Day-Night Variations in the Concentration of Neurotransmitters in the Rat Lumbar Spinal Cord.

Luis Antonio Jiménez-Zamudio,Marina Rodríguez-Sánchez,Beatriz Shantal Jiménez-Zárate,Benjamín Florán-Garduño,Ismael Jiménez-Estrada,Celia Piña-Leyva

doi:10.5334/jcr.215

Abstract

The purpose of this study was to analyze the light-dark variations in the concentrations of several neurotransmitters in the lumbar spinal cord of rats. Six groups of male Wistar rats were exposed to a 12 h light-12 h dark cycle for 70 days. At different time points of the experimental day (8, 12, 16, 20, 24 and 4 h), one of the groups of rats was randomly selected to be sacrificed, and the spinal cords were removed. The gamma-aminobutyric acid (GABA), glutamate (GLU), dopamine, serotonin, epinephrine (E), and norepinephrine (NE) levels in each extracted spinal cord were measured with high-pressure liquid chromatography (HPLC)-EQ and HPLC-fluorescence systems. Our results indicate that the spinal concentrations of GABA and GLU showed sinusoidal variation in a 24 h cycle, with the highest peak in the dark period (~20 h). Dopamine and serotonin also fluctuated in concentration but peaked in the light period (between 8 and 12 h), while E and NE concentrations showed no significant fluctuations. The possible relationship between neurotransmitter spinal concentration and sensitivity to pain and locomotor activity is discussed. It was concluded that most of the neurotransmitter levels in the lumbar spinal cord showed circadian fluctuations coupled to a light-dark cycle.

Highlights

Circadian rhythmicity is inherent to all organisms and is one of the main characteristics of biological systems
Significant differences in GLU levels were determined between 08:00 h and 16:00 h and between 08:00 h and 20:00 h. These results indicate that the concentration of gamma-aminobutyric acid (GABA) and GLU in the spinal cord varied during the light-dark cycle
We found that the level of GABA, GLU, DA, and SER in the lumbar spinal cord appears to fluctuate in a sinusoidal oscillation during a 12:12 light-dark cycle, while the levels of E and NE do not seem to fluctuate in a circadian day-night cycle

Summary

Introduction

Circadian rhythmicity is inherent to all organisms and is one of the main characteristics of biological systems. It is present in most biochemical and molecular processes, from the transcription of genes in cellular nuclei to the control of the cell cycle [1], and it participates considerably in physiological and behavioral mechanisms. The rhythmic expression of the same clock genes that regulate the oscillator in the SCN is widely distributed among other areas of the brain and the spinal cord [4] and many peripheral cells and tissues, including the liver, intestine, heart, and retina [5,6]

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