Alternative testing methodologies--scientific update.
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Animal Testing Alternatives↗
Biomedical subjects
R E Shapiro
Publications and source records attributed to R E Shapiro.
The central organization of the vagus nerve innervating the stomach of the rat.
We employed the neural tracers cholera toxin-horseradish peroxidase and wheat germ agglutinin-horseradish peroxidase to examine the organization of the afferent and efferent connections of the stomach within the medulla oblongata of the rat. The major finding of this study is that gastric motoneurons of the dorsal motor nucleus (DMN) possess numerous dendrites penetrating discrete regions of the overlying nucleus of the solitary tract (NTS). In particular, dendritic labelling was present in areas of NTS which also received terminals of gastric vagal afferent fibers such as the subnucleus gelatinosus, nucleus commissuralis, and medial nucleus of NTS. This codistribution of afferent and efferent elements of the gastric vagus may provide loci for monosynaptic vagovagal interactions. A small number of dendrites of DMN neurons penetrated the ependyma of the fourth ventricle and a few others entered the ventral aspect of the area postrema, thus making possible the direct contact of preganglionic neurons with humoral input from the cerebrospinal fluid and/or the peripheral plasma. Nucleus ambiguus neurons projecting to the stomach predominantly innervate the forestomach. The dendrites of these cells, when labelled, were generally short, and extended beyond the compact cluster of ambiguus neurons in a ventrolateral direction, parallel to the fascicles of vagal efferent fibers traversing the medulla.
Afferent Pathways↗
The central neural connections of the area postrema of the rat.
We applied the neuroanatomical tracers cholera toxin-horseradish peroxidase and wheat germ agglutinin-horseradish peroxidase to investigate the neural connections of the area postrema (AP) in the rat. We find that the AP projects to the nucleus of the solitary tract (NTS) and dorsal motor nucleus of the vagus bilaterally both rostral and caudal to obex; the nucleus ambiguus; the dorsal aspect of the spinal trigeminal tract and nucelus and the paratrigeminal nucleus; the region of the ventrolateral medullary catecholaminergic column; the cerebellar vermis; and a cluster of structures in the dorsolateral pons which prominently include a discrete set of subnuclei in the lateral parabrachial nucleus. The major central afferent input to the area postrema is provided by a group of neurons in the paraventricular and dorsomedial hypothalamic nuclei whose collective dendrites describe a horizontally oriented plexus which encircles the parvocellular nucleus of the hypothalamus bilaterally. In addition, the caudal NTS may project lightly to the AP. The lateral parabrachial nucleus provides a very light input as well. These connections, when considered in the context of the known vagal afferent input and reduced blood-brain barrier of AP, place this structure in a unique position to receive and modulate ascending interoceptive information and to influence autonomic outflow as well.
Afferent Pathways↗
Subfornical organ efferents to neural systems for control of body water.
The subfornical organ, a circumventricular structure of the central nervous system, has efferent neural projections to sites within the brain known to be involved in drinking behavior and secretion of antidiuretic hormone. By using anterograde tracing techniques, it is shown that the subfornical organ projects to the nucleus medians of the medial preoptic area, to the organum vasculosum of the lamina terminalis, and to the supraoptic nuclei bilaterally. Its efferent connectivity is confirmed by retrograde transport of horseradish peroxidase. The organum vasculosum of the lamina terminalis, another circumventricular organ and a suspected receptor site for angiotensin II, is involved in the circuitry of the subfornical organ and also has an efferent projection to the supraoptic nuclei.
Animals↗