Figure 4.

Qualitative characteristics in the differential appearance of anterogradely labeled axon fibers and boutons in the PBL depending on the size and density of BDA deposits in the cNTS. (A) Photograph of maximal axon labeling in the PBL following a large injection in the cNTS (See also C1,D). Case 1a #3. A particularly dense field of BDA-labeled axon boutons was noted in the inner portion of the PBL (PBLi, Bernard et al., 1993). The bouton aggregate appeared to be provided by several smaller bundles of axon fibers piercing the outer layer (PBLo, Bernard et al., 1993) from parent axons traveling along the ventral spinocerebellar tract (VSC: arrows in A) and more numerously by those of axons entering from the ventral aspect (B). In addition to the dense terminal field, moderate-to-few boutons and varicose axons were scattered throughout the PBL. See also (C1,3). (C1–3) Drawings of characteristic axon fibers and boutons in the PBL following injections of BDA into the cNTS shown in each photograph. (C1) Maximal axon labeling. Case 1a #2. (C2,3) Weak-to-moderate labeling was observed differentially in the inner and outer layers of the PBL, according to the size and density of BDA deposits. Case 2 #1 and Case 3c #1, respectively (Table 2). (D) Mapping of each area of (A–C). Note labeled axons in the contralateral parabrachial nucleus (PB) and LC via axons traveling in the superior medullary velum (arrowheads). See also Figure 1G. (E) Ascending axons of both passing and terminating types from the cNTS in the PB and surrounding regions at the level of ponto-midbrain juncture. They seem to contain at least three axon bundle systems, indicated here by different colors: blue, MFB; green, DLF; red, those terminating in the PBL.