Predicting population responses to environmental change from individual-level mechanisms: towards a standardized mechanistic approach.

Animal populations will mediate the response of global biodiversity to environmental changes. Population models are thus important tools for both understanding and predicting animal responses to uncertain future conditions. Most approaches, however, are correlative and ignore the individual-level mechanisms that give rise to population dynamics. Here, we assess several existing population modelling approaches and find limitations to both 'correlative' and 'mechanistic' models. We advocate the need for a standardized mechanistic approach for linking individual mechanisms (physiology, behaviour, and evolution) to population dynamics in spatially explicit landscapes. Such an approach is potentially more flexible and informative than current population models. Key to realizing this goal, however, is overcoming current data limitations, the development and testing of eco-evolutionary theory to represent interactions between individual mechanisms, and standardized multi-dimensional environmental change scenarios which incorporate multiple stressors. Such progress is essential in supporting environmental decisions in uncertain future conditions.

Development and initial characterization of a novel ghrelin receptor CRISPR/Cas9 knockout wistar rat model.

BACKGROUND/OBJECTIVES: Ghrelin, a stomach-derived hormone implicated in numerous behaviors including feeding, reward, stress, and addictive behaviors, acts by binding to the growth hormone secretagogue receptor (GHSR). Here, we present the development, verification, and initial characterization of a novel GHSR knockout (KO) Wistar rat model created with CRISPR genome editing. METHODS: Using CRISPR/Cas9, we developed a GHSR KO in a Wistar background. Loss of GHSR mRNA expression was histologically verified using RNAscope in wild-type (WT; n = 2) and KO (n = 2) rats. We tested the effects of intraperitoneal acyl-ghrelin administration on food consumption and plasma growth hormone (GH) concentrations in WT (n = 8) and KO (n = 8) rats. We also analyzed locomotion, food consumption, and body fat composition in these animals. Body weight was monitored from early development to adulthood. RESULTS: The RNAscope analysis revealed an abundance of GHSR mRNA expression in the hypothalamus, midbrain, and hippocampus in WTs, and no observed probe binding in KOs. Ghrelin administration increased plasma GH levels (p = 0.0067) and food consumption (p = 0.0448) in WT rats but not KOs. KO rats consumed less food overall at basal conditions and weighed significantly less compared with WTs throughout development (p = 0.0001). Compared with WTs, KOs presented higher concentrations of brown adipose tissue (BAT; p = 0.0322). CONCLUSIONS: We have verified GHSR deletion in our KO model using histological, physiological, neuroendocrinological, and behavioral measures. Our findings indicate that GHSR deletion in rats is not only associated with a lack of response to ghrelin, but also associated with decreases in daily food consumption and body growth, and increases in BAT. This GHSR KO Wistar rat model provides a novel tool for studying the role of the ghrelin system in obesity and in a wide range of medical and neuropsychiatric disorders.

Relapse to cocaine-seeking after hippocampal theta burst stimulation.

Treatment efforts for cocaine addiction are hampered by high relapse rates. To map brain areas underlying relapse, we used electrical brain stimulation and intracranial injection of pharmacological compounds after extinction of cocaine self-administration behavior in rats. Electrical stimulation of the hippocampus containing glutamatergic fibers, but not the medial forebrain bundle containing dopaminergic fibers, elicited cocaine-seeking behavior dependent on glutamate in the ventral tegmental area. This suggests a role for glutamatergic neurotransmission in relapse to cocaine abuse. The medial forebrain bundle electrodes supported intense electrical self-stimulation. These findings suggest a dissociation of neural systems subserving positive reinforcement (self-stimulation) and incentive motivation (relapse).

Heterogeneity of the mesotelencephalic dopamine fibers: physiology and pharmacology.

The mesotelencephalic dopamine (DA) system is heterogeneous with respect to nuclei, terminal loci, DA receptor subtypes, electrophysiological characteristics and response patterns, and neuropharmacological response to a range of agents. The majority of mesocortical and mesolimbic DA neurons originate in the ventral tegmental area. Mesostriatal DA neurons originate in substantia nigra pars compacta. DA neurons originating from the retrorubal field primarily innervate subcortical limbic and neostriatal loci. Mesostriatal terminal loci have relatively low densities of D3 and D4 receptors, compared to mesolimbic and mesocortical loci. The D1 and D2 receptors appear more homogeneously distributed. Electrophysiologically, mesostriatal DA neurons show more regularity in firing pattern (fewer bursting events), and a lower basal firing rate than mesolimbic or mesocortical neurons. Neuropharmacologically, mesocortical DA neurons are less responsive to intravenous d-amphetamine, (+)apomorphine, and chronic antipsychotic drug treatment. Mesocortical DA neurons are also relatively insensitive to iontophoretically applied DA, a finding congruent with their reported relative lack of somatodendritic autoreceptors. Neurochemically, mesoaccumbens DA neurons are more sensitive to systemic administration of drugs with addictive liability.

