Phylogenetic conservation of the benzodiazepine binding sites: pharmacological evidence

Effects of super-class cannabis terpenes beta-caryophyllene and alpha-pinene on zebrafish behavioural biomarkers

Terpenes possess a wide range of medicinal properties and are potential therapeutics for a variety of pathological conditions. This study investigated the acute effects of two cannabis terpenes, β-caryophyllene and α-pinene, on zebrafish locomotion, anxiety-like, and boldness behaviour using the open field exploration and novel object approach tests. β-caryophyllene was administered in 0.02%, 0.2%, 2.0%, and 4% doses. α-pinene was administered in 0.01%, 0.02%, and 0.1% doses. As α-pinene is a racemic compound, we also tested its (+) and (-) enantiomers to observe any differential effects. β-caryophyllene had only a sedative effect at the highest dose tested. α-pinene had differing dose-dependent effects on anxiety-like and motor variables. Specifically, (+)-α-pinene and (-)-α-pinene had significant effects on anxiety measures, time spent in the thigmotaxis (outer) or center zone, in the open field test, as well as locomotor variables, swimming velocity and immobility. (+ /-)-α-pinene showed only a small effect on the open field test on immobility at the 0.1% dose. This study demonstrates that α-pinene can have a sedative or anxiolytic effect in zebrafish and may have different medicinal properties when isolated into its (+) or (-) enantiomers.

Larval Zebrafish as a Model for Mechanistic Discovery in Mental Health

Animal models are essential for the discovery of mechanisms and treatments for neuropsychiatric disorders. However, complex mental health disorders such as depression and anxiety are difficult to fully recapitulate in these models. Borrowing from the field of psychiatric genetics, we reiterate the framework of 'endophenotypes' - biological or behavioral markers with cellular, molecular or genetic underpinnings - to reduce complex disorders into measurable behaviors that can be compared across organisms. Zebrafish are popular disease models due to the conserved genetic, physiological and anatomical pathways between zebrafish and humans. Adult zebrafish, which display more sophisticated behaviors and cognition, have long been used to model psychiatric disorders. However, larvae (up to 1 month old) are more numerous and also optically transparent, and hence are particularly suited for high-throughput screening and brain-wide neural circuit imaging. A number of behavioral assays have been developed to quantify neuropsychiatric phenomena in larval zebrafish. Here, we will review these assays and the current knowledge regarding the underlying mechanisms of their behavioral readouts. We will also discuss the existing evidence linking larval zebrafish behavior to specific human behavioral traits and how the endophenotype framework can be applied. Importantly, many of the endophenotypes we review do not solely define a diseased state but could manifest as a spectrum across the general population. As such, we make the case for larval zebrafish as a promising model for extending our understanding of population mental health, and for identifying novel therapeutics and interventions with broad impact.

Pharmaceuticals and alkylphenols in transplanted Pacific oysters (Crassostrea gigas): Spatial variation and growth effects

Pharmaceuticals and personal care products in wastewater discharge can be stressors to estuarine species. We transplanted juvenile Pacific oysters at varying distances within sites near wastewater treatment plant outfalls or oyster aquaculture control sites to assess small scale spatial variation in contaminant uptake and oyster condition. Oysters were transplanted to sites in Coos and Netarts Bays, Oregon and Grays Harbor, Washington, then collected after 9 and 12 months. Two pharmaceuticals (miconazole and virginiamycin M1) were detected in spring samples and four alkylphenols (NP1EO, NP2EO, NP and OP) were detected in summer samples, with more frequent detections at wastewater sites. Contaminant concentrations were similar across site types, indicating that even in sparsely populated coastal areas (<25,000 in the watershed), shellfish are exposed to and uptake wastewater contaminants. Additionally, oyster condition was lower at wastewater sites compared to aquaculture sites, indicating a need to better understand whether contaminant exposure affects oyster condition.

Biochemical properties of the sensitivity to GABAAergic ligands, Cl-/HCO3--ATPase isolated from fish (Cyprinus carpio) olfactory mucosa and brain

