[3H]Fluphenazine binding to brain membranes: simultaneous measurement of D-1 and D-2 receptor sites

Phenotypical Screening of an MMV Open Box Library and Identification of Compounds with Antiviral Activity against St. Louis Encephalitis Virus

St. Louis encephalitis virus (SLEV) is a neglected mosquito-borne Flavivirus that may cause severe neurological disease in humans and other animals. There are no specific treatments against SLEV infection or disease approved for human use, and drug repurposing may represent an opportunity to accelerate the development of treatments against SLEV. Here we present a scalable, medium-throughput phenotypic cell culture-based screening assay on Vero CCL81 cells to identify bioactive compounds that could be repurposed against SLEV infection. We screened eighty compounds from the Medicines for Malaria Venture (MMV) COVID Box library to identify nine (11%) compounds that protected cell cultures from SLEV-induced cytopathic effects, with low- to mid-micromolar potencies. We validated six hit compounds using viral plaque-forming assays to find that the compounds ABT-239, Amiodarone, Fluphenazine, Posaconazole, Triparanol, and Vidofludimus presented varied levels of antiviral activity and selectivity depending on the mammalian cell type used for testing. Importantly, we identified and validated the antiviral activity of the anti-flavivirus nucleoside analog 7DMA against SLEV. Triparanol and Fluphenazine reduced infectious viral loads in both Vero CCL81 and HBEC-5i cell cultures and, similar to the other validated compounds, are likely to exert antiviral activity through a molecular target in the host.

The Acute Pharmacological Manipulation of Dopamine Receptors Modulates Judgment Bias in Japanese Quail

We have studied the effects of dopamine antagonists and agonists on Japanese quail behavior in the spatial judgment task. Twenty-four Japanese quail hens were trained in the spatial discrimination task to approach the feeder placed in the rewarded location (Go response, feeder containing mealworms) and to not approach the punished location (No-Go response, empty feeder plus aversive sound). In a subsequent spatial judgment task, the proportion of Go responses as well as approach latencies to rewarded, punished, and three ambiguous locations (near-positive, middle, near-negative, all neither rewarded nor punished) were assessed in 20 quail hens that successfully mastered the discrimination task. In Experiment 1, each bird received five treatments (0.1 and 1.0 mg/kg of dopamine D1 receptor antagonist SCH 23390, 0.05 and 0.5 mg/kg of dopamine D2 receptor antagonist haloperidol, and saline control) in a different order, according to a Latin square design. All drugs were administered intramuscularly 15 min before the spatial judgment test, with 2 days break between the treatments. Both antagonists caused a significant dose-dependent increase in the approach latencies as well as a decrease in the proportion of Go responses. In Experiment 2, with the design analogous to Experiment 1, the hens received again five treatments (1.0 and 10.0 mg/kg of dopamine D1 receptor agonist SKF 38393, 1.0 and 10.0 mg/kg of dopamine D2 receptor agonist bromocriptine, and saline control), applied intramuscularly 2 h before the test. The agonists did not have any significant effect on approach latencies and the proportion of Go responses in the spatial judgment task, as compared to the saline control, except for 10.0 mg/kg SKF 38393, which caused a decrease in the proportion of Go responses. The approach latency and the proportion of Go responses were affected by the cue location in both experiments. Our data suggest that the dopamine D1 and D2 receptor blockade leads to a decrease in the reward expectation and the negative judgment of stimuli. The effect of dopamine receptor activation is less clear. The results reveal that dopamine receptor manipulation alters the evaluation of the reward and punishment in the spatial judgment task.

