Mapping of the fluoride resistant acid phosphatase (FRAP) activity in cervico-thoracic-lumbar spinal dorsal horn in rats

Abstract

The fluoride resistant acid phosphatase (FRAP) is considered a biomarker enzyme of presence and function in nociceptive fibers. Its well described spinal dorsal horn (DH) superficial lamina location contrasts to its less known cervico-lumbar DH distribution. Thus, 15 male Sprague Dawley rats (300–400 g) were anaesthetized (thiopental 60 mg kg−1 i.p.) and laminectomized (C 1-L 5) to extract and fix (formaline 4% + NaF 1%) spinal cords. Cervical, thoracic and lumbar segments were coronally cut (1 mm slices) and micropunched (1 mmO) at the dorsal horn (both left and right). Samples were diluted in NaF 1% in saline (1000 μL: fragment) and homogenized. Protein concentration of the homogenate was determined by Bradford method to correct variation on tissue sampling and used to compensate enzymatic dilution. FRAP activity was determined by the Gomorri method and expressed as U gr prot−1 L−1. No differences were found between left and right DH FRAP activities (Mann-Whitney U Test, P > 0.05) in any metamera. DH segment values were: cervical 2.53 (2.67–2.40 U gr prot−1 L−1; mean ± 95% CI), thoracic 3.59 (3.96–3.21) and lumbar 2.42 (2.75–2.09). Thoracic FRAP activity was statistically higher (+45.3%) than those from cervical and lumbar DH segments (ANOVA; Ω2 = 0.29; F = 17.78; P = 0.000001; Levene test P = 0.000006). No significant correlation was found among cervicotoraco-lumbar FRAP activity. The increased FRAP activity for thoracic DH could be explained by the thoracic overlapped primary afferents and collateral fibers with cervical or lumbar input added to the basal thoracic FRAP expression.