Nutrient digestibility, rumen parameters and (cannabinoid) residues in sheep fed a pelleted diet containing green hemp (Cannabis sativa L.) biomass

The feeding value for ruminants of green hemp biomass, from the low Δ⁹-tetrahydrocannabinol (Δ⁹-THC) variety of Cannabis sativa L., is unknown. Twelve Merino ewes were individually penned and randomly allocated on a stratified liveweight basis to one of two pelleted dietary treatments, control (0% hemp, n = 6) or hemp (42% green hemp biomass, n = 6) that delivered a diet meeting the nutrient requirements of the animals. The experimental period consisted of 17 d dietary and housing adaptation, followed by 7 d total urine and feces collection for determination of apparent nutrient digestibility. A ruminal fluid sample was collected on day 27 and assessed for pH, ammonia, volatile fatty acid (VFA), and cannabinoid concentrations. A blood sample from the jugular vein and incisional subcutaneous fat biopsy from an area around the base of the tail were collected on day 28 with additional fat biopsies taken 35 d and 140 d post-feeding to measure cannabinoids. The dry matter (DM), organic matter (OM), and crude protein (CP) digestibilities, along with total VFA concentration did not differ (P = 0.713) between the two diets; however, acid detergent fiber (ADF) and neutral detergent fiber (NDF) digestibilities (P < 0.001), water intake (P = 0.023), and fecal water output (P < 0.001) were significantly lower for the sheep-fed Hemp. Rumen pH did not vary (P = 0.256) between diets, but ruminal ammonia concentration was significantly lower (P = 0.024) for sheep consuming Hemp. Sheep-fed Hemp had significantly greater molar proportions of butyric (P = 0.039) and hexanoic (P = 0.012) acids and lower molar proportions of propionic acid (P = 0.003). There were no differences between diets for N intake (P = 0.175), fecal N output (P = 0.253), and N balance (P = 0.695), with all sheep in positive N balance; however, there was significantly lower (P = 0.001) urinary N output for sheep-fed Hemp. Cannabidiolic acid (CBDA) and tetrahydrocannabinolic acid (THCA) were detected in plasma of all sheep-fed Hemp. ∆⁹-tetrahydrocannabinol was present in the subcutaneous fat of four of the six sheep on the final day of being fed Hemp, and in all (six) sheep 35 d post-feeding and one sheep 140 d post-feeding Hemp. No cannabinoids were detected in the corresponding samples taken from the sheep-fed Control. Thus, despite green hemp biomass being nutritionally a suitable feed for ruminants, under current Food Standards in Australia, the presence of these cannabinoid residues restricts its use in ruminant diets.

Opposing actions of hippocampus TNFα receptors on limbic seizure susceptibility

Resected epileptic tissues exhibit elements of chronic neuroinflammation that include elevated TNFα and increased TNFα receptor activation, but the seizure related consequences of chronic TNFα expression remain unknown. Twenty four hours after acute limbic seizures the rat hippocampus exhibited a rapid upregulation of TNFR1, but a simultaneous downregulation of TNFR2. These limbic seizures also evoked significant increases in measures of neuroinflammation and caused significant neuronal cell death in both the hilus and CA3 of the hippocampus. In order to mimic a state of chronic TNFα exposure, adeno-associated viral vectors were packaged with a TNF receptor 1 (TNFR1) specific agonist, human TNFα, or a TNF receptor 1/2 agonist, rat TNFα. Subsequently, chronic hippocampal overexpression of either TNFR ligand caused microglial activation and blood-brain barrier compromise, a pattern similar to limbic seizure-induced neuroinflammation. However, no evidence was found for neuronal cell death or spontaneous seizure activity. Thus, chronic, in vivo TNFα expression and the subsequent neuroinflammation alone did not cause cell death or elicit seizure activity. In contrast, chronic hippocampal activation of TNFR1 alone significantly increased limbic seizure sensitivity in both amygdala kainic acid and electrical amygdala kindling models, while chronic activation of both TNFR1 and TNFR2 significantly attenuated the amygdala kindling rate. With regard to endogenous TNFα, chronic hippocampal expression of a TNFα decoy receptor significantly reduced seizure-induced cell death in the hippocampus, but did not alter seizure susceptibility. These findings suggest that blockade of endogenous TNFα could attenuate seizure related neuropathology, while selective activation of TNFR2 could exert beneficial therapeutic effects on in vivo seizure sensitivity.

