Glutamatergic system in the pelagic tunicates
Tunicates are a sister lineage to vertebrates, with compact, relatively simple nervous systems featuring a single central ganglion, reflecting a minimal complement of chordate functional architecture. Although glutamatergic neurons are the most abundant population in vertebrates, their ancestry remains unclear. Here, we used glutamate immunohistochemical labeling (Glutamate IR) to identify…
The research into the neural systems of pelagic tunicates has revealed intriguing insights about the evolutionary origins of glutamatergic neurons. As distant relatives to vertebrates, tunicates possess simplified nervous structures, featuring just one central ganglion. Despite glutamatergic neurons being the predominant population in vertebrates, their evolutionary origins have been a subject of curiosity.
Utilizing glutamate immunohistochemical labeling (Glutamate IR), scientists successfully identified these glutamatergic elements within the neural framework of the pelagic tunicate Doliolum sp. The labeling was observed in all the major nerves of the central ganglion, including motor-like terminations on the circular bundles responsible for swimming. Notably, the neuronal somata within the central ganglion remained unlabeled, indicating that glutamate accumulated primarily in the axonal processes and terminals.
Interestingly, the study did not detect any GABA-containing neural elements in the tunicate's nervous system. This finding suggests that the elaboration of glutamatergic systems might have taken place in the common ancestor of both tunicates and vertebrates. Nevertheless, the functional implications of glutamate and its role in muscular control within these pelagic tunicates demand further investigation.
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