Anxiolytic-like effects of an mGluR 5 antagonist and a mGluR 2/3 agonist, and antidepressant-like effects of an mGluR 7 agonist in the chick social separation stress test, a dual-drug screening model of treatment-resistant depression.

Modulation of glutamate receptors has demonstrated anxiolytic and/or antidepressant effects in rodent stress models. The chick social-separation stress paradigm exposes socially raised aves to an isolation stressor which elicits distress vocalizations (DVocs) in an attempt to re-establish contact. The model presents a state of panic during the first 5 min followed by a state of behavioral despair during the last 60 to 90 min. Making it useful as a dual anxiolytic/antidepressant screening assay. Further research has identified the Black Australorp strain as a stress-vulnerable, treatment-resistant, and ketamine-sensitive genetic line. Utilizing this genetic line, we sought to evaluate modulation of glutamatergic receptors for potential anxiolytic and/or antidepressant effects. Separate dose-response studies were conducted for the following drugs: the AMPA PAM LY392098, the mGluR 5 antagonist MPEP, the mGluR 2/3 agonist LY404039, the mGluR 2/3 antagonist LY341495, and the mGluR 7 agonist AMN082. The norepinephrine α2 agonist clonidine and the NMDA antagonist ketamine were included as comparison for anxiolytic (anti-panic) and antidepressant effects, respectively. As in previous studies, clonidine reduced DVoc rates during the first 5 min (attenuation of panic) and ketamine elevated DVoc rates (attenuation of behavioral despair) during the last 60 min of isolation. The mGluR 2/3 agonist LY404039 and the mGluR 5 antagonist MPEP decreased DVoc rates during the first 5 min of isolation indicative of anxiolytic effects like that of clonidine while the mGluR 7 agonist AMN082 elevated DVoc rates in the later hour of isolation, representative of antidepressant effects like that of ketamine. Collectively, these findings suggest that certain glutamate targets may be clinically useful in treating panic disorder and/or treatment-resistant depression.

Differential Effects of Cannabidiol and a Novel Cannabidiol Analog on Oxycodone Place Preference and Analgesia in Mice: an Opioid Abuse Deterrent with Analgesic Properties.

Background and Purpose: This study sought to determine whether cannabidiol (CBD) or a CBD derivative, CBD monovalinate monohemisuccinate (CBD-val-HS), could attenuate the development of oxycodone reward while retaining its analgesic effects. Experimental Approach: To determine the effect on oxycodone reward, animals were enrolled in the conditioned place preference paradigm and received either saline or oxycodone (3.0 mg/kg) in combination with either CBD or CBD-val-HS utilizing three sets of drug-/no drug-conditioning trials. To determine if the doses of CBD or CBD-val-HS that blocked opioid reward would affect nociceptive processes, animals were enrolled in the hot plate and abdominal writhing assays when administered alone or in combination with a subanalgesic (1.0 mg/kg) or analgesic (3.0 mg/kg) dose of oxycodone. Key Results: Results from condition place preference demonstrated CBD was not able attenuate oxycodone place preference while CBD-val-HS attenuated these rewarding effects at 8.0 mg/kg and was void of rewarding or aversive properties. In contrast to CBD, CBD-val-HS alone produced analgesic effects in both nociceptive assays but was most effective compared with oxycodone against thermal nociception. Of interest, there was a differential interaction of CBD and CBD-val-HS×oxycodone across the two nociceptive assays producing subadditive responses on the hot plate assay, whereas additive responses were observed in the abdominal writhing assay. Conclusion: These findings suggest CBD-val-HS alone, a nonrewarding analgesic compound, could be useful in pain management and addiction treatment settings.

The kappa-opioid receptor agonist, triazole 1.1, reduces oxycodone self-administration and enhances oxycodone-induced thermal antinociception in male rats.