Directed evolution of a novel adeno-associated virus (AAV) vector that crosses the seizure-compromised blood-brain barrier (BBB)

DNA shuffling and directed evolution were employed to develop a novel adeno-associated virus (AAV) vector capable of crossing the seizure-compromised blood-brain barrier (BBB) and transducing cells in the brain. Capsid DNA from AAV serotypes 1-6, 8, and 9 were shuffled and recombined to create a library of chimeric AAVs. One day after kainic acid-induced limbic seizure activity in rats, the virus library was infused intravenously (i.v.), and 3 days later, neuron-rich cells were mechanically dissociated from seizure-sensitive brain sites, collected and viral DNA extracted. After three cycles of selection, green fluorescent protein (GFP)-packaged clones were administered directly into brain or i.v. 1 day after kainic acid-induced seizures. Several clones that were effective after intracranial administration did not transduce brain cells after the i.v. administration. However, two clones (32 and 83) transduced the cells after direct brain infusion and after i.v. administration transduced the cells that were localized to the piriform cortex and ventral hippocampus, areas exhibiting a seizure-compromised BBB. No transduction occurred in areas devoid of BBB compromise. Only one parental serotype (AAV8) exhibited a similar expression profile, but the biodistribution of 32 and 83 diverged dramatically from this parental serotype. Thus, novel AAV vectors have been created that can selectively cross the seizure-compromised BBB and transduce cells.

Changes in apical dendritic structure correlate with sustained ERK1/2 phosphorylation in medial prefrontal cortex of a rat model of dopamine D1 receptor agonist sensitization

Rats lesioned with 6-hydroxydopamine (6-OHDA) as neonates exhibit behavioral and neurochemical abnormalities in adulthood that mimic Lesch-Nyhan disease, schizophrenia, and other developmental disorders of frontostriatal circuit dysfunction. In these animals a latent sensitivity to D1 agonists is maximally exposed by repeated administration of dopamine agonists in the postpubertal period (D1 priming). In neonate-lesioned, adult rats primed with SKF-38393, we found selective, persistent alterations in the morphology of pyramidal neuron apical dendrites in the prelimbic area of the medial prefrontal cortex (mPFC). In these animals, dendrite bundling patterns and the typically straight trajectories of primary dendritic shafts were disrupted, whereas the diameter of higher-order oblique branches was increased. Although not present in neonate-lesioned rats treated with saline, these morphological changes persisted at least 21 days after repeated dosing with SKF-38393, and were not accompanied by markers of neurodegenerative change. A sustained increase in phospho-ERK immunoreactivity in wavy dendritic shafts over the same period suggested a relationship between prolonged ERK phosphorylation and dendritic remodeling in D1-primed rats. In support of this hypothesis, pretreatment with the MEK1/2-ERK1/2 pathway inhibitors PD98059 or SL327, prior to each priming dose of SKF-38393, prevented the morphological changes associated with D1 priming. Together, these findings demonstrate that repeated stimulation of D1 receptors in adulthood interacts with the developmental loss of dopamine to profoundly and persistently modify neuronal signaling and dendrite morphology in the mature prefrontal cortex. Furthermore, sustained elevation of ERK activity in mPFC pyramidal neurons may play a role in guiding these morphological changes in vivo.

False-positive results on colorimetric carbon dioxide analysis in neonatal resuscitation: potential for serious patient harm

A term infant requiring resuscitation was found to have a false-positive color change on a colorimetric carbon dioxide device as a result of administration of epinephrine via an endotracheal tube. Using models of direct application and vapor exposure with a test lung, we discovered that epinephrine, atropine, infasurf and naloxone may result in false-positive color change. This false-positive response may lead to delayed recognition of esophageal intubation.

