Lateralisation of projections from the rostral ventrolateral medulla to sympathetic preganglionic neurons in the rat

• Published in: Brain research Vol. 929; no. 2; pp. 181 - 190
• Main Authors: Moon, Elizabeth A, Goodchild, Ann K, Pilowsky, Paul M
• Format: Journal Article
• Language: English
• Published: London Elsevier B.V 08.03.2002; Amsterdam Elsevier; New York, NY
• Subjects: Adrenal Glands - innervation; Adrenal sympathetic preganglionic neuron; Animals; Autonomic Fibers, Preganglionic - physiology; Biological and medical sciences; Cervical sympathetic preganglionic neuron; Cholera Toxin; Functional Laterality; Fundamental and applied biological sciences. Psychology; Glutamic Acid - administration & dosage; Lateralization; Male; Medulla Oblongata - drug effects; Medulla Oblongata - physiology; Microinjections; Motor control and motor pathways. Reflexes. Control centers of vegetative functions. Vestibular system and equilibration; Neurons - drug effects; Neurons - physiology; Phytohemagglutinins; Rats; Rats, Sprague-Dawley; Spinal Cord - physiology; Superior Cervical Ganglion - physiology; Sympathetic Nervous System - physiology; Synaptic Transmission; Vertebrates: nervous system and sense organs; Endocrine and autonomic regulation; Cervical sympathetic preganglionic neuron; Adrenal sympathetic preganglionic neuron; Lateralization; Preganglionic neuron; Vertebrata; Cardiovascular control; Mammalia; Rat; Autonomic nervous system; Rodentia; Central nervous system; Projection; Medulla oblongata; Sympathetic nervous system; Brain (vertebrata)
• ISSN: 0006-8993; 1872-6240
• DOI: 10.1016/S0006-8993(01)03388-1

Spinally projecting sympathoexcitatory neurons in the rostral ventrolateral medulla (RVLM), synapse with sympathetic preganglionic neurons (SPN) and regulate the activity of sympathetic nerves that control the heart, blood pressure and the adrenal medulla (AM). However, the degree of lateralization of the bulbospinal projections to SPN innervating specific targets is poorly understood. Three approaches were used in this study. Anterograde tracer was iontophoresed into a pressor site in the RVLM (left or right) and retrograde tracer injected into the superior cervical ganglion (SCG, right) and the AM (left). Close appositions between anterogradely labelled axons and retrogradely labelled SCG- or AM-SPN were counted. Projections to the SCG were bilateral. Projections to the AM were markedly ipsilateral. In the second part, retrograde tracers were injected unilaterally into the region of the intermediolateral cell column at spinal segment T2 or T8 on one side and the number of labelled neurons in the RVLM counted. The results from each level of injection were similar showing that ∼63–64% of the neurons were ipsilateral. Responses to glutamate microinjection into the RVLM on adrenal nerve (left) and superior cervical nerve (left) activity were measured. The ratio of the nerve responses was the same even when different sides of the RVLM were injected. The anterograde data strongly suggest that the RVLM projections to AM-SPN are predominantly ipsilateral. Although other experimental approaches also attempted to investigate lateralization, the retrograde data target different and functionally heterogeneous pools of SPN that may mask the ipsilateral projection to the AM. Similarly, chemical stimulation of the RVLM will excite not only monosynaptic projections but also polysynaptic projections that may also mask the predominant ipsilateral monosynaptic projection to AM.