The Chemorepulsive Protein Semaphorin 3A and Perineuronal Net-Mediated Plasticity

Figure 2

Sema3A expression in the rat brain from rostral to caudal. In the olfactory bulb (a), faint Sema3A-immunoreactive labeling was detected between mitral cells (arrowheads) as well as around the initial segments of the mitral cell dendrites in the external plexiform layer (arrow). A coronal section of the lateral olfactory tract (b) showed strong Sema3A-immunostaining in myelinated axons (arrowheads). In the reticular thalamic nucleus (c), intense diffuse labeling is present throughout the nucleus. The neurons in the reticular thalamic nucleus are surrounded by strongly Sema3A-labelled PNNs. Sema3A immunoreactivity in the hippocampus was observed in various structures. Interneurons in the stratum oriens of CA1 (so, arrow) (d) and in the stratum oriens (so, arrow) and stratum radiatum (sr, arrowhead) of CA2 (e) displayed Sema3A positive PNNs. Only the pyramidal neurons in CA2 and not in CA1 and CA3 displayed striking intense Sema3A-labelled PNNs with strong diffuse labeling between the cell bodies of pyramidal neurons (sps) (f). The polymorph layer (po) of the dentate gyrus displayed a weak diffuse staining for Sema3A. In the neocortex, neurons with a Sema3A-positive PNN are scattered throughout layers II to VI (g). This typical Sema3A labeling in the cortical layers was observed in various anatomical subdivisions of the neocortex, including the somatosensory cortex (h) and the visual cortex (i). Well defined Sema3A-labelled PNNs are present around neurons in the deep gray of the superior colliculus (j); this is in contrast to the weakly labelled PNNs surrounding the neurons of the intermediate gray of the superior colliculus (arrowheads) (k). The red nucleus shows a large number of strongly Sema3A-labelled PNNs around the magnocellular neurons. In addition, an intense diffuse Sema3A staining was observed between neurons (l). Also the external nucleus of the inferior colliculus displayed strong and well-defined Sema3A immunoreactive PNNs and strong diffuse labeling between the neurons throughout the nucleus (m). The vestibular nucleus of the hindbrain contains many large neurons with robust Sema3A-positive PNNs and strong diffuse immunoreactivity between the cells in the nucleus (n). Moderately Sema3A-labelled PNNs were observed around neurons in the inferior olive while throughout the nucleus a diffuse Sema3A labeling was present (o). In the cerebellum, some Golgi neurons bear Sema3A-positive PNNs ((p), arrow). Many Purkinje cells displayed a semiorganized Sema3A-pattern which is typical for the PNNs found around Purkinje cells (q). Deep cerebellar nuclei display well-defined large Sema3A and Sema3B immunoreactive neurons (resp., (r) and (s)). Images (d)–(s) have been reproduced with permission from Vo et al. [51]. Scale bar for (a) and (b) is 25 µm; for (c) and (j)–(o) is 100 µm; for (d)–(f) is 200 µm; for (g) is 300 µm; for (h) and (i) is 33 µm; and for (p)–(s) is 35 µm.