Synaptic structure and its alteration with environmental temperature: a study by light and electron microscopy of the central nervous system of lizards

Abstract

Three types of structural change can be produced in the nervous system of lizards by altering the environmental temperature from 19 to 32°C. These changes are reversible and take from 1 to 4 weeks to occur. (1) In the nucleus sphericus the fibre plexus within the zone of cells becomes filled with argyrophilic spheres, 2 to 3 μ in diameter, when the animals are kept at the higher temperature. (2) In the cochlear grey, the superior olivary nucleus and the hippocampus there is a loss of neurofibrillar rings when the animals are kept at the higher temperature. This is accompanied by: (3) a loss of mitochondrial material. Electron microscopical studies show that both these last changes occur in synaptic terminals. Within the terminal bags neurofilaments can be seen orientated in the form of a ring, encircling a dense group of mitochondria. Around the neurofilaments is a zone of pale-staining cytoplasm, which is free from synaptic vesicles. The classical neurofibrillar boutons are seen in the regions that show neurofilaments in electron micrographs. Regions that show no neurofibrillar boutons appear to be free of terminal neurofilaments.