This paper presents a comparative study of the roles of Cl^- and HCO₃^- in the functioning of the GABA_AR-associated Cl^-/HCO₃^--ATPase of the plasma membranes of the olfactory sensory neurons (OSNs) and mature brain neurons (MBNs) of fish. The ATPase activity of OSNs and its dephosphorylation were increased twofold by Cl^-(15-30 mmol l^-1), whereas the enzyme from MBNs was not significantly affected by Cl^-. By contrast, HCO₃^-(15-30 mmol l^-1) significantly activated the MBN enzyme and its dephosphorylation, but had no effect on the OSN ATPase. The maximum ATPase activity and protein dephosphorylation was observed in the presence of both Cl^-(15 mmol l^-1)/HCO₃^-(27 mmol l^-1) and these activities were inhibited in the presence of picrotoxin (100 μmol l^-1), bumetanide (150 μmol l^-1), and DIDS (1000 μmol l^-1). SDS-PAGE revealed that ATPases purified from the neuronal membrane have a subunit with molecular mass of ~ 56 kDa that binds [³H]muscimol and [³H]flunitrazepam. Direct phosphorylation of the enzymes in the presence of ATP-γ-³²P and Mg²⁺, as well as Cl^-/HCO₃^- sensitive dephosphorylation, is also associated with this 56 kDa peptide. Both preparations also showed one subunit with molecular mass 56 kDa that was immunoreactive with GABA_AR β3 subunit. The use of a fluorescent dye for Cl^- demonstrated that HCO₃^-(27 mmol l^-1) causes a twofold increase in Cl^- influx into proteoliposomes containing reconstituted ATPases from MBNs, but HCO₃^- had no effect on the reconstituted enzyme from OSNs. These data are the first to demonstrate a differential effect of Cl^- and HCO₃^- in the regulation of the Cl^-/HCO₃^--ATPases functioning in neurons with different specializations.

No evidence of increased growth or mortality in fish exposed to oxazepam in semi-natural ecosystems

An increasing number of short-term laboratory studies on fish reports behavioral effects from exposure to aquatic contaminants or raised carbon dioxide levels affecting the GABA_A receptor. However, how such GABAergic behavioral modifications (GBMs) impact populations in more complex natural systems is not known. In this study, we induced GBMs in European perch (Perca fluviatilis) via exposure to a GABA agonist (oxazepam) and followed the effects on growth and survival over one summer (70days) in replicated pond ecosystems. We hypothesized that anticipated GBMs, expressed as anti-anxiety like behaviors (higher activity and boldness levels), that increase feeding rates in laboratory assays, would; i) increase growth and ii) increase mortality from predation. To test our hypotheses, 480 PIT tagged perch of known individual weights, and 12 predators (northern pike, Esox lucius) were evenly distributed in 12 ponds; six control (no oxazepam) and six spiked (15.5±4μgl^-1 oxazepam [mean±1S.E.]) ponds. Contrary to our hypotheses, even though perch grew on average 16% more when exposed to oxazepam, we found no significant difference between exposed and control fish in growth (exposed: 3.9±1.2g, control: 2.9±1g [mean±1S.E.], respectively) or mortality (exposed: 26.5±1.8individuals pond^-1, control: 24.5±2.6individuals pond^-1, respectively). In addition, we show that reduced prey capture efficiency in exposed pike may explain the lack of significant differences in predation. Hence, our results suggest that GBMs, which in laboratory studies impact fish behavior, and subsequently also feeding rates, do not seem to generate strong effects on growth and predation-risk in more complex and resource limited natural environments.

Anti-anxiety drugs and fish behavior: Establishing the link between internal concentrations of oxazepam and behavioral effects

Psychoactive drugs are frequently detected in the aquatic environment. The evolutionary conservation of the molecular targets of these drugs in fish suggests that they may elicit mode of action-mediated effects in fish as they do in humans, and the key open question is at what exposure concentrations these effects might occur. In the present study, the authors investigated the uptake and tissue distribution of the benzodiazepine oxazepam in the fathead minnow (Pimephales promelas) after 28 d of waterborne exposure to 0.8 μg L^-1 , 4.7 μg L^-1 , and 30.6 μg L^-1 . Successively, they explored the relationship between the internal concentrations of oxazepam and the effects on fish exploratory behavior quantified by performing 2 types of behavioral tests, the novel tank diving test and the shelter-seeking test. The highest internal concentrations of oxazepam were found in brain, followed by plasma and liver, whereas muscle presented the lowest values. Average concentrations measured in the plasma of fish from the 3 exposure groups were, respectively, 8.7 ± 5.7 μg L^-1 , 30.3 ± 16.1 μg L^-1 , and 98.8 ± 72.9 μg L^-1 . Significant correlations between plasma and tissue concentrations of oxazepam were found in all 3 groups. Exposure of fish to 30.6 µg L^-1 in water produced plasma concentrations within or just below the human therapeutic plasma concentration (H_T PC) range in many individuals. Statistically significant behavioral effects in the novel tank diving test were observed in fish exposed to 4.7 μg L^-1 . In this group, plasma concentrations of oxazepam were approximately one-third of the lowest H_T PC value. No significant effects were observed in fish exposed to the lowest and highest concentrations. The significance of these results is discussed in the context of the species-specific behavior of fathead minnow and existing knowledge of oxazepam pharmacology. Environ Toxicol Chem 2016;35:2782-2790. © 2016 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Buspirone, chlordiazepoxide and diazepam effects in a zebrafish model of anxiety