The role of dopamine receptors in the neurobehavioral syndrome provoked by activation of L-type calcium channels in rodents

In rodents, activation of L-type calcium channels with +/-BayK 8644 causes an unusual behavioral syndrome that includes dystonia and self-biting. Prior studies have linked both of these behaviors to dysfunction of dopaminergic transmission in the striatum. The current studies were designed to further elucidate the relationship between +/-BayK 8644 and dopaminergic transmission in the expression of the behavioral syndrome. The drug does not appear to release presynaptic dopamine stores, since microdialysis of the striatum revealed dopamine release was unaltered by +/-BayK 8644. In addition, the behaviors were preserved or even exaggerated in mice or rats with virtually complete dopamine depletion. On the other hand, pretreatment of mice with D(3) or D(1/5) dopamine receptor antagonists attenuated the behavioral effects of +/-BayK 8644, while pretreatment with D(2) or D(4) antagonists had no effect. In D(3) receptor knockout mice, +/-BayK 8644 elicited both dystonia and self-biting, but these behaviors were less severe than in matched controls. In D(1) receptor knockout mice, behavioral responses to +/-BayK 8644 appeared exaggerated. These results argue that the behavioral effects of +/-BayK 8644 are not mediated by a presynaptic influence. Instead, the behaviors appear to result from a postsynaptic activation of the drug, which does not require but can be modified by D(3) or D(1/5) receptors.

Nifedipine suppresses self-injurious behaviors in animals

Self-injurious behavior is a common problem in many developmental disorders. The neurobiology of this behavior is not well understood, but the differing behavioral manifestations and associations with different disorders suggest that the underlying biological mechanisms are heterogeneous. The behavioral and biological heterogeneity is also evident in several animal models, where different manifestations can be provoked under different experimental conditions. Identifying commonalities among the different mechanisms is likely to be helpful in the design of treatments useful for the broadest populations of patients. The current studies reveal that nifedipine suppresses self-injurious behavior in 4 unrelated animal models: acute administration of high doses of +/-BayK 8644 or methamphetamine in mice, dopamine agonist treatment in rats with lesions of dopamine pathways during early development and repeated administration of pemoline in rats. The effect of nifedipine does not appear to be due to nonspecific mechanisms, such as sedation, since other classes of behaviors are unaffected or exaggerated. These results suggest that nifedipine may target a common biological mechanism in the expression of self-injurious behavior, and they suggest it should be considered in the treatment of self-injury in humans.

The neonate-6-hydroxydopamine-lesioned rat: a model for clinical neuroscience and neurobiological principles

In 1973, a technique of administering 6-hydroxydopamine (2,4,5-trihydroxyphenylethylamine) intracisternally to neonate rats was introduced to selectively reduce brain dopamine (neonate-lesioned rat). This neonate treatment proved unique when compared to rats lesioned as adults with 6-hydroxydopamine--prompting the discovery of differing functional characteristics resulting from the age at which brain dopamine is reduced. A realization was that neonate-lesioned rats modeled the loss of central dopamine and the increased susceptibility for self-injury in Lesch-Nyhan disease, which allowed identification of drugs useful in treating self-injury in mentally retarded patients. The neonate-lesioned rat has also been proposed to model the hyperactivity observed in attention-deficit hyperactivity disorder. Because the neonate-lesioned rat exhibits enhanced sensitization to repeated NMDA receptor antagonist administration and has functional changes characteristic of schizophrenia, the neonate lesioning is believed to emulate the hypothesized NMDA hypofunction in this psychiatric disorder. Besides modeling features of neurological and psychiatric disorders, important neurobiological concepts emerged from pharmacological studies in the neonate-lesioned rats. One was the discovery of coupling of D1/D2-dopamine receptor function. Another was the progressive increase in responsiveness to repeated D1-dopamine agonist administration referred to as "priming" of D1-dopamine receptor function. Additionally, a unique profile of signaling protein expression related to neonate reduction of dopamine has been identified. Thus, from modeling characteristics of disease to defining adaptive mechanisms related to neonatal loss of dopamine, the neonate-lesioned rat has had a persisting influence on neuroscience. Despite an extraordinary legacy from studies of the neurobiology of this treatment, a host of unknowns remain that will inspire future investigations.

