Construction of the brain atlas of Amphioctopus fangsiao

Cephalopods possess the most complex brain structures among invertebrates. Due to the distinct functions regulated by various brain lobes, studying the anatomical structure of the brain and the distribution of neurotransmitters can lay the foundation for further in-depth research in neurobiology. To investigate the brain structure and neuronal distribution characteristics of Amphioctopus fangsiao, the anatomy and histology were used to obtain three consecutive slice images of the sagittal plane, coronal plane and transverse plane, and constructed the brain atlas of A. fangsiao. Using immunohistochemical technique, neuron nuclear antigen (NeuN) was used as the primary antibody to label the mature neurons, and the brain tissue structure and internal neuron distribution characteristics were analyzed. The results showed that the central brain of A. fangsiao surrounded the esophagus, which can be divided into the supraesophageal mass and subesophageal mass, optic lobes were located on both sides and were connected to the central brain through the optic nerve tract. According to the structure and function of each lobe, supraesophageal mass was divided into vertical lobe complex, basal lobe complex, buccal lobe complex, optic tract complex and other regions; subesophageal mass was consisted of anterior subesophageal mass, middle subesophageal mass and posterior subesophageal mass. NeuN immunoreactivity was observed in the central brain, and mostly concentrated in the large cells in the perinuclear layer of the subesophageal mass, and there was no NeuN immunoreactivity in the optic lobe. The brain structure and division of the A. fangsiao showed typical octopus brain characteristics, and there were structural differences in the neuronal cell types in the lobe of the brain.