Desensitization of the dopaminergic system in bovine retina following incubation with high potassium

The effect of potassium depolarization on dopamine D1 receptor activity in bovine retina was investigated. Preincubation of bovine retinas in buffer containing high KC1 (56 mM) as compared to a low KC1 control buffer resulted in a significant decrease in dopamine-stimulated adenylate cyclase with no change in basal or GTP-stimulated adenylate cyclase activity. The apparent Vmax for dopamine was decreased from 102 +/- 15 pmol/min/mg protein in retinas preincubated in high KC1 to 71 +/- 11 pmol/min/mg protein in control retinas (n = 5). The apparent Ka for dopamine stimulation of the enzyme did not change. The potassium-induced desentization could be blocked by preincubation with the dopamine antagonist cis-flupenthixol suggesting that the desentization was caused by the release of dopamine. The rapid desentization was not accompanied by a change in D1 receptor density as assessed by binding of [3H]SCH23390 nor in agonist binding as assessed by competition of the selective D1 agonist, SKF38393, for [3H]SCH23390 binding. The potassium-induced desentization was mimicked by preincubation of retinas in control medium containing isobutylmethylxanthine or dibutyryl cyclic AMP. Incubation of retinas in 56 mM KC1 also fed to a decrease in activation of adenylate cyclase by vasoactive intestinal polypeptide. These results strongly suggest that potassium depolarization leads to a very rapid heterologous desentization of adenylate cyclase in bovine retinas.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28516/1/0000313.pd

Chronic amphetamine treatment increases striatal calmodulin in rats

A radioimmunoassay was developed to measure calmodulin in striatum from rats treated with one dose or repeated injections of amphetamine. Chronic, but not acute, amphetamine treatment resulted in a significant increase in total calmodulin levels in striatal homogenates. This effect may be linked to the behavioral sensitization which develops after chronic amphetamine treatments.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26016/1/0000083.pd

Education & Entrepreneurship: Implications For Contemporary Microfinance

In world regions receiving direct foreign aid, beneficiaries of aid often lack the education required to remove themselves from poverty. Micro-lending refers to the initiation of small loans to the neediest of borrowers who are unable to secure traditional financing from financial intermediaries. In order for micro-lending to thrive as a viable alternative to traditional government aid, borrowers must not only receive a loan, but also an education in business to fully equip borrowers with necessary resources to establish and operate a prosperous business entity. The authors will argue for the provision of increased educational resources and discuss the disparities between the US model of education and that of third-world nations. Furthermore, the authors will prescribe steps to develop educational materials and train micro-credit borrowers to better guarantee the viability of microfinance

Endogenous Bax Translocation in SH-SY5Y Human Neuroblastoma Cells and Cerebellar Granule Neurons Undergoing Apoptosis

Changes at the mitochondria are an early, required step in apoptosis in various cell types. We used western blot analysis to demonstrate that the proapoptotic protein Bax translocated from the cytosolic to the mitochondrial fraction in SH-SY5Y human neuroblastoma cells undergoing staurosporine- or EGTA-mediated apoptosis. Levels of mitochondrial Bax increased 15 min after staurosporine treatment. In EGTA-treated cells, increased levels of mitochondrial Bax were seen at 4 h, consistent with a slower onset of apoptosis in EGTA versus staurosporine treatments. We also demonstrate the concomitant translocation of cytochrome c from the mitochondrial to the cytosolic fractions. We correlated these translocations with changes in caspase-3-like activity. An increase in caspase-3-like activity was evident 2 h after staurosporine treatment. Inhibition of the mitochondrial permeability transition had no effect on Bax translocation or caspase-3-like activity in staurosporine-treated SH-SY5Y cells. In primary cultures of cerebellar granule neurons undergoing low K + -mediated apoptosis, Bax translocation to the mitochondrial fraction was evident at 3 h. Cytochrome c release into the cytosol was not significant until 8 h after treatment. These data support a model of apoptosis in which Bax acts directly at the mitochondria to allow the release of cytochrome c.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66150/1/j.1471-4159.1999.0721899.x.pd

Protein kinase C inhibitors block amphetaminemediated dopamine release in rat striatal slices

ABSTRACT The stimulant drug amphetamine is postulated to enhance dopamine release through the plasmalemmal dopamine transporter by an exchange diffusion with synaptosomal dopamine. Because protein kinase C has been shown to have an effect on dopamine transporter activity, we examined the effect of protein kinase C inhibitors on endogenous dopamine release stimulated by amphetamine in perfused rat striatal slices. At concentrations of 1 M, the selective protein kinase C inhibitors chelerythrine, Ro31-8220 and calphostin C nearly completely inhibited endogenous dopamine release elicited by 1 M amphetamine. The inactive analog bisindoylmaleimide V had no effect. Extracellular Ca ϩϩ was not required for the effect of the inhibitors. The importance of vesicular dopamine release was examined by determining inhibitor activity in reserpine-treated rats. Dopamine release elicited by 1 M amphetamine was not significantly altered in reserpine-treated rats compared with control animals. Ro31-8220 at 1 M completely blocked amphetamine-induced dopamine release in reserpine-treated rats. Activation of protein kinase C with 250 nM of the phorbol ester 12-O-tetradecanoylphorbol 13-acetate increased dopamine release, and the release was not additive with 1 M amphetamine. Both chelerythrine and Ro31-8220 at 1 M increased [ 3 H]dopamine uptake by 17% and 30%, respectively, whereas a brief exposure to 12-O-tetradecanoylphorbol 13-acetate slightly inhibited [ 3 H]dopamine uptake. Our results suggest that amphetamine-mediated dopamine release through the plasmalemmal transporter is highly dependent on protein kinase C activity

The effect of environment on the changes in calmodulin in rat brain produced by repeated amphetamine treatment

Rats were given repeated infusions of i.v. amphetamine in association with placement in a novel test environment, a protocol that produces behavioral sensitization, or in the home cage, a protocol that fails to induce sensitization. In several brain areas amphetamine altered calmodulin content, but only in the group treated in a novel environment, suggesting that amphetamine-induced alterations in calmodulin may occur only when drug treatments induce behavioral sensitization