Cannabinoid receptor-mediated disruption of sensory gating and neural oscillations: A translational study in rats and humans.

Cannabis use has been associated with altered sensory gating and neural oscillations. However, it is unclear which constituent in cannabis is responsible for these effects, or whether these are cannabinoid receptor 1 (CB1R) mediated. Therefore, the present study in humans and rats examined whether cannabinoid administration would disrupt sensory gating and evoked oscillations utilizing electroencephalography (EEG) and local field potentials (LFPs), respectively. Human subjects (n = 15) completed four test days during which they received intravenous delta-9-tetrahydrocannabinol (Δ9-THC), cannabidiol (CBD), Δ9-THC + CBD, or placebo. Subjects engaged in a dual-click paradigm, and outcome measures included P50 gating ratio (S2/S1) and evoked power to S1 and S2. In order to examine CB1R specificity, rats (n = 6) were administered the CB1R agonist CP-55940, CP-55940+AM-251 (a CB1R antagonist), or vehicle using the same paradigm. LFPs were recorded from CA3 and entorhinal cortex. Both Δ9-THC (p < 0.007) and Δ9-THC + CBD (p < 0.004) disrupted P50 gating ratio compared to placebo, while CBD alone had no effect. Δ9-THC (p < 0.048) and Δ9-THC + CBD (p < 0.035) decreased S1 evoked theta power, and in the Δ9-THC condition, S1 theta negatively correlated with gating ratios (r = -0.629, p < 0.012 (p < 0.048 adjusted)). In rats, CP-55940 disrupted gating in both brain regions (p < 0.0001), and this was reversed by AM-251. Further, CP-55940 decreased evoked theta (p < 0.0077) and gamma (p < 0.011) power to S1, which was partially blocked by AM-251. These convergent human/animal data suggest that CB1R agonists disrupt sensory gating by altering neural oscillations in the theta-band. Moreover, this suggests that the endocannabinoid system mediates theta oscillations relevant to perception and cognition.

The effect of chronic cannabinoids on broadband EEG neural oscillations in humans.

Animal and cellular work has shown that central cannabinoid-1 receptors modulate neural oscillations in the gamma range (40 Hz), which may be important for normal perceptual and cognitive processes. In order to assess the effect of cannabinoids on broadband-frequency neural oscillations in humans, the current study examined the effect of chronic cannabis use on auditory steady-state responses (ASSRs) utilizing electroencephalography (EEG). Passive ASSRs were assessed using varying rates of binaural stimulation (auditory click-trains; 10-50 Hz in increments of 5 Hz; 80 dB SPL) in carefully screened cannabis users and controls. Chronic cannabis users (n=22; 12 h abstinence before study; positive 11-nor-9-carboxy-delta-9-tetrahydrocannabinol urine levels) and cannabis naïve controls (n=24) were evaluated. Time X frequency analyses on EEG data were performed using Fourier-based mean trial power (MTP) and phase-locking (inter-trial coherence; ITC). Transient ERPs to stimulus onset (auditory N100 components) were also evaluated. As predicted, a decrease in spectral power (MTP) at 40 Hz was observed in the cannabis group (p<0.018). No effects on phase-locking (ITC) or the N100 were observed. Further, within the cannabis group, lower 40 Hz power correlated with an earlier age of onset of cannabis use (p<0.04). These data suggest that chronic exposure to exogenous cannabinoids can alter the ability to generate neural oscillations, particularly in the gamma range. This is consistent with preclinical animal and cellular data, which may have implications for understanding the short- and long-term psychopharmacological effects of cannabis.

Examining the effects of former cannabis use on cerebellum-dependent eyeblink conditioning in humans.

