Gs signaling pathway distinguishes hallucinogenic and nonhallucinogenic 5-HT2AR agonists induced head twitch response in mice

5- HT2A receptor is a member of the family A G-protein-coupled receptor. It is involved in many psychiatric disorders, such as depression, addiction and Parkinson's disease. 5-HT2AR targeted drugs play an important role in regulating cognition, memory, emotion and other physiological function by coupling G proteins, and their most notable function is stimulating the serotonergic hallucination. However, not all 5-HT2AR agonists exhibit hallucinogenic activity, such as lisuride. Molecular mechanisms of these different effects are not well illustrated. This study suggested that 5-HT2AR coupled both Gs and Gq protein under hallucinogenic agonists DOM and 25CN-NBOH stimulation, but nonhallucinogenic agonist lisuride and TBG only activates Gq signaling. Moreover, in head twitch response (HTR) model, we found that cAMP analogs 8-Bromo-cAMP and PDE4 inhibitor Rolipram could increase HTR, while Gs protein inhibitor Melittin could reduce HTR. Collectively, these results revealed that Gs signaling is a key signaling pathway that may distinguish hallucinogenic agonists and nonhallucinogenic agonists.

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.

The effect of the sigma-1 receptor selective compound LS-1-137 on the DOI-induced head twitch response in mice

Several receptor mediated pathways have been shown to modulate the murine head twitch response (HTR). However, the role of sigma receptors in the murine (±)-2,5-dimethoxy-4-iodoamphetamine (DOI)-induced HTR has not been previously investigated. We examined the ability of LS-1-137, a novel sigma-1 vs. sigma-2 receptor selective phenylacetamide, to modulate the DOI-induced HTR in DBA/2J mice. We also assessed the in vivo efficacy of reference sigma-1 receptor antagonists and agonists PRE-084 and PPCC. The effect of the sigma-2 receptor selective antagonist RHM-1-86 was also examined. Rotarod analysis was performed to monitor motor coordination after LS-1-137 administration. Radioligand binding techniques were used to determine the affinity of LS-1-137 at 5-HT2A and 5-HT2C receptors. LS-1-137 and the sigma-1 receptor antagonists haloperidol and BD 1047 were able to attenuate a DOI-induced HTR, indicating that LS-1-137 was acting in vivo as a sigma-1 receptor antagonist. LS-1-137 did not compromise rotarod performance within a dose range capable of attenuating the effects of DOI. Radioligand binding studies indicate that LS-1-137 exhibits low affinity binding at both 5-HT2A and 5-HT2C receptors. Based upon the results from these and our previous studies, LS-1-137 is a neuroprotective agent that attenuates the murine DOI-induced HTR independent of activity at 5-HT2 receptor subtypes, D2-like dopamine receptors, sigma-2 receptors and NMDA receptors. LS-1-137 appears to act as a sigma-1 receptor antagonist to inhibit the DOI-induced HTR. Therefore, the DOI-induced HTR can be used to assess the in vivo efficacy of sigma-1 receptor selective compounds.

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.

Directly Observable Behavioral Effects of Lorcaserin in Rats

(1R)-8-chloro-1-methyl-2,3,4,5-tetrahydro-1H-3-benzazepine (lorcaserin) is approved by the United States Food and Drug Administration for treating obesity, and its therapeutic effects are thought to result from agonist activity at serotonin (5-HT)2C receptors. Lorcaserin has affinity for other 5-HT receptor subtypes, although its activity at those subtypes is not fully described. The current study compared the behavioral effects of lorcaserin (0.0032-32.0 mg/kg) to the effects of other 5-HT receptor selective agonists in rats (n = 8). The 5-HT2C receptor selective agonist 1-(3-chlorophenyl)piperazine (mCPP, 0.032-1.0 mg/kg) and lorcaserin induced yawning which was attenuated by the 5-HT2C receptor selective antagonist 6-chloro-5-methyl-N-(6-[(2-methylpyridin-3-yl)oxy]pydidin-3-yl)indoline-1-carboxamide (1.0 mg/kg). The 5-HT2A receptor selective agonist 2,5-dimethoxy-4-methylamphetamine (0.1-3.2 mg/kg) induced head twitching, which was attenuated by the 5-HT2A receptor selective antagonist R-(+)-2,3-dimethoxyphenyl-1-[2-(4-piperidine)-methanol] (MDL 100907, 0.01 mg/kg), lorcaserin (3.2 mg/kg), and mCPP (3.2 mg/kg). In rats pretreated with MDL 100907 (1.0 mg/kg), lorcaserin also induced head twitching. At larger doses, lorcaserin produced forepaw treading, which was attenuated by the 5-HT1A receptor selective antagonist N-(2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl)-N-(2-pyridyl)cyclohexanecarboxamide (0.178 mg/kg). While the behavioral effects of lorcaserin in rats are consistent with it having agonist activity at 5-HT2C receptors, these data suggest that at larger doses it also has agonist activity at 5-HT2A and possibly 5-HT1A receptors. Mounting evidence suggests that 5-HT2C receptor agonists might be effective for treating drug abuse. A more complete description of the activity of lorcaserin at 5-HT receptor subtypes will facilitate a better understanding of the mechanisms that mediate its therapeutic effects.

N-Benzyl-5-methoxytryptamines as Potent Serotonin 5-HT2 Receptor Family Agonists and Comparison with a Series of Phenethylamine Analogues

A series of N-benzylated-5-methoxytryptamine analogues was prepared and investigated, with special emphasis on substituents in the meta position of the benzyl group. A parallel series of several N-benzylated analogues of 2,5-dimethoxy-4-iodophenethylamine (2C-I) also was included for comparison of the two major templates (i.e., tryptamine and phenethylamine). A broad affinity screen at serotonin receptors showed that most of the compounds had the highest affinity at the 5-HT2 family receptors. Substitution at the para position of the benzyl group resulted in reduced affinity, whereas substitution in either the ortho or the meta position enhanced affinity. In general, introduction of a large lipophilic group improved affinity, whereas functional activity often followed the opposite trend. Tests of the compounds for functional activity utilized intracellular Ca(2+) mobilization. Function was measured at the human 5-HT2A, 5-HT2B, and 5-HT2C receptors, as well as at the rat 5-HT2A and 5-HT2C receptors. There was no general correlation between affinity and function. Several of the tryptamine congeners were very potent functionally (EC50 values from 7.6 to 63 nM), but most were partial agonists. Tests in the mouse head twitch assay revealed that many of the compounds induced the head twitch and that there was a significant correlation between this behavior and functional potency at the rat 5-HT2A receptor.

Pharmacological modulation of abnormal involuntary DOI-induced head twitch response movements in male DBA/2J mice: II. Effects of D3 dopamine receptor selective compounds

We recently reported on the characterization of the hallucinogen 2,5-dimethoxy-4-methylamphetamine's (DOI) ability to elicit a head twitch response (HTR) in DBA/2J mice and the ability of D2 vs. D3 dopamine receptor selective compounds to modulate that response. For these studies, the ability of D3 vs. D2 dopamine receptor selective compounds to attenuate the DOI-dependent HTR was examined. WC 10, a D3 dopamine receptor weak partial agonist with 40-fold binding selectivity for D3 vs. D2 dopamine receptors, produced a dose-dependent decrease in the DOI-induced HTR (IC50 = 3.7 mg/kg). WC 44, a D3 receptor selective full agonist, also inhibited the DOI-induced HTR (IC50 = 5.1 mg/kg). The effect of two D3 receptor selective partial agonists, LAX-4-136 and WW-III-55, were also evaluated. These analogs exhibit 150-fold and 800-fold D3 vs. D2 binding selectivity, respectively. Both compounds inhibited the HTR with similar potency but with different maximum efficacies. At 10 mg/kg WW-III-55 inhibited the HTR by 95%, while LAX-4-136 administration resulted in a 50% reduction. In addition, DOI (5 mg/kg) was administered at various times after LAX-4-136 or WW-III-55 administration to compare the duration of action. The homopiperazine analog LAX-4-136 exhibited greater stability. An assessment of our test compounds on motor performance and coordination was performed using a rotarod test. None of the D3 dopamine receptor selective compounds significantly altered latency to fall, suggesting that these compounds a) did not attenuate the DOI-dependent HTR due to sedative or adverse motor effects and b) may have antipsychotic/antihallucinogenic activity.

