Automated detection of the head-twitch response using wavelet scalograms and a deep convolutional neural network.

Hallucinogens induce the head-twitch response (HTR), a rapid reciprocal head movement, in mice. Although head twitches are usually identified by direct observation, they can also be assessed using a head-mounted magnet and a magnetometer. Procedures have been developed to automate the analysis of magnetometer recordings by detecting events that match the frequency, duration, and amplitude of the HTR. However, there is considerable variability in the features of head twitches, and behaviors such as jumping have similar characteristics, reducing the reliability of these methods. We have developed an automated method that can detect head twitches unambiguously, without relying on features in the amplitude-time domain. To detect the behavior, events are transformed into a visual representation in the time-frequency domain (a scalogram), deep features are extracted using the pretrained convolutional neural network (CNN) ResNet-50, and then the images are classified using a Support Vector Machine (SVM) algorithm. These procedures were used to analyze recordings from 237 mice containing 11,312 HTR. After transformation to scalograms, the multistage CNN-SVM approach detected 11,244 (99.4%) of the HTR. The procedures were insensitive to other behaviors, including jumping and seizures. Deep learning based on scalograms can be used to automate HTR detection with robust sensitivity and reliability.

Fully automated head-twitch detection system for the study of 5-HT2A receptor pharmacology in vivo.

Head-twitch behavior (HTR) is the behavioral signature of psychedelic drugs upon stimulation of the serotonin 5-HT2A receptor (5-HT2AR) in rodents. Following the previous report of a semi-automated detection of HTR based on the dynamics of mouse's head movement, here we present a system for the identification of individual HTR events in a fully automated fashion. The validity of this fully automated HTR detection system was tested with the psychedelic drug DOI in 5-HT2AR-KO mice, and via evaluation of potential sources of false-positive and false-negative HTR events. The increased throughput in data processing achieved via automation afforded the possibility of conducting otherwise time consuming HTR time-course studies. To further assess the versatility of our system, we also explored the pharmacological interactions between 5-HT2AR and the metabotropic glutamate receptor 2 (mGluR2). Our data demonstrate the potentiation effect of the mGluR2/3 antagonist LY341495 on DOI-induced HTR, as well as the HTR-blocking effect of the mGluR2/3 agonist and antipsychotic drug in development LY404039. This fully automated system can contribute to speed up our understanding of 5-HT2AR's pharmacology and its characteristic behavioral outputs in rodents.

Hallucinogen-Like Action of the Novel Designer Drug 25I-NBOMe and Its Effect on Cortical Neurotransmitters in Rats.

NBOMes are N-benzylmethoxy derivatives of the 2C family hallucinogens. 4-Iodo-2,5-dimethoxy-N-(2-methoxybenzyl)phenethylamine (25I-NBOMe) is one of the commonly used illicit drugs. It exhibits high binding affinity for 5-HT2A/C and 5-HT1A serotonin receptors. Activation of 5-HT2A receptor induces head-twitch response (HTR) in rodents, a behavioral marker of hallucinogen effect in humans. There is not much data on neurochemical properties of NBOMes. Therefore, we aimed to investigate the effect of 25I-NBOMe on extracellular level of dopamine (DA), serotonin (5-HT), and glutamate (GLU) in the rat frontal cortex, tissue contents of monoamines, and hallucinogenic activity in rats. The extracellular levels of DA, 5-HT, and GLU were studied using microdialysis in freely moving animals. The tissue contents of DA, 5-HT and their metabolites 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) were determined in the rat frontal cortex. We also tested a drug-elicited HTR. 25I-NBOMe at doses 1, 3, and 10 mg/kg (sc) increased extracellular DA, 5-HT, and GLU levels, enhanced tissue content of 5-HT and 5-HIAA, but did not affect tissue level of DA and its metabolites. The compound exhibited an inverted U-shaped dose-response curve with respect to the effect on extracellular DA and 5-HT levels, but a U-shaped dose-response curve was observed for its effect on GLU release and HTR. The data from our study suggest that hallucinogenic activity of 25I-NBOMe seems to be related with the increase in extracellular GLU level-mediated via cortical 5-HT2A receptors. The influence of 25I-NBOMe on 5-HT2C and 5-HT1A receptors may modulate its effect on neurotransmitters and HTR.

