Glucostatic regulation of (+)-[3H]amphetamine binding in the hypothalamus: correlation with Na+,K+-ATPase activity.

Abstract

Preincubation of rat hypothalamic slices in glucose-free Krebs-Ringer buffer (370C) resulted in a timedependent decrease in specific (+)-[3H]amphetamine binding in the crude synaptosomal fraction prepared from these slices.The addition of D-glucose resulted in a dose-and timedependent stimulation of (+) Further, when food-deprived rats are allowed access to either rat chow or a 10% glucose solution, there is a rapid reversal of the food deprivation-induced decrease in hypothalamic (+)-[3H]amphetamine binding, and this effect is highly correlated with changes in blood glucose concentration. Glucose, the principle energy source of brain, has been postulated to directly regulate "appetite" or food intake through a central mechanism (the so-called "glucostatic hypothesis of feeding") (4, 5). In the present study we have investigated the effects of glucose on hypothalamic (+)-[3H]amphetamine binding in vitro and in vivo and now report that glucose rapidly and stereoselectively increases the number of (+)-[3H]amphetamine binding sites in the hypothalamus. This stimulation is highly correlated with increases in Na+,K+-ATPase activity and the number of specific "high-affinity" [3H]ouabain binding sites, suggesting that glucose and amphetamine may interact through a coupled system in the hypothalamus to regulate Na+,K+-ATPase activity, and that this site may also be involved in the "glucostatic" regulation of appetite.- MATERIALS AND METHODSTissue Preparation. Adult male Osborne-Mendel rats (120-200 g) housed under diurnal lighting conditions (12:12) with free access to food and water were killed by decapitation, and their brains were quickly removed and dissected on ice. Pooled hypothalami were chopped into 350 x 350 Atm slices using a McIlwain tissue chopper (Brinkmann). The slices were washed twice in 10 ml of Krebs-Ringer bicarbonate buffer (pH 7.4) and incubated at 37°C in the same volume in a gently shaking water bath under a constant stream of 95% 02/5% CO2. D-Glucose and (or) other compounds were added, and after various times the tubes were transferred to an ice bath, the buffer was aspirated, and the slices were washed twice in fresh Krebs-Ringer bicarbonate buffer. Hypothalamic slices were then gently homogenized in 10 volumes (wt/vol) of ice-cold 0.32 M sucrose by using a Teflon/glass homogenizer, and a crude synaptosomal pellet was prepared as described (3).Radioreceptor and Enzyme Assays. The binding of (+)-[3H]amphetamine sulfate was carried out as described by using both filtration and centrifugation assays (3). Briefly, 100-200 ug of membrane protein (crude P2 fraction) and 50 ,ul of (+)-[3H]amphetamine (200-300 nM unless otherwise specified; specific activity, 20-30 Ci/mmol; New England Nuclear; 1 Ci = 37 GBq) were added in a total incubation volume of 300 ,ul. After a 30-min incubation at 0-4°C, the tubes were rapidly filtered over Whatman GF/B glass fiber filters under tTo whom reprint requests should be addressed at: Section on Molecular Pharmacology, Clinical Neuroscience Branch, NIMH, Bldg....

Inhibitors of Na+/H+ and Na+/Ca2+ exchange potentiate methamphetamine‐induced dopamine neurotoxicity: possible role of ionic dysregulation in methamphetamine neurotoxicity

“…(1994); Sonders et al . (1997); B Angel et al (1985); Jeffrey and Gibbs (1976); Rangaraj and Kalant (1978); C Manning et al . (1974); Stephans et al .…”

“…For instance, AMIL can inhibit Na 1 and Ca 21 channels, interfere with DA release, inhibit monoamine oxidase (MAO), act as a weak base, inhibit Na 1 /K 1 ATPase, interfere with bprotein synthesis, deplete ATP and in¯uence apoptosis (see Kleyman and Cragoe 1988). Some of these effects would be expected to attenuate or have no effect on substituted amphetamine neurotoxicity [inhibition of DA release, Kaczorowski et al (1984); Tolkovsky and Richards (1987); Koch and Barish (1994); Orlowski and Grinstein (1997); Yamamoto (1994, 1995); Ferreira et al Rangaraj and Kalant (1978); Angel et al (1985); Komissarov et al (1985); Shulman and Fox (1996); Nishi et al (1999).…”

Effects of nimodipine on the discriminative stimulus properties ofd-amphetamine in rats

“…Under physiological conditions, stimulus-secretion coupling in monoaminergic terminals involves a redistribution of transmembrane cations, particularly calcium (Zucker and Lando 1986). Therefore, it is possible that amphetamines, for example, facilitate monoamine release by altering cation redistribution, as suggested by the recent finding that AMP activates a K-dependent ATPase (Angel et al 1985). In addition, several antidopaminergic compounds that inhibit AMP effects have been found also to function as calcium channel blockers (Gould et al 1983;Flaim et al 1985;Wolfe and Brostrom 1986).…”

Evaluation of Na+, K+-ATPase activity in the brain of young rats after acute administration of fenproporex

“…31 Indeed, both AMPH and fenfluramine selectively stimulate Na + , K + -ATPase activity in the hypothalamus. 32 On the other hand, administration of fenproporex decreased Na + , K + -ATPase activity in the striatum. Wistar rats that receive an acute dose of fencamfamine (FCF) --a CNS stimulant, which has the same pharmacological profile as amphetamine and cocaine --exhibit a strong reduction in Na + , K + -ATPase activity in the striatum and nucleus accumbens.…”