The first brain: Species comparisons and evolutionary implications for the enteric and central nervous systems

Abstract

To explore relationships between the ENS and CNS across the animal kingdom. We found that an ENS occurs in all animals investigated, including hydra, echinoderms and hemichordates that do not have a CNS. The general form of the ENS, which consists of plexuses of neurons intrinsic to the gut wall and an innervation that controls muscle movements, is similar in species as varied and as far apart as hydra, sea cucumbers, annelid worms, octopus and humans. Moreover, neurochemical similarities across phyla imply a common origin of the ENS. Investigation of extant species suggests that the ENS developed in animals that preceded the division that led to cnidaria (exemplified by hydra) and bilateria, which includes the vertebrates. The CNS is deduced to be a bilaterian development, later than the divergence from cnidaria. Consistent with the ENS having developed independent of the CNS, reciprocal connections between ENS and CNS occur in mammals, and separate neurons of ENS and CNS origin converge on visceral organs and prevertebral ganglia. We conclude that an ENS arose before and independently of the CNS. Thus the ENS can be regarded as the first brain.

Down-regulation of circ-PRKCI inhibits cell migration and proliferation in Hirschsprung disease by suppressing the expression of miR-1324 target PLCB1

“…These circRNAs species possess potential value as non-invasive clinical biomarkers in complex disorders of the central nervous system (CNS) [28]. However, few researches pay attention to the role of circRNAs in disorders of enteric nervous system (ENS), which has been likened to a second brain because of the similar microstructure of enteric ganglia with central nervous system (CNS) [29,30]. Regarded as a prototypical hypogenesis of ENS, HSCR is a potentially fatal birth defect which resulted from the lack of the enteric ganglia along a variable length of the gut [31,32].…”

Neuro-immune regulation of mucosal physiology

“…8,9 Reciprocally, the ENS can also project axons outwards to the periphery through vagal, spinal, pelvic and sympathetic pathways. 9,19,20 Notably, 90% of the vagal fibres that transit between the gut and the brain are of afferent origin, suggesting that the brain may be more of a receiver than a transmitter in the so-called gut-brain axis. 19 Pulmonary innervation The nervous system in the respiratory tract plays an important role in the maintenance of lung homeostasis, via regulation of mucus secretion, vascular permeability, airway smooth muscle tone and blood flow.…”

To learn, to remember, to forget—How smart is the gut?

“…For example, Hydra has no central nervous system but it contains enteric neurons that control gut movement very much like they do in vertebrates . The implication is that the brain develops as an encephalized ENS which by definition is then the first brain which Mother Nature has established …”