Difference in sensitivity of the mu and kappa systems in cafeteria rats

Potential functional and pathological side effects related to off-target pharmacological activity

Most pharmaceutical companies test their discovery-stage proprietary molecules in a battery of in vitro pharmacology assays to try to determine off-target interactions. During all phases of drug discovery and development, various questions arise regarding potential side effects associated with such off-target pharmacological activity. Here we present a scientific literature curation effort undertaken to determine and summarize the most likely functional and pathological outcomes associated with interactions at 70 receptors, enzymes, ion channels and transporters with established links to adverse effects. To that end, the scientific literature was reviewed using an on-line database, and the most commonly reported effects were summarized in tabular format. The resultant table should serve as a practical guide for research scientists and clinical investigators for the prediction and interpretation of adverse side effects associated with molecules interacting with components of this screening battery.

Translational Research on Nicotine Dependence

Nicotine dependence is a chronic, relapsing disorder with complex biological mechanisms underlying the motivational basis for this behavior. Although more than 70 % of current smokers express a desire to quit, most relapse within one year, underscoring the need for novel treatments. A key focus of translational research models addressing nicotine dependence has been on cross-validation of human and animal models in order to improve the predictive value of medication screening paradigms. In this chapter, we review several lines of research highlighting the utility of cross-validation models in elucidating the biological underpinnings of nicotine reward and reinforcement, identifying factors which may influence individual response to treatment, and facilitating rapid translation of findings to practice.

Involvement of hypothalamic neuropeptide Y in pentazocine induced suppression of food intake in rats

The potent orexigenic peptide neuropeptide Y (NPY) has been considered as a possible endogenous ligand for a subpopulation of sigma receptors (SigR). However, their mutual interaction with reference to feeding behavior remains poorly understood. In the present study, we explored the possible interaction between sigma1 receptors (Sig1R) agonist, pentazocine, and NPY on food intake in satiated rats. While pentazocine dose-dependently reduced the food intake, NPY significantly increased it at 2, 4 and 6h post injection time points. In combination studies, pretreatment with NPY (0.1 nmol/rat, intra-PVN) normalized the inhibitory effect of pentazocine (60 μg/rat, intra-PVN) on food intake. Similarly, pre-treatment with pentazocine (30 μg/rat, intra-PVN) significantly antagonized the orexigenic effect of NPY (0.5 and 1.0 nmol/rat, intra-PVN). Moreover, pentazocine treatment decreased NPY immunoreactivity in arcuate (ARC), paraventricular (PVN), dorsomedial (DMH) and ventromedial (VMH) nuclei of hypothalamus. However, no change was observed in lateral hypothalamus (LH). Study implicates the reduced NPY immunoreactivity for the anorectic effect observed following pentazocine injections. Therefore, the concomitant activation of the NPYergic system along with the Sig1R agonist treatment may serve a useful purpose in the management of the unwanted side effects related to energy homeostasis.

Neonatal maternal deprivation modifies feeding in response to pharmacological and behavioural factors in adult rats

Neonatal maternal deprivation permanently modifies the hypothalamo-pituitary-adrenal (HPA) axis and other neurobiological and behavioural parameters in rats. The HPA axis plays a central role in the control of feeding, and participates in the anorexigenic action of dexfenfluramine and restraint stress, and in the orexigenic action of a cafeteria diet. Therefore, we investigated whether maternal deprivation modifies feeding responses to these factors. Experimental pups were separated for 24h from the mother 5 or 14 days after birth. The anorexigenic response to both dexfenfluramine and restraint stress was increased, and body weight as well as subcutaneous adipose tissue gain induced by cafeteria diet was higher in early deprived adult rats. However, these effects were dependent on the time of maternal deprivation. According to our predictions, the feeding response of maternally deprived rats to anorexigenic and orexigenic agents was altered, which is probably partly due to an altered HPA function, but the participation of the serotonergic, the opioid and/or the dopaminergic system cannot be ruled out. Additional studies are needed to detail precisely the neurobiological substrates of modified feeding behaviour of maternally deprived animals. This early stress paradigm altering feeding behaviour could become an interesting model for research into human eating disorders.

A kappa opiate agonist, U50,488H, enhances energy expenditure in rats

The effect of U50,488H (a selective kappa opiate agonist) on oxygen consumption was measured in either resting and free-moving rats. In both states, U50,488H provokes an increase in oxygen consumption. In resting rats, the increase occurs at lower doses than in free-moving rats. The explanation could be that in the free-moving rats the drug results in an increase in energy expenditure, partially compensated by a decrease in activity.

Selective opioid receptor antagonist effects upon intake of a high-fat diet in rats

Short-term (2 h) intake of a high-fat diet in rats was significantly inhibited by intravenous (0.1-10 mg/kg: 39-67%) and central (1-5 micrograms, i.c.v.: 51%) naloxone. The irreversible mu opioid antagonist, beta-funaltrexamine (10 micrograms, i.c.v.: 37%), but not the irreversible mu 1 antagonist, naloxonazine (10 mg/kg, i.v.) inhibited intake, suggesting mu 2 receptor mediation. The delta antagonist, ICI 174864 (1-10 micrograms, i.c.v.: 41%) inhibited high-fat diet intake only at doses that also produced motor dysfunction.

Effects of kappa opiate agonists on palatable food consumption in non-deprived rats, with and without food preloads

There is increasing evidence to suggest that kappa opiate receptors may be importantly involved in the mediation of feeding responses in the rat. A series of experiments is reported in which the effects of four kappa receptor agonists (ethylketocyclazocine, U-50,488H, tifluadom, bremazocine) on the consumption of a highly palatable diet were investigated. Under one condition, non-deprived male rats were administered drug treatments before a 30 min feeding test. Bremazocine (0.1 mg/kg) and ethylketocyclazocine (3.0 mg/kg) both significantly decreased the level of food consumption. In contrast, U-50,488H and tifluadom each produced significant increases in food intake. In a second condition, non-deprived male rats were first allowed to consume some of the palatable diet to achieve partial satiation, prior to the administration of the drug treatments. In this case, evidence for hyperphagic effects of all four kappa agonists was obtained, within the first 30 min access to the palatable diet. Thus, hyperphagia occurred with 0.01 mg/kg bremazocine and 0.1 mg/kg ethylketocyclazocine. We conclude that some kappa agonists have mixed stimulant/inhibitory effects on food intake, whereas others are more consistent in producing hyperphagia. In neither condition did morphine (0.3-10.0 mg/kg) show any hyperphagic effect. Our data support an involvement of kappa opiate receptors in mechanisms which control palatable food consumption in non-deprived rats.