DIFFUSE SEROTONINERGIC NEUROHEMAL SYSTEMS ASSOCIATED WITH CEREBRAL AND SUBESOPHAGEAL NERVES IN THE HEAD OF THE COLORADO POTATO BEETLE LEPTINOTARSA-DECEMLINEATA

We analyzed the anatomy of two diffuse neurohemal systems for serotoni n in the head of the Colorado potato beetle Leptinotarsa decemlineata by means of immunohistochemistry. One system is formed by axons from t wo bilateral pairs of neurons in the frontal margin of the suboesophag eal ganglion that enter the ipsilateral mandibular nerve, emerge from this nerve at some distance from the suboesophageal ganglion, and cove r all branches of the mandibular nerve with a dense plexus of immunore active axon swellings. The other system is formed by axons from two la rge neurons in the frontal ganglion that enter the ipsilateral frontal connectives, emerge from these connectives, and form a network of axo n swellings on the labrofrontal, pharyngeal, and antennal nerves and o n the surface of the frontal ganglion. Immunohistochemical electron mi croscopy demonstrated that the axon swellings are located outside the neural sheaths of the nerves and hence in close contact with the hemol ymph. We therefore suggest that these plexuses represent extensive neu rohemal systems for serotonin. Most immunoreactive terminals are in di rect contact with the hemolymph, and other terminals are closely assoc iated with the muscles of the mandibles, labrum, and anterior pharynx, as well as with the salivary glands, indicating that these organs are under serotoninergic control.