THE ORGANIZATION OF SYNAPTIC AXOPLASM IN THE LAMPREY (PETROMYZON MARINUS) CENTRAL NERVOUS SYSTEM

Abstract

The fine structure of synapses in the central nervous system of lamprey (Petromyzon marinus) ammocoetes has been investigated. Both synapses within the neuropil and synaptic links between giant fibers (including Müller cells) and small postsynaptic units are described. The distribution of neurofilaments and microtubules in nerve profiles over a wide diameter range is described, and the possible role of these structures in intracellular transport is discussed. Electron micrographs indicate that small lucent "synaptic vesicles" occur sparsely throughout the axoplasm and in regular arrays in association with microtubules in the vicinity of synapses. Within a synaptic focus, immediately adjoining the presynaptic membrane, vesicles are randomly arranged and are not associated with microtubules. Neurofilaments are present, generally in large numbers, but these are not associated with vesicles or other particulates. The structural findings are considered in terms of current concepts of fast and slow transport in neurons and the mechanochemical control of intracellular movement of materials.

Luminal material in microtubules of frog olfactory axons: structure and distribution.

“…The present work generally confirms this observation . Other workers have made passing reference to the occurrence of dense luminal material in various kinds of microtubules (1, 2,5,11,13,14,21,24,26,29,31,34) . As to the detailed morphology of luminal material, only Echandia et al .…”

Physiological and anatomical characteristics of reticulospinal neurones in lamprey

“…electrical stimulation of cranial nerves and spinal cord and natural photic, tactile, and vestibular stimulation). Rovainen (1967) (Bertolini, 1964;Smith et al 1970). Some of the post-synaptic neurones are primary motoneurones as demonstrated by the presence of monosynaptic post-synaptic potentials in spinal motoneurones in response to action potentials in single Muller axons (Rovainen, 1974).…”

“…The large axons of the Muller cells run ipsilaterally down the spinal cord, where they make frequent en passant synapses with the dendrites of spinal neurones (Bertolini, 1964;Smith, Jarlfors & Beranek, 1970). Electrical stimulation of a number of different cranial nerves produces synaptic potentials in Muller cells, and high frequency bursts of action potentials in Muller axons cause trunk and fin movements (Rovainen, 1967).…”

Evidence for firm linkages between microtubules and membrane-bounded vesicles.

“…This situation is true of neuron axons (e.g. 24,25), of the heliozoan axopodia (22,26), and of the suctorian tentacles (4,23) and, to a lesser extent, it is true in the processes of melanophores (5,12,19,28,29) and chromatophores (21). It could be argued that the proximal association between the microtubules and particles in these cells is more a result of the small diameter of the cell process than of an actual physical linkage between the two.…”