José N. Nobrega

Less is more: antipsychotic drug effects are greater with transient rather than continuous delivery.

BACKGROUND Most studies on the effects of antipsychotics focus on achieving threshold levels of the drug. The speed and frequency with which drug concentrations reach threshold levels and rise and fall within the day are generally ignored. Based on prior data, we predicted that variations in the within-day kinetics of antipsychotic drug delivery would produce different outcomes, even if we held achieved dose, route, and total duration of treatment constant. METHODS We compared the effects of within-day continuous (via minipump) versus transient (via subcutaneous injection) haloperidol treatment (n = 4-9/condition/experiment) at doses that yield equivalent peak levels of striatal D2 receptor occupancy (approximately 74%). RESULTS Over time, transient haloperidol gained efficacy, while continuous haloperidol lost efficacy in two animal models of antipsychotic-like effects (the suppression of amphetamine-induced locomotion and conditioned avoidance responding). This was related to the fact that continuous treatment led to a greater increase in striatal D2 receptor numbers--particularly D2 receptors in a high-affinity state for dopamine--relative to transient treatment and produced behavioral dopamine supersensitivity (as indicated by an enhanced locomotor response to amphetamine following antipsychotic treatment cessation). Treatment kinetics also influenced the postsynaptic response to haloperidol. Transient treatment increased striatal c-fos messenger RNA (mRNA) expression, while continuous treatment did not. CONCLUSIONS Relative to continuous antipsychotic exposure, within-day transient exposure is more efficacious behaviorally and is associated with a distinct molecular and gene expression profile. Thus, differences in the within-day kinetics of antipsychotic treatment can have different efficacy, and the potential clinical implications of this should be explored further.

Insulin resistance and secretion in vivo: Effects of different antipsychotics in an animal model

Atypical antipsychotics now represent the mainstay of treatment for patients with schizophrenia. Unfortunately, as a class they have also been associated with an increased risk of weight gain and metabolic abnormalities, including type 2 diabetes. We have investigated the diabetogenic effects of a spectrum of antipsychotics, both atypical and typical. Healthy animals were treated acutely with clozapine (10 mg/kg), olanzapine (3.0 mg/kg), risperidone (1 mg/kg), ziprasidone (3 mg/kg) or haloperidol (0.25 mg/kg) and tested using the hyperinsulinemic-euglycemic and hyperglycemic clamp procedures. Clozapine and olanzapine had a rapid and potent effect on insulin sensitivity by lowering the glucose infusion rate and increasing hepatic glucose production. Both clozapine and olanzapine, as well as risperidone, decreased peripheral glucose utilization. Neither ziprasidone nor haloperidol had a significant impact on insulin sensitivity. In the hyperglycemic clamp, clozapine and olanzapine impaired beta cell function as reflected by a decrease in insulin secretion. Results confirm that 1) antipsychotic medications have an immediate impact on metabolic parameters and 2) the various atypical antipsychotics differ in their propensity to acutely induce metabolic side effects. Our data also support the preclinical use of these clamp procedures in screening putative antipsychotics.

A Dopamine D2 Receptor-DISC1 Protein Complex may Contribute to Antipsychotic-Like Effects

Current antipsychotic drugs primarily target dopamine D2 receptors (D2Rs), in conjunction with other receptors such as those for serotonin. However, these drugs have serious side effects such as extrapyramidal symptoms (EPS) and diabetes. Identifying a specific D2R signaling pathway that could be targeted for antipsychotic effects, without inducing EPS, would be a significant improvement in the treatment of schizophrenia. We report here that the D2R forms a protein complex with Disrupted in Schizophrenia 1 (DISC1) that facilitates D2R-mediated glycogen synthase kinase (GSK)-3 signaling and inhibits agonist-induced D2R internalization. D2R-DISC1 complex levels are increased in conjunction with decreased GSK-3α/β (Ser21/9) phosphorylation in both postmortem brain tissue from schizophrenia patients and in Disc1-L100P mutant mice, an animal model with behavioral abnormalities related to schizophrenia. Administration of an interfering peptide that disrupts the D2R-DISC1 complex successfully reverses behaviors relevant to schizophrenia but does not induce catalepsy, a strong predictor of EPS in humans.

