Structure of the pecten neuropil pathway and its innervation by bimodal peg afferents in two scorpion species
Fig 13
Schematic summary of the pecten neuropils and their innervation in Mesobuthus eupeus (left) and Heterometrus petersii (right). Posterior part of the synganglion in horizontal section. The pecten neuropil of M. eupeus exhibits a compartmentalisation into different subregions: The anterior pecten neuropil (APN) at the level of walking leg neuropil 3 (WLN3), the accessory neuropils 1, 2 (AN1,2) (cyan) and the posterior pecten neuropils1-3 (PPN1-3) in the more posterior part of the synganglion. PPN consists of three conspicuous subregions: The laminar PPN1, the glomerular PPN2 and the lobular PPN3. The pecten neuropil of H. petersii contains an ellipsoid APN, an AN (cyan) and a PPN with probably two main regions (PPN1 and 2). The structures of PPN1 and PPN2 are intertwined, although PPN2 appears more lobular. The PPN of H. petersii is interspersed with somata. The subregions of the PPN are delimited (indicated by dark grey areas in PPN1 and PPN2). PPN and APN are connected by a longitudinal tract (indicated by dark grey area between PPN and APN. The innervation of peg afferents exhibits a somatotopic organisation in the PPN: afferents of distal pegs project into lateral regions (red), afferents of median pegs into the central region (blue) and proximal peg afferents into medial regions (green) of the PPN. Innervation areas overlap, but the exact quantity of afferent overlap is not known. APN is innervated homogenously by all afferent fibres. Abbreviations: a: anterior; AN1,2: accessory neuropil1, 2; APN: anterior pecten neuropil; AT: ascending tract; LtT: longitudinal tract; p: posterior; PPN1-3: posterior pecten neuropil 1–3; PT: proceeding tract; WLN2-4: walking leg neuromere 2–4.