Pancreatic mitochondrial complex I exhibits aberrant hyperactivity in diabetes.

It is well established that NADH/NAD+ redox balance is heavily perturbed in diabetes, and the NADH/NAD+ redox imbalance is a major source of oxidative stress in diabetic tissues. In mitochondria, complex I is the only site for NADH oxidation and NAD+ regeneration and is also a major site for production of mitochondrial reactive oxygen species (ROS). Yet how complex I responds to the NADH/NAD+ redox imbalance and any potential consequences of such response in diabetic pancreas have not been investigated. We report here that pancreatic mitochondrial complex I showed aberrant hyperactivity in either type 1 or type 2 diabetes. Further studies focusing on streptozotocin (STZ)-induced diabetes indicate that complex I hyperactivity could be attenuated by metformin. Moreover, complex I hyperactivity was accompanied by increased activities of complexes II to IV, but not complex V, suggesting that overflow of NADH via complex I in diabetes could be diverted to ROS production. Indeed in diabetic pancreas, ROS production and oxidative stress increased and mitochondrial ATP production decreased, which can be attributed to impaired pancreatic mitochondrial membrane potential that is responsible for increased cell death. Additionally, cellular defense systems such as glucose 6-phosphate dehydrogenase, sirtuin 3, and NQO1 were found to be compromised in diabetic pancreas. Our findings point to the direction that complex I aberrant hyperactivity in pancreas could be a major source of oxidative stress and ß cell failure in diabetes. Therefore, inhibiting pancreatic complex I hyperactivity and attenuating its ROS production by various means in diabetes might serve as a promising approach for anti-diabetic therapies.

Retrograde conditioning of place preference and motor activity with cocaine in mice.

RATIONALE: In order to improve understanding of the nature of drug-associated memory, the current studies addressed whether conditioned place preference (CPP) could develop under conditions in which there was a delay between presentation of context and drug exposure (i.e., retrograde or trace conditioning). OBJECTIVES: The objective was to assess development of CPP when cocaine or methamphetamine was injected simultaneously with exposure to a salient context (S+), or after delays differing in length. METHODS: Dose response curves for conventional CPP were established using separate groups of Swiss-Webster mice injected with cocaine or methamphetamine just prior to S+ exposure. To assess the development of retrograde CPP, other groups received trace conditioning, where cocaine (15 mg/kg) or methamphetamine (0.5 mg/kg) was injected after a delay of 15, 60, 120, 180, 240, or 480 min following the end of the S+ session. RESULTS: Mice receiving conventional CPP with cocaine or methamphetamine during S+ showed significant place preference. None of the groups receiving delayed methamphetamine showed significant CPP; however, CPP was evident in mice receiving cocaine after delays of up to 4 h following S+. In a separate study, delayed methamphetamine also did not result in significant place preference when presented in doses of 0.25 or 1 mg/kg. CONCLUSIONS: These results suggest that psychostimulant drug taking may be broadly generalized to context through retrograde association with events in recent memory, a factor that may contribute to drug-seeking and relapse following abstinence.

Neuroprotective effects of transcription factor Brn3b in an ocular hypertension rat model of glaucoma.

PURPOSE: Glaucoma is an optic neuropathy commonly associated with elevated intraocular pressure (IOP), leading to optic nerve head (ONH) cupping, axon loss, and apoptosis of retinal ganglion cells (RGCs), which could ultimately result in blindness. Brn3b is a class-4 POU domain transcription factor that plays a key role in RGC development, axon outgrowth, and pathfinding. Previous studies suggest that a decrease in Brn3b levels occurs in animal models of glaucoma. The goal of this study was to determine if adeno-associated virus (AAV)-directed overexpression of the Brn3b protein could have neuroprotective effects following elevated IOP-mediated neurodegeneration. METHODS: Intraocular pressure was elevated in one eye of Brown Norway rats (Rattus norvegicus), following which the IOP-elevated eyes were intravitreally injected with AAV constructs encoding either the GFP (rAAV-CMV-GFP and rAAV-hsyn-GFP) or Brn3b (rAAV-CMV-Brn3b and rAAV-hsyn-Brn3b). Retina sections through the ONH were stained for synaptic plasticity markers and neuroprotection was assessed by RGC counts and visual acuity tests. RESULTS: Adeno-associated virus-mediated expression of the Brn3b protein in IOP-elevated rat eyes promoted an upregulation of growth associated protein-43 (GAP-43), actin binding LIM protein (abLIM) and acetylated α-tubulin (ac-Tuba) both posterior to the ONH and in RGCs. The RGC survival as well as axon integrity score were significantly improved in IOP-elevated rAAV-hsyn-Brn3b-injected rats compared with those of the IOP-elevated rAAV-hsyn-GFP- injected rats. Additionally, intravitreal rAAV-hsyn-Brn3b administration significantly restored the visual optomotor response in IOP-elevated rat eyes. CONCLUSIONS: Adeno-associated virus-mediated Brn3b protein expression may be a suitable approach for promoting neuroprotection in animal models of glaucoma.