Electrical Stimulation of the Insular Region Attenuates Nicotine-Taking and Nicotine-Seeking Behaviors

Pharmacological inactivation of the granular insular cortex is able to block nicotine-taking and -seeking behaviors in rats. In this study, we explored the potential of modulating activity in the insular region using electrical stimulation. Animals were trained to self-administer nicotine (0.03 mg/kg per infusion) under a fixed ratio-5 (FR-5) schedule of reinforcement followed by a progressive ratio (PR) schedule. Evaluation of the effect of stimulation in the insular region was performed on nicotine self-administration under FR-5 and PR schedules, as well on reinstatement of nicotine-seeking behavior induced by nicotine-associated cues or nicotine-priming injections. The effect of stimulation was also examined in brain slices containing insular neurons. Stimulation significantly attenuated nicotine-taking, under both schedules of reinforcement, as well as nicotine-seeking behavior induced by cues and priming. These effects appear to be specific to nicotine-associated behaviors, as stimulation did not have any effect on food-taking behavior. They appear to be anatomically specific, as stimulation surrounding the insular region had no effect on behavior. Stimulation of brain slices containing the insular region was found to inactivate insular neurons. Our results suggest that deep brain stimulation to modulate insular activity should be further explored.

Dopamine D2‐like sites in schizophrenia, but not in Alzheimer's, Huntington's, or control brains, for [3H]benzquinoline

Although the basis of schizophrenia is not known, evidence indicates a possible overactivity of dopamine pathways. In order to detect any new dopamine receptor‐like sites which may be altered in schizophrenia, the present study used a new radioligand, a [3H]benzo[g]quinoline. The receptors were labelled by this ligand in the presence of other drugs to block the known dopamine D1, D2, D3, or D5 receptors (no D4‐selective ligands are available to block D4). Using this method, we found that schizophrenia brain striata had elevated levels of a D2‐like site not detected in control human postmortem brains or in Alzheimers, Huntingtons, or Parkinsons disease brains. The ligand acted as an agonist at this D2‐like site, because binding was abolished by guanine nucleotide. The binding of the ligand to the D4 receptor, however, was not sensitive to guanine nucleotide. The site differed from D2 itself, because S‐ and R‐sulpiride were equally potent at the D2‐like site. The D2‐like sites were present in rat and mouse brain but were absent in brain slices from transgenic mice where D2 had been knocked out. The abundance of the receptor was not related to premortem use of antipsychotic drugs. Future research should examine the biochemical differences between the D2 dopamine receptor and these D2‐like sites in schizophrenia. Synapse 25:137–146, 1997.

HEMA/MMMA microcapsule implants in hemiparkinsonian rat brain : Biocompatibility assessment using [3H]PK11195 as a marker for gliosis

Microencapsulation of dopamine-secreting cells in biocompatible, semi-permeable polymer membranes has been proposed as an alternative strategy for dopamine replacement for Parkinsons disease. In order to assess the viability of this proposal, dopamine-secreting PC12 cells were immunoisolated via microencapsulation in a 75:25 2-hydroxyethyl methacrylate/methyl methacrylate (HEMA/MMA) copolymer. A submerged nozzle-liquid jet method was used to produce small diameter (400 microm) microcapsules, which were stereotaxically implanted in the denervated striatum of hemi-Parkinsonian rats. A 96% survival rate was associated with the implantation surgery and no deleterious side effects were apparent. Light microscopy revealed good biocompatibility between the HEMA/MMA copolymer and the host brain, as evidenced by the absence of gross tissue damage at the neuronal tissue/capsule interface. Autoradiographic analyses using [3H]PK11195 as marker for reactive astrocytes revealed a moderate inflammatory response, confined to the immediate vicinity of the injection tract. Quantitative analyses indicated that the local tissue response did not differ significantly between brains implanted with PC12-containing capsules and those implanted with vehicle-containing capsules. Taken together, these results support the biocompatibility of HEMA/MMA copolymer as well as the feasibility and safety of stereotaxic implantation of microcapsules.

Increased homocysteine levels associated with sex and stress in the learned helplessness model of depression.

