right frontal pole; s = nasal septum; Scale bar in A = 250 μm.