RATIONALE: Previous work in humans has shown that chronic cannabis users exhibit disruptions in classical eyeblink conditioning (EBC), a form of associative learning that is known to be dependent on the cerebellum. Based upon previous work in animals, it was hypothesized that these learning deficits were related to cannabinoid receptor (CB1R) downregulation. However, it remains unclear whether there is a recovery of cerebellum-dependent learning after the cessation of cannabis use. METHODS: Therefore, former cannabis users (n=10), current cannabis users (n=10), and cannabis-naïve controls (n=10), all free of DSM-IV Axis-I or -II disorders, were evaluated. A standard delay EBC procedure was utilized in which paired presentations of a conditioned stimulus (CS; e.g., tone) and a co-terminating unconditioned stimulus (US; e.g., ocular airpuff) were administered, thus eliciting a conditioned eyeblink response (CR). The primary dependent measures were percentage of CRs and CR latency across conditioning blocks. RESULTS: Similar to prior studies, current cannabis users exhibited marked impairments in both the acquisition and timing of CRs compared to controls. Although former cannabis users showed intact CR acquisition compared to controls, they exhibited significantly impaired (shorter) CR latencies. In both cannabis groups, UR amplitude did not differ from controls, indicating normal US processing. CONCLUSIONS: These data suggest that a recovery of function has occurred for the learning of the CS-US association, while the accurate timing of the CR shows lasting impairments. Taken together, these results suggest that heavy cannabis use can disrupt timing-related synaptic plasticity within the cerebellum, even after the cessation of cannabis use.

Evaluation of bidirectional interstimulus interval (ISI) shift in auditory delay eye-blink conditioning in healthy humans.

Delay eye-blink conditioning is an associative learning task that can be utilized to probe the functional integrity of the cerebellum and related neural circuits. Typically, a single interstimulus interval (ISI) is utilized, and the amplitude of the conditioned response (CR) is the primary dependent variable. To study the timing of the CR, an ISI shift can be introduced (e.g., shifting the ISI from 350 to 850 ms). In each phase, a conditioned stimulus (e.g., a 400- or 900-ms tone) coterminates with a 50-ms corneal air puff unconditioned stimulus. The ability of a subject to adjust the CR to the changing ISI constitutes a critical timing shift. The feasibility of this procedure was examined in healthy human participants (N = 58) using a bidirectional ISI shift procedure while cortical event-related brain potentials were measured. CR acquisition was faster and the responses better timed when a short ISI was used. After the ISI shift, additional training was necessary to allow asymptotic responding at the new ISI. Interestingly, auditory event-related potentials to the CR were not associated with conditioning measures at either ISI.

The interacting role of media violence exposure and aggressive-disruptive behavior in adolescent brain activation during an emotional Stroop task.

Only recently have investigations of the relationship between media violence exposure (MVE) and aggressive behavior focused on brain functioning. In this study, we examined the relationship between brain activation and history of media violence exposure in adolescents, using functional magnetic resonance imaging (fMRI). Samples of adolescents with no psychiatric diagnosis or with disruptive behavior disorder (DBD) with aggression were compared to investigate whether the association of MVE history and brain activation is moderated by aggressive behavior/personality. Twenty-two adolescents with a history of aggressive behavior and diagnosis of either conduct disorder or oppositional-defiant disorder (DBD sample) and 22 controls completed an emotional Stroop task during fMRI. Primary imaging results indicated that controls with a history of low MVE demonstrated greater activity in the right inferior frontal gyrus and rostral anterior cingulate during the violent word condition. In contrast, in adolescents with DBD, those with high MVE exhibited decreased activation in the right amygdala, compared with those with low MVE. These findings are consistent with research demonstrating the importance of fronto-limbic structures for processing emotional stimuli, and with research suggesting that media violence may affect individuals in different ways depending on the presence of aggressive traits.

Comparison of auditory and visual conditioning stimuli in delay eyeblink conditioning in healthy young adults.