Restricted access to standard or high fat chow alters sensitivity of rats to the 5-HT(2A/2C) receptor agonist 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane

Feeding conditions can impact sensitivity to drugs acting on dopamine receptors; less is known about the impact of feeding conditions on the effects of drugs acting on serotonin (5-HT) receptors. This study examined the effects of feeding conditions on sensitivity to the direct-acting 5-HT(2A/2C) receptor agonist 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM; 0.1-3.2 mg/kg) and the direct-acting dopamine D3/D2 receptor agonist quinpirole (0.0032-0.32 mg/kg). Male Sprague-Dawley rats had free access (11 weeks), followed by restricted access (6 weeks), to high fat (34.3%, n=8) or standard (5.7% fat; n=7) chow. Rats eating high fat chow became insulin resistant and gained more weight than rats eating standard chow. Free access to high fat chow did not alter sensitivity to DOM-induced head twitch but increased sensitivity to quinpirole-induced yawning. Restricting access to high fat or standard chow shifted the DOM-induced head twitch dose-response curve to the right and shifted the quinpirole-induced yawning dose-response curve downward in both groups of rats. Some drugs of abuse and many therapeutic drugs act on 5-HT and dopamine systems; these results show that feeding conditions impact sensitivity to drugs acting on these systems, thereby possibly affecting vulnerability to abuse, as well as the therapeutic effectiveness of drugs.

Characterization of the head-twitch response induced by hallucinogens in mice: detection of the behavior based on the dynamics of head movement

RATIONALE

The head-twitch response (HTR) is a rapid side-to-side rotational head movement that occurs in rats and mice after administration of serotonergic hallucinogens and other 5-HT2A agonists. The HTR is widely used as a behavioral assay for 5-HT2A activation and to probe for interactions between the 5-HT2A receptor and other transmitter systems.

OBJECTIVE

High-speed video recordings were used to analyze the head movement that occurs during head twitches in C57BL/6J mice. Experiments were also conducted in C57BL/6J mice to determine whether a head-mounted magnet and a magnetometer coil could be used to detect the HTR induced by serotonergic hallucinations based on the dynamics of the response.

RESULTS

Head movement during the HTR was highly rhythmic and occurred within a specific frequency range (mean head movement frequency of 90.3 Hz). Head twitches produced wave-like oscillations of magnetometer coil voltage that matched the frequency of head movement during the response. The magnetometer coil detected the HTR induced by the serotonergic hallucinogens 2,5-dimethoxy-4-iodoamphetamine (DOI; 0.25, 0.5, and 1.0 mg/kg, i.p.) and lysergic acid diethylamide (LSD; 0.05, 0.1, 0.2, and 0.4 mg/kg, i.p.) with extremely high sensitivity and specificity. Magnetometer coil recordings demonstrated that the non-hallucinogenic compounds (+)-amphetamine (2.5 and 5.0 mg/kg, i.p.) and lisuride (0.8, 1.6, and 3.2 mg/kg, i.p.) did not induce the HTR.

CONCLUSIONS

These studies confirm that a magnetometer coil can be used to detect the HTR induced by hallucinogens. The use of magnetometer-based HTR detection provides a high-throughput, semi-automated assay for this behavior, and offers several advantages over traditional assessment methods.

Serotonin2c receptor constitutive activity: in vivo direct and indirect evidence and functional significance

Serotonin2c (5-HT2c) receptors are widely expressed in the central nervous system where they play a pivotal role in the regulation of neuronal network excitability. Along with this fundamental physiological function, 5-HT2c receptors are thought to be implicated in the pathophysiology of several neuropsychiatric disorders and have become a major pharmacological target for the development of improved treatments of these disorders. In the past decade, many studies have focused on the constitutive activity of 5-HT2c receptors and the therapeutic potential of drugs acting as inverse agonists. Although the constitutive activity of the 5-HT2c receptor has been clearly described in vitro, the transposition of this concept to living animals is often difficult to ascertain. Nevertheless, cumulating evidence has demonstrated the functional relevance of such property in regulating physiological systems in vivo both at the level of the central and peripheral nervous systems. The present review provides an update of the growing number of studies that show, by means of pharmacological tools, the participation of the constitutive activity of 5-HT2c receptors in the control of various biochemical and behavioural functions in vivo and emphasizes the functional organization of this constitutive control together with the phasic and tonic (involving the spontaneous release of 5-HT) modalities of the 5-HT2c receptor in the brain.

Amphetamine's dose-dependent effects on dorsolateral striatum sensorimotor neuron firing

Amphetamine elicits motoric changes by increasing the activity of central neurotransmitters such as dopamine and serotonin, but how these neurochemical signals are transduced into motor commands is unclear. The dorsolateral striatum (DLS), a component of the cortico-subcortical reentrant motor loop, contains abundant neurotransmitter transporters that amphetamine could affect. It has been hypothesized that DLS medium spiny neurons contribute to amphetamine's motor effects. To study striatal activity contributing to amphetamine-induced movements, activity of DLS neurons related to vertical head movement was recorded while tracking head movements before and after acute amphetamine injection. Relative to saline, all amphetamine doses induced head movements above pre-injection levels, revealing an inverted U-shaped dose-response function. Lower doses (1 mg/kg and 2 mg/kg, intraperitoneal) induced a greater number of long (distance and duration) movements than the high dose (4 mg/kg), which induced stereotypy. Firing rates (FR) of individual head movement neurons were compared before and after injection during similar head movements, defined by direction, distance, duration, and apex. Changes in FR induced by amphetamine were co-determined by dose and pre-injection FR of the neuron. Specifically, all doses increased the FRs of slower firing neurons but decreased the FRs of faster firing neurons. The magnitudes of elevation or reduction were greater at lower doses, but less pronounced at the high dose, forming an inverted U function. Modulation of DLS firing may interfere with sensorimotor processing. Furthermore, pervasive elevation of slow firing neurons' FRs may feed-forward and increase excitability in thalamocortical premotor areas, contributing to the increased movement initiation rate.

Icilin-evoked behavioral stimulation is attenuated by alpha₂-adrenoceptor activation

Icilin is a transient receptor potential cation channel subfamily M (TRPM8) agonist that produces behavioral activation in rats and mice. Its hallmark overt pharmacological effect is wet-dog shakes (WDS) in rats. The vigorous shaking associated with icilin is dependent on NMDA receptor activation and nitric oxide production, but little else is known about the biological systems that modulate the behavioral phenomenon. The present study investigated the hypothesis that alpha(2)-adrenoceptor activation inhibits icilin-induced WDS. Rats injected with icilin (0.5, 1, 2.5, 5mg/kg, i.p.) displayed dose-related WDS that were inhibited by pretreatment with a fixed dose of clonidine (0.15 mg/kg, s.c.). Shaking behavior caused by a fixed dose (2.5mg/kg) of icilin was also inhibited in a dose-related manner by clonidine pretreatment (0.03-0.15 mg/kg, s.c.) and reduced by clonidine posttreatment (0.15 mg/kg, s.c.). Pretreatment with a peripherally restricted alpha(2)-adrenoceptor agonist, ST91 (0.075, 0.15 mg/kg), also decreased the incidence of shaking elicited by 2.5mg/kg of icilin. Pretreatment with yohimbine (2mg/kg, i.p.) enhanced the shaking induced by a low dose of icilin (0.5mg/kg). The imidazoline site agonists, agmatine (150mg/kg, i.p.) and 2-BFI (7 mg/kg, i.p.), did not affect icilin-evoked shaking. These results suggest that alpha(2)-adrenoceptor activation inhibits shaking induced by icilin and that increases in peripheral, as well as central, alpha(2)-adrenoceptor signaling oppose the behavioral stimulant effect of icilin.

