Distribution of glutamic acid decarboxylase immunoreactivity within the brain of oval squid Sepioteuthis lessoniana
Coleoid cephalopods (squid, cuttlefish, and octopus) have the largest and most complex brains amongst the invertebrates and show remarkable behavioral abilities such as learning ability or cognition. Among the coleoids, the oval squid Sepioteuthis lessoniana forms schools that are indicative of sociality. However, little is known about the functional network in the brain that underlies these behaviors. We examined the distribution of glutamic acid decarboxylase (GAD)—the synthetic enzyme of GABA—in the brain of S. lessoniana. This was distributed across the brain with variations in intensity, especially strong in the nerve tract related to higher brain functions and lobes controlling mobility. These results suggest the involvement of GABA in both cognitive behaviors and movement in S. lessoniana.