RATIONALE: Triazole 1.1 is a novel kappa-opioid receptor (KOR) agonist reported to produce antinociception without KOR-typical adverse effects. When combined with the mu-opioid receptor (MOR) agonist, oxycodone, triazole 1.1 blocks oxycodone-induced pruritis without producing sedation-like effects in nonhuman primates. However, it is unknown if triazole 1.1 can reduce the abuse-related effects or enhance the antinociceptive effects of oxycodone similarly to other KOR agonists. OBJECTIVES: The aim of the present study was to quantitatively compare the behavioral effects of triazole 1.1 to the KOR agonists, U50,488h and nalfurafine, on oxycodone self-administration and oxycodone-induced thermal antinociception when administered as mixtures with oxycodone. METHODS: In the self-administration study, male Sprague-Dawley (SD) rats (n = 6) self-administered intravenous (i.v.) oxycodone alone (0.056 mg/kg/inj) or combined with U50,488 h (0.032-0.32 mg/kg/inj), nalfurafine (0.00032-0.0032 mg/kg/inj), or triazole 1.1 (0.32-1.8 mg/kg/inj) under a progressive-ratio schedule of reinforcement. In a hot plate assay, male SD rats (n = 6) received i.v. injections of oxycodone (1.0-5.6 mg/kg), U50,488h (1.0-18.0 mg/kg), nalfurafine (0.01-1.0 mg/kg), or triazole 1.1 (3.2-32.0 mg/kg) alone or in combinations of fixed proportion with oxycodone based on the relative potencies of the single drugs. Each study concluded with administration of the KOR antagonist nor-BNI and some degree of retesting of the previous conditions to verify that the behavioral effects were mediated by KOR activation. RESULTS: All KOR agonists reduced oxycodone self-administration in a dose-dependent manner. Moreover, all single drugs and drug combinations produced dose-dependent, fully efficacious thermal antinociception. All KOR agonist:oxycodone combinations produced either additive or super-additive thermal antinociception. Finally, each KOR agonist was blocked in effect by nor-BNI in both behavioral measures. CONCLUSION: This study demonstrates that triazole 1.1 reduces oxycodone's reinforcing effects and enhances oxycodone-induced antinociception to degrees that are comparable to typical KOR agonists. Given triazole 1.1's mild adverse-effect profile, developing MOR-KOR agonist combinations from the triazole 1.1 series may render new pain therapeutics with reduced abuse liability.

Role of Cannabinoids and Terpenes in Cannabis-Mediated Analgesia in Rats.

Introduction: Cannabis sativa has been used for centuries in treating pain. However, the analgesic role of many of its constituents including terpenes is unknown. This research examined the contributions of terpenes (volatile oil) and cannabinoids in cannabis-mediated analgesia in rats. Methods: Animals received intraperitoneal administration of either vehicle, 10.0 or 18.0 mg/kg morphine, or various doses of the extract without terpenes, isolated terpenes, Δ9-tetrahydrocannabinol (THC), or the full extract. Thirty minutes later animals were tested on hotplate and tail-flick tests of thermal nociception. One week later, rats received a second administration of test articles and were tested 30 min later in the abdominal writhing test of inflammatory nociception. Results: In the thermal assays, hotplate and tail-flick latencies for morphine-treated rats were dose dependent and significantly higher than vehicle-treated animals. All the cannabinoid compounds except for the isolated terpenes produced dose-dependent increases in hotplate and tail-flick latencies. In the inflammatory nociceptive assay, animals treated with vehicle and isolated terpenes demonstrated increased abdominal writhing, whereas all the cannabinoid compounds significantly decreased abdominal writhing responses. Conclusions: Overall, THC alone produced robust analgesia equivalent to the full cannabis extract, whereas terpenes alone did not produce analgesia. These data suggest the analgesic activity of cannabis is largely mediated by THC, whereas terpenes alone do not cause alterations in cannabis-mediated analgesia.

Effects of Cannabidiol on Morphine Conditioned Place Preference in Mice.

This study sought to determine whether the cannabis constituent cannabidiol attenuates the development of morphine reward in the conditioned place preference paradigm. Separate groups of mice received either saline or morphine in combination with one of four doses of cannabidiol using three sets of drug/no-drug conditioning trials. After drug-place conditioning, morphine mice displayed robust place preference that was attenuated by 10 mg/kg cannabidiol. Further, when administered alone, this dose of cannabidiol was void of rewarding and aversive properties. The finding that cannabidiol blocks opioid reward suggests that this compound may be useful in addiction treatment settings.