Zebrafish are becoming more widely used to study neurobehavioral pharmacology. We have developed a method to assess novel environment diving behavior of zebrafish as a model of stress response and anxiolytic drug effects. In a novel tank, zebrafish dwell in the bottom of the tank initially and then increase their swimming exploration to higher levels over time. We previously found that nicotine, which has anxiolytic effects in rodents and humans, significantly lessens the novel tank diving response in zebrafish. The specificity of the diving effect was validated with a novel vs. non-novel test tank. The novel tank diving response of zebrafish was tested when given three anxiolytic drugs from two different chemical and pharmacological classes: buspirone, chlordiazepoxide and diazepam. When the test tank was novel the diving response was clearly seen whereas it was significantly reduced when the test tank was not novel. Buspirone, a serotonergic (5HT(1A) receptor agonist) anxiolytic drug with some D(2) dopaminergic effect, had a pronounced anxiolytic-like effect in the zebrafish diving model at doses that did not have sedative effects. In contrast, chlordiazepoxide, a benzodiazepine anxiolytic drug, which is an effective agonist at GABA-A receptors, did not produce signs of anxiolysis in zebrafish over a broad dose range up to those that caused sedation. Diazepam another benzodiazepine anxiolytic drug did produce an anxiolytic effect at doses that did not cause sedation. The zebrafish novel tank diving task can be useful in discriminating anxiolytic drugs of several classes (serotonergic, benzodiazepines and nicotinic).

Fish, amphibian, and reptile analgesia

Pain perception and appropriate behavioral responses are important for survival. The conservation of the opioid ligand and receptor suggests evolution of opioid receptors mediating antinociception throughout vertebrate phylogeny. Fish, amphibians, and reptiles have appropriate neurologic components, display the appropriate behavior in response to a painful stimulus, and possess antinociceptive mechanisms to modulate pain. Because pain perception in these species is therefore likely to be analogous to that of mammals, invasive and painful procedures should always be accompanied by appropriate analgesia and anesthesia. Although specific doses have not been established in clinical trials, clinicians should attempt to provide lower vertebrates with appropriate analgesia during painful procedures. Further experimental and clinical investigations are necessary to expand the current veterinary literature in the area of pain and analgesia in lower vertebrates such as fish, amphibians, and reptiles.

The interaction of chlorinated alicyclic insecticides with brain GABA(A) receptors in channel catfish (Ictalurus punctatus)

Chlorinated alicyclic insecticides are believed to antagonize the action of the neurotransmitter gamma-aminobutyric acid (GABA) at its receptor in vertebrates. Binding of the specific GABA(A) receptor ligand [35S]-t-butylbicyclophosphorothionate (TBPS) to channel catfish brain P2 membranes suggested a single population of receptors with a Kd (56.6+/-2.6 nM) and Bmax (2435+/-276 fmol/mg protein) that are similar to published values for other fish species. The competition of several chlorinated compounds for TBPS binding was investigated. The most potent inhibitors of TBPS binding were 12-ketoendrin, photoheptachlor epoxide, photoheptachlor, telodrin, and endrin, respectively, with IC50s of 20-90 nM. Photooxychlordane, photo alpha-chlordane, and oxychlordane were intermediate in potency (122-219 nM), as were isodrin, dihydroisodrin, heptachlor epoxide, and alpha-chlordane, which were similar in potency (311-397 nM). Dieldrin, lindane, and dihydroaldrin were much less potent (592-1103 nM). Heptachlor, aldrin, and gamma-chlordane were weak inhibitors of TBPS binding (2073-2738 nM). Chlordene and chlordecone had the lowest potency of all compounds studied (10,201-21,178 nM) with the exception of mirex, which did not inhibit binding at a concentration of 50 microM. There is a good correlation between binding potency and the available toxicity data for several of these compounds in channel catfish. There is also a good correlation between the inhibitory potency in channel catfish by these types of compounds with that in rats.

