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Distribution of low Km GTPase activity in mouse CNS: effect of chronic morphine
1Department of Neuropharmacology, Cajal Institute, C.S.I.C., Madrid, Spain.
Abstract:
The low Km GTPase displayed an apparent Km value of 0.2-0.4 microM in P2 fractions from whole mouse brain. The activity of this enzyme ranged from 102 (pmols of GTP hydrolysed per micrograms of protein per min) in the striatum to 39 in the pons-medulla oblongata. Intermediate values were found in other structures, 74-62 in thalamus, hypothalamus, periaqueductal gray matter (PAG), rest of mesencephalon, cortex and spinal cord. The Km also varied throughout the mouse CNS: the spinal cord, striatum and PAG exhibited Km values (0.308-0.271 microM) higher than cortex, thalamus, pons-medulla, hypothalamus and remaining mesencephalon (0.239-0.193 microM). Chronic morphine (3 days) decreased the low Km GTPase activity of PAG (42), whereas it increased the one of thalamus (99). After chronic exposure to the opioid the Km values of the enzyme in striatum (0.193), PAG (0.192) and spinal cord (0.201) diminished, and the ones of hypothalamus (0.357) and rest of mesencephalon (0.287) augmented. The herein reported diversity of low GTPase activity might be due to the presence of different ratios of G alpha types/subtypes in the neural structures studied. As a result of chronic morphine the ratio and/or the functionality of G proteins would be altered in particular areas of mouse CNS.
Insights
Low Km GTPase activity varies across the mouse central nervous system (CNS). Chronic morphine alters this enzyme's activity and kinetics in specific brain regions, suggesting changes in G protein signaling.
Area of Science:
- Neuroscience
- Biochemistry
- Pharmacology
Background:
- Low Km GTPase enzymes play crucial roles in cellular signaling pathways within the central nervous system (CNS).
- Understanding the regional distribution and regulation of these enzymes is vital for comprehending brain function and drug effects.
Purpose of the Study:
- To investigate the regional variations in low Km GTPase activity and kinetics across different mouse brain structures.
- To examine the impact of chronic morphine exposure on low Km GTPase activity and kinetics in specific CNS regions.
Main Methods:
- Enzyme activity assays were performed on P2 fractions from various mouse brain regions to determine GTPase activity and Km values.
- Animals were subjected to chronic morphine administration for 3 days to assess drug-induced alterations.
Main Results:
- Significant regional differences in low Km GTPase activity and Km values were observed across the mouse CNS.
- Chronic morphine treatment modulated low Km GTPase activity in the periaqueductal gray matter (PAG) and thalamus.
- Morphine exposure altered the enzyme's kinetics (Km values) in regions including the striatum, PAG, spinal cord, hypothalamus, and mesencephalon.
Conclusions:
- The observed heterogeneity in low Km GTPase activity likely reflects variations in G alpha protein subtypes across neural structures.
- Chronic morphine administration alters G protein signaling pathways in a region-specific manner within the mouse CNS.