Effects of Cannabidiol and a Novel Cannabidiol Analog against Tactile Allodynia in a Murine Model of Cisplatin-Induced Neuropathy: Enhanced Effects of Sub-Analgesic Doses of Morphine.

OBJECTIVE: This research examined whether a cannabidiol (CBD)-opioid pharmacotherapy could attenuate cisplatin-induced tactile allodynia. METHODS: Mice (C57BL/6) were given 6 doses of 2.3 mg/kg cisplatin intraperitoneally (IP) on alternating days to induce tactile allodynia as quantified using an electric von Frey (eVF). Test groups in Experiment 1 received either vehicle, 0.1 or 2.5 mg/kg morphine, 1.0 or 2.0 CBD, or the 2 drugs in combination. Test groups in Experiment 2 received either vehicle, 0.1 or 2.5 mg/kg morphine, 1.0, 2.0, 3.0, or 4.0 mg/kg NB2111 (a long-acting CBD analogue), or the 2 drugs in combination. Drugs were administered IP 45 min before eVF assessment. RESULTS: Cisplatin produced tactile allodynia that was attenuated by 2.5 mg/kg morphine. Both CBD and NB2111 produced dose-dependent attenuation of tactile allodynia. CBD and NB2111, given in combination with sub-analgesic doses of morphine, produced attenuation of tactile allodynia equivalent to 2.5 mg/kg morphine. CONCLUSIONS: While both CBD and NB2111, either alone or in combination with sub-analgesic doses of opioids, exhibited analgesic effects, NB2111 could be capable of superior analgesia over time by virtue of enhanced pharmacokinetics.

Effects of nalfurafine on the reinforcing, thermal antinociceptive, and respiratory-depressant effects of oxycodone: modeling an abuse-deterrent opioid analgesic in rats.

RATIONALE: Strategies to reduce the misuse of mu opioid agonists are critically needed. Previous work has shown that kappa opioid agonists can diminish the abuse-related effects and augment the antinociceptive effects of mu agonists. However, use of traditional kappa agonists is limited by their dysphoric side effects. OBJECTIVES: The current study examined the effects of nalfurafine, a clinically available atypical kappa agonist, on the reinforcing, thermal antinociceptive, and respiratory-depressant effects of oxycodone in male rats. METHODS: To determine oxycodone/nalfurafine mixture proportions to be examined intravenously across procedures, a progressive ratio (PR) self-administration procedure compared the reinforcing effects of oxycodone (56 µg/kg/inj) available alone or as a mixture with co-administered nalfurafine (0.32, 1, or 3.2 µg/kg/inj), corresponding to oxycodone/nalfurafine proportions of 175:1, 56:1, and 18:1, respectively. Next, PR and thermal antinociception dose-effect functions were each determined for oxycodone, nalfurafine, and the same oxycodone/nalfurafine mixture proportions. Finally, the respiratory-depressant effects of equi-antinociceptive doses of oxycodone, nalfurafine, and the mixtures were compared. RESULTS: Nalfurafine decreased the reinforcing effects of oxycodone, and the 18:1 mixture did not function as a reinforcer. Oxycodone and nalfurafine each produced dose-dependent antinociception, and the mixtures produced additive antinociception. In addition, antinociceptive doses of the 56:1 and 18:1 mixtures did not produce respiratory depression. CONCLUSIONS: These results suggest that nalfurafine may augment the thermal antinociceptive effects while reducing the reinforcing and respiratory-depressant effects of oxycodone.

The effects of repeated nitroglycerin administrations in rats; modeling migraine-related endpoints and chronification.