Distributions of GABAA, GABAB, and benzodiazepine receptors in the forebrain and midbrain of pigeons

Autoradiographic and immunohistochemical methods were used to study the distributions of GABAA, GABAB and benzodiazepine (BDZ) receptors in the pigeon fore- and midbrain. GABAA, GABAB and BDZ binding sites were found to be abundant although heterogeneously distributed in the telencephalon. The primary sensory areas of the pallium of the avian telencephalon (Wulst and dorsal ventricular ridge) tended to be low in all three binding sites, while the surrounding second order belt regions of the pallium were typically high in all three. Finally, the outermost rind of the pallium (termed the pallium externum by us), which surrounds the belt regions and projects to the striatum of the basal ganglia, was intermediate in all three GABAergic receptors types. Although both GABAA and benzodiazepine receptors were abundant within the basal ganglia, GABAA binding sites were densest in the striatum and BDZ binding sites were densest in the pallidum. Among the brainstem regions receiving GABAergic basal ganglia input, the anterior and posterior nuclei of the ansa lenticularis showed very low levels of all three receptors, while the lateral spiriform nucleus and the ventral tegmental area/substantia nigra complex contained moderate abundance of the three binding sites. The dorsalmost part of the dorsal thalamus (containing nonspecific nuclei) was rich in all three binding sites, while the more ventral part of the dorsal thalamus (containing specific sensory nuclei), the ventral thalamus and the hypothalamus were poor in all three binding sites. The pretectum was also generally poor in all three, although some nuclei displayed higher levels of one or more binding sites. The optic tectum, inferior colliculus, and central gray were rich in all three sites, while among the isthmic nuclei, the parvicellular isthmic nucleus was conspicuously rich in BDZ sites. The results show a strong correlation of the regional abundance of GABA binding sites with previously described distributions of GABAergic fibers and terminals in the avian forebrain and midbrain. The regional distribution of these binding sites is also remarkably similar to that in mammals, indicating a conservative evolution of forebrain and midbrain GABA systems among amniotes.

GABAA, GABAB, and benzodiazepine binding sites in the cerebellar cortex of the red-eared turtle (Pseudemys scripta)

We used receptor autoradiography to ascertain the distribution of GABAA and GABAB binding sites in the cerebellar cortex of the red-eared turtle (Pseudemys scripta). GABAA binding sites were found in both molecular and granule cell layers with highest levels in the granule cell layer. GABAB binding sites were found at highest level in the molecular layer. Benzodiazepine binding sites were found in approximately equal abundance in both layers. Little binding of any ligand was seen in the Purkinje cell layer. Our results are similar to those found in mammals and other non-mammalian vertebrates and indicate that the organization of inhibitory pathways of the cerebellar cortex has been conserved in the course of vertebrate evolution.

Excitatory and inhibitory amino acid neurotransmitter binding sites in the cerebellar cortex of the pigeon (Columba livia)

We used receptor autoradiography to determine the distribution of excitatory and inhibitory amino acid neurotransmitter binding sites in the cerebellar cortex of the pigeon (Columba livia). alpha-Amino-3-hydroxy-5-methylisoxazole-4-propionic acid, kainate and metabotropic binding sites had highest levels in the molecular layer. N-methyl-D-aspartate binding sites, assayed with both [3H]glutamate under selective conditions and with [3H]glycine binding to the associated strychnine-insensitive glycine site, had highest levels in the granule cell layer. There was little specific binding of the non-competitive N-methyl-D-aspartate antagonist, [3H]MK-801. The level of gamma-aminobutyric acid (GABA)-A binding sites was higher than GABA-B binding sites in both molecular and granule cell layers with the highest level of GABA-A sites in the granule cell layer. The highest level of GABA-B binding sites was in the molecular layer. [3H]Flunitrazepam binding levels were approximately the same in both molecular and granule cell layers. With the exception of kainate binding sites, the distribution of binding sites was identical to that seen in the cerebellar cortex of mammals. Our results support the concept that the chemoarchitecture of the cerebellar cortex has been conserved in the course of vertebrate evolution.

Kindling does not induce persistent changes in fluorographic labeling patterns of benzodiazepine binding proteins in various rat brain regions

The GABAA receptor has been implicated in the mechanisms underlying the phenomenon of kindling. Photoaffinity labeling with 3H-flunitrazepam followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis allows the fluorographic visualization of GABAA receptor proteins with benzodiazepine binding sites which presumably correspond to different alpha-subtypes. This method offers an opportunity to investigate whether up- or down-regulation of single benzodiazepine binding proteins occurs. In the present study, labeling patterns of benzodiazepine binding proteins were determined in 12 brains regions of amygdala-kindled rats (2 weeks after the last fully kindled seizure) and sham-operated controls. For most brain regions, labeling patterns were separately determined for the ipsi- and contralateral side. A comparison of the labeling patterns thus obtained revealed no persistent changes between kindled animals and controls in any of the brain regions, including amygdala, substantia nigra and hippocampus. Thus, we conclude that kindling does not induce fluorographically detectable changes in the expression patterns of the benzodiazepine binding proteins. The results confirm the existence of regional heterogeneity of benzodiazepine binding proteins and extend the findings to brain regions which had previously not been investigated.

