Repeated spinal cord stimulation decreases the extracellular level of γ-aminobutyric acid in the periaqueductal gray matter of freely moving rats

• Published in: Brain research Vol. 699; no. 2; pp. 231 - 241
• Main Authors: Stiller, Carl-Olav, Linderoth, Bengt, T. O'Connor, William, Franck, Johan, Falkenberg, Torkel, Ungerstedt, Urban, Brodin, Ernst
• Format: Journal Article
• Language: English
• Published: London Elsevier B.V 20.11.1995; Amsterdam Elsevier; New York, NY
• Subjects: 5-Hydroxytryptamine; Animals; Biological and medical sciences; Calcium - physiology; Central nervous system; Central neurotransmission. Neuromudulation. Pathways and receptors; Electric Stimulation; Fundamental and applied biological sciences. Psychology; gamma-Aminobutyric Acid - metabolism; Glutamate; Glutamic Acid - metabolism; Male; Medicin och hälsovetenskap; Microdialysis; Pain Measurement; Periaqueductal Gray - metabolism; Periaqueductal gray matter; Rat; Rats; Rats, Sprague-Dawley; Serotonin - metabolism; Spinal Cord - physiology; Spinal cord stimulation; Substance P; Vertebrates: nervous system and sense organs; γ-Amino-butyric-acid; 5-Hydroxytryptamine; γ-Amino-butyric-acid; Microdialysis; Rat; Periaqueductal gray matter; Substance P; Spinal cord stimulation; Glutamate; Spinal cord; Electrical stimulus; Rodentia; Central nervous system; Vertebrata; Mammalia; Pain; Treatment; Neurotransmitter; GABA; Brain (vertebrata)
• ISSN: 0006-8993; 1872-6240
• DOI: 10.1016/0006-8993(95)00911-9

Most of the previous experimental studies on the antinociceptive effects of electrical spinal cord stimulation (SCS) have focused on short-lasting effects mainly depending on spinal mechanisms. However, patients treated with SCS for chronic pain often report pain relief exceeding the period of stimulation for several hours. The long lasting effect of SCS might not only involve spinal, but also supraspinal mechanisms. A supraspinal region of major importance for the coordination of descending pain inhibition is the periaqueductal grey matter (PAG). The aim of the present microdialysis study, performed in awake freely moving rats, was to investigate if repeated SCS (two 30 min periods separated by a 90 min resting period) alters the extracellular neurotransmitter concentrations in the ventrolateral PAG. In a first series of experiments significantly decreased (−30%; P < 0.05; n = 7) γ-aminobutyric acid (GABA) levels were detected immediately after the second SCS session. Neither the concentration of serotonin nor that of substance P-like immunoreactivity (SP-LI) was affected by SCS. The decrease of GABA after two SCS sessions was confirmed in a second series of experiments (−30%; P < 0.05; n = 7). No spontaneous decline of GABA was observed in sham-stimulated animals ( n = 6). The glutamate concentration was also determined in this latter series of experiments and a significant decrease (−23%; P < 0.05; n = 5) was observed after the second SCS session. As GABA-neurons in the PAG exert a tonic depressive effect on the activity in descending pain inhibitory pathways, a decreased extracellular GABA level in this region, as detected following repeated SCS, might indicate an increased pain inhibition.