Effects of magnesium with or without boron on headshaking behavior in horses with trigeminal-mediated headshaking.

BACKGROUND: Oral administration of magnesium and boron might have a beneficial effect on headshaking behavior in horses. OBJECTIVE: Evaluate the effects of oral magnesium alone or in combination with boron on headshaking behavior in affected horses. ANIMALS: Twelve geldings (6 healthy controls and 6 affected). METHODS: Prospective randomized controlled dietary trial over 42 days in 12 horses (6 horses diagnosed with trigeminal-mediated headshaking and 6 unaffected healthy controls). All horses received a hay diet and were randomized into 3 treatment groups: pelleted feed combination (PF), pelleted feed combination with magnesium (M), and pelleted feed combination with magnesium-boron (MB) with a week washout of hay only between treatments. Headshaking behavior and biochemical blood variables were assessed at baseline (hay only) and then after each week of supplementation. RESULTS: All 3 diet interventions increased blood ionized and total magnesium. Groups M and MB further increased Mg2+ when compared to PF. Horses receiving treatments had a significant reduction in headshaking behavior, as measured by incidence rate ratio (IRR), when compared to unsupplemented hay diet (44% for PF, IRR, 0.558; CI, 0.44, 0.72; P < .001; 52% for M, IRR, 0.476; CI, 0.37, 0.62; P < .001; and 64% for MB, IRR, 0.358; CI, 0.27, 0.48; P < .001). CONCLUSIONS AND CLINICAL IMPORTANCE: Magnesium in combination with boron had the greatest decrease in headshaking. Oral supplementation with magnesium or magnesium in combination with boron should be considered in horses affected with headshaking.

Comparison of the behavioral responses induced by phenylalkylamine hallucinogens and their tetrahydrobenzodifuran ("FLY") and benzodifuran ("DragonFLY") analogs.

In recent years, rigid analogs of phenylalkylamine hallucinogens have appeared as recreational drugs. Examples include 2-(8-bromo-2,3,6,7-tetrahydrobenzo[1,2-b:4,5-b']difuran-4-yl)ethan-1-amine (2C-B-FLY) and 1-(8-bromobenzo[1,2-b;4,5-b']difuran-4-yl)-2-aminopropane (Bromo-DragonFLY, DOB-DFLY). Although some rigid compounds such as DOB-DFLY reportedly have higher potency than their non-rigid counterparts, it is not clear whether the same is true for 2C-B-FLY and other tetrahydrobenzodifurans. In the present study, the head twitch response (HTR), a 5-HT2A receptor-mediated behavior induced by serotonergic hallucinogens, was used to assess the effects of 2,5-dimethoxy-4-bromoamphetamine (DOB) and its α-desmethyl homologue 2,5-dimethoxy-4-bromophenethylamine (2C-B), as well as their benzodifuranyl and tetrahydrobenzodifuranyl analogs, in C57BL/6J mice. DOB (ED50 = 0.75 µmol/kg) and 2C-B (ED50 = 2.43 µmol/kg) induced the HTR. The benzodifurans DOB-DFLY (ED50 = 0.20 µmol/kg) and 2C-B-DFLY (ED50 = 1.07 µmol/kg) had significantly higher potency than DOB and 2C-B, respectively. The tetrahydrobenzodifurans DOB-FLY (ED50 = 0.67 µmol/kg) and 2C-B-FLY (ED50 = 1.79 µmol/kg), by contrast, were approximately equipotent with their non-rigid counterparts. Three novel tetrahydrobenzodifurans (2C-I-FLY, 2C-E-FLY and 2C-EF-FLY) were also active in the HTR assay but had relatively low potency. In summary, the in vivo potency of 2,5-dimethoxyphenylalkylamines is enhanced when the 2- and 5-methoxy groups are incorporated into aromatic furan rings, whereas potency is not altered if the methoxy groups are incorporated into dihydrofuran rings. The potency relationships for these compounds in mice closely parallel the human hallucinogenic data. The high potency of DOB-DFLY is probably linked to the presence of two structural features (a benzodifuran nucleus and an α-methyl group) known to enhance the potency of phenylalkylamine hallucinogens.