The infralimbic and prelimbic cortices contribute to the inhibitory control of cocaine-seeking behavior during a discriminative stimulus task in rats

The infralimbic and prelimbic (IL and PL, respectively) regions of the medial prefrontal cortex regulate the control of drug-seeking behavior. However, their roles in cocaine seeking in a discriminative stimulus (DS)-based self-administration task are unclear. To address this issue, male Sprague Dawley rats were trained on a DS task in which, on a trial-by-trial basis, a DS+ indicated that a lever press would produce a cocaine infusion, whereas a distinct DS- indicated that a lever press would produce nothing. IL and PL inactivation via GABA receptor activation decreased performance accuracy and disinhibited behavioral responding on DS- trials, resulting in greater lever pressing during the DS- presentation. This was accompanied by a decrease in cocaine infusions obtained, a finding confirmed in a subsequent experiment using a standard FR1 cocaine self-administration paradigm. We repeated the DS study using a food reward and found that inactivation of each region decreased performance accuracy but had no effect on the total number of food pellets earned. Additional experiments with the cocaine DS task found that dopamine receptor blockade in the IL, but not PL, reduced performance accuracy and disinhibited behavioral responding on DS- trials, whereas AMPA receptor blockade in the IL and PL had no effect on performance accuracy. These findings strongly suggest that, in a DS-based self-administration task in which rats must actively decide whether to engage in lever pressing (DS+) or withhold lever pressing (DS-) on a trial-by-trial basis, both the IL and PL contribute to the inhibitory control of drug-seeking behavior.

Dysregulation of Corticostriatal Connectivity in Huntington's Disease: A Role for Dopamine Modulation

Aberrant communication between striatum, the main information processing unit of the basal ganglia, and cerebral cortex plays a critical role in the emergence of Huntington’s disease (HD), a fatal monogenetic condition that typically strikes in the prime of life. Although both striatum and cortex undergo substantial cell loss over the course of HD, corticostriatal circuits become dysfunctional long before neurons die. Understanding the dysfunction is key to developing effective strategies for treating a progressively worsening triad of motor, cognitive, and psychiatric symptoms. Cortical output neurons drive striatal activity through the release of glutamate, an excitatory amino acid. Striatal outputs, in turn, release γ-amino butyric acid (GABA) and exert inhibitory control over downstream basal ganglia targets. Ample evidence from transgenic rodent models points to dysregulation of corticostriatal glutamate transmission along with corresponding changes in striatal GABA release as underlying factors in the HD behavioral phenotype. Another contributor is dysregulation of dopamine (DA), a modulator of both glutamate and GABA transmission. In fact, pharmacological manipulation of DA is the only currently available treatment for HD symptoms. Here, we review data from animal models and human patients to evaluate the role of DA in HD, including DA interactions with glutamate and GABA within the context of dysfunctional corticostriatal circuitry.

The neuroleptic drug, fluphenazine, blocks neuronal voltage-gated sodium channels

Fluphenazine (Prolixin(R)) is a potent phenothiazine-based dopamine receptor antagonist, first introduced into clinical practice in the late 1950s as a novel antipsychotic. The drug emerged as a 'hit' during a routine ion channel screening assay, the present studies describe our electrophysiological examination of fluphenazine at tetrodotoxin-sensitive (TTX-S) and resistant (TTX-R) voltage-gated sodium channel variants expressed in three different cell populations. Constitutively expressed TTX-S conductances were studied in ND7/23 cells (a dorsal root ganglion-derived clonal cell line) and rat primary cerebrocortical neurons. Recombinant rat Na(V)1.8 currents were studied using ND7/23 cells as a host line for heterologous expression. Sodium currents were examined using standard whole-cell voltage-clamp electrophysiology. Current-voltage relationships for either ND7/23 cell or Na(V)1.8 currents revealed a prominent fluphenazine block of sodium channel activity. Steady-state inactivation curves were shifted by approximately 10 mV in the hyperpolarizing direction by fluphenazine (3 microM for ND7/23 currents and 10 microM for Na(V)1.8), suggesting that the drug stabilizes the inactivated channel state. Fluphenazine's apparent potency for blocking either ND7/23 or Na(V)1.8 sodium channels was increased by membrane depolarization, corresponding IC(50) values for the ND7/23 cell conductances were 18 microM and 960 nM at holding potentials of -120 mV and -50 mV, respectively. Frequency-dependent channel block was evident for each of the cell/channel variants, again suggesting a preferential binding to inactivated channel state(s). These experiments show fluphenazine to be capable of blocking neuronal sodium channels. Several unusual pharmacokinetic features of this drug suggest that sodium channel block may contribute to the overall clinical profile of this classical neuroleptic agent.