Intrahippocampal LSD accelerates learning and desensitizes the 5-HT(2A) receptor in the rabbit, Romano et al

RATIONALE

Parenteral injections of d-lysergic acid diethylamide (LSD), a serotonin 5-HT(2A) receptor agonist, enhance eyeblink conditioning. Another hallucinogen, (±)-1(2, 5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride (DOI), was shown to elicit a 5-HT(2A)-mediated behavior (head bobs) after injection into the hippocampus, a structure known to mediate trace eyeblink conditioning.

OBJECTIVE

This study aims to determine if parenteral injections of the hallucinogens LSD, d,l-2,5-dimethoxy-4-methylamphetamine, and 5-methoxy-dimethyltryptamine elicit the 5-HT(2A)-mediated behavior of head bobs and whether intrahippocampal injections of LSD would produce head bobs and enhance trace eyeblink conditioning.

MATERIALS AND METHODS

LSD was infused into the dorsal hippocampus just prior to each of eight conditioning sessions. One day after the last infusion of LSD, DOI was infused into the hippocampus to determine whether there had been a desensitization of the 5-HT(2A) receptor as measured by a decrease in DOI-elicited head bobs.

RESULTS

Acute parenteral or intrahippocampal LSD elicited a 5-HT(2A) but not a 5-HT(2C)-mediated behavior, and chronic administration enhanced conditioned responding relative to vehicle controls. Rabbits that had been chronically infused with 3 or 10 nmol per side of LSD during Pavlovian conditioning and then infused with DOI demonstrated a smaller increase in head bobs relative to controls.

CONCLUSIONS

LSD produced its enhancement of Pavlovian conditioning through an effect on 5-HT(2A) receptors located in the dorsal hippocampus. The slight, short-lived enhancement of learning produced by LSD appears to be due to the development of desensitization of the 5-HT(2A) receptor within the hippocampus as a result of repeated administration of its agonist (LSD).

The serotonin 5-HT(2A) receptor agonist TCB-2: a behavioral and neurophysiological analysis

RATIONALE

There are few reports on the high-affinity 5-HT(2A) agonist (4-Bromo-3,6-dimethoxybenzocyclobuten-1-yl)methylamine hydrobromide (TCB-2).

OBJECTIVES

Here we provide the first behavioral and neurophysiological profile of TCB-2 in C57BL/6J mice, with direct comparisons to the 5-HT(2A/2C) agonist (+/-)-2,5-dimethoxy-4-iodophenyl-2-aminopropane (DOI), in addition to determinations of 5-HT(2A) mediation via pretreatment with the selective 5-HT(2A) antagonist MDL 11,939.

RESULTS

In a dose-dependent manner, TCB-2 induced head twitches, decreased food consumption in food-deprived mice, induced hypothermia, and increased corticosterone levels, with no effects on locomotor activity or anxiety-like behaviors in the open field. Similar effects were observed in side-by-side dose-response comparisons with DOI; although at the highest dose tested (5.0 mg/kg), TCB-2 induced significantly fewer head twitches, and a significantly enhanced hypothermic response, versus DOI. Pretreatment with MDL 11,939 blocked head twitches and temperature change following TCB-2 and DOI, confirming 5-HT(2A) mediation of these responses. Although MDL 11,939 pretreatment blocked DOI-induced suppression of feeding, MDL 11,939 had no effect on TCB-2-induced suppression of feeding. Previous studies show that 5-HT(2A) function is altered by changes in serotonin transporter (SERT) expression and function. In SERT knockout (-/-) mice, TCB-2-induced head twitches and hypothermia were greatly diminished compared to SERT wild-type (+/+) mice.

CONCLUSIONS

The current studies are important, as they are the first to assess the effects of TCB-2 in mice, and are among the first to report the behavioral and neurophysiological effects of this conformationally restricted phenethylamine analog compound, which has 65-fold greater effects on signaling via the phosphoinositide versus arachidonic acid pathways.

The serotonin 2C receptor potently modulates the head-twitch response in mice induced by a phenethylamine hallucinogen

RATIONALE

Hallucinogenic serotonin 2A (5-HT(2A)) receptor partial agonists, such as (+ or -)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride (DOI), induce a frontal cortex-dependent head-twitch response (HTR) in rodents, a behavioral proxy of a hallucinogenic response that is blocked by 5-HT(2A) receptor antagonists. In addition to 5-HT(2A) receptors, DOI and most other serotonin-like hallucinogens have high affinity and potency as partial agonists at 5-HT(2C) receptors.

OBJECTIVES

We tested for involvement of 5-HT(2C) receptors in the HTR induced by DOI.

RESULTS

Comparison of 5-HT(2C) receptor knockout and wild-type littermates revealed an approximately 50% reduction in DOI-induced HTR in knockout mice. Also, pretreatment with either the 5-HT(2C) receptor antagonist SB206553 or SB242084 eradicated a twofold difference in DOI-induced HTR between the standard inbred mouse strains C57BL/6J and DBA/2J, and decreased the DOI-induced HTR by at least 50% in both strains. None of several measures of 5-HT(2A) receptors in frontal cortex explained the strain difference, including 5-HT(2A) receptor density, Galpha(q) or Galpha(i/o) protein levels, phospholipase C activity, or DOI-induced expression of Egr1 and Egr2. 5-HT(2C) receptor density in the brains of C57BL/6J and DBA/2J was also equivalent, suggesting that 5-HT(2C) receptor-mediated intracellular signaling or other physiological modulators of the HTR may explain the strain difference in response to DOI.

CONCLUSIONS

We conclude that the HTR to DOI in mice is strongly modulated by 5-HT(2C) receptor activity. This novel finding invites reassessment of hallucinogenic mechanisms involving 5-HT(2) receptors.

Endocrine and gene expression changes following forced swim stress exposure during cocaine abstinence in mice

RATIONALE

Stress can reinstate previous cocaine-seeking long after drug is no longer present. However, little is known regarding the effect of chronic drug exposure and subsequent drug abstinence on responsivity to stress.

OBJECTIVE

To determine the effect of acute (24-h) and prolonged (14-day) drug-free periods in cocaine-experienced mice on behavioral, endocrine, and molecular outputs following stress exposure.

MATERIALS AND METHODS

Mice were administered a cocaine binge (15 mg/kg, every hour for 3h) for 2 weeks. Following a 24-h or 14-day drug-free period, stress responsivity, along with levels of anxiety, were measured using the forced swim test and elevated zero maze, respectively. In addition, alterations in the levels of plasma corticosterone, corticotrophin-releasing factor (CRF) mRNA, brain-derived neurotrophic factor (BDNF) mRNA, and histone acetylation at their respective promoters were examined following stress exposure.

RESULTS

At both acute and prolonged abstinence time points, behavioral measures were essentially unaltered; however, cocaine-experienced mice exhibited an augmented corticosterone response to the forced swim stress compared to saline-treated mice. Stress exposure increased BDNF mRNA levels in the ventral tegmental area (VTA) and nucleus accumbens (NAc) only in cocaine-experienced mice following a prolonged, but not acute, drug-free period. Increased BDNF mRNA in the NAc was associated with an increase in acetylated histone 3 (AcH3) at the BDNF I promoter. CRF mRNA levels were increased in the amygdala (AMYG); however, this was not associated with alterations in histone acetylation at the promoter.

CONCLUSION

These results demonstrate that drug history and prolonged abstinence can alter the endocrine and molecular responses to stress, which may facilitate the reinstatement of drug-seeking behaviors.

