Christopher A. Ross

Adrenaline neurons in the rostral ventrolateral medulla innervate thoracic spinal cord: A combined immunocytochemical and retrograde transport demonstration

Adrenaline-containing neurons in the C1 group of the ventrolateral rostral medullary reticular formation which project to the thoracic spinal cord were identified by a combined retrograde transport immunocytochemical technique. No other medullary catecholamine neurons, including the A1 and A2 noradrenaline cells, project to thoracic spinal cord. These data, taken with results of other studies of spinal catecholamine innervation, suggest a segmental segregation of projections to spinal cord by dopaminergic, noradrenergic, and adrenergic neurons.

Adrenaline synthesizing neurons in the rostral ventrolateral medulla: a possible role in tonic vasomotor control

Adrenaline-containing neurons of the rostral ventrolateral medulla (the C1 group) project selectively to autonomic spinal neurons in rats. Stimulation of these neurons electrically or chemically elevates arterial pressure, while neuronal blockade by microinjection of tetrodotoxin bilaterally drops arterial pressure to levels comparable to those produced by spinal cord transection. Adrenaline neurons of the ventral medulla appear necessary for maintaining normal levels of blood pressure, and thus may constitute a tonic vasomotor center.

Afferent projections to cardiovascular portions of the nucleus of the tractus solitarius in the rat

Horseradish peroxidase was injected unilaterally into the intermediate portion of the nucleus of the tractus solitarius. The most extensive retrograde labeling was present contralaterally in the rostral fastigial nucleus, bilaterally in the Koelliker-Fuse nucleus, and bilaterally with ipsilateral predominance in the posterolateral hypothalamus and paraventricular hypothalamic nucleus. These projections may represent the anatomical substrates by which these brain areas modulate baroreceptor reflex function.

Projections from the spinal trigeminal nucleus to the entire length of the spinal cord in the rat

Using retrograde transport of horseradish peroxidase, projections were found from the spinal trigeminal nucleus to all levels of the spinal cord in rat. In addition to the previously described projections from nucleus caudalis, axons originate from two areas - one overlapping the nucleus caudalis and interpolaris and one in the ventral division of nucleus oralis - and descend as far as the lumbosacral cord. Projections from the nucleus caudalis and interpolaris are primarily ipsilateral to all levels of the spinal cord. Cells in the nucleus oralis innervating the cervical cord are distributed bilaterally. Projections from the nucleus oralis to the thoracic and lumbosacral segments are entirely crossed, lighter and less extensive than those to cervical levels. Trigeminospinal cells originate from several loci that strongly overlap the distributions of both trigeminotectal and trigeminocerebellar neurons. These findings thus reveal a new and more complexly organized system of trigeminospinal projections than previously recognized.

Role of Adrenaline Neurons of Ventrolateral Medulla (The C1 Group) in the Tonic and Phasic Control of Arterial Pressure

We have sought to determine if adrenaline neurons of the C1 group are responsible for cardiovascular functions heretofore attributed to neurons in the rostral ventrolateral medulla. C1 neurons were identified in rat with antibodies to the adrenaline synthesizing enzyme, PNMT. These project to spinal cord wherein they selectively innervate the sympathetic columns. C1 neurons are also innervated by projections, mostly unilateral, from the nucleus tractus solitarii (NTS). Stimulation of the C1 area electrically, by local injection of the excitatory amino acid, L-glutamate, or with the GABA antagonist bicuculline, elevates arterial pressure (AP). Bilateral electrolytic lesions, microinjection of GABA, or administration of tetrodotoxin, in contrast, collapses AP to levels comparable to that of spinal cord transection. After lesions of one NTS, a lesion of the contralateral C1 area abolishes all reflex activity elicited by electrical or natural stimulation of baroreceptors on the side of C1 lesion without modifying resting AP. Lesions of axon bundles of PNMT neurons in the medulla also abolish baroreflexes after unilateral NTS lesions. C1 neurons appear to be the neurons mediating cardiovascular effects of application of drugs or cold to rostral portions of the ventrolateral medulla. We conclude adrenaline neurons of the C1 area represent the purportedly tonic vasomotor neurons of the rostral ventrolateral medulla and mediate the vasodepressor limb of reflexes arising from arterial baroreceptors and other cardiopulmonary afferents. Whether the tonic vasomotor response to stimulation of C1 neurons is dependent upon the release of adrenaline is not yet certain.

A new group of neurons in hypothalamus containing phenylethanolamine N-methyltransferase (PNMT) but not tyrosine hydroxylase

Intraventricular injection of colchicine in rat results in the appearance within hypothalamus of numerous neurons containing the adrenaline-synthesizing enzyme, phenylethanolamine N-methyltransferase, but not the other catecholamine biosynthetic enzymes. Increased PNMT staining in hypothalamus was paralleled by an increase in PNMT activity measured in micropunch preparations. Immunotitration demonstrated that this increase was due to accumulation of specific enzyme protein. The finding that hypothalamic neurons express PNMT without tyrosine hydroxylase suggests that such neurons may produce methylated amines other than adrenaline.

Projections to the spinal cord from neurons close to the ventral surface of the hindbrain in the rat

Neurons located within 100 micron of the ventral surface of the hindbrain were labeled following injections of horseradish peroxidase into the thoracic and lumbar spinal cord in the rat. Labeled neurons were distributed into two groups, one ventrolateral to the inferior olive and ventral to the facial nucleus, and one ventral to the raphe pallidus. The location of the ventrolateral subpial group is very similar to that of the brain stem chemosensitive zones, and suggests that the neurons in this group may be important in cardiovascular regulation.