BACKGROUND: Rodent models typically use a single nitroglycerin injection to induce migraine, yet migraine in clinical populations presents as recurrent episodes. Further, these models quantify behavioral endpoints that do not align with the clinical features of episodic migraine or migraine chronification and therefore may limit translational relevance. NEW METHOD: Rats received 5 nitroglycerin (10mg/kg/2ml), propylene glycol/ethanol vehicle, or saline injections every third day over 15days. Behavioral endpoints were assessed 110min post nitroglycerin administration and included time spent light/dark chambers for photophobia as well as activity, facial pain expressions, and tactile allodynia. RESULTS: Animals administered nitroglycerin displayed photophobia, decreased activity, and increased facial pain expression. Similar alterations in photophobia and activity were seen in the vehicle treated animals, but these tended to diminish by the 4th or 5th injection. The presentation of spontaneous tactile allodynia was observed in the nitroglycerin group by the 5th episode. COMPARISON WITH EXISTING METHODS: Most NTG migraine models entail a single NTG administration and quantification of evoked allodynia. This paradigm employs recurring NTG episodes and clinically-relevant measures of photophobia, hypoactivity and facial grimace endpoints as well as introduces a novel arena apparatus to quantify spontaneous allodynia. CONCLUSIONS: This repeated NTG procedure and endpoint measures aligns with the frequency and clinical presentation of episodic migraine and its chronification, respectively. Further, propylene glycol ethanol vehicle contributes to migraine endpoints.

The effects of Sceletium tortuosum (L.) N.E. Br. extract fraction in the chick anxiety-depression model.

ETHNOPHARMACOLOGICAL RELEVANCE: Sceletium tortuosum (L.) N.E. Br. has been reported to elevate mood, reduce anxiety and stress and alleviate pain. AIM OF STUDY: This study sought to examine the effects of an S. tortuosum alkaloid enriched fraction in the chick anxiety-depression model, a model that shows high predictive validity as a pharmacological screening assay. MATERIAL AND METHODS: Socially-raised male Silver Laced Wyandotte chicks (4-6 days old) were given IP vehicle, imipramine (10mg/kg), or S. tortuosum fraction (10, 20, 30mg/kg in Exp. 1 or 50, 75, 100mg/kg in Exp. 2) 15min prior to a 60min isolation test period in which distress vocalizations (DVoc) were continuously recorded. RESULTS: Vehicle chicks displayed high DVoc rates in the anxiety phase (first 3min). DVoc rates declined about 50% (i.e., behavioral despair) in the depression phase (30-60min). S. tortuosum fraction at 75 and 100mg/kg decreased DVoc rates during the anxiety phase indicative of an anxiolytic effect. Imipramine, but not S. tortuosum groups, increased DVoc rates in the depression phase indicative of an antidepressant effect. CONCLUSIONS: The findings suggest that an alkaloid enriched S. tortuosum fraction may benefit some forms of stress-related disorders.

Effects of Delta-9-Tetrahydrocannabinol and Cannabidiol on Cisplatin-Induced Neuropathy in Mice.

Sativex, a cannabinoid extract with a 1 : 1 ratio of tetrahydocannabinol and cannabidiol, has been shown to alleviate neuropathic pain associated with chemotherapy. This research examined whether tetrahydocannabinol or cannabidiol alone could attenuate or prevent cisplatin-induced tactile allodynia. In experiment 1, mice (C57BL/6) received eight administrations of 2.3 mg/kg cisplatin or saline solution IP every other day to induce tactile allodynia. Mice were then administered vehicle, 100 mg/kg gabapentin, 2 mg/kg tetrahydocannabinol, or 2 mg/kg cannabidiol IP and tested 60 min later on an electronic Von Frey. In experiment 2, prevention studies, cannabidiol (0.0, 0.5, 1.0, and 2.0 mg/kg) or tetrahydocannabinol (0.0, 0.5, 1.0, and 2.0 mg/kg) was given IP 30 min prior to cisplatin administration (2.3 or 1.0 mg/kg) utilizing a six-dose alternate day protocol. In both studies, tactile responses to the hind paws were quantified in g of force using an electronic Von Frey prior to and after the cisplatin administration protocol. Cisplatin produced a reduction in g of force indicative of neuropathy that was attenuated by gabapentin, tetrahydocannabinol, and cannabidiol but not prevented by either cannabinoid. These data demonstrate that each of the major constituents of Sativex alone can achieve analgesic effects against cisplatin neuropathy.

Clinically relevant behavioral endpoints in a recurrent nitroglycerin migraine model in rats.

