Pattern of substance P‐ and cholecystokinin‐like immunoreactivity during regeneration of the neural complex in the ascidian Ciona intestinalis

The neural ganglion of ascidians exhibits a novel and rapid pattern of regeneration whereby within approximately 28–35 days of total ablation an entirely new neural complex is formed. In normal adults, neuronal cell bodies expressing substance P‐ (SP‐Li), neurokinin A‐(NKA‐Li), CCK/gastrin‐ (CCK‐Li), and insulin‐like immunoreactivity exhibit a clearly defined pattern of localization in the cortical rind of the ganglion with characteristic long processes arising from the perikarya running throughout the neuropile. CCK‐Li cell bodies are particularly concentrated close to the points of exit of the main nerve trunks. We have used antisera raised against these peptides to monitor the process of regeneration up to postoperative (pa) day 35. Only SP and CGK antisera produced positive staining in the regenerating tissue. Immunoreactive cell bodies first appear following 14 days pa. At this time CCK‐Li neurons are more abundant than SP‐Li neurons and in contrast to the pattern found in the normal adult ganglion, immunoreactive cell bodies are located both peripherally and centrally in the core of the ganglion and processes were rarely seen. Later stages exhibited an increasing number of SP‐Li neurons and at 35 days pa SP‐Li cell bodies clearly predominate. CCK‐Li neurons typically become clustered close to the points of emergence of the anterior nerve roots. The early expression of CCK‐Li and SP‐Li molecules during regeneration is considered in terms of their potential role in development and cell proliferation in the newly forming ganglion. © 1992 Wiley‐Liss, Inc.