Classical eyeblink conditioning (EBC) has been widely used to probe cerebellar function in humans and nonhuman mammals. Although the neural pathways governing behavior in this task are well understood and fairly discrete, it remains unclear in the human literature how conditioned stimuli (CSs) of different modalities (e.g., visual and auditory) influence the exhibition of conditioned responses (CRs). In the present study, therefore, CRs to a visual CS and an auditory CS were examined with the single-cue delay EBC procedure. An initial experiment (N = 61) was conducted to identify visual and auditory stimuli that had equal perceived intensities. Using these perceptually equivalent stimuli, a second group of 25 subjects completed auditory and visual EBC procedures in two testing sessions 5-8 days apart. Whereas the acquisition of CRs was similar between the CS modality conditions, the timing of the CRs differed such that earlier CR onset and peak latencies were associated with the visual CS. In addition, CR timing improved across testing sessions, as indicated by the later CR peak latencies exhibited during the second testing session, as compared with the first.

Sensory gating impairments in heavy cannabis users are associated with altered neural oscillations.

Central cannabinoid receptors mediate neural oscillations and are localized to networks implicated in auditory P50 sensory gating, including the hippocampus and neocortex. The current study examined whether neural oscillations evoked by the paired clicks (S1, S2) are associated with abnormal P50 gating reported in cannabis users. Seventeen heavy cannabis users and 16 cannabis naïve controls participated. Analyses included P50 amplitudes, and time-frequency analyses (event-related spectral perturbations, ERSPs; intertrial coherence, ITC). Consistent with prior studies, cannabis users exhibited reduced P50 gating. The ERSP analysis yielded attenuated high frequency activity in the beta range (13-29 Hz) post-S1 and in the gamma range (30-50 Hz) post-S2 in the cannabis group, compared with the control group. Greater levels of cannabis use were positively associated with high P50 ratios and negatively with post-S2 ERSP gamma power. Findings suggest that heavy cannabis use is associated with aberrant beta and gamma activity in the dual-click procedure, which corroborates recent work demonstrating disruption of beta/gamma by cannabinoid receptor (CB1) agonists in a rat analogue of this task and highlights the translational potential of the dual-click procedure [corrected]

Treatment of gallbladder disease during operations Iraqi Freedom and Enduring Freedom.

BACKGROUND: We examined the outcome after treatment for gallbladder disease in deployed military service members and the impact of instituting a clinical pathway to expedite return to duty (RTD). METHODS: A retrospective chart review of 97 medically evacuated patients with gallbladder disease was carried out. These patients were evacuated from the field to Landstuhl Regional Medical Center (LRMC), Germany, between March 2003 and November 2004. In October 2003, a clinical pathway was established to facilitate returning these deployed patients back to their combat units. These service members were compared with 90 local patients who underwent the same surgery during the study period. RESULTS: Twenty-nine patients were treated before the implementation of the clinical pathway. Of those, five had complications, five were converted to open, and 52% returned to their deployed units. After the clinical pathway was established, there were no complications (p = 0.023), two were converted to open (p = 0.002), and 84% returned to duty (p = 0.002). The Operation Iraqi Freedom (OIF) and Operation Enduring Freedom (OEF) service members had delayed presentations for definitive treatment. When compared with the local patient group, OIF/OEF surgical cases were more often male (78 vs. 32%, p < 0.001), younger (average 31 vs. 35 years, p < 0.001), and associated with longer operative times (89 vs. 52 min, p < 0.001), and had higher conversion rate to open (7.2 vs. 2.2%, p = 0.17) and higher major complication rate (5.1 vs. 0%, p = 0.06). Time to operation and final pathologic diagnosis were significantly different between the two groups. CONCLUSIONS: Gallbladder surgery can be performed in a delayed manner in the deployed service member, although with a significantly higher morbidity as compared with the local population. We suggest that changes in the immediate treatment and transportation of these service members should occur at the theater level. The use of a clinical pathway facilitates the rapid RTD of soldiers diagnosed with gallbladder disease.

Eye-blink conditioning deficits indicate temporal processing abnormalities in schizophrenia.