Differential associations of combined vs. isolated cannabis and nicotine on brain resting state networks.

Concomitant cannabis and nicotine use is more prevalent than cannabis use alone; however, to date, most of the literature has focused on associations of isolated cannabis and nicotine use limiting the generalizability of existing research. To determine differential associations of concomitant use of cannabis and nicotine, isolated cannabis use and isolated nicotine use on brain network connectivity, we examined systems-level neural functioning via independent components analysis (ICA) on resting state networks (RSNs) in cannabis users (CAN, n = 53), nicotine users (NIC, n = 28), concomitant nicotine and cannabis users (NIC + CAN, n = 26), and non-users (CTRL, n = 30). Our results indicated that the CTRL group and NIC + CAN users had the greatest functional connectivity relative to CAN users and NIC users in 12 RSNs: anterior default mode network (DMN), posterior DMN, left frontal parietal network, lingual gyrus, salience network, right frontal parietal network, higher visual network, insular cortex, cuneus/precuneus, posterior cingulate gyrus/middle temporal gyrus, dorsal attention network, and basal ganglia network. Post hoc tests showed no significant differences between (1) CTRL and NIC + CAN and (2) NIC and CAN users. These findings of differential associations of isolated vs. combined nicotine and cannabis use demonstrate an interaction between cannabis and nicotine use on RSNs. These unique and combined mechanisms through which cannabis and nicotine influence cortical network functional connectivity are important to consider when evaluating the neurobiological pathways associated with cannabis and nicotine use.

Pharmacological profile of vestibular inhibitory inputs to superior oblique motoneurons.

Vestibulo-ocular reflexes (VOR) are mediated by three-neuronal brainstem pathways that transform semicircular canal and otolith sensory signals into motor commands for the contraction of spatially specific sets of eye muscles. The vestibular excitation and inhibition of extraocular motoneurons underlying this reflex is reciprocally organized and allows coordinated activation of particular eye muscles and concurrent relaxation of their antagonistic counterparts. Here, we demonstrate in isolated preparations of Xenopus laevis tadpoles that the discharge modulation of superior oblique motoneurons during cyclic head motion derives from an alternating excitation and inhibition. The latter component is mediated exclusively by GABA, at variance with the glycinergic inhibitory component in lateral rectus motoneurons. The different pharmacological profile of the inhibition correlates with rhombomere-specific origins of vestibulo-ocular projection neurons and the complementary segmental abundance of GABAergic and glycinergic vestibular neurons. The evolutionary conserved rhombomeric topography of vestibulo-ocular projections makes it likely that a similar pharmacological organization of inhibitory VOR neurons as reported here for anurans is also implemented in mammalian species including humans.

Involvement of glutamatergic N-methyl-d-aspartate receptors in the expression of increased head-dipping behaviors in the hole-board tests of olfactory bulbectomized mice.

Olfactory bulbectomized (OB) mice produce agitated anxiety-like behaviors in the hole-board test, which was expressed by an increase in head-dipping counts and a decrease in head-dipping latencies. However, the associated mechanisms remain unclear. In the present study, MK-801 (10, 100µg/kg), a selective N-methyl-d-aspartate (NMDA) receptor antagonist, significantly and dose-dependently suppressed the increased head-dipping behaviors in OB mice, without affecting sham mice. Similar results were obtained with another selective NMDA receptor antagonist D-AP5 treatment in OB mice. On the other hand, muscimol, a selective aminobutyric acid type A (GABAA) receptor agonist produced no effects on these hyperemotional behaviors in OB mice at a dose (100µg/kg) that produced anxiolytic-like effects in sham mice. Interestingly, glutamine contents and glutamine/glutamate ratios were significantly increased in the amygdala and frontal cortex of OB mice compared to sham mice. Based on these results, we concluded that the glutamatergic NMDA receptors are involved in the expression of increased head-dipping behaviors in the hole-board tests of OB mice. Accordingly, the changes in glutamatergic transmission in frontal cortex and amygdala may play important roles in the expression of these abnormal behaviors in OB mice.

