Fig. 3. Immunolocalization of synapsin in serotonergic nerve fibres at the release sites for neurotransmitters or neurohormones. (A–C) Nerve fibres in a cockroach muscle double-stained with anti-serotonin and anti-synapsin. Anti-synapsin immunoreactivity is highly concentrated at the sides of the nerve terminals (arrowheads in C). (D–F) A salivary duct nerve costained with anti-serotonin and anti-synapsin. The salivary duct nerve contains two thick, centrally localized axons that are non-serotonergic and homogeneously stained with anti-synapsin (E, arrows). These axons are surrounded by several thin serotonergic axons that ramify and have numerous short sidebranches forming a neurohaemal organ. Anti-synapsin is highly concentrated at the distal ends of these sidebranches (arrowheads in F). Bars, 50 µm.