Sustained extracellular signal-regulated kinase 1/2 phosphorylation in neonate 6-hydroxydopamine-lesioned rats after repeated D1-dopamine receptor agonist administration: implications for NMDA receptor involvement

Extracellular signal-regulated kinase (ERK) 1/2, a well known regulator of gene expression, is likely to contribute to signaling events underlying enduring neural adaptations. Phosphorylated (phospho)-ERK was examined immunohistochemically after both single and repeated (i.e., sensitizing) doses of the partial D1-dopamine (DA) receptor agonist SKF-38393 (2,3,4,5-tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benazepine HCl) to adult rats lesioned as neonates (neonate lesioned) with 6-hydroxydopamine. Remarkably, prolonged phospho-ERK accumulated primarily in layers II-III of medial prefrontal cortex (MPC), where it declined gradually yet remained significantly elevated for at least 36 d after repeated doses of SKF-38393. Sustained (> or =7 d) phospho-ERK was observed for shorter periods in various other cortical regions but was not detectable in striatum or nucleus accumbens. At 36 d, an additional injection of SKF-38393 to sensitized rats restored phospho-ERK to maximal levels only in MPC when examined 7 d later. Phosphorylated cAMP response element-binding protein (CREB), examined 7 d after the sensitizing regimen, was observed exclusively in MPC, where it was abundant throughout all layers. Systemic injections of SL327 (alpha-[amino[(4-aminophenyl)thio]methylene]-2-(trifluoromethyl)benzeneacetonitrile), an inhibitor of the upstream ERK activator mitogen ERK kinase, attenuated both ERK and CREB phosphorylation in layers II-III of MPC. Pretreatment with the D1 antagonist SCH-23390 ((R)-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepine-7-OL maleate) inhibited the prolonged increase in MPC phospho-ERK, whereas the 5-HT2 receptor antagonist ketanserin (3-[2-[4-(4-fluorobenzoyl)-1-piperidinyl]ethyl]-2,4(1H,3H)-quinazolinedione tartrate) was ineffective. Competitive and noncompetitive NMDA receptor antagonists also blocked sustained ERK phosphorylation. Collectively, the present results demonstrate coupling of D1 and NMDA receptor function reflected in sustained activation of the ERK signaling pathway in MPC of SKF-38393-sensitized neonate-lesioned rats. Ultimately, long-lasting phosphorylation of ERK and CREB in MPC may play a pivotal role in any permanent adaptive change(s) in these animals.

Functional selectivity of dopamine receptor agonists. II. Actions of dihydrexidine in D2L receptor-transfected MN9D cells and pituitary lactotrophs

D(2)-like dopamine receptors mediate functional changes via activation of inhibitory G proteins, including those that affect adenylate cyclase activity, and potassium and calcium channels. Although it is assumed that the binding of a drug to a single isoform of a D(2)-like receptor will cause similar changes in all receptor-mediated functions, it has been demonstrated in brain that the dopamine agonists dihydrexidine (DHX) and N-n-propyl-DHX are "functionally selective". The current study explores the underlying mechanism using transfected MN9D cells and D(2)-producing anterior pituitary lactotrophs. Both dopamine and DHX inhibited adenylate cyclase activity in a concentration-dependent manner in both systems, effects blocked by D(2), but not D(1), antagonists. In the MN9D cells, quinpirole and R-(-)-N-propylnorapomorphine (NPA) also inhibited the K(+)-stimulated release of [(3)H]dopamine in a concentration-responsive, antagonist-reversible manner. Conversely, neither DHX, nor its analogs, inhibited K(+)-stimulated [(3)H]dopamine release, although they antagonized the effects of quinpirole. S-(+)-NPA actually had the reverse functional selectivity profile from DHX (i.e., it was a full agonist at D(2L) receptors coupled to inhibition of dopamine release, but a weak partial agonist at D(2L) receptor-mediated inhibition of adenylate cyclase). In lactotrophs, DHX had little intrinsic activity at D(2) receptors coupled to G protein-coupled inwardly rectifying potassium channels, and actually antagonized the effects of dopamine at these D(2) receptors. Together, these findings provide compelling evidence for agonist-induced functional selectivity with the D(2L) receptor. Although the underlying molecular mechanism is controversial (e.g., "conformational induction" versus "drug-active state selection"), such data are irreconcilable with the widely held view that drugs have "intrinsic efficacy".