BACKGROUND: This research sought to further validate the rat nitroglycerin (NTG) migraine model by comparing the effects of single versus recurrent NTG episodes on behavioral endpoints that mirror ICHD-3 diagnostic criteria for migraine, and to determine if the altered behavioral endpoints are reduced after administration of sumatriptan. METHODS: Separate cohorts of rats were administered NTG (10 mg/kg/2 ml) or saline (Experiment 1: single injection; Experiment 2: repeated injections; Experiment 3: repeated injections with sumatriptan [0.0, 0.3 and 1.0 mg/kg/ml] rescue. Behavioral endpoints were assessed 2 h after final NTG administration and included time in light/dark chambers for photophobia and activity, pain facial ratings, and cool (5 °C) and warm (46 °C) tail dip. RESULTS: The first two experiments demonstrated that repeated (n = 5) but not single NTG injections produced photophobia, decreased activity, and yielded less weight gain than saline injections. Experiment 3 showed that sumatriptan attenuated hypoactivity, reduced facial expressions of pain, and reversed weight alterations in a dose-dependent manner. CONCLUSIONS: These findings identify numerous clinical homologies of a recurrent NTG rat migraine model that may be useful for screening novel pharmacotherapies.

Comparative effects of Mitragyna speciosa extract, mitragynine, and opioid agonists on thermal nociception in rats.

This study sought to compare the effects of Mitragyna speciosa (Korth.) Havil. extract, alkaloids fraction, and mitragynine, a µ-opioid receptor agonist, to that of morphine and oxycodone in a test of thermal nociception. In Experiment 1, male Sprague-Dawley rats were administered test articles intraperitoneally (IP) 30 min prior to testing to compare the effects of M. speciosa articles to opioid reference compounds on the hotplate assay. Test articles were vehicle, 10 mg/kg morphine, 3 mg/kg oxycodone, 300 mg/kg M. speciosa extract, 75 mg/kg M. speciosa alkaloids fraction, or 30 mg/kg mitragynine. To mirror consumer usage, Experiment 2 sought to determine whether M. speciosa articles retained their biological activity when given orally (PO). Test articles were vehicle, 6 mg/kg oxycodone, 300 mg/kg M. speciosa extract, or 100mg/kg mitragynine with hotplate tests conducted 30 and 60 min after administration. Mitragynine produced antinociceptive effects similar to the reference opioid agonists when administered IP and PO routes. These data suggest that M. speciosa extracts containing significant quantities of mitragynine may warrant consideration for further studies in primate self-administration models to yield insight into the abuse liability of this commercially available product.

Design, synthesis and biological evaluation of bivalent benzoxazolone and benzothiazolone ligands as potential anti-inflammatory/analgesic agents.

Benzoxazolone and benzothiazolone were used as template blocks to develop two series of dimers as anti-inflammatory and analgesic agents based on the concept of bivalent ligands. The first series (I) involved varying the carbon chain lengths extending from the piperazine core to the nitrogen atom of the dibenzo[d]oxazol-2(3H)-one or dibenzo[d]thiazol-2(3H)-one. The second series (II) was designed by changing the attachment point. All compounds were screened for their in vitro anti-inflammatory activity in terms of the inhibition of inducible nitric oxide synthase (iNOS) and nuclear factor kappa B (NF-κB). Seventeen compounds inhibited both targets. Eleven of them exhibited IC50 values below 3µM while five compounds showed IC50 values of 1µM or below. Most of the compounds were found to be devoid of cytotoxicity against mammalian kidney and solid tumors cell lines up to 25µg/mL. In vivo anti-inflammatory and antinociceptive studies revealed that compounds 3j, 5t and 8b have significant anti-inflammatory and analgesic activity comparable to that of indomethacin and ketorolac, respectively.

The conditioned place preference test for assessing welfare consequences and potential refinements in a mouse bladder cancer model.