Theoretical models suggest that symptoms of schizophrenia may be due to a dysfunctional modulatory system associated with the cerebellum. Although it has long been known that the cerebellum plays a critical role in associative learning and motor timing, recent evidence suggests that it also plays a role in nonmotor psychological processes. Indeed, cerebellar anomalies in schizophrenia have been linked to cognitive dysfunction and poor long-term outcome. To test the hypothesis that schizophrenia is associated with cerebellar dysfunction, cerebellar-dependent, delay eye-blink conditioning was examined in 62 individuals with schizophrenia and 62 age-matched non-psychiatric comparison subjects. The conditioned stimulus was a 400 ms tone, which co-terminated with a 50 ms unconditioned stimulus air puff. A subset of participants (25 with schizophrenia and 29 controls) also completed the Wechsler Abbreviated Scale of Intelligence. Participants with schizophrenia exhibited lower rates of eye-blink conditioning, including earlier (less adaptively timed) conditioned response latencies. Cognitive functioning was correlated with the rate of conditioned responsing in the non-psychiatric comparison subjects but not among those with schizophrenia, and the magnitude of these correlations significantly differed between groups. These findings are consistent with models of schizophrenia in which disruptions within the cortico-cerebellar-thalamic-cortical (CCTC) brain circuit are postulated to underlie the cognitive fragmentation that characterizes the disorder.

Eyeblink conditioning anomalies in bipolar disorder suggest cerebellar dysfunction.

OBJECTIVES: Accumulating research implicates the cerebellum in non-motor psychological processes and psychiatric diseases, including bipolar disorder (BD). Despite recent evidence that cerebellar lesions have been documented to trigger bipolar-like symptoms, few studies have directly examined the functional integrity of the cerebellum in those afflicted with BD. METHODS: Using a single-cue delay eyeblink conditioning procedure, the functional integrity of the cerebellum was examined in 28 individuals with BD (9 manic, 8 mixed, and 11 euthymic) and 28 age-matched healthy controls. RESULTS: Analysis of the bipolar group as a whole indicated a conditioned response acquisition and timing deficit compared to controls. However, when the bipolar group was categorized according to mood state (mixed, manic, euthymic), individuals tested during mixed episodes were strikingly impaired, performing significantly worse than all other groups on both the acquisition and timing of conditioned responses. CONCLUSIONS: These findings extend prior research implicating cerebellar functional abnormalities in BD and suggest that cerebellar dysfunction may be associated with mood state and course of illness.

Assessment of forebrain-dependent trace eyeblink conditioning in chronic cannabis users.

While CB1 knockout mice exhibit striking impairments on a cerebellar-dependent task called delay eyeblink conditioning (dEBC), these animals demonstrate intact forebrain-dependent trace EBC (tEBC). Although heavy human cannabis users also show impaired delay EBC, their performance on tEBC is currently unknown. Therefore, 13 heavy cannabis users and 13 cannabis naive controls completed a tEBC procedure. The cannabis group exhibited similar rates of conditioned responding compared to controls in the acquisition and extinction phase. Consistent with reports of overt attentional abnormalities, the cannabis group exhibited decreased N100 ERP amplitudes to the tone CS that were unrelated to mean levels of conditioning across blocks during the acquisition phase. The lack of a significant effect of heavy cannabis use on tEBC reported here, combined with the previous report of impaired dEBC in such users, mirrors the findings observed in CB1 knockout mice, and suggests that the cannabinoid system differentially mediates forebrain- and cerebellar-dependent learning processes in both humans and animals.

Cerebellum volume and eyeblink conditioning in schizophrenia.

Although accumulating evidence suggests that cerebellar abnormalities may be linked to the symptoms and course of schizophrenia, few studies have related structural and functional indices of cerebellar integrity. The present study examined the relationship between the volume of specific subregions of the cerebellum and cerebellar function, as measured by eyeblink conditioning (EBC). Nine individuals with schizophrenia and six healthy comparison participants completed structural magnetic resonance imaging of the brain and a delay EBC procedure. Volumetric measurements were taken for the whole brain, whole cerebellum, cerebellar anterior lobules I-V and posterior lobules VI-VII. The schizophrenia group had smaller cerebellar anterior lobes and exhibited impaired EBC relative to the comparison group. In the comparison group, larger anterior volume correlated with earlier conditioned response onset latencies and increased amplitudes of the unconditioned blink response during paired trials (i.e., when the conditioned and unconditioned stimuli co-occurred). The findings that smaller anterior cerebellar volumes and EBC impairments were associated with schizophrenia are consistent with non-human studies showing that anterior cerebellar abnormalities are associated with deficits in delay EBC. The lack of a significant correlation between indices of EBC and cerebellar volume within the schizophrenia group suggests an aberrant relationship between cerebellar structure and function.