Neurobehavioral evidence for mesolimbic specificity of action by clozapine: studies using electrical intracranial self-stimulation.

The ability of chronic treatment with the atypical neuroleptic clozapine to induce functional dopaminergic hypersensitivity in laboratory rats was assessed. The intracranial electrical self-stimulation paradigm, known to be sensitive to changes in functional dopaminergic sensitivity, was used. Animals with electrodes in the ventral tegmental nucleus (mesolimbic dopamine cell body area) showed a marked increase in self-stimulation rate following 3 weeks of chronic clozapine. This increase was similar in magnitude and duration to that shown by animals given 3 weeks of chronic haloperidol. In contrast, animals with electrodes in the substantia nigra (nigrostriatal dopamine cell body area) showed no change in self-stimulation rate following 3 weeks of chronic clozapine. These data are interpreted in the light of previous suggestions that clozapine and other atypical neuroleptics may possess functional selectivity for the mesolimbic dopamine system.

In vivo electrochemical and behavioral evidence for specific neural substrates modulated differentially by enkephalin in rat stimulant stereotypy and locomotion.

The enkephalinamide, D-Ala2-D-Pro5-enkephalinamide monoacetate (WY 42, 186), when systemically administered to male Sprague-Dawley rats, significantly inhibited sniffing, repetitive head movements, and frequency of rearing, stereotyped behaviors which are often associated with nigrostriatal dopamine activation. On the other hand, the locomotor component of amphetamine-induced stereotyped behavior, which is associated with mesolimbic dopaminergic activation, was not inhibited. In vivo electrochemical analysis showed a significant decrease in striatal dopamine release from striatum after systemic administration of D-Ala2-D-Pro5-enkephalinamide monoacetate in chloral hydrate anesthetized rats, whereas the dopamine signal from the nucleus accumbens, a mesolimbic neuroanatomigic modulation of dopamine both behaviorally and biochemically. Also, the concept of separate neural systems for the stereotypic and locomotor components of amphetamine-induced stereotypy is reinforced.

Slow-onset, long-duration 3-(3',4'-dichlorophenyl)-1-indanamine monoamine reuptake blockers as potential medications to treat cocaine abuse.

A series of 3-(3',4'-dichlorophenyl)-1-indanamine monoamine reuptake blockers have been synthesized in an effort to develop a compound that could be used as a maintenance therapy to treat cocaine abuse. Since the effects of cocaine on dopamine (DA) and serotonin (5HT) transporters are important components of its pharmacological activity, the focus was on nonselective inhibitors of monoamine transport. To reduce or eliminate the abuse potential of a DA reuptake blocker, the compounds were designed to be slow-onset, long-duration prodrugs whose N-demethylated metabolites would have increased activity over the parent compound with the ideal being a parent compound that has little or no activity. To achieve this, pairs of compounds with different groups on the amine nitrogen and with and without an additional N-methyl group were synthesized. All of the synthesized compounds were screened for binding and reuptake at the cloned human DA, 5HT, and norepinephrine (NE) transporters. As previously found, trans isomers are nonselective blockers of DA, 5HT, and NE reuptake, cis isomers with small N-alkyl groups are selective blockers of 5HT reuptake, and tertiary amines of the trans compounds are less potent than the corresponding N-demethylated secondary amines as blockers of DA reuptake. Larger N-alkyl groups in both the trans and cis series were found to reduce activity for the 5HT and NE transporters with less effect at DA transporters. Selected trans compounds were also screened for locomotor activity in mice and generalization to a cocaine-like profile in rats. With intraperitoneal administration, all of the trans isomers showed a slow onset of at least 20 min and an extremely long duration of action in the locomotor assays. Several of the trans compounds also fully generalized to a cocaine-like pharmacological profile. An initial lead compound, the N,N-dimethyl analogue trans-1b, was resolved into chirally pure enantiomers. Surprisingly, both enantiomers were found to have significant affinity for the DA transporter and to cause locomotor activation. This is in contrast to the N-methyl compound in which only the (+)-enantiomer had significant activity. The absolute configuration of the more active enantiomer was determined by X-ray crystallography to be 3R,1S.