Dopamine Antagonist Alters Serum Cortisol and Prolactin Secretion in Lactating Holstein Cows

The role of dopamine in regulating glucocorticoid and prolactin secretion was investigated in lactating Holstein cows by characterizing serum cortisol and prolactin responses to fluphenazine, a dopamine receptor antagonist. Twelve anovulatory cows received an intravenous bolus injection of either saline (n = 6) or 0.3 mg of fluphenazine/kg of body weight (n = 6) in wk 2 postpartum. Blood samples were collected every 30 min for 4 h before and 4 h after saline or fluphenazine injection. Serum progesterone concentration was 0.13 +/- 0.1 ng/mL and did not differ between groups. No difference in serum cortisol concentrations was detected between groups before treatments. Fluphenazine increased serum cortisol concentrations within 30 min after fluphenazine administration (>30 ng/mL) and concentrations remained elevated throughout the sampling period. Cortisol remained unchanged in saline-treated cows (<10 ng/mL). Prolactin concentrations also increased after fluphenazine administration (103.1 +/- 3.1 ng/mL), but were unaffected by saline (18 +/- 3.1 ng/mL). Prolactin concentrations remained elevated throughout the sampling period in fluphenazine-treated cows. Our results indicated that a dopamine antagonist increased cortisol, suggesting that endogenous dopamine, at least in part, regulates cortisol and prolactin secretion. These effects are regulated through dopamine receptors in anovulatory lactating dairy cows during the early postpartum period.

Antiestrogen binding sites in brain and pituitary of ovariectomized rats

In addition to interacting with estrogen binding sites in a number of tissues, antiestrogens have recently been shown to interact with a separate, estrogen-non-compatible, antiestrogen-specific binding site (AEBS). In order to better understand possible mechanisms by which the antiestrogens may effect behavioral and physiological changes, we have examined AEBS in several areas of the brain and pituitary in adult, ovariectomized rats. Single point binding assays with 2 nM [3H]tamoxifen (TAM) in the presence of saturating amounts (1 microM) E and +/- 1 microM TAM indicated the existence of specific binding to AEBS throughout the brain and pituitary. In most areas of the brain (cortex, cerebellum, amygdala, area postrema/nucleus of the solitary tract region) as well as pituitary. Scatchard analyses revealed the presence of a single AEBS with a dissociation constant (Kd = 1-4 x 10(-9) M) similar to that previously reported for other tissues. However, in both hypothalamus and preoptic area, an additional, higher affinity site (Kd = 6-9 x 10(-11) M) was found. Competitive inhibition studies revealed that there was little competition by the potent estrogen agonist, diethylstilbesterol, for AEBS binding. Antiestrogens competed in the following order: tamoxifen greater than or equal to nafoxidine much greater than keoxifene. Additional competitive inhibition studies were run using neurotransmitter antagonists. The phenothiazines, chlorpromazine and fluphenazine, bind to both D1 and D2 dopamine receptors and effectively compete with [3H]TAM for binding at the AEBS. Other pharmacological substances, including specific antagonists of the D2 sites, as well as antagonists of the norepinephrine, opiate, histamine, GABA and acetylcholine systems, were ineffective competitors for [3H]TAM binding.