Pramipexole-induced antecollis in Parkinson's disease

We report a case of antecollis, or dropped head with Parkinson's disease (PD) induced by pramipexole, a nonergot dopamine agonist. An 80-year-old woman presented with progressively severe neck flexion, which developed within a few weeks of taking pramipexole at 3 mg/day. She had a disturbed gait and complained of difficulty in daily activity because of restricted visual field and severe stooped posture. Surface EMG showed disproportionate tonus of the neck muscles but needle EMG of the neck muscles was normal. Withdrawal of pramipexole resulted in immediate improvement; the patient could keep the head in natural position and walk normally. Pramipexole-induced antecollis may be serious, but is a reversible dystonia in patients with PD. Clinicians should be aware of such complication.

Behavioral response to emotional stress in rabbits: role of serotonin and serotonin2A receptors

Exposure to a novel environment is a stressor which modulates behavior, increases stress hormones and enhances the release of several neurotransmitters including serotonin (5-HT). Exposing rabbits to a novel environment significantly increases head-bob behavior but fails to alter either grooming or wet dog shakes compared with those observed in the home-cage. The goal of this study was to determine the role of 5-HT and its receptors in mediating novelty-elicited head-bob behavior. Reduction of central 5-HT levels after treatment with the serotonergic neurotoxin 5,7-DHT significantly decreased novelty-elicited head bobs by 40% compared with those in sham-lesioned rabbits, indicating that 5-HT mediates, in part, this behavior. Additionally, pretreatment with the 5-HT1A partial agonist and clinically used anxiolytic buspirone also significantly attenuated novelty-elicited head bobs. Pretreatment with the selective 5-HT2A antagonist M 100,907 significantly reduced novel environment-elicited head bobs by 40%. Furthermore, agonist-induced reduction of cortical 5-HT2A receptor density resulted in a significant 40% reduction in the number of head bobs elicited by the novel environment. These data demonstrate that rabbit head-bob behavior, an index of the response to novelty stress, is mediated, in part, by 5-HT activation of 5-HT2A receptors.

Clozapine and prazosin slow the rhythm of head movements during focused stereotypy induced by d-amphetamine in rats

RATIONALE

Clozapine is an efficacious, symptom-ameliorating, atypical antipsychotic drug with few extrapyramidal side effects. Clozapine has been reported either not to affect or to increase d-amphetamine-induced stereotypy, a behavior that is blocked by typical antipsychotic drugs.

OBJECTIVES

This work used a high-resolution measurement system to reassess clozapine's effects on d-amphetamine-induced focused stereotypy (FS) in rats.

MATERIALS AND METHODS

A force-plate actometer permitted the quantitation of the rhythm and vigor of movements during FS. Eight rats received a sensitizing series of doses of 5.0 mg/kg d-amphetamine sulfate, and this dosing regimen induced head movements with a rhythm near 10 Hz. Thirty minutes after d-amphetamine treatment, rats received acute clozapine (2.5-10.0 mg/kg), followed by eight, daily clozapine injections (5.0 mg/kg) given with d-amphetamine on days 2, 5, and 8. Effects of acute doses of the alpha1-noradrenergic antagonist prazosin (0.5-2.0 mg/kg) on the d-amphetamine response were also examined.

RESULTS

Clozapine dose-dependently slowed the near 10-Hz rhythm and reduced the vigor of the d-amphetamine-induced FS. Clozapine significantly lengthened the duration of the FS phase, but the rhythm remained slowed. No evidence for tolerance to clozapine's rhythm-slowing effects was seen in the subchronic phase. Prazosin dose-dependently reduced the near 10-Hz rhythm induced by d-amphetamine, but prazosin did not lengthen the FS phase.

CONCLUSIONS

The results show that clozapine diminished the rhythm and vigor of d-amphetamine-induced stereotyped head movements but, at the same time, lengthened the duration of the expression of the stereotypy. alpha1 antagonism is a likely contributor to the rhythm-modulating effects of clozapine.

ACP-103, a 5-Hydroxytryptamine 2A Receptor Inverse Agonist, Improves the Antipsychotic Efficacy and Side-Effect Profile of Haloperidol and Risperidone in Experimental Models

Dopamine D(2) receptor antagonism contributes to the therapeutic action of antipsychotic drugs (APDs) but also produces undesirable side effects, including extrapyramidal motor deficits, cognitive dulling, and prolactinemia. The introduction of atypical APDs was a significant advancement in the treatment of schizophrenia. Whereas these agents are D(2) receptor antagonists, they are also potent 5-hydroxytryptamine (5-HT)(2A) receptor inverse agonists, a feature that may explain their improved efficacy and tolerability. Recently, we reported that N-(4-fluorophenylmethyl)-N-(1-methylpiperidin-4-yl)-N'-(4-(2-methylpropyloxy)phenylmethyl) carbamide (2R,3R)-dihydroxybutanedioate (2:1) (ACP-103), a novel selective 5-HT(2A) receptor inverse agonist that fails to bind D(2) receptors, is active in several models predictive of antipsychotic activity. Using ACP-103, we tested the hypothesis that combining high levels of 5-HT(2A) inverse agonism with low levels of D(2) antagonism would result in a favorable interaction, such that antipsychotic efficacy could be achieved with reduced D(2) receptor-related adverse effects. Here we show that ACP-103 1) potently inhibited head-twitching produced by the 5-HT(2A/2C) receptor agonist (+/-)-2,5-dimethoxy-4-iodoamphetamine, 2) increased the potency of haloperidol against amphetamine-induced hyperactivity, 3) interacted synergistically with haloperidol or risperidone to suppress hyperactivity induced by the N-methyl-d-aspartate receptor antagonist (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (MK-801), and, by contrast, 4) attenuated haloperido-l- or risperidone-induced prolactinemia. ACP-103 also attenuated catalepsy produced by haloperidol or risperidone. However, the doses that were required for this effect were higher than would be expected for a 5-HT(2A) receptor-mediated mechanism. These data indicate that utilizing ACP-103 as an adjunctive therapy to currently used APDs may result in enhanced antipsychotic efficacy while reducing adverse effects including those attributable to D(2) receptor antagonism.

Role of G(q) protein in behavioral effects of the hallucinogenic drug 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane

Extensive evidence suggests that 5-HT2 receptors may play a role in mental disorders including schizophrenia. In addition, several studies indicate that G(q)-coupled 5-HT(2A) receptors are likely targets for the initiation of events leading to the hallucinogenic behavior elicited by lysergic acid diethylamide (LSD), (+/-)1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), and related drugs. However, 5-HT(2A) receptors couple to other G proteins in addition to G(q) protein. To evaluate the role of the G(q) signaling pathway in DOI-induced behaviors, we utilized two behavioral models of 5-HT(2A) receptor activation: induction of head-twitches by DOI, a common response to hallucinogenic drugs in rodents, and DOI elicited anxiolytic-like effects in the elevated plus maze. Experimental subjects were genetically modified mice [Galpha(q)(-/-)] in which the G(q) alpha gene was eliminated. Galpha(q)(-/-) mice exhibited a decrease in DOI-induced head-twitches, when compared to wild-type littermates. In addition, the DOI-induced increase in anxiolytic-like behavior was abolished in Galpha(q)(-/-) mice. These results, combined with our finding that DOI-induced FOS expression in the medial prefrontal cortex was also eliminated in Galpha(q)(-/-) mice, suggests a key role for G(q) protein in hallucinogenic drug effects.