Elevated levels of homocysteine (Hcy) have been associated with major depressive (MD) illness. As human females show a higher predisposition towards depression, this study examined how Hcy levels in rats are affected by sex and estrous cycle in the learned helplessness (LH) model of depression. Male and female rats in either estrus or diestrus were subjected to LH, with intervals of 4 days between the two stress tests and between tests and sacrifice, in order to accommodate the female estrous cycle. No differences were found in LH behavior between males and females at either estrous phase. Control Hcy levels were significantly lower in females than in males (-36%, P<.001), with no further differences between estrous and diestrus phases in females. Stress exposure increased plasma Hcy by approximately 26% in females, both in estrus and diestrus, but not in males. However, when behavioral responses to stress were considered, no association was found between increased Hcy levels and propensity to develop helpless behavior. Therefore, while male rats have higher basal Hcy levels than females, females appear to be more vulnerable than males to stress-induced elevations in Hcy, although this did not correlate with behavioral responses to stress. Neither was this vulnerability influenced by estrous phase. These results imply that both stress and sex should be considered as risk factors for increased plasma Hcy.

Acute stress increases thyroid hormone levels in rat brain

BACKGROUND In experimental animals, exposure to uncontrollable stress induces a number of behavioral and biochemical changes that resemble symptoms seen in human depression and other psychiatric conditions. The present study used a yoked design to examine the effects of uncontrollable footshock stress on brain thyroid hormones in male and female rats. METHODS Animals in one group received 15 trials where footshock could be terminated by pressing a lever (escapable shock). Rats in a second group received the same amount of shock, but had no control over shock termination (inescapable shock). Control rats received no shock. RESULTS No significant differences were found among the three groups, for either males or females, in whole brain levels of thyroxine (T4) 3 hours after the footshock session. In contrast, significant group differences in brain levels of triiodothyronine (T3) were found for both males and females. In males, brain T3 was elevated by 21% in the inescapable shock group when compared to controls (p < .012). In females, brain T3 increased by 19% in the escapable shock group when compared to controls (p < .026). Plasma levels of both T3 and T4 were at control levels for all groups. CONCLUSIONS These results provide the first demonstration that brain T3 levels change rapidly in response to acute stress. The data further suggest that the effects of stress controllability on brain T3 levels may be different for males and females.

Aged dogs demonstrate both increased sensitivity to scopolamine impairment and decreased muscarinic receptor density

Memory deficits associated with aging and Alzheimers disease have been linked to cholinergic dysfunction. The present study investigated this hypothesis by comparing the effects of the muscarinic cholinergic receptor antagonist scopolamine on recent memory performance and by examining muscarinic receptor density in aged and young dogs. Scopolamine (15 μg/kg; SC) was administered prior to testing young (M=2.8 years) and aged (M=13.0 years) dogs on a delayed-non-matching-to-position task (DNMP). Scopolamine significantly impaired performance of aged, but not young dogs. Muscarinic receptor density was assessed autoradiographically using the non-selective radioligand [(3)H]quinuclidinylbenzilate. Aged dogs (M=14.1 years) showed significantly decreased density of muscarinic receptors in all brain regions examined except the cerebellum compared to young dogs (M=3.7 years). The results are consistent with those seen in aged humans and Alzheimers patients and support the hypothesis of age-dependent cholinergic dysfunction in the dog, although this was not directly determined in the current study. These findings demonstrate that markers of cholinergic hypofunction, in addition to the natural cognitive decline and amyloid pathology previously noted, are seen in canine aging. Collectively, this supports the use of the aged dog as a model for examining early pathological events in the development of Alzheimers disease.

Neonatal 6-hydroxydopamine alters the behavior of enriched-impoverished rats in a novel test environment

The hypothesis that neonatal norepinephrine (NE) depletion lessens the behavioral consequences of differential housing was tested. Male Wistar rats were injected with 6-hydroxydopamine (6-OHDA) or vehicle twice within 24 hr of birth, weaned at 25 days, and reared under either impoverished (IC) or enriched conditions (EC) for 30 days. In 3 experiments, rats were tested in the Morris water maze, the colony-intruder test, and 2 tests of dominance. 6-OHDA treatment reduced cortical and hypothalamic NE concentrations and increased brainstem NE concentrations. EC housing increased cortical dopamine (DA). Behavioral differences caused by postweaning enrichment-isolation were reduced by neonatal NE depletion, primarily in early test trials. The authors conclude that forebrain NE afferents from the locus coeruleus are important for housing-related behavioral changes and responsivity to novel testing environments.