Most pre-clinical analgesic efficacy assays still involve nociceptive testing in rodents. This is despite concerns as to the relevance of these tests for evaluating the pain-preventative properties of drugs. More appropriate methods would target pain rather than nociception, but these are currently not available, so it remains unknown whether animal pain equates to the negatively affective and subjective/emotional state it causes in humans. Mouse cancer models are common despite the likelihood of substantial pain. We used Conditioned Place Preference (CPP) testing, assessments of thermal hyperalgesia and behaviour to determine the likelihood that MBT-2 bladder cancer impacts negatively on mouse welfare, such as by causing pain. There was no CPP to saline, but morphine preference in tumour bearing mice exceeded that seen in tumour-free controls. This occurred up to 10 days before the study end-point alongside reduced body weight, development of hyperalgesia and behaviour changes. These effects indicated mice experienced a negative welfare state caused by malaise (if not pain) before euthanasia. Due to the complexity of the assessments needed to demonstrate this, it is unlikely that this approach could be used for routine welfare assessment on a study-by-study basis. However, our results show mice in sufficiently similar studies are likely to benefit from more intensive severity assessment and re-evaluation of end-points with a view to implementing appropriate refinements. In this particular case, a refinement would have been to have euthanased mice at least 7 days earlier or possibly by provision of end-stage pain relief. CPP testing was found to be a helpful method to investigate the responses of mice to analgesics, possibly on a subjective level. These findings and those of other recent studies show it could be a valuable method of screening candidate analgesics for efficacy against cancer pain and possibly other pain or disease models.

Effects of Sceletium tortuosum in rats.

ETHNOPHARMACOLOGICAL RELEVANCE: Broad historical and current uses in addition to diverse activity on CNS targets may make Sceletium tortuosum a useful therapeutic in a variety of clinical settings. This study sought to more broadly characterize activity of Sceletium tortuosum and mesembrine in a number of common, rodent-based assays that model nociception, depression, anxiety, ataxia, and abuse liability. MATERIALS AND METHODS: Male Sprague-Dawley were administered Sceletium tortuosum extract products and behavioral responses were evaluated in the conditioned place preference (CPP), hot plate, forced swim, elevated plus, and rotarod tests. RESULTS AND CONCLUSIONS: Sceletium tortuosum does not cause preference or aversion in CPP. Mesembrine appears to have analgesic properties without abuse liabilities or ataxia. The Sceletium tortuosum fraction has antidepressant properties but does produce ataxia. The ataxia may limit its usefulness as an antidepressant unless the antidepressant activity is associated with one constituent and the ataxia is associated with a separate constituent.

The effect of Salvia divinorum and Mitragyna speciosa extracts, fraction and major constituents on place aversion and place preference in rats.

ETHNOPHARMACOLOGICAL RELEVANCE: Consumer use of botanicals has increased despite, in many instances, the paucity of research demonstrating efficacy or identifying liabilities. This research employed the place preference/aversion paradigm to characterize the psychoactive properties of Salvia divinorum extract (10, 30, 100mg/kg), salvinorin A (0.1, 0.3, 1.0mg/kg), Mitragyna speciosa MeOH extract (50, 100, 300 mg/kg), Mitragyna speciosa alkaloid-enriched fraction (12.5, 25, 75 mg/kg) and mitragynine (5, 10, 30 mg/kg) in rats. MATERIAL AND METHODS: Following apparatus habituation and baseline preference scores, male Sprague-Dawley rats were given eight counter-balanced drug versus vehicle conditioning trials followed by a preference test conducted under drug-free states. S(+)-amphetamine (1mg/kg) served as the positive control (in Exp. 2) and haloperidol (0.8, 1.0mg/kg) served as the negative control in both studies. RESULTS: Rats displayed place aversion to both Salvia divinorum and salvinorin A that exceeded that of haloperidol. Rats showed place preference to mitragynine that was similar to that of S(+)-amphetamine. This CPP effect was much less pronounced with the Mitragyna speciosa extract and its fraction. CONCLUSIONS: These findings suggest that both botanicals possess liabilities, albeit somewhat different, that warrant caution in their use.

In vitro structure-activity relationships of aplysinopsin analogs and their in vivo evaluation in the chick anxiety-depression model.

Aplysinopsins are tryptophan-derived natural products that have been isolated from a variety of marine organisms and have been shown to possess a range of biological activities. In vitro receptor binding assays showed that of the 12 serotonin receptor subtypes, analogues showed a high affinity for the 5-HT2B and 5-HT2C receptor subtypes, with selectivity for 5-HT2B over 5-HT2C. While no conclusions could be drawn about the number and position of N-methylations, bromination at C-4 and C-5 of the indole ring resulted in greater binding affinities, with Ki's as low as 35 nM. This data, combined with previous knowledge of the CNS activity of aplysinopsin analogs, suggested that these compounds may have potential as leads for antidepressant drugs. Compounds 3c, 3u, and 3x were evaluated in the chick anxiety-depression model to assess their in vivo efficacy. Compound 3c showed a modest antidepressant effect at a dose of 30 nM/kg in the animal model.