Enhanced head-twitch response to 5-HT-related agonists in thiamine-deficient mice

While many studies suggest an involvement of brain serotonergic systems in neuro-psychiatric disorders such as schizophrenia and depression, their role in Wernicke-Korsakoff syndrome (WKS) remains unclear. Since dietary thiamine deficiency (TD) in mice is considered as a putative model of WKS, it was used in the present study to investigate the function of serotonergic neurons in this disorder. After 20 days of TD feeding, the intensity of tryptophan hydroxylase immunofluorescence was found to be significantly decreased in the dorsal and medial raphe nuclei. In addition, the head-twitch response (HTR) elicited by the intracerebroventricular administration of the 5-HT(2A) agonist 2,5-dimethoxy-4-iodoamphetamine hydrochloride (DOI) was significantly increased in TD versus control mice, whereas the injection of ketanserin, a 5-HT(2A) receptor antagonist, prevented this enhancement. A single injection of thiamine HCl on the 19th day of TD feeding did not reduce the enhanced DOI-induced HTR. On the other hand, the administration of d-fenfluramine, a 5-HT releaser, did not enhance the HTR in TD mice. Together, our results indicate that TD causes a super-sensitivity of 5-HT(2A) receptors by reducing presynaptic 5-HT synthesis derived from degenerating neurons projecting from the raphe nucleus.

Selective serotonin reuptake inhibitors, fluoxetine and paroxetine, attenuate the expression of the established behavioral sensitization induced by methamphetamine

To obtain an insight into the development of a new pharmacotherapy that prevents the treatment-resistant relapse of psychostimulant-induced psychosis and schizophrenia, we have investigated in the mouse the effects of selective serotonin reuptake inhibitors (SSRI), fluoxetine (FLX) and paroxetine (PRX), on the established sensitization induced by methamphetamine (MAP), a model of the relapse of these psychoses, because the modifications of the brain serotonergic transmission have been reported to antagonize the sensitization phenomenon. In agreement with previous reports, repeated MAP treatment (1.0 mg/kg a day, subcutaneously (s.c.)) for 10 days induced a long-lasting enhancement of the increasing effects of a challenge dose of MAP (0.24 mg/kg, s.c.) on motor activity on day 12 or 29 of withdrawal. The daily injection of FLX (10 mg/kg, s.c.) or PRX (8 mg/kg, s.c.) from 12 to 16 days of withdrawal of repeated MAP administration markedly attenuated the ability of the MAP pretreatment to augment the motor responses to the challenge dose of the stimulant 13 days after the SSRI injection. The repeated treatment with FLX or PRX alone failed to affect the motor stimulation following the challenge of saline and MAP 13 days later. These results suggest that the intermittent and repetitive elevation of serotonergic tone may inhibit the expression of the motor sensitization induced by pretreatment with MAP. It is proposed that clinically available serotonin reuptake inhibitors could be useful for preventing the recurrence of hallucinatory-paranoid state in drug-induced psychosis and schizophrenia.

Three-Dimensional Eye–Head Coordination After Injection of Muscimol Into the Interstitial Nucleus of Cajal (INC)

The interstitial nucleus of Cajal (INC) is thought to be the “neural integrator” for torsional/vertical eye position and head posture. Here, we investigated the coordination of eye and head movements after reversible INC inactivation. Three-dimensional (3-D) eye–head movements were recorded in three head-unrestrained monkeys using search coils. INC sites were identified by unit recording/electrical stimulation and then reversibly inactivated by 0.3 μl of 0.05% muscimol injection into 26 INC sites. After muscimol injection, the eye and head 1) began to drift (an inability to maintain stable fixation) torsionally: clockwise (CW)/counterclockwise (CCW) after left/right INC inactivation respectively. 2) The eye and head tilted torsionally CW/CCW after left/right INC inactivation, respectively. Horizontal gaze/head drifts were inconsistently present and did not result in considerable position offsets. Vertical eye drift was dependent on both vertical eye position and the magnitude of the previous vertical saccade, as in head-fixed condition. This correlation was smaller for gaze and head drift, suggesting that the gaze and head deficits could not be explained by a first-order integrator model. Ocular counterroll (OC) was completely disrupted. The gain of torsional vestibuloocular reflex (VOR) during spontaneous eye and head movements was reduced by 22% in both CW/CCW directions after either left or right INC inactivation. Our results suggest a complex interdependence of eye and head deficits after INC inactivation during fixation, gaze shifts, and VOR. Some of our results resemble the symptoms of spasmodic torticollis (ST).

Balance in Parkinson's disease under static and dynamic conditions

We tested balance performance in 15 on phase Parkinson's disease (PD) patients (8 nonfallers, PD-NF; 7 fallers, PD-F) during quiet stance (stabilometry) and on a platform continuously moving in the anteroposterior direction (dynamic test). Neither stabilometry (eyes open or closed) nor the dynamic test (eyes open) separated PD-F from PD-NF. With the dynamic test, eyes closed, PD-F with respect to PD-NF showed larger head oscillations, smaller cross-correlation between head and malleolus motion (more so in patients with low Unified Parkinson's Disease Rating Scale, or UPDRS), and larger delays of head with respect to platform motion. Further, across all PD patients, head displacement increased with the equivalent levodopa dose, indicating a trend for medication to worsen balancing capacity while improving UPDRS. The dynamic test is a sensitive tool for detecting instability in PD-F since absence of visual flow selectively impairs both association between body segment movements and anticipatory adjustments.

Antidepressant-Like Effect of Cordyceps sinensis in the Mouse Tail Suspension Test

Cordyceps sinensis (CS) has been known as a component of traditional medicines that elicit various biological effects such as anti-fatigue, immunomodulatory, and hypoglycemic actions. Since it has been well-established that fatigue is closely related to depression, we used the tail suspension test (TST) in mice to examine the antidepressant-like effects of hot water extract (HWCS) and supercritical fluid extract (SCCS) of CS. Immobility time in the TST was reduced by administration of SCCS (2.5-10 ml/kg, p.o.) dose-dependently though it was not reduced by treatment with HWCS (500-2000 mg/kg, p.o.). Neither HWCS nor SCCS altered locomotor activity in the open field test, excluding the possibility that the effect of SCCS is due to activation of locomotion. Pretreatment with prazosin (an adrenoreceptor antagonist) or sulpiride (a dopamine D2 receptor antagonist) reduced the effect of SCCS on the immobility time. In contrast, pretreatment with p-chlorophenylalanine (p-CPA, a serotonin synthesis inhibitor) did not alter the anti-immobility effect of SCCS. The last finding is consistent with an additional observation that SCCS had no effect on head twitch response induced by 5-hydroxy-L-tryptophan in mice. Taken altogether, these results suggest that SCCS may elicit an antidepressant-like effect by affecting the adrenergic and dopaminergic systems, but not by affecting the serotonergic system.

Developmental and Behavioral Consequences of Prenatal Fluoxetine

BACKGROUND

Fluoxetine, a selective serotonin reuptake inhibitor, is the most commonly prescribed antidepressant drug for pregnant women. Studies regarding the teratogenic effect of fluoxetine on human and animal models are mainly concerned with structural malformation (congenital anomalies).

AIM

Hence, the present study was planned to evaluate the postnatal behavioral effects of fluoxetine on albino rats.

METHODS

Three groups of female rats received either distilled water or doses of fluoxetine 8 and 12 mg/kg orally from the 6th to the 20th day of pregnancy. Weaning of the pups was done on the 21st day followed by a battery of behavioral tests to assess for any behavioral effect. The tests included negative geotaxis, open field exploration, rota-rod test, elevated plus maze and passive avoidance test.

RESULTS

In the present study there was no change in the gestational length of pregnancy, no premature birth or miscarriage during pregnancy. A high dose of in utero fluoxetine resulted in a decrease in birth weight of the offspring and also reduced weight gain during the preweaning period. No major congenital abnormalities were observed in the offspring exposed to fluoxetine. Prenatal fluoxetine exposure at high dose caused an initial transient delay in motor development and this poor motor activity was transient and not permanent. However, prenatal exposure to fluoxetine at a higher dose showed a favorable effect on learning and memory in water maze and passive avoidance tests.

CONCLUSIONS

From the present study, it may be concluded that prenatal fluoxetine causes a transient delay in motor development but does not adversely affect the postnatal behavioral consequences.

