Ultrastructure and function in sympathetic ganglia isolated from rats infected with pseudorabies virus.

(1) After inoculation of the pseudorabies virus in the anterior chamber of the eye of the rat, virions can be found only in the neurons of the superior cervical sympathetic ganglion and in the sensory ganglion of the fifth nerve on the inoculated side. Other nervous structures--central or peripheral--are not infected. (2) It is shown that the retrograde axonal flow carries the virus from the eye to the sympathetic neurons. (3) The ultrastructure of the infected neuron has been studied at various intervals after inoculation and at different stages of the viral replication. (4) Excised infected ganglia in vitro show a spontaneous electrophysiological activity that can be recorded on both the post- and preganglionic nerve. Such an activity has never been seen in normal excised ganglion of rat. (5) The shape and frequency of the electrophysiological discharges recorded on the postganglionic nerve have been analyzed at various intervals after inoculation. (6) Correlations established between the ultrastructure, the effect of various drugs and the electrophysiological activity permit the proposal of various hypothesis about the abnormal activity of the infected neurons.

Organization of crustacean neuropil. II. Distribution of synaptic contacts on identified motor neurons in lobster stomatogastric ganglion.

Identified neurons in the stomatogastric ganglion of the lobster were examined and reconstructed by serial section electron microscopy. Each motor neuron consists of a soma, a primary process leading directly from the soma to the motor axon which leaves the ganglion, and a group of secondary processes which branch from the primary process and ramify within the neuropil. Synapses are found only on small processes in the synaptic neuropil, never on the primary processes or on larger secondary processes in the coarse neuropil. Nearly every secondary process of every neuron examined makes both pre- and postsynaptic contacts. Hence these neurons are not polarized into distinct pre- and postsynaptic regions but have both input and output distributed over each of the secondary processes in the neuropil. The conncetion between a specific pair of neurons is also distributed over several branches of both the pre- and the postsynaptic neurons. The restriction of synapses to the more distal portions of the secondary processes suggests that no single contact or localized group of contacts can exert an overrriding influence on the neuron by virtue of an especially advantageous position. The close proximity of input and output on most secondary processes suggests that synaptic input may be capable of directly influencing output without the intervention of action potentials. The distribution of specific synapses over several branches of both pre- and postsynaptic neurons suggests that each neuron functions as a whole without differentiation into specialized branches.

Organization of crustacean neuropil. I. Patterns of synaptic connections in lobster stomatogastric ganglion.

The stomatogastric ganglion of the lobster consists of about thiry neurons, mainly large monopolar cells, which have been well characterized physiologically. This paper presents an anatomical description of this ganglion, emphasizing synaptic connections in the neuropil. The neuron cell bodies are located on the dorsal surface of the ganglion. They send processes into the underlying neuropil mass. The neuropil is differentiated into two regions: a core of coarse neuropil consists of large heavily ensheathed processes; a surrounding region of fine-textured synaptic neuropil consists of smaller unsheather processes. Synapses are found only in synaptic neuropil, not in the core of coarse neuropil. Synaptic contacts, about one million in the entire neuropil, are easily recognized by a set of criteria including presynaptic vesicles and pre- and postsynaptic membrane specializations. Most synaptic contacts invole at least three neural processes, usually one pre- and two postsynaptic elements. Synapses are clustered onto irregular swellings or varicosities on neural processes. These varicosities make both pre- and postsynaptic contacts. Three differenty types of presynaptic profile are recognized. Pyloric dilator, ventricular dilator and lateral posterior gastric neurons belong to type A with clear irregular synaptic vesicles. Lateral pyloric, pyloric, anterior median and dorsal gastric neurons belong to type B with larger clear round vesicles. Many unidentified fibres, presumably stomatogastric nerve afferents, blong to type C with both small clear irregular vesicles and also large dense-core vesicles. The synaptic vesicle types are tentatively correlated with neurotransmitter: type A with acetylcholine, type B with an unknown transmitter, possibly glutamate, and type C with dopamine. The distribution of synaptic contacts on the processes of identified neurons reconstructed from serial section is presented in the following paper.