Clozapine produces potent antidopaminergic effects anatomically specific to the mesolimbic system.

Although weak as an antagonist at brain dopamine receptors, clozapine is very strongly antidopaminergic when measured by in vivo single-neuron electrophysiologic recording, in vivo brain microdialysis, in vivo brain voltammetric electrochemistry, in vivo electrical brain stimulation, or in vivo neurobehavioral techniques. Three aspects of clozapine's strong antidopaminergic actions are remarkable. First, clozapine's antidopaminergic potency is stronger than can be explained by its comparatively weak interaction with dopamine receptors, implying that a significant portion of its antidopaminergic action may be transsynaptic and secondary to actions on nondopamine neurotransmitter systems. Second, clozapine's strong antidopaminergic action is seen more reliably with chronic rather than acute administration, implying that some cumulative neurochemical process underlies the gradual recruitment of dopamine blockade. Third, and most remarkably, clozapine's strong antidopaminergic action is anatomically specific--present in the mesolimbic dopamine system but absent in the nigrostriatal dopamine system. This mesolimbic-specific dopamine blockade may underlie at least a portion of clozapine's atypical clinical profile.

Behavioral and biochemical aspects of neuroleptic-induced dopaminergic supersensitivity: studies with chronic clozapine and haloperidol.

Rats were chronically injected with saline, clozapine, or haloperidol and tested for alterations in dopamine (DA)-mediated behavior, DA receptor binding, and both acetylcholine (ACH) concentration and choline acetylase activity. Behaviorally, chronic haloperidol significantly enhanced apomorphine-induced chewing and sniffing stereotypies, associated with DA nigrostriatal activation, while clozapine selectively enhanced apomorphine locomotor activity and cage-floor crossing, behavior associated with DA mesolimbic activation. Biochemically, chronic haloperidol significantly enhanced 3H-spiroperidol binding in striatum and in mesolimbic loci (nucleus accumbens/olfactory tubercle) while chronic clozapine failed to produce such enhancement. Acute haloperidol induced an initial decrease in striatal ACH concentration followed by a return of ACH to normal levels within 1 week. There was no change in choline acetylase activity during the same time interval. These findings suggest that haloperidol may inhibit DA mechanisms in both the nigrostriatal may inhibit DA mechanisms in both the nigrostriatal and mesolimbic systems, but that the effect of clozapine on DA mechanisms may be specific to mesolimbic rather than striatal structures. At the same time, the lack of effect of clozapine on 3H-spiroperidol binding may indicate that behaviorally important changes in DA sensitivity can develop independent of changes in post-synaptic DA receptors. The pattern of cholinergic changes with chronic haloperidol suggests that the increase in striatal DA receptor number seen with chronic treatment re-establishes DA inhibition of cholinergic firing within the striatum.

Clozapine's functional mesolimbic selectivity is not duplicated by the addition of anticholinergic action to haloperidol: a brain stimulation study in the rat.

This study examined whether the anticholinergic potency of the clinically superior antipsychotic drug clozapine contributes to clozapine's anatomically-selective functional inhibition of the mesolimbic dopamine (DA) system, using an electrical brain-stimulation reward (BSR) paradigm in rats that has been previously shown to be highly sensitive to clozapine's mesolimbic functional selectivity. Rats were chronically administered saline, clozapine, haloperidol, or haloperidol plus the anticholinergic compound trihexyphenidyl, and threshold sensitivity of the mesolimbic and nigrostriatal DA systems was assessed using the BSR paradigm, to infer degree of functional DA blockade produced by the chronic drug regimens. Chronic saline produced no change in either DA system. Congruent with previous findings, chronic clozapine powerfully inhibited the mesolimbic DA system but spared the nigrostriatal DA system. Also congruent with previous findings, chronic haloperidol powerfully inhibited both DA systems. Compared to chronic haloperidol alone, chronic haloperidol plus chronic trihexyphenidyl exerted diminished anti-DA action in both the mesolimbic and nigrostriatal DA systems. These results suggest that clozapine's anticholinergic potency is not an adequate explanation for its functional mesolimbic selectivity.

Facilitation of brain stimulation reward by delta 9-tetrahydrocannabinol.

The present experiment explored whether delta 9-tetrahydrocannabinol (delta 9-THC), the psychoactive ingredient in marijuana, shares with other drugs of abuse the ability to facilitate brain stimulation reward acutely, as measured by electrical intracranial self-stimulation (ICSS). Laboratory rats were implanted with stimulation electrodes in the medial forebrain bundle, and trained to stable performance on a self-titrating threshold ICSS paradigm. delta 9-THC, at a dose believed pharmacologically relevant to moderate human use of marijuana, acutely lowered ICSS thresholds, suggesting that marijuana acts on similar CNS hedonic systems to most other drugs of abuse.