Hippocampal partial kindling decreased hippocampal GABAB receptor efficacy and wet dog shakes in rats

To test the hypothesis that GABA(B) receptor efficacy in the behaving rat decreases after partial hippocampal kindling, we measured GABA(B) receptor efficacy by the number of wet dog shakes (WDSs) induced by baclofen (5mM in 0.2muL of saline) infusion into the dorsal hippocampus; these WDSs were blocked by prior infusion of GABA(B) receptor antagonist CGP55845A. Rats were given 15 afterdischarges (ADs) evoked in CA1 over 3 days or control stimulations. The partially kindled rats (after 15 ADs) showed a significant decrease in baclofen-induced WDSs as compared to control rats, on days 1, 4 and 21 after kindling. In contrast, kindled and control rats did not show a significant difference in WDSs induced by hippocampal infusion of GABA(A) receptor antagonist bicuculline. Also, the number of WDSs induced after subcutaneous injection of serotonin-2A/2C agonist+/-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane was not different between kindled and control rats on 4 and 21 days after kindling. We further tested the hypothesis that the decrease in hippocampal AD-induced WDSs during kindling is caused by a decrease in GABA(B) receptor efficacy. However, we found no convincing evidence to support the latter hypothesis since the AD-induced WDSs were not suppressed by hippocampal infusion of CGP55845A, with the exception that CGP55845A infusion into ventral hippocampus suppressed both hippocampal ADs and WDSs. Together with results derived from previous electrophysiological studies in vitro, it is suggested that a decrease of GABA(B) receptor, possibly GABA(B) autoreceptor, efficacy may explain the decrease of baclofen-induced WDSs after hippocampal kindling.

Gentamicin ototoxicity: clinical features and the effect on the human vestibulo-ocular reflex

CONCLUSIONS

Gentamicin ototoxicity presents with gait imbalance and oscillopsia, but only rarely with hearing loss and vertigo. Sinusoidal rotational stimuli with high accelerations such as the bedside head-thrust test or rotational step changes in velocity are useful to diagnose bilateral vestibulopathy.

OBJECTIVE

To describe the salient clinical features and vestibular testing results in gentamicin ototoxicity.

PATIENTS AND METHODS

A retrospective review of the quantitative vestibular function testing results for patients presenting to the UCLA Neurotology Clinic with gentamicin ototoxicity over the past 10 years (n=35).

RESULTS

All patients presented with imbalance and 33 out of 35 had oscillopsia. Three patients reported a noticeable change in hearing and five reported vertigo. Of the 35 patients, 15 were in renal failure at the time of gentamicin administration. Patients with pre-existing peripheral neuropathy compensated poorly. Sinusoidal rotational testing demonstrated profoundly decreased gain and increased phase lead over the entire frequency range, with a subset of patients having relatively preserved gain at the intermediate frequencies (0.8-1.6 Hz) and low acceleration (<30 degrees/s). There was little or no response to high acceleration step changes in velocity. The time constant measured both by sinusoidal and step responses was ultra-low. All patients tested had a positive head-thrust test bilaterally.

Antidepressant-like action of nicotine in forced swimming test and brain serotonin in mice

An antidepressant-like action of nicotine has been suggested in the forced swimming test. The aim of the present study was to evaluate the relationship between the antidepressant-like action of nicotine and brain serotonin (5-HT) in mice. Nicotine at a dose of 0.2 mg/kg significantly (p < 0.05) decreased the duration of immobility time in forced swimming test. However, nicotine (0.01-1 mg/kg, s.c.) had no effect on locomotor activity in open-field test. Dopamine turnover in mouse whole brain was increased by nicotine (0.01-1 mg/kg, s.c.) in a dose-dependent manner, and nicotine at a dose of 0.05 mg/kg showed a significant increases in 5-HT turnover. Nicotine at a dose of 0.05 mg/kg markedly enhanced head twitch responses induced by (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), a selective 5-HT2A/2C receptor agonist. These findings suggest that the involvement of nicotinic and serotonergic systems in the antidepressant-like effects of nicotine.

ROCK inhibition produces anxiety-related behaviors in mice

RATIONALE

The role of Rho/Rho-associated kinase (ROCK) in regulating dendritic and axonal morphology during development has gained much attention. Very little is known, however, about the role of the Rho/ROCK pathway in emotional behavior.

OBJECTIVE

To investigate the role of ROCK in emotional behaviors. We examined how the ROCK inhibitor Y27632 affects the performance of mice on three behavioral tests that measure anxiety-related behaviors.

RESULTS

In the elevated plus-maze test, Y27632 (10 nmol, intracerebroventricular) induced a significant decrease in the percentage of time spent in the open arms and in the percentage of entries into open arms. In the fear conditioning test, Y27632-treated mice froze significantly more often and longer than did saline-treated mice. In the hole-board test, Y27632 significantly suppressed head-dipping behavior in Y27632-treated mice than in saline-treated mice. On the other hand, Y27632 did not produce on spontaneous alteration performance in the Y-maze test. These results indicate that ROCK inhibition increased anxiety-related behaviors.

CONCLUSION

Our findings suggest that the ROCK pathway is involved in the expression of anxiety- and fear-related behaviors. Furthermore, we propose that if the Rho/ROCK pathway plays an important role in mediating anxiety-related behaviors in humans, it may prove to be a novel system for anxiolytics to target.

The effects of unilateral eighth nerve block on fictive VOR in the turtle

Multiunit activity during horizontal sinusoidal motion was recorded from pairs of oculomotor, trochlear, or abducens nerves of an in vitro turtle brainstem preparation that received inputs from intact semicircular canals. Responses of left oculomotor, right trochlear and right abducens nerves were approximately aligned with leftward head velocity, and that of the respective contralateral nerves were in-phase with rightward velocity. We examined the effect of sectioning or injecting lidocaine (1-2 microL of 0.5%) into the right vestibular nerve. Nerve block caused a striking phase shift in the evoked response of right oculomotor and left trochlear nerves, in which (rightward) control responses were replaced by a smaller-amplitude response to leftward table motion. Such "phase-reversed" responses were poorly defined in abducens nerve recordings. Frequency analysis demonstrated that this activity was advanced in phase relative to post-block responses of the respective contralateral nerves, which were in turn phase-advanced relative to pre-block controls. Phase differences were largest (approximately 10 degrees) at low frequencies (approximately 0.1 Hz) and statistically absent at 1 Hz. The phase-reversed responses were further investigated by eliminating individual canal input from the left labyrinth following right nVIII block, which indicated that the activation of the vertical canal afferents is the source of this activity.

In vitro and in vivo characterization of F-97013-GD, a partial 5-HT1A agonist with antipsychotic- and antiparkinsonian-like properties

In order to better define the role of 5-HT(1A) receptors in the modulation of extrapyramidal motor functions, we investigated the effect of 5-HT(1A) agonists on tacrine-induced tremulous jaw movements (TJM) in rats, a putative model of parkinsonian tremor. Acute injection of 5-HT(1A) agonists 8-OH-DPAT and buspirone dose-dependently counteracted the tacrine-induced oral movements (ED(50)=0.04 and 1.0mg/kg, respectively), an effect reversed by the selective 5-HT(1A) antagonist WAY 100,635. In contrast to classical antipsychotics, the atypical antipsychotics risperidone (ED(50)=0.3mg/kg) and clozapine (ED(50)=1.5mg/kg) blocked the oral movements induced by the cholinomimetic agent at or below the doses required for suppression of conditioned avoidance response. The compound F-97013-GD (6-methyl-2-[4-(naphtylpiperazin-1-yl)butyl]-3-(2H)-pyridazinone), a putative antipsychotic drug that in functional in vitro and in vivo assays behaved as a mixed dopamine D(2)-antagonist and 5-HT(1A)-partial agonist, also displayed a potent antitremorgenic effect in this paradigm (ED(50)=0.5mg/kg). Interestingly, pretreatment with WAY 100,635 blocked the inhibitory effect of F-97013-GD but not that of clozapine. The 5-HT depleting agent para-chlorophenylalanine (PCPA) partially attenuated tacrine-induced TJM but did not block the suppressive effect of 5-HT(1A) agonists. In addition, only high doses of F-97013-GD induced catalepsy in rodents and, like 8-OH-DPAT and clozapine, the compound reversed the haloperidol-induced catalepsy in rats. These results show that 5-HT(1A) receptors play a role in the regulation of tacrine-induced TJM and suggest that their activation by novel antipsychotics may not only reduce the extrapyramidal side effects EPS liability, but also be effective in the treatment of parkinsonian tremor.

