Electron microscopy of the glio-vascular organization of the brain of octopus

Abstract

The glio-vascular organization of the octopus brain has been studied by light and electron microscopy. The structure of the walls of the blood vessels has been described. Two types of neuroglia can be recognized, the fibrous and protoplasmic glia; also enigmatic dark cells. Most blood vessels in the neuropil are surrounded by extracellular zones containing collagen. These zones give off glio-vascular tunnels (strands) that penetrate the neuropil in a complex network. The extracellular zones and tunnels contain in addition to collagen, smooth muscle cells and fibrocytes. Glial processes surround the extracellular zones and incompletely partition them from the neuropil. The small neuronal perikarya have no glial folds around them. The medium-size cells have thin glial sheets or finger processes related to their surfaces, which may indent the cells to form small trophospongia. The large neurons of the suboesophageal lobe have complex glial sheaths interspersed with extracellular channels. Both penetrate the neurons to form complex trophospongia. A new form of extracellular material has been observed in these extracellular channels. The occurrence of trophospongia in vertebrate and invertebrate neurons may be correlated with the absence of dendrites. Special problems discussed include the nature of the trophospongial function, the question of fluid-filled extracellular zones and their possible function as lymph channels, and the presence in some of them of haemocyanin molecules identical with those in the blood vessels. Perhaps of special importance is the observation that the lobes of the octopus brain are permeated with extracellular tunnels containing smooth muscle fibres, but it still needs to be determined whether or not the muscle cells in the tunnels of the neuropil actively contract and massage the neuropil to facilitate metabolic and other exchanges.

Comparative immunohistochemical study of glial filament proteins (glial fibrillary acidic protein and vimentin) in goldfish, octopus, and snail

“…With increasing nervous system complexity, glial cells take on specialized roles, as, for example, the perineural glia of the arthropods (Smith and Treherne, 1963), or the cells of the glio-vascular system of the cephalopods (Gray, 1969). Morphological comparisons between the glia of vertebrates and invertebrates would suggest that these structures exhibit some degree of relationship.…”

Diffusion MRI Connections in the Octopus Brain

“…Following the pioneering work of Young [ 22 ], a large number of anatomical and physiological studies of the octopus and related coleoid cephalopods have been undertaken. In addition to detailed histological studies [ 8 , 12 , 15 , 16 , 23 - 36 ], other efforts have utilized computed tomography [ 37 , 38 ], electron microscopy [ 39 , 40 ], positron emission tomography [ 41 ], fluorescent dye labeling of neuronal connections [ 42 - 44 ] and magnetic resonance imaging [ 45 - 48 ].…”

“…Although the nervous system is composed of some half a billions neurons, over half are found in the ganglia of the eight arms [ 36 , 51 ]. While much is known about the octopus brain anatomy [ 22 , 25 , 33 , 40 , 52 - 54 ], there is a paucity of neuroimaging information about connectivity of regions that would lead to information about functional organization and circuitry underpinnings behavior. In this work we employ high resolution magnetic resonance imaging (MRI) to construct a mesoscale digital three-dimensional brain atlas of the adult Octopus bimaculoides , including assessment of connectivity between anatomic regions.…”

“…Thus, the octopus is a compelling system for comparison with mammals due to its ancient origin and great anatomical differences combined with fascinating similarities in problem solving skills, learning and memory [11,21] Following the pioneering work of Young [22], a large number of anatomical and physiological studies of the octopus and related coleoid cephalopods have been undertaken. In addition to detailed histological studies [8,12,15,16,[23][24][25][26][27][28][29][30][31][32][33][34][35][36], other efforts have utilized computed tomography [37,38], electron microscopy [39,40], positron emission tomography [41], fluorescent dye labeling of neuronal connections [42][43][44] and magnetic resonance imaging [45][46][47][48].…”