Perverted head-shaking and positional downbeat nystagmus in pregabalin intoxication.

Dizziness and ataxia are known adverse effects of pregabalin, but characteristic oculomotor signs in pregabalin intoxication have not been reported. Here we describe a patient who displayed perverted head-shaking and positional downbeat nystagmus after prescription of a high dosage of pregabalin. Since pregabalin reduces excitatory neurotransmitter secretion in the central nervous system, decreased excitatory inputs from the brainstem may lead to cerebellar dysfunction, causing perverted head-shaking and positional downbeat nystagmus.

Involvement of the benzodiazepine system in the anxiolytic-like effect of Yokukansan (Yi-gan san).

The traditional Japanese Kampo medicine Yokukansan (YKS, Yi-gan san in Chinese) has been demonstrated to improve the behavioral and psychological symptoms of dementia (BPSD), such as anxiety, hallucinations, agitation and irritability. The aim of this study was to elucidate the mechanism of the anxiolytic-like effects of YKS and Chotoko, which is an active component of YKS. Oral treatment with YKS (300 and 1000 mg/kg) significantly increased the number of head-dipping behaviors in mice in the hole-board test. Head-dipping behavior in mice was also significantly increased by treatment with Chotoko (50 and 100mg/kg, p.o.). In addition, oral treatment with the water-extracted fractions from YKS (YKS-W; 250 and 500 mg/kg, p.o.) and Chotoko (Chotoko-W; 10 and 30 mg/kg) significantly increased the number of head-dipping behaviors in mice. On the other hand, treatment with the methanol-extracted fraction of YKS (YKS-Met; 15 and 30 mg/kg, p.o.) did not affect head-dipping behavior. The total distance and number of rearing behaviors were not affected by treatment with any of these drugs. The increase in the number of head-dipping behaviors by treatment with YKS-W (500 mg/kg, p.o.) and Chotoko-W (30 mg/kg, p.o.) was inhibited by pretreatment with the benzodiazepine receptor antagonist flumazenil (1mg/kg, i.v.). In the elevated plus-maze test, the percentage of time spent in open arms was increased in YKS (1000 mg, p.o.) treatment. Based on these results, we suggest that YKS produces an anxiolytic-like effect mediated by the benzodiazepine system. Chotoko is an effective component of YKS for producing an anxiolytic-like effect. The effective compound(s) should be contained, at least in part, in the water-soluble fraction of YKS.

Peripheral and central mediators of lipopolysaccharide induced suppression of defensive rage behavior in the cat.

Based upon recent findings in our laboratory that cytokines microinjected into the medial hypothalamus or periaqueductal gray (PAG) powerfully modulate defensive rage behavior in cat, the present study determined the effects of peripherally released cytokines following lipopolysaccharide (LPS) challenge upon defensive rage. The study involved initial identification of the effects of peripheral administration of LPS upon defensive rage by electrical stimulation from PAG and subsequent determination of the peripheral and central mechanisms governing this process. The results revealed significant elevation in response latencies for defensive rage from 60 to 300 min, post LPS injection, with no detectable signs of sickness behavior present at 60 min. In contrast, head turning behavior elicited by stimulation of adjoining midbrain sites was not affected by LPS administration, suggesting a specificity of the effects of LPS upon defensive rage. Direct administration of LPS into the medial hypothalamus had no effect on defensive rage, suggesting that the effects of LPS were mediated by peripheral cytokines rather than by any direct actions upon hypothalamic neurons. Complete blockade of the suppressive effects of LPS by peripheral pretreatment with an Anti-tumor necrosis factor-alpha (TNFalpha) antibody but not with an anti- interleukin-1 (IL-1) antibody demonstrated that the effects of LPS were mediated through TNF-alpha rather than through an IL-1 mechanism. A determination of the central mechanisms governing LPS suppression revealed that pretreatment of the medial hypothalamus with PGE(2) or 5-HT(1A) receptor antagonists each completely blocked the suppressive effects of LPS, while microinjections of a TNF-alpha antibody into the medial hypothalamus were ineffective. Microinjections of -Iodo-N-[2-[4-(methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) benzamide monohydrochloride (p-MPPI) into lateral hypothalamus (to test for anatomical specificity) had no effect upon LPS induced suppression of defensive rage. The results demonstrate that LPS suppresses defensive rage by acting through peripheral TNF-alpha in periphery and that central effects of LPS suppression of defensive rage are mediated through PGE(2) and 5-HT(1A) receptors in the medial hypothalamus.