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.

The site of a motor memory shifts with consolidation

The basis for the consolidation of memory is a controversial topic, particularly in the case of motor memory. One view is that motor memory is transferred, partially or completely, to a new location during the consolidation process ("systems consolidation"). We investigated this possibility in a primitive motor system, the vestibulo-ocular reflex (VOR). In the simple circuitry of the VOR, there are relatively few possible storage sites for memory. We partially blocked excitatory neurotransmission in the cerebellar cortex of cats with the glutamate antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). If CNQX was injected immediately after 60 min of rotation under conditions that induced a learned decrease in the gain of the VOR, gain was returned to its baseline value. Expression of the new memory could also be disrupted by rotation in darkness, suggesting that consolidation had not taken place; however, after learning had continued for 3 d, expression of the learned change was diminished only slightly by blockade and was unaffected by rotation in darkness. Our interpretation of these results is that learning may take place initially in the cerebellar cortex and that during consolidation, motor memories are converted to a more distributed representation that includes the cerebellar cortex and another site.

Behavioral and electrophysiological changes induced by acetyl-L-carnitine in aged freely-moving rats

In chronically-implanted, drug-free, behaving aged Fischer rats, intracerebroventricularly (i.c.v.) and intraperitoneally (i.p.) acetyl-L-carnitine (ALCAR) injections powerfully enhanced motor behavior and head movements aimed at attention and exploratory activity. This effect was dose-dependent and associated with the abolition or substantial reduction of the incidence and duration of the spontaneous EEG generalized hypersynchronous patterns termed High Voltage Spindle (HVS), with an increase in EEG monitored theta activity. The results suggest that ALCAR may stimulate the motivational system and disrupt the hypersynchronous processes by inhibiting the GABAergic thalamic reticular neurons and/or activating the brain stem cholinergic reticular system (pedunculo pontine tegmental, PPT and laterodorsal tegmental, LDT nuclei).

Changes in Emotional Behavior of Mice in the Hole-Board Test After Olfactory Bulbectomy

The most consistent behavioral change caused by olfactory bulbectomy (OBX) is a hyperemotional response to novel environmental stimuli. The aim of this study was to characterize the emotional behavior of OBX mice using the hole-board test. After the olfactory bulbs were lesioned, sham and OBX mice were housed in single cages for 14 days. The number of head-dips in the hole-board test in single-housed OBX mice was significantly greater than that in single-housed sham mice. The head-dipping behaviors in single-housed sham and OBX mice were reversed by treatment with diazepam, a typical benzodiazepine anxiolytic. (+/-)-8-Hydroxy-2-(di-n-propylamino) tetraline hydrobromide (8-OH-DPAT), a selective 5-HT(1A)-receptor agonist that has a non-benzodiazepine anxiolytic-like effect, and (+)-4-[(aR)-a-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethyl benzamide (SNC80), a delta-opioid-receptor agonist, also significantly reversed the number of head-dips in single-housed sham and OBX mice. In conclusion, we suggest that the single-housed OBX mice showed heightened emotional behavior (e.g., increase in head-dipping behavior) in the hole-board test. In addition, we suggest that the hyperemotional behavior characterized by head-dipping behavior in OBX mice was selectively reversed by benzodiazepine and non-benzodiazepine anxiolytics.

1-((S)-2-Aminopropyl)-1H-indazol-6-ol: A Potent Peripherally Acting 5-HT2 Receptor Agonist with Ocular Hypotensive Activity

Serotonin 5-HT(2) receptor agonists have been identified as a potential new class of agents for the treatment of ocular hypertension and glaucoma. The initially reported tryptamine analogues displayed either poor solution stability, potent central nervous system activity, or both of these undesirable characteristics and were unacceptable for clinical evaluation. A series of 1-(2-aminopropyl)-1H-indazole analogues was synthesized and evaluated for their suitability for consideration as clinical candidates. 1-((S)-2-Aminopropyl)-1H-indazol-6-ol (9) was identified as a peripherally acting potent 5-HT(2) receptor agonist (EC(50) = 42.7 nM, E(max) = 89%) with high selectivity for the 5-HT(2) receptors relative to other serotonergic receptor subtypes and other families of receptors and has significantly greater solution stability than alpha-methyl-5-hydroxytryptamine. Additionally, 9 potently lowers intraocular pressure in conscious ocular hypertensive monkeys (-13 mmHg, 33%); this reduction appears to be through a local rather than a centrally mediated effect. Compound 9 appears to be an excellent 5-HT(2) receptor agonist for conducting further studies directed toward a clinical proof-of-concept study for this class of ocular hypotensive agents.

Neural and behavioral plasticity associated with the transition from controlled to escalated cocaine use

BACKGROUND

Rats given extended access to cocaine develop several symptoms of addiction, including a gradual escalation of drug intake, whereas rats given limited access do not. We asked here whether extended access to cocaine also produces drug-induced sensitization, a form of neurobehavioral plasticity implicated in addiction.

METHODS

Rats were given limited (1 hour/session) or extended access (6 hours/session) to self-administered cocaine. Following a period of abstinence, rats were selected at random for assessment of their psychomotor response to cocaine or drug-seeking during extinction or for anatomic studies.

RESULTS

When re-exposed to cocaine, rats allowed extended drug access showed greater drug-seeking behavior and were hypersensitive (sensitized) to the psychomotor activating effects of cocaine compared with rats given limited access. Extended access to cocaine was also associated with a greater increase in the density of dendritic spines on neurons specifically in the core of the nucleus accumbens (and not in the shell or medial or orbital frontal cortex).

CONCLUSIONS

The transition from stable to escalated cocaine use, a hallmark of addiction, is associated with especially robust behavioral sensitization and synaptic reorganization in the core of the nucleus accumbens.

MDMA (‘Ecstasy’) and methamphetamine combined: Order of administration influences hyperthermic and long-term adverse effects in female rats

The acute and long-term dangers of 3,4-methylenedioxymethamphetamine (MDMA, 'Ecstasy') and methamphetamine (METH) are well described individually, but their effect in combination is largely unknown. Here groups of female rats were given four MDMA or METH injections within a single session with each injection separated by 2h. Treatments included MDMA only, METH only, MDMA and METH in a cocktail (MDMA/METH), MDMA (two injections) followed by METH (two injections) (MDMA-->METH), or METH followed by MDMA (METH-->MDMA). Each injection involved 4mg/kg of total drug. Drug administration occurred at a high ambient temperature of 28 degrees C. All treatments produced hyperactivity while the treatments where MDMA was administered first (MDMA, MDMA-->METH and MDMA/METH) produced hyperthermia. All treatments involving METH caused significant head weaving. Six weeks after drug treatment all groups showed reduced social interaction relative to controls. MDMA/METH treatment was associated with reduced swimming in the forced swim test. MDMA given alone caused 5-HT depletion in several brain regions while METH given alone caused dopamine depletion in the striatum. The three treatments involving MDMA and METH combinations caused significant depletion of serotonin, dopamine and noradrenaline in several brain regions. Interestingly, the MDMA-->METH treatment produced greater hippocampal and cortical 5-HT depletion than the METH-->MDMA treatment suggesting an effect of order. These results extend our recent findings of additive toxic effects when METH is combined with MDMA. This has potentially important implications for party drug users who appear to frequently use this combination.