Identification of a treatment-resistant, ketamine-sensitive genetic line in the chick anxiety-depression model.

The introduction of pharmacotherapies for treatment-resistant depression is hindered by translational challenges with existing preclinical screening models that fail to adequately model the clinical features of this syndrome. This research sought to screen antidepressants in two selected genetic lines previously identified as stress-vulnerable and -resilient in the chick anxiety-depression model. Separate groups of socially-raised 5-6 day-old Black Australorps (stress-vulnerable) and Production Reds (stress-resilient) were administered imipramine (0-20 mg/kg), fluoxetine (0-10 mg/kg), maprotiline (0-10 mg/kg) or ketamine 0-15 mg/kg) IP (1 ml/kg) and placed into isolation for 90 min. Distress vocalizations (DVoc) were recorded. Onset of behavioral despair and Dvoc rates during the depression-like phase (30-90 min) were calculated. Black Australorps entered behavioral despair approximately 25% faster than Productions Reds highlighting stress-vulnerability in this Black Australorp line. In the depression-like phase, Black Australorps were insensitive to imipramine and fluoxetine but sensitive to ketamine, a finding that parallels stress-vulnerable, treatment resistant depressive disorder. The chick anxiety-depression model using the Black Australorp line may prove useful in pre-clinical screening of novel antidepressant targets for use in treatment-resistant depression.

Strain vulnerability and resiliency in the chick anxiety-depression model.

Increasing research is focused on genetic contributions to variability in stress-related endophenotypes in humans and animal model simulations. The current study sought to identify strain vulnerabilities and resiliencies to an isolation-stressor in the chick anxiety-depression model. Nine different strains of socially raised chicks were tested in isolated or non-isolated conditions for 90 min in which distress vocalization (DVoc) rates were collected and then transformed to depression-like phase threshold (@ 25, 50, 75 and 95%) latencies. In general, chicks in the non-isolated condition displayed relatively low DVoc rates throughout the test session, despite some variability in initial rates. Chicks in the isolated condition displayed relatively high DVoc rates in the first 3 min, indicative of an anxiety-like state, which declined by approximately 50% within 10-25 min in all strains and remained stable thereafter, indicative of a depression-like state. Contrast effects revealed that, relative to all other strains, the Black Australorp strain displayed shorter and the Producrain displayed longer depression threshold latencies, respectively. Of the remaining strains, the Silver Laced Wyandotte displayed depression thresholds that best represent an intermediate stress response. These findings identify vulnerable and resilient strains for examining depression-related endophenotypes in the chick anxiety-depression model.

Brain-derived neurotrophic factor response in vulnerable and resilient genetic lines in the chick anxiety-depression model.

Altered BDNF-mediated synaptogenesis is a major contributor to stress-vulnerability and depression. This study sought to determine patterns of hippocampal BDNF expression in stress-vulnerable and -resilient strains in the chick anxiety-depression model. Socially raised Black Australorp and Production Red strains were tested at 5-6 days post hatch under either 30, 60, 90, or 120 min of social separation stress; chicks tested with 2 social companions for 120 min served as controls. Distress vocalizations were recorded throughout the test session and latency to behavioral despair calculated. Following tests, bilateral hippocampal sections were harvested and analyzed via ELISA for BDNF levels. Black Australorps had shorter latencies to behavioral despair than Production Reds reflecting greater stress vulnerability. No differences were detected in BDNF levels between a No-Test and Social group within or between strains. The stress resilient Production Reds showed stable BDNF levels across the isolation test period whereas the vulnerable Black Australorps showed an increase in hippocampal BDNF levels that peaked at 90 min and declined thereafter. These findings fit well with the notion that strain-dependent stress-vulnerability reflects, in part, poor homeostatic mechanisms controlling synaptogenesis.