Discriminative and locomotor effects of five synthetic cathinones in rats and mice.

RATIONALE: Synthetic cathinones continue to be sold as "legal" alternatives to methamphetamine or cocaine. As these marginally legal compounds become controlled, suppliers move to other, unregulated compounds. OBJECTIVES: The purpose of these experiments was to determine whether several temporarily controlled cathinone compounds, which are currently abused on the street, stimulate motor activity and have discriminative stimulus effects similar to cocaine and/or methamphetamine. METHODS: Methcathinone, pentedrone, pentylone, 3-fluoromethcathinone (3-FMC), and 4-methylethcathinone (4-MEC) were tested for locomotor stimulant effects in mice and subsequently for substitution in rats trained to discriminate cocaine (10 mg/kg, i.p.) or methamphetamine (1 mg/kg, i.p.) from saline. RESULTS: Methcathinone, pentedrone, and pentylone produced locomotor stimulant effects which lasted up to 6 h. In addition, pentylone produced convulsions and lethality at 100 mg/kg. 4-MEC produced locomotor stimulant effects which lasted up to 2 h. Methcathinone, pentedrone, pentylone, 3-FMC, and 4-MEC each produced discriminative stimulus effects similar to those of cocaine and methamphetamine. CONCLUSIONS: All of the tested compounds produce discriminative stimulus effects similar to either those of cocaine, methamphetamine, or both, which suggests that these compounds are likely to have similar abuse liability to cocaine and/or methamphetamine. Pentylone may be more dangerous on the street, as it produced adverse effects at doses that produced maximal stimulant-like effects.

Comparison of the discriminative stimulus effects of dimethyltryptamine with different classes of psychoactive compounds in rats.

RATIONALE: There has been increased recreational use of dimethyltryptamine (DMT), but little is known of its discriminative stimulus effects. OBJECTIVES: The present study assessed the similarity of the discriminative stimulus effects of DMT to other types of hallucinogens and to psychostimulants. METHODS: Rats were trained to discriminate DMT from saline. To test the similarity of DMT to known hallucinogens, the ability of (+)-lysergic acid diethylamide (LSD), (-)-2,5-dimethoxy-4-methylamphetamine (DOM), (+)-methamphetamine, or (+/-)3,4-methylenedioxymethyl amphetamine (MDMA) to substitute in DMT-trained rats was tested. The ability of DMT to substitute in rats trained to discriminate each of these compounds was also tested. To assess the degree of similarity in discriminative stimulus effects, each of the compounds was tested for substitution in all of the other training groups. RESULTS: LSD, DOM, and MDMA all fully substituted in DMT-trained rats, whereas DMT fully substituted only in DOM-trained rats. Full cross-substitution occurred between DMT and DOM, LSD and DOM, and (+)-methamphetamine and MDMA. MDMA fully substituted for (+)-methamphetamine, DOM, and DMT, but only partially for LSD. In MDMA-trained rats, LSD and (+)-methamphetamine fully substituted, whereas DMT and DOM did not fully substitute. No cross-substitution was evident between (+)-methamphetamine and DMT, LSD, or DOM. CONCLUSIONS: DMT produces discriminative stimulus effects most similar to those of DOM, with some similarity to the discriminative stimulus effects of LSD and MDMA. Like DOM and LSD, DMT seems to produce predominately hallucinogenic-like discriminative stimulus effects and minimal psychostimulant effects, in contrast to MDMA which produced hallucinogen- and psychostimulant-like effects.

Differential effect of anterior cingulate cortex lesion on mechanical hypersensitivity and escape/avoidance behavior in an animal model of neuropathic pain.

Various limbic system structures have been implicated in processing noxious information. One such structure is the anterior cingulate cortex (ACC), a region that is thought to modulate higher order processing of noxious input related to the affective/motivational component of pain. The present experiment examined the involvement of the ACC in higher order pain processing by measuring paw withdrawal threshold and escape/avoidance responses in the L5 spinal nerve ligation model of neuropathic pain before and following electrolytic lesion of the ACC. In the place/escape avoidance paradigm, the afflicted paw is mechanically stimulated when the animal is in the preferred dark area of the chamber and the contralateral paw is stimulated when the animal is in the light area. Escape/avoidance was defined as a shift from the preferred dark area to an increase of time spent in the light area of the chamber. Animals with L5 ligation had significantly lower mechanical paw withdrawal threshold (hypersensitivity) and enhanced escape/avoidance behavior. ACC lesion in animals with L5 ligation did not alter mechanical hypersensitivity, but did significantly decrease escape/avoidance behavior. Anxiety, as measured using the light-enhanced startle paradigm, was not altered by ACC lesion. These results highlight the utility of novel behavioral test paradigms and provide additional support for the role of the ACC in higher order processing of noxious information, suggesting that ACC lesions selectively decrease negative affect associated with neuropathy-induced hypersensitivity.