Delta 9-tetrahydrocannabinol produces naloxone-blockable enhancement of presynaptic basal dopamine efflux in nucleus accumbens of conscious, freely-moving rats as measured by intracerebral microdialysis.

This study examined the effects of acute administration of delta-9-tetrahydrocannabinol (delta 9-THC), the psychoactive ingredient in marijuana, on extracellular efflux of dopamine (DA) and its metabolites as measured by in vivo microdialysis in nucleus accumbens of conscious, freely-moving rats. delta 9-THC, at low doses (0.5-1.0 mg/kg), which significantly enhance brain stimulation reward (intracranial self-stimulation), significantly increased DA efflux in nucleus accumbens. Augmentation of DA efflux by delta 9-THC was abolished by removal of calcium (Ca++) ions from the perfusion fluid, indicating a Ca(++)-dependence of delta 9-THC's action. Augmentation of DA efflux by delta 9-THC was either totally blocked or significantly attenuated by doses of naloxone as low as 0.1 mg/kg. Given the postulated role of mesocorticolimbic DA circuits in mediating and/or modulating brain stimulation reward, the present data raise the possibility that marijuana's rewarding effects, and hence its euphorigenic effects and abuse potential, may be related to pharmacological augmentation of presynaptic DA mechanisms. Additionally, the DA mechanisms enhanced by marijuana appear to be modulated by an endogenous opioid peptide system.

Effects of haloperidol on human plasma magnesium.

The effect of haloperidol treatment on human plasma levels of magnesium (Mg), calcium (Ca) and phosphorus (P) was assessed. Haloperidol treatment significantly reduced plasma Mg but not plasma Ca or P levels. This finding contrasts with studies using other neuroleptics where reductions in both Mg and Ca concentrations were observed. The addition of lithium to haloperidol treatment resulted in an elevation of plasma Mg, but not Ca or P, to levels significantly greater than those at baseline. The reduction of Mg levels by haloperidol may reflect the ion's involvement in the pathology of psychosis and/or in the mechanism of generating extrapyramidal side effects.

Overview of chemical sampling techniques.

Although many of the ideas for sampling the chemical microenvironment of the brain were present, at least in nascent form, three decades ago or more, the last 10 years have witnessed a particularly spectacular surge of development, refinement, and use. We are now able to measure virtually any endogenous brain chemical in vivo at commendable levels of sensitivity, selectivity, and speed. The long-dreamt-of goal of being able to correlate neurochemical events with ongoing behavior and/or presentation of salient environmental cues and stimuli has already been largely achieved. Further refinements of existing techniques may well lead to levels of analysis inconceivable even a few years ago. The implications for theory-building and hypothesis-testing are enormous, particularly within such essentially virgin domains as behavioral neuroscience and biological psychiatry. These are truly exciting times.

Enhancement of self-stimulation behavior in rats and monkeys after chronic neuroleptic treatment: evidence for mesolimbic supersensitivity.

The effect of chronic neuroleptic drug treatment on self-stimulation of the mesolimbic dopamine system was tested. Rats with electrodes implanted into the ventral tegmental nucleus (A10 cell body area) were treated with haloperidol for three weeks. Afterwards, the rats showed a 35% increase in self-stimulation rate, as compared to pre-drug control rates. This increase persisted for three weeks after drug withdrawal before returning to baseline rates. Rats treated for three weeks with the atypical neuroleptic, clozapine, also showed an increase, the duration and magnitude of which was similar to that seen in the haloperidol group. In addition, four rhesus monkeys with electrodes in the nucleus accumbens (one of the terminal projection areas of the A10 mesolimbic dopamine system) were given a three week treatment with haloperidol, after which all animals showed a significant, long-lasting decrease in self-stimulation threshold, as measured by a rate-independent reward paradigm. Taken together, these results suggest the induction of receptor supersensitivity in the mesolimbic dopamine system by long-term treatment with neuroleptic drugs.

Serotonin denervation enhances responsiveness of presynaptic dopamine efflux to acute clozapine in nucleus accumbens but not in caudate-putamen.