Synthesis and preliminary screening of novel N-{2-[4-(substituted)piperazin-1-yl]-2-oxoethyl}acetamides as potential atypical antipsychotic agents.

A series of N-{2-[4-(substituted)piperazin-1-yl]-2-oxoethyl}acetamides were synthesized as prospective novel atypical antipsychotic agents. Microwave irradiation of acetyl glycine (I) with substituted piperazines in the presence of DCC in DMF for about 3-5 min gave the titled compounds (P:1-7). All the synthesized compounds were screened for their in vivo pharmacological activity in Swiss albino mice. D(2) antagonism studies were performed using the climbing mouse assay model and 5-HT(2A) antagonism studies were performed using quipazine induced head twitches in mice. Among the synthesized compounds P4 was found to be the most active compound.

Antidepressant activity of Asparagus racemosus in rodent models.

Asparagus racemosus Linn. (AR) is an Ayurvedic rasayana used as an adaptogen. Adaptogenic drugs are those which are useful as anti-stress agents by promoting non-specific resistance of the body. Although, the adaptogenic effect of AR is well documented, its use in psychological disorders like depression is not scientifically evaluated. Hence, the present investigation evaluates the antidepressant effect of methanolic extract of roots of AR (MAR) standardized to saponins (62.2% w/w). Rats were given MAR in the doses of 100, 200 and 400 mg/kg daily for 7 days and then subjected to forced swim test (FST) and learned helplessness test (LH). The results show that MAR decreases immobility in FST and increases avoidance response in LH indicating antidepressant activity. In behavioral experiments, MAR increased the number of head twitches produced by 5-HTP and increased clonidine-induced aggressive behavior indicating facilitatory effect on both serotonergic and adrenergic systems respectively. However, MAR had insignificant effect on l-DOPA-induced aggressive behavior indicating absence of activity on dopaminergic system. MAR also reversed changes to the endogenous antioxidant system induced by FST. Thus, MAR has significant antidepressant activity and this effect is probably mediated through the serotonergic and the noradrenergic systems and augmentation of antioxidant defenses.

Protopine inhibits serotonin transporter and noradrenaline transporter and has the antidepressant-like effect in mice models.

The protopine isolated from a Chinese herb Dactylicapnos scandens Hutch was identified as an inhibitor of both serotonin transporter and noradrenaline transporter in vitro assays. 5-hydroxy-DL-tryptophan(5-HTP)-induced head twitch response (HTR) and tail suspension test were adopted to study whether protopine has anti-depression effect in mice using reference antidepressant fluoxetine and desipramine as positive controls. In HTR test, protopine at doses of 5, 10, 20 mg/kg dose dependently increase the number of 5-HTP-induced HTR. Protopine at doses of 3.75 mg/kg, 7.5 mg/kg and 30 mg/kg also produces a dose-dependent reduction in immobility in the tail suspension test. The present results open up new possibilities for the use of protopine in the treatment of mood disorders, such as mild and moderate states of depression.

Characterization and opioid modulation of inflammatory temporomandibular joint pain in the rat.

