5-ht Neurons In The Camponotus Japonicus Three Kinds Of Ants In The Brain Distribution Of A Comparative Study

The distribution of serotonin immunoreactive (5-HTi) neurons is described for the brain of three ant castes (large workers, small workers and soldiers) of Camponotus japonicus. The Colophony-Paraffin (CP) embedding technique combined with SP (Streptaridin-peroxidase)method were used for immunohistochemical identification of 5-HTi neurons on sections. All protocerebral neuropile regions of the three ant castes are innervated by extensive aborizations of 5-HTi fibers. The most intense immunoreactivity is found in the central body, the newly described precerebral bridge (Prb), and the neuropil surrounding of the central body and the mushroom bodies (except for three pairs of optic tubercles). Fainter immunoreactivity appears in the mushroom bodies (excluding calyxes), postcerebral bridge (Pob) and three pairs of optic tubercles; The calyces show the weakest immunoreactivity. Staining intensity varies across the mushroom body lobes and peduncle of large workers and soldiers, and dense concentration of immunoreactivity appear at the area where the pedunculi and calyce's basal rings meet (the end of the pedunculi), whereas it appears more uniform in small workers. A relatively small number of 5-HT-positive somata (small worker about 90-93, large worker about 118-122, soldier about 148-152somata) are grouped into clusters and are mainly located in the posterior and ventral protocerebrum. The antennal lobes have relatively weak 5-HT immunoreactivity. The antennal mechanosensory and motor centers, in contrast, have relatively strong 5-HT immunoreactivity. There is one 5-HT-positive projection neuron in the lateral cell group of the antennal lobe .The tritocerebrum neuropile regions of the three ant castes hasn't distinct limit with the protocerebrum and the suboesophageal ganglion, appears 5-HT immunoreactivity. 5–HTi neurons share physiological characteristics in the three ant castes and are not crucial for regulation of aggression behavior, but have tight contact with regulation of visual information. By tracking the serial sections, many thick fibers that derived from 5-HTi neurons were discovered projecting into the distant region to somata, some even project from one side to the other side, and send out many tiny branches contralaterally distributing in the wide field of the brain, so we can conclude that 5-HT may modulate distant and wide-field neural interactions.