G beta association and effector interaction selectivities of the divergent G gamma subunit G gamma(13)

G gamma(13) is a divergent member of the G gamma subunit family considered to be a component of the gustducin G-protein heterotrimer involved in bitter and sweet taste reception in taste bud cells. G gamma(13) contains a C-terminal asparagine-proline-tryptophan (NPW) tripeptide, a hallmark of RGS protein G gamma-like (GGL) domains which dimerize exclusively with G beta(5) subunits. In this study, we investigated the functional range of G gamma(13) assembly with G beta subunits using multiple assays of G beta association and G beta gamma effector modulation. G gamma(13) was observed to associate with all five G beta subunits (G beta(1-5)) upon co-translation in vitro, as well as function with all five G beta subunits in the modulation of Kir3.1/3.4 (GIRK1/4) potassium and N-type (alpha(1B)) calcium channels. Multiple G beta/G gamma(13) pairings were also functional in cellular assays of phospholipase C (PLC) beta 2 activation and inhibition of G alpha(q)-stimulated PLC beta 1 activity. However, upon cellular co-expression of G gamma(13) with different G beta subunits, only G beta(1)/G gamma(13), G beta(3)/G gamma(13), and G beta(4)/G gamma(13) pairings were found to form stable dimers detectable by co-immunoprecipitation under high-detergent cell lysis conditions. Collectively, these data indicate that G gamma(13) forms functional G beta gamma dimers with a range of G beta subunits. Coupled with our detection of G gamma(13) mRNA in mouse and human brain and retina, these results imply that this divergent G gamma subunit can act in signal transduction pathways other than that dedicated to taste reception in sensory lingual tissue.

Xenobiotic biotransforming enzymes in the central nervous system: an isoform of flavin-containing monooxygenase (FMO4) is expressed in rabbit brain

The flavin-containing monooxygenase (FMO, EC 1.14.13.8) is involved in the metabolism of a number of important xenobiotics including many which affect the central nervous system (CNS). Recently, reports in the literature concerning the amount, activity, location, and isozyme characteristics of this enzyme in the brain have presented conflicting evidence. In order to resolve some of the controversy surrounding FMO in the brain, a highly sensitive method for the detection of flavin-containing monooxygenase (FMO) mRNA in whole brain was employed. A poorly conserved region of FMO transcripts was used to design five sets of oligonucleotide primers. Each primer set was specific for one of the five currently known isoforms of FMO. Four and five isoforms, respectively, are expressed in rabbit liver and kidney, as determined by reverse transcription-polymerase chain reaction. However, only one set of primers amplified a specific rabbit brain cDNA fragment. The sequence of the amplification produced affirmed its identity as a segment of FMO4 cDNA. Thus, the FMO of rabbit brain may consist of a single, as yet uncharacterized isozyme and, contrary to several recent reports, is likely to be expressed at low levels.

Pesticide-metabolizing enzymes

Pesticides are known to function as substrates, inhibitors and inducers of drug-metabolizing enzymes, with the same compound frequently acting in more than one of these roles. Current studies of phase I metabolism of pesticides include cytochrome P450 (P450) and the flavin-containing monooxygenase (FMO), with particular reference to individual isozymes. In mouse liver, the level of FMO1 is gender dependent, FMO3 is gender specific, while FMO5 appears to be gender independent. The isozyme specificity of methylenedioxyphenyl synergists for induction of P450 in mouse liver involves P450s 1A1, 1A2 and 2B10, including a non-Ah receptor-dependent mechanism for 1A2 induction. The substrate specificity of mouse and human P450 and FMO isozymes is discussed.