Binding sites for [3H]2-oxo-quazepam in the brain of the cat: evidence for heterogeneity of benzodiazepine recognition sites

In the present study, the distribution of benzodiazepine recognition site subtypes in the brain of the cat was investigated. To this aim, the binding properties of [3H]2-oxo-quazepam ([3H]2OXOQ) and [3H]beta-CCE, two ligands with preferential affinity for Type I benzodiazepine recognition sites, were compared to binding parameters for [3H]flunitrazepam ([3H]FNT) in different areas of the cat brain. The ratio of [3H]2OXOQ to [3H]FNT binding sites indicated that, in the cerebellum, Type I sites accounted for 90% of the total number of benzodiazepine recognition sites. The cerebral cortex, thalamus and mesencephalic reticular formation had also a high proportion of Type I sites (73-78%), whilst the two subtypes were almost equally distributed in the hippocampus, amygdala and bulbar reticular formation. A similar distribution of subtypes of benzodiazepine recognition sites was indicated by the ratio of [3H]beta CCE to [3H]FNT binding sites for different areas of the brain. These results demonstrate the existence of heterogeneity of recognition sites for benzodiazepines in the brain of the cat and support the view that [3H]2OXOQ preferentially labels Type I sites.

Photolabeled tryptic degradation products of benzodiazepine-binding proteins are glycopeptides. Implications for localization of cleavage sites

Crude synaptic membranes of avian and mammalian brain tissue were photolabeled with the benzodiazepine-receptor ligand [3H]flunitrazepam and subsequently treated extensively with trypsin followed by incubation with endoglycosidase F. SDS-polyacrylamide gel electrophoresis and fluorography revealed that the final tryptic degradation product of 25 kDa in both pigeon and calf brain is deglycosylated in two steps. These results were confirmed by immunoblots of similarly pretreated membranes of pig brain using the alpha-subunit-specific monoclonal antibody bd-24. Benzodiazepine-receptor binding and its enhancement by GABA are largely retained after trypsinization. Based on the proposed transmembrane topology for the alpha-subunits of the GABA/benzodiazepine receptor, we suggest that the large N-terminal domain of benzodiazepine-binding proteins is protected against tryptic cleavage.

Limited tryptic proteolysis of the benzodiazepine binding proteins in different species reveals structural homologies

Peptide mapping can be used to elucidate further the structural similarities of the benzodiazepine binding proteins in different vertebrate species. Crude synaptic membrane preparations were photoaffinity-labeled with [3H]flunitrazepam and subsequently degraded with various concentrations of trypsin. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by fluorography allowed a comparison of the molecular weights of photolabeled peptides in different species. Tryptic degradation led to a common peptide of 40K in all species investigated, a finding indicating that the benzodiazepine binding proteins are structurally homologous in higher bony fishes and tetrapods.

The shark GABA-benzodiazepine receptor: further evidence for a not so late phylogenetic appearance of the benzodiazepine receptor

Whilst the brain-specific benzodiazepine receptor has been assumed to show a late evolutionary appearance, we present evidence for the presence of a central benzodiazepine binding site in sharks, which shows a high affinity for [3H]Ro 15-1788. However, the receptor density and the affinities of several benzodiazepine receptor ligands are lower than in mammals, thus presumably explaining why the benzodiazepine binding sites had previously escaped detection in elasmobranchs. Additionally, radio- and immunohistochemistry were performed to localize the radioligand binding sites and the antigenic sites of the shark gamma-aminobutyric acid (GABA)-benzodiazepine receptor. In cerebellum, the granular layer reveals a high density of [3H]muscimol binding sites. The immunoreaction obtained with the beta-subunit-specific monoclonal antibody bd-17 seemingly parallels the distribution of high-affinity GABA binding sites. In contrast, [3H]Ro 15-1788 binding sites are evenly distributed in the molecular and granular layers, thus the results are similar to those previously described for rat cerebellum. Apparently, the respective distributions in this brain region are well conserved throughout vertebrate evolution.