PURPOSE: Experimental inflammation of the rat temporomandibular joint (TMJ) is commonly used to study trigeminal nociceptive processing. This study describes spontaneous pain-related behaviors following TMJ inflammation in the rat. The ability of preemptive systemic morphine to attenuate behaviors as well as immediate-early gene expression in the trigeminal nucleus is described. MATERIALS AND METHODS: Adult male Sprague-Dawley rats received an intra-articular injection of mustard oil (0% to 20%, 50 microL) and were observed for behavioral changes. Morphine sulfate (0 to 10 mg/kg SC) was given 30 minutes before mustard oil; this was reversed in one group with naltrexone hydrochloride (5 mg/kg SC). Two hours after injection rats were killed and perfused. Immunohistochemistry for the protein product of the immediate-early gene c-fos was performed, and brain stem sections including the trigeminal subnucleus caudalis were examined for positive nuclei. RESULTS: Mustard oil inflammation of the rat TMJ induces dose-dependent, morphine-sensitive behaviors. Behaviors observed included excessive grooming of the region, a chewing-like behavior, and head shaking. Fos expression in the trigeminal subnucleus caudalis parallels changes in behaviors. Morphine dose dependently attenuates the number of behaviors, as well as Fos expression; this effect is reversed by the micro-opioid receptor antagonist naltrexone. CONCLUSIONS: Mustard oil inflammation of the rat TMJ causes reliable behavioral changes, which may be quantified and, together with Fos expression, used to assess various experimental TMJ treatment modalities.

5-hydroxytryptamine2A receptor inverse agonists as antipsychotics.

We have used a cell-based functional assay to define the pharmacological profiles of a wide range of central nervous system active compounds as agonists, competitive antagonists, and inverse agonists at almost all known monoaminergic G-protein-coupled receptor (GPCR) subtypes. Detailed profiling of 40 antipsychotics confirmed that as expected, most of these agents are potent competitive antagonists of the dopamine D2 receptor. Surprisingly, this analysis also revealed that most are potent and fully efficacious 5-hydroxytryptamine (5-HT)2A receptor inverse agonists. No other molecular property was shared as universally by this class of compounds. Furthermore, comparisons of receptor potencies revealed that antipsychotics with the highest extrapyramidal side effects (EPS) liability are significantly more potent at D2 receptors, the EPS-sparing atypical agents had relatively higher potencies at 5-HT2A receptors, while three were significantly more potent at 5-HT2A receptors. Functional high-throughput screening of a diverse chemical library identified 530 ligands with inverse agonist activity at 5-HT2A receptors, including several series of compounds related to known antipsychotics, as well as a number of novel chemistries. An analog of one of the novel chemical series, AC-90179, was pharmacologically profiled against the remaining monoaminergic GPCRs and found to be a highly selective 5-HT2A receptor inverse agonist. The behavioral pharmacology of AC-90179 is characteristic of an atypical antipsychotic agent.

Interference of propylene glycol with the hole-board test.

Experimental drugs and/or plant extracts are often dissolved in solvents, including propylene glycol. Nevertheless, there is evidence for psychoactive properties of this alcohol. In this study we found that in the hole-board test 10% propylene glycol did not modify the head-dipping behavior. However, 30% propylene glycol induced an increase in the number of head-dips (46.92 +/- 2.37 compared to 33.83 +/- 4.39, P<0.05, ANOVA/Student-Newman-Keuls), an effect comparable to that obtained with 0.5 mg/kg diazepam (from 33.83 +/- 4.39 to 54 +/- 3.8, P<0.01, ANOVA/Student-Newman-Keuls). These results demonstrate that 30% propylene glycol has significant anxiolytic effects in this model and therefore cannot be used as an innocuous solvent.

