NEUROENDOCRINOLOGY LETTERS
including Psychoneuroimmunology, Neuropsychopharmacology,
Reproductive Medicine, Chronobiology and Human Ethology
ISSN 0172–780X

NEL Vol.23 No.4, August 2002

ORIGINAL ARTICLE
C-fos gene expression in hypothalamic cells after pain and EHF irradiation

2002; 23:315–320
pii: NEL230402A04
PMID:12195233

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C-fos gene expression induced in cells in specific hypothalamic structures by noxious mechanical stimulation and it's modification by exposure of the skin to extremely high frequency irradiation
Natalia S. Novikova 1, Tatiana B. Kazakova 1,
Vernon J. Rogers 2 & Elena A. Korneva 1

1. Department of General Pathology and Pathophysiology, Institute of Experimental Medicine, Russian Academy of Medical Sciences; RUSSIA.
2. Institute for Bio-Information Research, Wayne, Pennsylvania, USA.

Key words:
hypothalamus; c-fos gene expression; noxious mechanical stimulation; EHF irradiation

Submitted: July 10, 2002
Accepted: July 15, 2002

ABSTRACT

OBJECTIVES: The purpose of this study was to determine: 1. The spatial pattern of c-fos gene expression in rat hypothalamic neurons after exposure to NMS and 2. The expression of c-fos gene after combined exposure to NMS and EHF irradiation of the rat skin.

METHODS: The experiments were performed on 28 male adult Sprague-Dawley rats. After rats were subjected to noxious mechanical stimulation (NMS) or its combination with EHF irradiation of the skin, cells in various hypothalamic structures were analyzed to determine theirs effects on c-fos gene expression, an accepted marker of the activation of neurons. C-Fos-like protein was revealed by an indirect immunoperoxidase method.

RESULTS: This study revealed that NMS stimulates c-fos gene expression in the anterior hypothalamic nucleus (AHN), dorsomedial hypothalamic nucleus (DMH), ventromedial hypothalamic nucleus (VMH), and lateral hypothalamic area (LHA) by 157, 101, 199 and 115% respectively compared to control animals. Combined exposure to NMS and EHF irradiation directed at the skin in the region of the St36 acupuncture point projection site (left side) results in a decrease of the number of neurons that are activared in the AHN, DMH, VMH, and LHA by 33.6, 13.2, 31.0 and 32.9% respectively compared to the number of neurons activated by exposure to NMS by itself. EHF exposure of the skin of rats not subjected to NMS differentially effects the number of c-Fos positive cells expressed in hypothalamic structures: a decrease of 39.7% was observed in the number of activated neurons in the central part of LHA (level 28) compared to sham-irradiated animals, while an increase of 80.95% was noted in the number of c-Fos positive cells in the DMH compared to sham-irradiated animals.

CONCLUSIONS: The spatial pattern and degree of activation of c-fos gene expression has been shown in cells of the hypothalamus of rats after exposure to NMS by itself and after NMS combined with EHF irradiation of the skin. The "stress" reaction of cells in specific hypothalamic structures has been shown to be decreased after EHF exposure of the skin.

ABBREVIATIONS
AHN – anterior hypothalamic nucleus
DMH – dorsomedial hypothalamic nucleus
VMH – ventramedial hypothalamic nucleus
LHA – lateral hypothalamic area
SCH – suprachiasmatic hypothalamic nucleus
SO – supraoptic hypothalamic nucleus
PVH – paraventricular nucleus hypothalamus
Arc – arcuate hypothalamic nucleus
NMS – noxious mechanical stimulation
EHF – extremely high frequency
McH – melanin-concentrating hormone
ORX – orexin

Introduction

It is known that expression of the immediate early response gene, c-fos, an accepted marker of the activation of neurons, permits detection of both the brain structures as well as the specific cells within those structures that participate in the realization of reactions to specific stimuli. It has been shown that, after exposure to different stimuli, c-fos gene expression occurs in different brain structures, including those in the hypothalamus [1–3]. There are no studies in the literature in which an analysis of c-Fos positive neurons was performed for the purpose of revealing the possible effects of other stimuli on the reactions of hypothalamic neurons to noxious stimuli. Interest in hypothalamic structures stems from the fact that the hypothalamus is the most important formation participating in the regulation of visceral functions, sensory processes, hormonal balance and in the realization of neuroendocrine system reactions to any stimuli of a stressful nature [4]. The number and spatial pattern of c-Fos positive hypothalamic neurons may differ as a function of the nature of the stimulus [1,3,5], which may make it possible to determine the extent of the effect of different types of external stimuli on hypothalamic functions. EHF radiation has been used in animal studies and in medical practice for the treatment of patients with different diseases, including pain syndromes [6–8]. Combined exposure to two or more stimuli may result in a summation or, on the contrary, a reduction of their effects on c-fos gene expression.
The goals of this study were to determine 1. The spatial pattern of c-fos gene expression in rat hypothalamic neurons after exposure to NMS and 2. The expression of c-fos gene after combined exposure to NMS and EHF irradiation of the rat skin.

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