The open field as a paradigm to measure the effects of drugs on anxiety-like behaviors: a review

The neurobiology and control of anxious states

Drug transporters are increasingly recognized to be important to drug disposition and response. P-glycoprotein, the encoded product of the human MDR1 (ABCB1) gene, is of particular clinical relevance in that this transporter has broad substrate specificity, including a variety of structurally divergent drugs in clinical use today. Moreover, expression of this efflux transporter in certain tissue compartments such as the gastrointestinal tract and brain capillary endothelial cells limits oral absorption and central nervous system entry of many drugs. Recently, a number of single-nucleotide polymorphisms (SNPs) in MDR1 have been identified. An increasing number of studies have also implicated certain commonly occurring SNPs in MDR1 in problems including altered drug levels and host susceptibility to diseases such as Parkinson's disease, inflammatory bowel disease, refractory seizures, and CD4 cell recovery during human immunodeficiency virus therapy. However, in many such cases, the reported effects of MDR1 SNPs have been inconsistent and, in some cases, conflicting. In this review SNPs in MDR1 in relation to population frequencies, drug levels, and phenotypes are outlined. In addition, issues relating to MDR1 haplotypes, environmental factors, and study design, as potential confounding factors of the observed MDR1 polymorphism effect in vivo, are also discussed.

Polymorphisms in human MDR1 (P-glycoprotein): recent advances and clinical relevance.

Neurosteroids: Biosynthesis and Function of These Novel Neuromodulators

Stress-induced relapse to heroin and cocaine seeking in rats: a review.

Induction of P-glycoprotein expression by HIV protease inhibitors in cell culture.

Pregnenolone sulfate potentiation of NMDA-mediated increases in intracellular calcium in cultured chick cortical neurons

Extended treatment with human immunodeficiency virus (HIV) protease inhibitors (HPIs) is standard in HIV/AIDS therapy. While these drugs have helped decrease the overall incidence of AIDS defining illnesses, the relative prevalence of HIV/AIDS dementia has increased. HPIs may cause induction of blood-brain barrier (BBB) drug transporters (P-glycoprotein; P-gp) and thereby limit entry of HPIs into brain tissue, increasing the probability that the brain could become an HIV sanctuary site. Using bovine brain microvessel endothelial cells (BMEC) as an in-vitro model of the BBB, the potential for the HIV protease inhibitor ritonavir to cause induction of P-gp activity and expression was examined. BMEC were isolated from fresh cow brain by enzymatic digest and density centrifugation. Primary culture BMEC were co-incubated with ritonavir or vehicle control for 120 h. Quantitative drug accumulation of rhodamine 123 (Rh123) and fluorescence microscopy were used as measures of P-gp activity. P-gp expression was assessed using quantitative Western blotting. Ritonavir decreased Rh123 cell accumulation and increased P-gp immunoreactive protein in a concentration-dependent manner. Fluorescent microscopy mirrored Rh123 quantitative studies. In BMEC pretreated with 30 microM ritonavir, Rh123 accumulation was decreased 40% and immunoreactive P-gp protein increased 2-fold. Collectively, a strong correlation between decreased Rh123 BMEC accumulation and increased P-gp immunoreactive protein was observed (Spearman r2 = 0.77, P < 0.0001). Thus extended exposure of BMEC to ritonavir caused a concentration-dependent increase in P-gp activity and expression. Similar findings may occur at the clinical level with prolonged HIV protease inhibitor use, giving insight into the central nervous system as an HIV sanctuary site and eventual development of HIV dementia.

Induction of P-glycoprotein expression and activity by ritonavir in bovine brain microvessel endothelial cells.

Interleukin-1 is a polypeptide cytokine involved in the acute-phase response. We examined the effects of IL-1 on the major inhibitory and excitatory neurotransmitter systems in brain mediated by GABA and glutamate, respectively. IL-1 enhanced the effects of GABA as determined by GABA-dependent chloride uptake at 1 and 10 ng/ml in cortical synaptoneurosomes. This effect was attenuated by pretreatment with the IL-1 receptor antagonist. Neither IL-6 nor TNF was effective in this system. IL-1 decreased the effect of NMDA and glycine on intracellular calcium concentrations in cultured chick cortical neurons in both the presence and absence of the endogenous polyamine spermine. This effect was attenuated by pretreatment with the AMPA/kainate antagonist CNQX. These data indicate that IL-1 modulates both inhibitory and excitatory neurotransmitter function in brain.

Interleukin-1 modulates GABAergic and glutamatergic function in brain.

We previously demonstrated that ketoconazole is a potent inhibitor of triazolam biotransformation in vitro and in vivo Despite significant elevations in triazolam plasma levels with coadministration of ketoconazole, the pharmacodynamic enhancement was lower than predicted based on plasma levels of triazolam The present study examines the effects of ketoconazole on benzodiazepine receptor binding in vitro as well as on open-field behavior in male CD-1 mice Triazolam alone inhibited [3H]flunitrazepam binding with an IC50 value of 085 nM and a Ki value of 050 nM Ketoconazole alone also competitively antagonized [3H]flunitrazepam binding in a concentration-dependent manner with an IC50 value of 156 microM and a Ki value of 117 microM In the presence of 1, 3 or 9 microM ketoconazole, the IC50 value of triazolam was increased to 111, 1 58 and 573 nM, respectively, whereas maximal binding was reduced by 36%, 69% and 89% Coadministration of 50 mg/kg ketoconazole and triazolam (01-03 mg/kg) to intact animals significantly elevated plasma and brain triazolam levels Ketoconazole could be measured in mouse brain at levels averaging 31% of those in plasma Ketoconazole alone had minimal or no effect on open field activity, but it significantly potentiated the decreased activity seen with triazolam administration The ability of ketoconazole to inhibit triazolam displacement of [3H]flunitrazepam binding may explain the muted pharmacodynamic effect of this benzodiazepine in the presence of ketoconazole Based on these results, it is likely that ketoconazole acts as a neutral ligand at the benzodiazepine receptor

Jeanne M. Fahey

Papers

Induction of P-glycoprotein expression by HIV protease inhibitors in cell culture.

Pregnenolone sulfate potentiation of NMDA-mediated increases in intracellular calcium in cultured chick cortical neurons

Induction of P-glycoprotein expression and activity by ritonavir in bovine brain microvessel endothelial cells.

Interleukin-1 modulates GABAergic and glutamatergic function in brain.

Effects of ketoconazole on triazolam pharmacokinetics, pharmacodynamics and benzodiazepine receptor binding in mice.