Clozapine alters mesolimbic dopamine (DA) function but spares nigrostriatal DA function in laboratory animals, but the underlying mechanism is unknown. In the present study, acute intraperitoneal injection of clozapine (5-40 mg/kg) increased extracellular DA levels in nucleus accumbens (Acb) and caudate-putamen (CPu) of awake, freely moving rats as measured by in vivo brain microdialysis, without anatomic selectivity. However, in serotonin (5HT)-denervated rats acute clozapine preferentially enhanced DA levels in Acb as compared to CPu. Since (i) up-regulation of 5HT receptors on DA neurons may result from 5HT denervation, (ii) clozapine has potent anti-5HT action, and (iii) 5HT receptors are more dense in Acb than CPu, these data appear to add additional weight to previous suggestions that a serotonergic mechanism may partly underlie clozapine's mesolimbic selectivity.

Effects of acute and chronic clozapine on dopaminergic function in medial prefrontal cortex of awake, freely moving rats.

We previously showed that chronic administration of the clinically atypical and clinically superior antipsychotic drug clozapine selectively reduces dopamine (DA) release in the nucleus accumbens but not neostriatum, and that this effect appears mediated by anatomically selective mesolimbic DA depolarization blockade. The present study extends that research to another mesocorticolimbic DA locus, the medial prefrontal cortex. Acute clozapine challenge (5-40 mg/kg i.p.) produced dose-dependent increased extracellular levels of DA and its metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), in the medial prefrontal cortex of awake, free-moving rats as measured by in vivo brain microdialysis. Chronic clozapine treatment (20 mg/kg/day for 21 days) did not significantly change basal extracellular levels of DA, DOPAC or HVA. Acute clozapine challenge on day 22 in the chronic clozapine-treated animals produced no significant differences in medial prefrontal cortex DA, DOPAC or HVA as compared to chronic vehicle-treated animals, indicating that tolerance to clozapine does not develop in the mesocortical DA system, in contrast to the mesolimbic system. The DA agonist apomorphine (100 micrograms/kg) produced decreased basal extracellular levels of DA, DOPAC and HVA in medial prefrontal cortex of both chronic clozapine-treated and chronic vehicle-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Increase in mesolimbic electrical self-stimulation after chronic haloperidol: reversal by L-DOPA or lithium.

After chronic neuroleptic drug treatment, an increase in electrical intracranial self-stimulation (ICSS) rate is seen from electrodes in the A10 dopaminergic nucleus. This increase, which persists for approximately 3 weeks following drug withdrawal, is believed to represent a behavioral manifestation of drug-induced dopaminergic synaptic supersensitivity. Chronic L-DOPA caused a partial reversal of haloperidol-induced ICSS increase. Lithium carbonate, given concurrently with the haloperidol, partially prevented the development of ICSS supersensitivity. It is concluded that dopaminergic synaptic sensitivity has a two-way modulatory capability.

Ventral tegmental microinjection of delta 9-tetrahydrocannabinol enhances ventral tegmental somatodendritic dopamine levels but not forebrain dopamine levels: evidence for local neural action by marijuana's psychoactive ingredient.

Basal extracellular levels of dopamine (DA) and its metabolites in both ventral tegmental area (VTA) and nucleus accumbens (Acb) were simultaneously monitored by in vivo brain microdialysis in laboratory rats. Microinjection of 12 micrograms or 24 micrograms delta 9-tetrahydrocannabinol (delta 9-THC), the psychoactive ingredient in marijuana and hashish, into the VTA produced a dose-dependent increase in somatodendritic DA levels in VTA but failed to produce any simultaneous change in extracellular DA in Acb. Direct delta 9-THC perfusion (5 x 10(-5) and 2 x 10(-4) M) into Acb via the microdialysis probes caused a significant increase in extracellular DA levels in Acb. These findings suggest that (1) delta 9-THC has a facilitating effect on somatodendritic DA efflux, and (2) the elevation of Acb DA levels seen in our previous studies with systemic administration of delta 9-THC may result from local actions of delta 9-THC at or near the DA terminal projections in Acb.

Activation of 5-HT3 receptor by 1-phenylbiguanide increases dopamine release in the rat nucleus accumbens.

The serotonin-3 (5-HT3) agonist 1-phenylbiguanide (0.1-1.0 mM in perfusate) caused a robust, dose-dependent enhancement of extracellular dopamine content in nucleus accumbens as measured by in vivo microdialysis. This action was antagonized by co-perfusion of the 5-HT3 antagonists zacopride and GR38032F (1 mM in perfusate). Similar effects were observed in 5-HT-denervated rats. These findings suggest that there is a potent modulation of dopamine (DA) release in the nucleus accumbens mediated via 5-HT3 receptors, which appear to be located presynaptically on DA terminals of the mesolimbic DA pathway.