The Role of Ascending Neuronal Pathways in Stress‐Induced Release of Noradrenaline in the Hypothalamic Paraventricular Nucleus of Rats

The Role of Ascending Neuronal Pathways in Stress‐Induced Release of Noradrenaline in the... Central catecholaminergic pathways carrying pain‐related signals to the hypothalamic paraventricular nucleus (PVN) were investigated in laboratory rats. Four per cent formalin injected subcutaneously was employed as a stressful stimulus. Neuronal activity in brainstem catecholaminergic and paraventricular neurones was assessed by Fos immunohistochemistry. Stress‐induced noradrenaline (NE) release from nerve terminals in the PVN was measured in extracellular fluid by in‐vivo microdialysis. Within 30 min, formalin elicited a four‐ to sixfold increase in plasma ACTH and corticosterone concentrations and intense Fos‐like activity was seen in the superficial zones of the lumbar spinal cord ipsilateral to the side of the formalin injection. In brainstem catecholaminergic neurones, the PVN, and midline thalamic nuclei, formalin‐induced Fos‐immunopositivity was equally present in the ipsi‐ and contralateral sides of the injection. An immediate elevation (4–5 times higher than baseline levels) of NE levels was measured in both the right and left PVN after a formalin injection into the right paw. Unilateral surgical transections at the medulla‐spinal cord junction failed to affect formalin‐induced elevations in NE levels in the PVN independently of the side of the formalin injection or the knife cut. Thus, this observation clearly shows that fibres carrying pain‐evoked signals ascend bilaterally from the spinal cord to the brainstem and forebrain. Hemisections of the medulla oblongata between the level of A1–A2 NE cell groups and the locus coeruleus reduced but did not eliminate formalin‐induced NE release from the PVN ipsilateral to the knife cut. This effect was independent of the side of the formalin injection. In the contralateral PVN, high and similar NE levels were measured in response to a formalin injection into the right or the left leg. The present study indicates that formalin‐induced pain signals are carried by sensory fibres to the ipsilateral spinal cord. From there, axons of different dorsal horn neurones reach noradrenergic cells on both sides of the medulla oblongata. The majority of noradrenergic fibers ascend on the same side and innervate the ipsilateral PVN. Since formalin administration resulted in a moderate elevation of NE levels in the PVN on the operated side, the role of other ascending noradrenergic (from the locus coeruleus) or noncatecholaminergic fibres that could modulate NE release from the PVN should be considered. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Neuroendocrinology Wiley

The Role of Ascending Neuronal Pathways in Stress‐Induced Release of Noradrenaline in the Hypothalamic Paraventricular Nucleus of Rats

Journal of Neuroendocrinology, Volume 11 (7) – Jul 1, 1999

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Publisher
Wiley
Copyright
Copyright © 1999 Wiley Subscription Services, Inc., A Wiley Company
ISSN
0953-8194
eISSN
1365-2826
DOI
10.1046/j.1365-2826.1999.00365.x
Publisher site
See Article on Publisher Site

Abstract

Central catecholaminergic pathways carrying pain‐related signals to the hypothalamic paraventricular nucleus (PVN) were investigated in laboratory rats. Four per cent formalin injected subcutaneously was employed as a stressful stimulus. Neuronal activity in brainstem catecholaminergic and paraventricular neurones was assessed by Fos immunohistochemistry. Stress‐induced noradrenaline (NE) release from nerve terminals in the PVN was measured in extracellular fluid by in‐vivo microdialysis. Within 30 min, formalin elicited a four‐ to sixfold increase in plasma ACTH and corticosterone concentrations and intense Fos‐like activity was seen in the superficial zones of the lumbar spinal cord ipsilateral to the side of the formalin injection. In brainstem catecholaminergic neurones, the PVN, and midline thalamic nuclei, formalin‐induced Fos‐immunopositivity was equally present in the ipsi‐ and contralateral sides of the injection. An immediate elevation (4–5 times higher than baseline levels) of NE levels was measured in both the right and left PVN after a formalin injection into the right paw. Unilateral surgical transections at the medulla‐spinal cord junction failed to affect formalin‐induced elevations in NE levels in the PVN independently of the side of the formalin injection or the knife cut. Thus, this observation clearly shows that fibres carrying pain‐evoked signals ascend bilaterally from the spinal cord to the brainstem and forebrain. Hemisections of the medulla oblongata between the level of A1–A2 NE cell groups and the locus coeruleus reduced but did not eliminate formalin‐induced NE release from the PVN ipsilateral to the knife cut. This effect was independent of the side of the formalin injection. In the contralateral PVN, high and similar NE levels were measured in response to a formalin injection into the right or the left leg. The present study indicates that formalin‐induced pain signals are carried by sensory fibres to the ipsilateral spinal cord. From there, axons of different dorsal horn neurones reach noradrenergic cells on both sides of the medulla oblongata. The majority of noradrenergic fibers ascend on the same side and innervate the ipsilateral PVN. Since formalin administration resulted in a moderate elevation of NE levels in the PVN on the operated side, the role of other ascending noradrenergic (from the locus coeruleus) or noncatecholaminergic fibres that could modulate NE release from the PVN should be considered.

Journal

Journal of NeuroendocrinologyWiley

Published: Jul 1, 1999

References

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  • Brainstem hemisection decreases corticotropin‐releasing hormone mRNA in the paraventricular nucleus but not in the central amygdaloid nucleus
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  • Neural regulation of corticotropin releasing hormone (CRH) and CRH receptor mRNA in the hypothalamic paraventricular nucleus in the rat
    Kiss, Kiss; Palkovits, Palkovits; Aguilera, Aguilera
  • Simultaneous liquid‐chromatographic determination of 3,4‐dihydroxyphenylglycol, catecholamines, and 3,4–dihydroxyphenylalanine in plasma, and their responses to inhibition of monoamine oxidase
    Eisenhofer, Eisenhofer; Goldstein, Goldstein; Stull, Stull; Keiser, Keiser; Sunderland, Sunderland; Murphy, Murphy; Kopin, Kopin
  • Stimulus‐transcription coupling in the nervous system: involvement of the inducible proto‐oncogenes fos and jun
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    Szafarczyk, Szafarczyk; Guillaume, Guillaume; Conte‐Devoix, Conte‐Devoix; Alonso, Alonso; Malaval, Malaval; Pares‐Herbute, Pares‐Herbute; Oliver, Oliver; Assenmacher, Assenmacher

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