Distribution of Adenosine Deaminase Activity in Rat Brain and Spinal Cord
Total Page：16
File Type：pdf, Size：1020Kb
The Journal of Neuroscience September 1996, 6(9): 2707-2714 Distribution of Adenosine Deaminase Activity in Rat Brain and Spinal Cord Jonathan D. Geiger* and James I. Nagy-f Departments of *Pharmacology and tPhysiology, University of Manitoba Faculty of Medicine, Winnipeg, Manitoba R3E OW3, Canada The activity of adenosine deaminase (ADA) was measured in matic activity, and its physiological function remains unclear 62 discrete regions of the CNS, and in some autonomic and (Andy and Kornfeld, 1982). Several lines of investigations on sensory ganglia, peripheral nerves, and peripheral tissues of the the cellular metabolism of purines in peripheral tissues have rat using an automated high-pressure liquid chromatography generated considerable interest in ADA. The recognition that (HPLC) method. The formation of inosine and hypoxanthine elevated levels of adenosine and deoxyadenosine are cytotoxic as a measure of ADA activity in homogenates of brain was to certain cell types suggests an important contribution by ADA optimal at pH 7.0, linear for up to 60 min at 37°C using 500 PM to the maintenance of appropriate cellular adenine nucleoside adenosine as substrate, and linear with protein concentrations and nucleotide concentrations (Fox and Kelley, 1978). The dis- ranging from 0.05 to 0.8 mg. The K,,, and V,, values for ADA covery that some patients with severe combined immunodefi- activity in homogenates of whole brain were 47 FM and 107 ciency disease (SCID) are genetically deficient in ADA activity nmol/mg protein/30 min, respectively. Among the CNS regions points to a crucial role of this enzyme in cells of the immune examined, the highest activity was found in posterior hypotha- system (Daddona et al, 1983; Giblett et al., 1972). The use of lamic magnocellular nuclei and the lowest in hippocampus. In adenine nucleoside analogs as chemotherapeutic agents has led general, spinal cord contained relatively low levels of ADA ac- to the development of potent ADA inhibitors, which, given in tivity, with that in dorsal cord approximately 40% higher than conjunction with these agents, prevent their deamination and ventral cord. In the periphery, parasympathetic ganglia con- prolong their effectiveness (Agarwal et al., 1975). The avail- tained higher levels of ADA than sensory ganglia and brain. ability of such inhibitors together with the consequences of ADA Most peripheral tissues-including adrenal gland, lung, liver, deficiency in patients suffering from SCID prompted clinical and anterior and posterior pituitary-exhibited activity com- trials of these inhibitors as treatments for certain forms of leu- parable to levels in the posterior hypothalamus. ADA activity kemia (Major et al., 198 1). in thymus was about 10 times higher than any other tissue ex- Our interest in the function of ADA in neural tissue was amined. kindled by the recent flood of reports supporting the notion that The uneven distribution of ADA activity in the rat CNS cor- adenosine serves in a neuromodulatory capacity in both the responds well with the immunohistochemical localization of this PNS and CNS (Phillis and Wu, 198 1; Stone, 198 1). Indirect enzyme in discrete neural systems of this species. Structures evidence suggests that ADA may have a role analagous to other that contain high ADA activity exhibit intense ADA immuno- catabolic enzymes that participate in the regulation of both syn- staining of neuronal perikarya and/or fibers. The 13-fold dif- aptoplasmic levels and the extracellular actions of transmitter ference between brain regions containing the highest and lowest substances. Thus, the depressive electrophysiological actions of ADA activity suggests that, in addition to its involvement in adenosine when applied to central neurons are potentiated by intermediary metabolism, this enzyme may have an important the concomitant application of potent ADA inhibitors such as role in regulating the putative neuromodulatory actions of aden- 2’-deoxycoformycin (DCF) or erythro-9-(2-hydroxy-3-nonyl) osine in the CNS. adenine and mimicked by the application of these inhibitors alone (Phillis and Wu, 1981; Phillis et al., 1979). Moreover, Adenosine deaminase (ADA, Adenosine aminohydrolase, EC ADA inhibitors administered to animals produce behavioral 3.5.4.4) is responsible for the deamination of adenosine to the effects similar to those of adenosine agonists and cause phys- physiologically less active compound inosine. Various forms of iological responses that are thought to be mediated through the this cytosolic enzyme have been identified with molecular weights action of adenosine on its receptors (Phillis et al., 1984, 1985; of 36,000, 114,000, and 298,000 (Van der Weyden and Kelley, Radulovacki