A novel method for subarachnoid drug delivery in the medullary region of rats

This study describes a novel method for direct subarachnoid drug delivery to the medullary dorsal horn region of rats, without introducing a catheter. The reliability of the method was demonstrated by a pharmacological validation; that is, morphine administration to the medullary region blocked the nociceptive response to formalin injected in the temporomandibular joint (TMJ) region, an effect that was prevented by co-administration of naloxone. The method proposed offers many advantages over the existing methods for medullary drug delivery with catheter implantation. It is easy to be employed, it does not induce any sign of motor impairment, and it does not require the neck surgery performed to implant a catheter in the medullary dorsal horn region. Therefore, it is a useful method for subarachnoid drug delivery in behavioral trigeminal pain studies, particularly when nociceptive behavioral measures that require normal neck muscle activity to occur, such as head withdraw or head flinch, are evaluated.

The course of cervical dystonia and patient satisfaction with long-term botulinum toxin A treatment

In 78 patients with idiopathic cervical dystonia (CD), we studied the course of the disease and the patients' satisfaction with long-term botulinum toxin A (BTX) treatment (median 5.5 years, range 1.5-10). On a seven-point scale ranging from excellent to worsening, the effect of treatment was scored as excellent or good by 52% of patients and moderate by 33%. The independent scores of the treating neurologists were excellent or good in 65% and moderate in 27%, respectively, and correlated well with the patients' scores. The 'Global Burden of Disease', as expressed on Visual Analog Scales (VAS, 0-10) before and at evaluation of treatment, was reduced by a median of 4 in individual patients. By combining these outcome measures, 67% of the patients were characterized as having a good effect, and 33% an unsatisfactory effect. This outcome (good or unsatisfactory effect) was independent of the severity of head deviation or complexity pattern of CD prior to treatment, the delay from onset to start of BTX treatment, or the number of treatments. The complexity pattern remained stable during treatment in 64% of the patients, became less complex in 19%, whereas 17% of the patients developed more complex patterns.

Saccade Dysmetria in Head-Unrestrained Gaze Shifts After Muscimol Inactivation of the Caudal Fastigial Nucleus in the Monkey

Lesions in the caudal fastigial nucleus (cFN) severely impair the accuracy of visually guided saccades in the head-restrained monkey. Is the saccade dysmetria a central perturbation in issuing commands for orienting gaze (eye in space) or is it a more peripheral impairment in generating oculomotor commands? This question was investigated in two head-unrestrained monkeys by analyzing the effect of inactivating one cFN on horizontal gaze shifts generated from a straight ahead fixation light-emitting diode (LED) toward a 40° eccentric target LED. After muscimol injections, when viewing the fixation LED, the starting position of the head was changed (ipsilesional and upward deviations). Ipsilesional gaze shifts were associated with a 24% increase in the eye saccade amplitude and a 58% reduction in the amplitude of the head contribution. Contralesional gaze shifts were associated with a decrease in the amplitude of both eye and head components (40 and 37% reduction, respectively). No correlation between the changes in the eye amplitude and in head contribution was observed. The amplitude of the complete head movement was decreased for ipsilesional movements (57% reduction) and unaffected for contralesional movements. For both ipsilesional and contralesional gaze shifts, the changes in eye saccade amplitude were strongly correlated with the changes in gaze amplitude and largely accounted for the gaze dysmetria. These results indicate a major role of cFN in the generation of appropriate saccadic oculomotor commands during head-unrestrained gaze shifts.

Individual differences in cocaine- and amphetamine-induced activation of male Sprague-Dawley rats: contribution of the dopamine transporter

Previously we found that outbred male Sprague-Dawley rats can be classified as either low or high cocaine responders (LCRs or HCRs, respectively), based on their open-field locomotor response to acute cocaine (COC; 10 mg/kg, i.p.). Here, we extended this analysis to amphetamine (AMPH; 0.5, 1, and 5 mg/kg, i.p.) and found that the individual differences in behavioral activation were not as pronounced as with COC. This was confirmed with observational analysis of behaviors. Differences in drug-induced activation could involve differential dopamine transporter (DAT) function/trafficking. To address this possibility, we measured [3H]DA uptake into dorsal striatal synaptosomes prepared from rats injected 30 min earlier with saline, COC, or AMPH to determine DAT activity, and radioligand binding to determine the total number of DATs. Striatal [3H]DA uptake in COC-treated HCRs was significantly higher than in LCRs. Furthermore, regardless of LCR/HCR classification, uptake in individual COC-treated rats was significantly correlated with their locomotor behavior in the 30 min after drug administration. In contrast, AMPH-treated rats did not differ in uptake, nor were uptake and locomotor activity correlated. DAT number did not differ between LCRs or HCRs, or between AMPH-treated rats. In addition, when individual differences in COC-induced behavior were no longer detected in LCRs and HCRs 1 week after initial classification, uptake was also similar. Together, these results suggest that a difference in expression of functional DATs on the cell surface contributes to the individual differences observed in COC-induced, but not AMPH-induced, behavioral activation of rats.

Topographical effects of D1-like dopamine receptor agonists on orofacial movements in mice and their differential regulation via oppositional versus synergistic D1-like: D2-like interactions: cautionary observations on SK&F 82958 as an anomalous agent

Using a novel procedure, the regulation of individual topographies of orofacial movement in the mouse by oppositional versus cooperative/synergistic D1-like: D2-like dopamine receptor interactions was studied. The D1-like agonists SK&F 38393 and SK&F 83959 each induced vertical, but not horizontal, jaw movements, together with tongue protrusions and incisor chattering; however, SK&F 82958 induced a different profile which, consistent with other neurochemical and neurophysiological studies, suggests that this agent shows anomalous properties relative to other D1-like agonists. When given alone, the D2-like agonist quinpirole reduced horizontal jaw movements and incisor chattering. On coadministration, both SK&F 38393- and SK&F 83959-induced vertical jaw movements and tongue protrusions were inhibited by quinpirole, while SK&F 82958 again showed an anomalous profile. These findings indicate that, in the mouse, vertical jaw movements and tongue protrusions are regulated by oppositional D1-like: D2-like interactions, and appear to involve a D1-like receptor that is not coupled to adenylyl cyclase, whereas horizontal jaw movements are inhibited by D2-like receptors. Additionally, results obtained using SK&F 82958 as a probe for D1-like mechanisms should be treated with considerable caution until they are confirmed using other D1-like agonists.

Diabetes inhibits the DOI-induced head-twitch response in mice

RATIONALE

Clinical studies suggest that the prevalence of psychiatric disorders is higher in diabetic patients than in the general population. It has been reported that central serotonin(2A) (5-HT(2A)) receptors may be involved in the pathogenesis and treatment of psychiatric disorders.

OBJECTIVES

We examined the effect of streptozotocin-induced diabetes on the function of central 5-HT(2A) receptors in mice.

METHODS

Male ICR mice were rendered diabetic by an injection of streptozotocin (200 mg/kg, i.v.). The experiments were conducted 2 weeks after the injection of streptozotocin. To evaluate the central 5-HT(2A) receptor function, head-twitch responses were measured for 15 min immediately after the treatment with (+/-)-2,5-dimethoxy-4-iodoamphetamine (DOI) (0.1-1 mg/kg, s.c.), a selective 5-HT(2) receptor agonist.

RESULTS

Significantly fewer head-twitch responses were induced by DOI in diabetic mice than in non-diabetic mice. The number and affinity of 5-HT(2A) receptors in the mouse frontal cortex were not affected by diabetes. The corticosterone response to DOI (1 mg/kg and 3 mg/kg, s.c.) was not different between non-diabetic and diabetic mice, although the baseline of plasma corticosterone levels was significantly higher in diabetic than in non-diabetic mice.

CONCLUSIONS

Our results suggest that a neuronal network that causes head-twitch responses by triggering by the activation of 5-HT(2A) receptors may be altered by type-1 diabetes in mice.