Fig. 4. Intrinsic neurons at the proximal region of the gill filaments in zebrafish innervate the base of the efferent filament artery. Confocal imaging was performed using antibodies against the synaptic vesicle protein SV2. (A) Multipolar superficial proximal neurons (SPNs) and deep proximal neurons (DPNs) extend processes towards the base of the efferent filament artery (eFA), where SV2-immunoreactive nerve endings (arrowheads) are found. Extrinsic nerve terminals surrounding the efferent branchial artery (eBA) are also visible. Scale bar, 20 µm. (B) Image in A rotated 70° depicting SPNs and DPNs as two distinct neuronal groups. Note the shape of the eFA outlined by SV2-positive nerve terminals. (Modified from Jonz and Nurse, 2003.)