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The retrograde transneuronal viral tracing method was used to study the CNS nuclei that innervate the parasympathetic preganglionic neurons controlling the submandibular gland in the rat. A genetically engineered beta-galactosidase expressing Bartha strain of pseudorabies virus (PRV) was injected into the submandibular gland of rats. After 4 days, PRV infected tissues were reacted with the Bluo-Gal substrate (halogenated indolyl-beta-D-galactoside) and labeled cell bodies were identified throughout the brain. In the medulla oblongata, cell body labeling was seen in the superior salivatory nucleus, and throughout the medullary reticular formation as well as in the nucleus of the solitary tract, spinal trigeminal nucleus, and deep cerebellar nuclei. In the pons, PRV labeled neurons were found bilaterally in the locus ceruleus, subceruleus region, and parabrachial complex. In the mesencephalon, labeled cells were found in the Edinger-Westphal nucleus, deep mesencephalic nucleus, and central grey matter. Several hypothalamic regions were labeled including the lateral, perifornical and paraventricular hypothalamic nuclei. In the telencephalon, PRV-positive cell bodies were observed in the substantia innominata, bed nucleus of the stria terminalis and central nucleus of the amygdala. The results suggest that widespread areas of the CNS are involved in control of salivation.

Publisher Summary There is a set of nuclei that are interconnected and have been termed the central autonomic network. Apart from its reciprocal interconnections, this network innervates both the vagal and sympathetic preganglionic neurons and thus regulates autonomic functions. This chapter provides a summary of this field with an emphasis on cardiovascular regulation. Several key regions of the forebrain are involved in the regulation of autonomic functions. These areas include the several areas within the hypothalamus, the basal forebrain, and the cerebral cortex. All these areas have been implicated on anatomical grounds to be part of a central autonomic network involving multiple interconnecting circuits. Apart from these complex interconnections, most of these areas project to the lower brain stem where they are capable of influencing the cell groups that innervate the vagal and sympathetic preganglionic neurons or in some cases, like the paraventricular hypothalamic nucleus and the lateral hypothalamic area, provide direct projections to these neurons.

Publisher Summary This chapter discusses descending pathways to the sympathetic preganglionic neurons. The neuroanatomical organization of the central neural pathways that control the cardio-vascular system has received considerable attention. While it has not been possible to identify any group of neurons in the midbrain that project to the intermediolateral cell column, it is known that the midbrain receives a widespread input from the hypothalamus by the periventricular-periaqueductal system, medial forebrain bundle, and central tegmental radiation. Autonomic responses can be elicited by electrical stimulation. After muscle paralysis with gallamine triethiodide or after transection of the spinal cord at the L4-S level (which leaves the sympathetic outflow to the hindlimbs intact), it was found in an earlier study that stimulation of the motor cortex had no effect on blood pressure or skeletal muscle blood flow. Thus, the autonomic responses elicited by motor cortex stimulation are not because of the activation of the sympathetic outflow.

Guanethidine-induced destruction of sympathetic postganglionic neurons in neonatal rats leads to transneuronal degeneration of the sympathetic preganglionic neurons. Using this model, we have been able to show a approximately 35% decrease in [3H]substance P ([3H]SP) binding in the intermediolateral cell column--suggesting that sympathetic preganglionic neurons possess substance P receptors. Our results show that [3H]substance P binding in the intermediolateral cell column is dependent on the integrity of sympathetic postganglionic neurons.