Dopamine receptors in human brain: autoradiographic distribution of D1 sites

The distribution of dopamine D1 receptors has been determined in post mortem human brain tissues using in vitro receptor autoradiography, with ([3H]N-methyl) SCH 23390 as ligand. The highest densities of dopamine D1 sites were seen in the nucleus caudatus, putamen, globus pallidus pars medialis and substantia nigra. Intermediate densities were associated with the amygdala, mammillary bodies, cerebral cortex and CA1. The remaining part of the hippocampus as well as the diencephalon, brainstem and cerebellum contained low levels of [3H]SCH 23390 binding sites. The distribution of D1 receptors in the human brain closely resembles that reported for the rat brain. In addition, there was a good correlation between the anatomical localization of D1 sites and the distribution of dopaminergic nerve terminals in the central nervous system. The densities of D1 receptors in the human brain were observed to markedly decrease with age during the first decades of life. However, no further modifications were found beyond the age of 40 years. We did not observe any significant influence of other parameters such as gender and post mortem delay in our samples.

Ontogeny of dopamine D1 receptors in rat striatum

The development of dopamine D1 receptors in rat striatum during the early postnatal period is described, using [3H]piflutixol as ligand. Dopamine D1 receptors increase in number from day of birth until about 21 days of age, when they reach adult levels. This increase in number parallels the increase in several other dopamine markers in striatum during the same time period. The increase is reflected in an increase in Bmax of ligand binding to D1 receptors. All other properties of D1 receptors that were examined do not change throughout this developmental period and are essentially the same as those found in adult tissue. These include association and dissociation rates, affinity for piflutixol as determined by kinetic and saturation studies, and pharmacology. These studies provide a biochemical and pharmacological basis for further studies on the ontogeny of dopamine receptors and of striatum and on factors regulating development of this region.

Divergent changes in D-1 and D-2 dopamine binding sites in human brain during aging

The density of D-1 and D-2 dopamine receptors in human caudate nucleus and putamen, obtained postmortem, were studied throughout the adult lifespan using [3H]fluphenazine as the dopamine receptor ligand. The D-1 subtype increased progressively with age in both regions, while the D-2 subtype declined in caudate nucleus. The ratio of D-1/D-2 Bmax in both regions increased from approximately 1 at age 20 to 2 by age 75. The dopamine content in putamen declined with age and was inversely correlated with D-1 receptor density. We suggest that D-1 receptor density is up-regulated by loss of dopamine during aging. The D-2 receptor density in caudate nucleus was positively correlated with choline acetyltransferase activity, suggesting that loss of intrastriatal neurons with age may contribute to the decrease in D-2 sites. These divergent changes in dopamine receptor subtypes with age result in an altered complement of dopamine receptors in older humans and may provide a basis for selective pharmacotherapy in disorders of the basal ganglia.

Dopamine and serotonin systems in human and rodent brain: effects of age and neurodegenerative disease

The nonpathological age-related changes in the dopamine- and serotonin-containing neurotransmitter systems in human and rodent brain are reviewed. The dopamine system exhibits age-related declines both presynaptically and postsynaptically. Presynaptically, both the levels of dopamine and the number of midbrain dopamine-containing neurons decline by up to 50% at advanced ages in the absence of neurological disease. Postsynaptically, the density of D-2 dopamine receptors decreases by 40%, while D-1 dopamine receptors either increase (man) or remain stable (rodents). Additional reductions of dopamine levels and D-2 receptors have been reported in Alzheimer's disease (AD), but these changes are relatively small, and not consistently observed. The levels of serotonin appear stable during normal aging, and presynaptic markers such as (3H)imipramine binding may actually increase. In human brain, the two major classes of serotonin receptor (S-1 and S-2) decrease by 30 to 50% over the lifespan. In AD, both presynaptic and postsynaptic markers of the serotonin system are reduced, including a loss of the serotonin-containing raphe neurons. The additional loss of serotonin receptors in AD approaches 80% when compared with young normals. A hypothesis is presented to explain the typically young age at onset of schizophrenia (usually before 30 years of age) and the older age at onset of parkinsonism (rarely before 50 years of age) within the context of normal age-related declines in the dopamine system occurring in the absence of neurological disorders. The possibility that chronic cocaine abuse might accelerate the development of parkinsonism is discussed.