Functional role for protein kinase Cbeta as a regulator of stress-activated protein kinase activation and monocytic differentiation of myeloid leukemia cells.

Human myeloid leukemia cells respond to 12-O-tetradecanoylphorbol-13-acetate (TPA) and other activators of protein kinase C (PKC) with induction of monocytic differentiation. The present studies demonstrated that treatment of U-937 and HL-60 myeloid leukemia cells with TPA, phorbol-12,13-dibutyrate, or bryostatin 1 was associated with the induction of stress-activated protein kinase (SAPK). In contrast, TPA-resistant TUR and HL-525 cell variants deficient in PKCbeta failed to respond to activators of PKC with the induction of SAPK. A direct role for PKCbeta in TPA-induced SAPK activity in TUR and HL-525 cells that stably express PKCbeta was confirmed. We showed that TPA induced the association of PKCbeta with MEK kinase 1 (MEKK-1), an upstream effector of the SAPK/ERK kinase 1 (SEK1)-->SAPK cascade. The results also demonstrated that PKCbeta phosphorylated and activated MEKK-1 in vitro. The functional role of MEKK-1 in TPA-induced SAPK activity was further supported by the demonstration that the expression of a dominant negative MEKK-1 mutant abrogated this response. These findings indicate that PKCbeta activation is necessary for activation of the MEKK-1-->SEK1-->SAPK cascade in the TPA response of myeloid leukemia cells.

Effect of trilinolein on the activity and gene expression of superoxide dismutase in cultured rat brain astrocytes.

Cerebrovascular disease is one of the major causes of morbidity and mortality in recent. Oxygen free radicals produced during cerebral infarction increases the damage to neurons. Superoxide dismutase (SOD) is the endogenous antioxidant enzyme that can effectively scavenge superoxide radicals. Trilinolein is a lipophilic antioxidant purified from the herb of Panax pseudoginseng. In the cultured rat brain astrocytes (RBA), the activity of SOD (both Cu,Zn-SOD and Mn-SOD subtypes) was markedly increased by incubation with trilinolein at low concentration (0.1 microM) for 2 days. This stimulatory effect of trilinolein was not related to the incubating concentration. However, long-term (7 days) incubation with trilinolein at same concentration decreased the activity. Similar changes were also observed in the gene expression of SOD in RBA; short-term (2 days) incubation of RBA by 0.1 microM trilinolein increased the mRNA level that was lowered in RBA received a long-term incubation with 0.1 microM trilinolein. This result shows that trilinolein is an effective antioxidant to increase the activity of SOD in RBA which would be beneficial to neurons subjected to oxygen free radical damage. However, long-term medication of antioxidant shall be concerned.

Haloperidol, raclopride, and eticlopride induce microcatalepsy during operant performance in rats, but clozapine and SCH 23390 do not.

The purpose of this work was (1) to assess the ability of selected antipsychotic and comparison drugs to induce arrest of movement phenomena during operant responding and (2) to evaluate the capacity of muscarinic anitcholinergics to block such effects. The effects of haloperidol (0.02-0.12 mg/kg, i.p., 45 min), raclopride (0.05-0.80 mg/kg, i.p., 30 min) eticlopride (0.02-0.16 mg/kg, i.p., 45 min), clozapine (1.0-8.0 mg/kg, i.p., 60 min) and SCH 23390 (0.01-0.16 mg/kg, i.p., 30 min) were administered to rats for 4 weeks in a between-groups dosing design. Operant responses in 15 min and the maximum duration of the rat's muzzle entry into the reinforcement dipper well (the measure of arrest of movement that reflected microcatalepsy) were the quantitative measures of behavior. The D2 antagonists dose-relatedly decreased operant responding and increased maximum muzzle duration, effects that were significantly reversed by the anticholinergic scopolamine (0.1 mg/kg) or atropine (6.0 mg/kg). Although the atypical antipsychotic drug clozapine and the selective D1 antagonist SCH 23390 both significantly reduced operant responding, these drugs did not produce microcatalepsy. The results suggested that microcatalepsy expressed in the context of ongoing operant behavior may model low-dose extrapyramidal side effects.

Microcatalepsy and disruption of forelimb usage during operant behavior: differences between dopamine D1 (SCH-23390) and D2 (raclopride) antagonists.

In an experiment designed to distinguish between the behavioral consequences of treatment with SCH-23390, a D1 dopamine receptor blocker, and raclopride, a D2 antagonist, rats were trained to perform a water-reinforced forelimb operant response. Response rate and the duration of each forelimb contact with the operandum were recorded. In addition, the durations of the rat's visits to the reward well were detected by a photobeam which was blocked by the rat's muzzle as it remained at the reward well. In a between-groups dosing design, separate groups of rats (11-13 rats/group) received SCH-23390 (0, 0.01, 0.02, 0.04, 0.08, 0.12 mg/kg, IP, 30 min) or raclopride (0. 0.05, 0.1, 0.2, 0.4, 0.8 mg/kg, IP, 30 min) for 21 consecutive days. Quantitative analyses indicated that for comparable amounts of operant rate reduction, raclopride had a significantly greater tendency than SCH-23390 to increase the duration of operant responses and to increase the maximum muzzle entry duration (i.e., to induce microcatalepsy). The results support the idea that at relatively low doses D2 antagonism is more likely than D1 antagonism to produce effects identified preclinically with extrapyramidal side effects.

In a drug discrimination procedure isolation-reared rats generalize to lower doses of cocaine and amphetamine than rats reared in an enriched environment.

Rats with different behavioral histories, defined by rearing and housing in either an enriched condition (EC) or an isolation condition (IC), were trained in a two-lever operant procedure to discriminate 5.0 mg/kg cocaine from saline. In cocaine dose-generalization tests, the IC rats exhibited an ED50 (1.01 mg/kg) significantly lower than the EC rats (ED50: 1.55 mg/kg). The cocaine-appropriate responding was emitted when the rats were treated with d-amphetamine, and for the d-amphetamine test doses the ED50 (0.19 mg/kg) was again significantly lower for the IC rats compared to the ECs (ED50: 0.33 mg/kg). These data suggest that IC rats are more sensitive to the stimulus properties of indirect dopaminergic agonists than EC rats and highlight the importance of environmental variables in governing an organism's response to the stimulus properties of abused drugs.