Nonhypotensive autonomic agents in veterinary ophthalmology
The autonomic nervous system is an involuntary motor system composed of the parasympathetic and sympathetic divisions, innervating secretory glands, cardiac muscle, and smooth muscle of blood vessels and viscera. Both divisions of the autonomic system have central and peripheral components. Higher centers for integration of the pars parasympathetica and pars sympathetica are located in the hypothalamus and reticular formation in the brain stem.
These neurons synapse with the lower motor neuron (LMN) of each division. In both divisions of the autonomic nervous system, the LMN is a two-neuron system (Fig. 1). The preganglionic neuron is located in the central nervous system (CNS), and synapses are located in a peripheral autonomic ganglion on the postganglionic neuron. The axon of the postganglionic neuron terminates at the effector organ. The LMN of the parasympathetic system arises from the nuclei of cranial nerves III, VII, IX, and X and the intermediolateral cell column of the first through third sacral spinal nerves in the dog and cat (craniosacral distribution).
The LMN of the sympathetic system arises from the intermediolateral cell column of the eighth cervical through fifth lumbar spinal nerves (thoracolumbar distribution).
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