Interference of propylene glycol with the hole-board test

Experimental drugs and/or plant extracts are often dissolved in solvents, including propylene glycol. Nevertheless, there is evidence for psychoactive properties of this alcohol. In this study we found that in the hole-board test 10 percent propylene glycol did not modify the head-dipping behavior. However, 30 percent propylene glycol induced an increase in the number of head-dips (46.92 + or - 2.37 compared to 33.83 + or - 4.39, P<0.05, ANOVA/Student-Newman-Keuls), an effect comparable to that obtained with 0.5 mg/kg diazepam (from 33.83 + or - 4.39 to 54 + or - 3.8, P<0.01, ANOVA/Student-Newman-Keuls). These results demonstrate that 30 percent propylene glycol has significant anxiolytic effects in this model and therefore cannot be used as an innocuous solvent

Recovery of the vestibulocolic reflex after aminoglycoside ototoxicity in domestic chickens.

Avian auditory and vestibular hair cells regenerate after damage by ototoxic drugs, but until recently there was little evidence that regenerated vestibular hair cells function normally. In an earlier study we showed that the vestibuloocular reflex (VOR) is eliminated with aminoglycoside antibiotic treatment and recovers as hair cells regenerate. The VOR, which stabilizes the eye in the head, is an open-loop system that is thought to depend largely on regularly firing afferents. Recovery of the VOR is highly correlated with the regeneration of type I hair cells. In contrast, the vestibulocolic reflex (VCR), which stabilizes the head in space, is a closed-loop, negative-feedback system that seems to depend more on irregularly firing afferent input and is thought to be subserved by different circuitry than the VOR. We examined whether this different reflex also of vestibular origin would show similar recovery after hair cell regeneration. Lesions of the vestibular hair cells of 10-day-old chicks were created by a 5-day course of streptomycin sulfate. One day after completion of streptomycin treatment there was no measurable VCR gain, and total hair cell density was approximately 35% of that in untreated, age-matched controls. At 2 wk postlesion there was significant recovery of the VCR; at this time two subjects showed VCR gains within the range of control chicks. At 3 wk postlesion all subjects showed VCR gains and phase shifts within the normal range. These data show that the VCR recovers before the VOR. Unlike VOR gain, recovering VCR gain correlates equally well with the density of regenerating type I and type II vestibular hair cells, except at high frequencies. Several factors other than hair cell regeneration, such as length of stereocilia, reafferentation of hair cells, and compensation involving central neural pathways, may be involved in behavioral recovery. Our data suggest that one or more of these factors differentially affect the recovery of these two vestibular reflexes.

Suppressive effect of mitragynine on the 5-methoxy-N,N-dimethyltryptamine-induced head-twitch response in mice.

We investigated the effects of mitragynine, a major alkaloid isolated from the leaves of Mitragyna speciosa Korth (Rubiaceae), on the 5-HT2A receptor-mediated head-twitch response in mice. Intraperitoneal injection of mitragynine (5-30 mg/kg), as well as intraperitoneal injection of 5-HT2A receptor antagonist ritanserin, inhibited the 5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT: 16 mg/kg, IP)-induced head-twitch response in a dose-dependent manner. In contrast, mitragynine affected neither head-weaving caused by 5-MeO-DMT, nor drug-free spontaneous motor activity. Pretreatment of mice with reserpine (5 mg/kg, IP), p-chlorophenylalanine (p-CPA, 300 mg/kg x 3 times, IP), or 6-hydroxydopamine (6-OHDA, 50 micrograms/mouse, ICV) plus nomifensine (5 mg/kg, IP) did not change the suppressant effect of mitragynine on the head-twitch response caused by 5-MeO-DMT. On the other hand, the alpha 2-adrenoceptor antagonists yohimbine (0.5 mg/kg, IP), and idazoxan (0.2 mg/kg, IP), significantly attenuated the suppressant effect of mitragynine. Lesion of central noradrenergic systems by 6-OHDA plus nomifensine did not alter the effect of idazoxan (0.2 mg/kg) on mitragynine-induced suppression of the head-twitch response. These results indicate that stimulation of postsynaptic alpha 2-adrenoceptor, blockade of 5-HT2A receptors, or both, are involved in suppression of 5-HT2A receptor-mediated head-twitch response by mitragynine.