et al., 1983). Anatomical evidence for a relation- 1976). By complexing with a membrane-bound binding protein, ship between ADA and the neuromodulatory actions of aden- low-molecular-weight ADA is convertible to the large form of osine is derived from recent immunohistochemical demonstra- the enzyme. The binding protein does not itself express enzy- tions of the uneven distribution of ADA-immunoreactive neurons in discrete neural systems in the rat CNS (Nagy and Daddona, 1985; Nagy et al., 1984a, b, 1985). Among these were Received Nov. 18, 1985; revised Feb. 18, 1986; accepted Mar. 10, 1986. ADA-containing preganglionic parasympathetic neurons (Senba We thank Mr. Mark Whittaker and Ms. Kosala Sivananthan for their excellent et al., 1985a) which in the cat have been shown to have an technical assistance. and Ms. Barb Hunt and Ms. Chervl Baraniuk for tvoine the manuscript. This work was supported by grants from the Medical Research Coun- adenosine neurotransmitter component (Akasu et al., 1984). cil of Canada (MRCC), Manitoba Health Research Council (MHRC), and the Moreover, structures immunoreactive for ADA in rat brain were Health Sciences Centre Research Foundation. JIN and JDG are Scholars of the found to correspond closely to those exhibiting the greatest den- MRCC. sity of binding sites for 3H-nitrobenzylthioinosine CH-NBI) (Nagy Correspondence should be addressed to Dr. Jonathan D. Geiger, Department of Pharmacology, University of Manitoba, Faculty of Medicine, 770 Bannatyne et al., 1984a, b), a putative ligand for adenosine uptake sites. Avenue, Winnipeg, Manitoba R3E OW3, Canada. The above findings, together with the now established concept Copytight 0 1986 Society for Neuroscience 0270-6474/86/092707-08$02.00/O that adenosine acts as a neuromodulator and/or neurotrans- 2707 2708 Geiger and Nagy Vol. 6, No. 9, Sep. 1986 mitter in CNS and some peripheral systems, warrant investi- M, pH 5.0) and 12% methanol was filtered through a 0.45 pm filter, gations aimed at elucidating the biochemical pathways govem- degassed under reduced pressure, and pumped at 1.5 ml/min through ing the metabolism of adenosine in neural tissue. As a first step a reverse-phase C,, analytical column (Spheri-5, OD-MP, 10 cm, Brownlee Lab., Santa Clara, CA) fitted with a 2.5 cm guard column of towards this goal we analyzed the characteristics and regional the same material. This solvent was not recycled. Unless otherwise distribution of ADA in the rat CNS. indicated these conditions were used throughout the present investi- gations. Injection volumes of 25 ~1 were chromatographed every 5 min. Materials and Methods Chromatographic peaks were identified according to retention times of Tissue dissections standards containing inosine, hypoxanthine, and adenosine. The iden- Male Sprague-Dawley rats weighing approximately 300 g were sacrificed tity of the peaks was verified by incubating samples of adenosine with by decapitation. The brain, spinal cord, and peripheral tissues were adenosine deaminase (Type VII, Sigma) or inosine with purine nucleo- removed, placed on an ice-cold metal tray, and dissected freehand or side phosphorylase (Sigma). Standard concentrations of hypoxanthine, from thick frozen sections as previously described (Geiger and Nagy, inosine, and adenosine were used to calibrate the integrator at the be- 1984, 1985) unless otherwise indicated. ginning of every set of assays. Calibration was rechecked midway through Cortical areas were subdivided according to the atlas of Paxinos and each assay and at the end. ADA activity was determined as nmol of Watson (1982), and all other areas were dissected according to the atlas product (inosine plus hypoxanthine) formedmg protein/30 min rather of Koning and Klippel(1963). No attempt was made to dissect specific than as adenosine utilized since product formation was found to be a subnuclei of the thalamus other than medial and lateral geniculate nu- more sensitive and reproducible measure of enzyme activity. Depending clei. The rest of the thalamus was divided into anterior and posterior on the amount of tissue used, however, adenosine utilization was found regions at a rostrocaudal level demarcated by the anterior border of the to equal inosine plus hypoxanthine formation using the assay conditions habenula, and each of these regions was subdivided into medial and routinely employed. Assay blanks were calculated from samples in which lateral areas. The anterior thalamic regions contained nucleus medialis, endogenous levels of adenosine, inosine, and hypoxanthine were mea- parstenialis, anterior medialis, rhomboideus, and reuniens medially, sured by adding tissue homogenates to reaction vessels already con- and the remaining nuclei laterally. The posterior thalamic regions con- taining 20% TCA. For each brain region and peripheral