Central nervous system innervation of the penis as revealed by the transneuronal transport of pseudorabies virus.

Transneuronal tracing techniques were used in order to identify putative spinal interneurons and brainstem sites involved in the control of penile function. Pseudorabies virus was injected into the corpus cavernosus tissue of the penis in rats. After a four day survival period, rats were perfused with fixative and virus-labelled neurons were identified by immunohistochemistry. Postganglionic neurons were retrogradely labelled in the major pelvic ganglia. In the spinal cord, sympathetic and parasympathetic preganglionic neurons were labelled transneuronally. Presumptive interneurons were also labelled in the lower thoracic and lumbosacral spinal cord in locations consistent with what is currently known about such interneurons. In the brainstem, transneuronally labelled neurons were found in the medulla, pons and hypothalamus. Regions consistently labelled included the nucleus paragigantocellularis, parapyramidal reticular formation of the medulla, raphe pallidus, raphe magnus, A5 noradrenergic cell group, Barrington's nucleus and the paraventricular nucleus of the hypothalamus. This study confirmed previous studies from our lab and others concerning the preganglionic and postganglionic neurons innervating the penis. The number, morphology and location of these neurons were consistent with labelling seen following injection of conventional tracers into the penis. The brainstem nuclei labelled in this study were also consistent with what is currently known about the brainstem control of penile function. The labelling appeared to be highly specific, in that descending systems involved in other functions were not labelled. These results provide further evidence that the pseudorabies virus transneuronal tracing technique is a valuable method for identifying neural circuits mediating specific functions.

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.