Olfactory toxicity of methimazole: dose-response and structure-activity studies and characterization of flavin-containing monooxygenase activity in the Long-Evans rat olfactory mucosa

Methimazole is a compound administered to humans for the treatment of hyperthyroidism and is used experimentally as a model substrate for the flavin-containing monooxygenase (FMO) system. Previous results from this laboratory demonstrated that methimazole is an olfactory system toxicant, causing nearly complete destruction of the olfactory epithelium in the male Long-Evans rat following a single ip dose of 300 mg/kg. The present studies were undertaken to determine the dose-response relationship for methimazole-induced olfactory mucosal damage and to determine whether or not similar damage occurs as a result of oral administration, mimicking the relevant route of human exposure. We also investigated the mechanism of olfactory toxicity of methimazole by means of a structure-activity study and began the characterization of the form(s) of FMO present in the olfactory mucosa of the male Long-Evans rat. Dose-response analysis demonstrated that methimazole causes olfactory mucosal damage at doses of 25 mg/kg ip and greater. The results of gavage studies showed that a single oral dose of 50 mg/kg also caused olfactory mucosal damage. Two structurally related compounds, methylimidazole and methylpyrrole, were not olfactory toxicants, suggesting that a reactive intermediate generated in the course of metabolizing methimazole to an S-oxide is the olfactory toxic species. Microsomal incubation studies revealed the presence of methimazole S-oxidation activity in olfactory mucosal microsomes at levels comparable to those in liver. An anti-mouse liver FMO antibody reacted on Western blots with olfactory mucosal microsomes. These findings demonstrate a dose-response for the olfactory toxicity of methimazole and suggest that characterization of human olfactory mucosal FMO activity may be necessary to assess the potential for human risk associated with therapeutic exposure to methimazole.

Gender differences in hepatic expression of flavin-containing monooxygenase isoforms (FMO1, FMO3, and FMO5) in mice

Hepatic flavin-containing monooxygenase (FMO) activity of microsomes from adult CD-1, Swiss-Webster, C57BL/6, and DBA/2 mice was found to be significantly higher in females than in males. Based on protein and mRNA levels in CD-1 mice, FMO forms responsible for the gender difference in FMO activity were FMO1 and FMO3. FMO1 expression was two to three times higher in female mice compared with males; FMO3, however, which was expressed at levels equivalent to FMO1 in female mice, was not detected in males. The expression of FMO5 was approximately equal in both sexes. FMO2 and FMO4 transcripts were not evident in hepatic mRNA from mice. Protein and mRNA levels appear to be coregulated with regard to gender-selective or gender-specific expression of FMO1 or FMO3, respectively. FMO5, which demonstrates no gender-selective expression in mice, may be regulated by different mechanisms. Examination of protein levels among Swiss-Webster, C57BL/6, and DBA/2 strains revealed a gender-dependent expression of FMO isozymes identical to the CD-1 strain.

Metabolism of thioridazine by microsomal monooxygenases: relative roles of P450 and flavin-containing monooxygenase

1. The metabolism of thioridazine by the flavin-containing monooxygenase (FMO) of mouse liver and several P450 isozymes was examined using microsomes, purified FMO, and expressed P450 isozymes. Metabolites were identified by hplc. 2. Thermal inactivation and antibodies to NADPH P450 reductase were used to selectively inactivate FMO and P450 respectively. Inactivation of FMO by heat-treatment reduced the formation of thioridazine-N-oxide and northioridazine, whereas inactivation of P450 resulted in decreased amounts of thioridazine-2-sulphoxide, northioridazine, and thioridazine-5-sulphoxide. 3. Liver microsomes from mouse induced with phenobarbital, 3-methylcholanthrene, or acetone were compared with control microsomes. Phenobarbital induction resulted in increased formation of all metabolites except thioridazine-N-oxide, while retaining a general metabolic profile similar to that achieved with control microsomes. Neither 3-methylcholanthrene nor acetone induction had any effect on the in vitro metabolism of thioridazine. 4. FMO purified from mouse liver produced thioridazine-N-oxide as the major metabolite. 5. Preliminary experiments with commercially prepared microsomes made from cells expressing recombinant human liver P450 2D6 and 3A4 suggested that thioridazine is metabolized by 2D6 but not 3A4.