5-Hydroxytryptamine-like immunoreactivity in the peripheral and central nervous systems of the leech Hirudo medicinalis

Chains of segmental ganglia and various peripheral tissues from the leech (Hirudo medicinalis ) were screened as whole-mount preparations for the presence of 5-hydroxytryptamine-like immunoreactivity. The gut was richly supplied with immunoreactive nerve fibres. The possible roles of the immunoreactive nerve fibres demonstrated in the various tissues of the leech have been discussed in relation to the known peripheral effects of serotoninergic neurone stimulation in the leech and to the actions of exogenously applied 5-hydroxytryptamine in these and other invertebrate tissues.