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Preproenkephalin mRNA is expressed by C1 and non‐C1 barosensitive bulbospinal neurons in the rostral ventrolateral medulla of the rat
Author(s) -
Stornetta Ruth L.,
Schreihofer Ann M.,
Pelaez Nicole M.,
Sevigny Charles P.,
Guyenet Patrice G.
Publication year - 2001
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.1196
Subject(s) - rostral ventrolateral medulla , medulla oblongata , spinal cord , medulla , tyrosine hydroxylase , anatomy , medicine , biology , neuroscience , central nervous system , immunohistochemistry
The autonomic regions of the thoracolumbar spinal cord receive a dense enkephalinergic (ENK) innervation from supraspinal sources, including the rostral ventrolateral medulla (RVLM). In the present study, we sought to determine whether the barosensitive bulbospinal (BSBS) neurons of the RVLM express preproenkephalin (PPE) mRNA. After injection of Fluoro‐Gold (FG) into the upper thoracic spinal cord, neurons with PPE mRNA (PPE + neurons) were retrogradely labeled throughout the ventrolateral medulla. At the most rostral RVLM level, 29% of bulbospinal PPE + cells were tyrosine hydroxylase–immunoreactive (TH‐ir) and the latter constituted 19.4% of the bulbospinal TH‐ir cells. We determined whether the bulbospinal PPE + RVLM neurons are barosensitive in two ways. First, we examined Fos production by FG‐labeled RVLM neurons after 2 hours of hydralazine‐induced hypotension (to 73 ± 2 mm Hg) in conscious rats. Hydralazine (10 mg/kg i.v.) increased the number of Fos‐ir neurons by two‐ to eightfold at all levels of the ventrolateral medulla examined. In the RVLM, 54% of bulbospinal PPE + neurons were Fos‐ir, whereas such cells were more rarely found at caudal ventrolateral medullary levels. Second, we recorded individual BSBS RVLM units extracellularly in anesthetized rats and filled them juxtacellularly with biotinamide. Most biotinamide‐filled neurons were PPE + (10 of 17), and the PPE + BSBS cells had a faster axonal conduction velocity than those without PPE mRNA (4.2 vs. 0.67 m/sec). Four of the 10 PPE + BSBS RVLM neurons were TH‐ir. In summary, PPE mRNA is predominantly expressed by RVLM BSBS neurons with lightly myelinated spinal axons. PPE mRNA is present in most noncatecholaminergic BSBS neurons and also in approximately 20% of the bulbospinal C1 neurons. BSBS RVLM neurons most likely provide a major ENK input to sympathetic preganglionic neurons and PPE mRNA is the first identified positive phenotype of the non‐C1 BSBS RVLM neurons. J. Comp. Neurol. 435:111–126, 2001. © 2001 Wiley‐Liss, Inc.