Cannabis use disrupts eyeblink conditioning: evidence for cannabinoid modulation of cerebellar-dependent learning.

While the cerebellum contains the highest density of cannabinoid receptor (CB1) in the brain, no studies have assessed the effect of exogenous cannabinoids on cerebellar-dependent learning in humans. The current study, therefore, examined the effect of chronic cannabis use on classical eyeblink conditioning (EBC), a cerebellar-mediated task which has been shown to be disrupted in CB1 knockout mice. Chronic cannabis users (24 h abstinence before study; positive THC urine drug test) free of DSM-IV Axis-I or -II disorders, were evaluated. A delay EBC task was utilized, in which a conditioned stimulus (CS; 400 ms tone) co-terminated with a corneal air puff unconditioned stimulus (US; 50 ms), thus eliciting a conditioned blink response (CR). The cannabis group exhibited markedly fewer, and more poorly timed CRs as compared to drug-naive controls. There were no differences between the groups in either the unconditioned response (UR) or an EEG measure of selective attention to the CS (N100 auditory ERP), indicating that the disruption observed in the cannabis group was specific to CR acquisition. These results suggest that cannabis use is associated with functional deficits in the cerebellar circuitry underlying EBC, a finding which corroborates the recent work in CB1 knockout mice.

Cerebellar-dependent learning as a neurobehavioral index of the cannabinoid system.

Delta-9-tetrahydrocannabinol (THC) is the primary psycho-active ingredient in Cannabis spp., the most widely used illicit drug in the United States. THC is an exogenous agonist of the central cannabinoid receptor (CB1), one of the most abundant G-coupled receptors in the mammalian brain. Although CB1 receptors are distributed throughout the brain, they are found at very high levels in the cerebellum. Despite the variety of disturbances associated with acute cannabis intoxication, including altered short-term memory, dissociation of thoughts, motor impairments, and paranoia, among others, a reliable index of cannabinoid system function has in large part eluded scientists. Thus, there is a demand in contemporary clinical neuroscience for methods sensitive to cannabinoid system function, not only for assessing how cannabis use influences human information processing, but also to assess the involvement of the endocannabinoid system (ECS) in clinical disease and evaluate the effects of CB1-based drug therapies. The purpose of the present article, therefore, is to address this current need by integrating two separate literatures. The first literature demonstrates that the ECS mediates synaptic plasticity, specifically, long-term depression (LTD) of parallel fibers at the parallel fiber-Purkinje junction in the cerebellar cortex. The second literature suggests that LTD at this junction is necessary for the acquisition of the primary dependent variable in delay eyeblink conditioning (EBC)--the exhibition of temporally measured conditioned responses. These two literatures are integrated by proposing an updated EBC circuit that incorporates the CB1 receptor and the endogenous cannabinoids. Finally, the implications of the model is discussed in consideration of recent evidence from CB1 knockout mice, human cannabis users, and schizophrenia patients, with the expectation that translational research on the cannabinoid system will be advanced.

P50 and acoustic startle gating are not related in healthy participants.

Although P50 event-related potential (ERP) suppression and acoustic startle prepulse inhibition are conceptualized as measures of sensory and sensorimotor gating, respectively, the relationship between these measures is unclear. In the present study, P50 and prepulse inhibition trials were interleaved in a single testing session to determine their relationship. Thirty-one healthy participants were presented with startle- and P50-eliciting stimuli across six trial blocks. Lead stimuli (i.e., the prepulse to the acoustic startle and the first click in the dual click ERP paradigm) resulted in significant gating, or amplitude attenuation, of responses to the startle probe and second paired click. There were no meaningful correlations between the P50 and prepulse inhibition variables, indicating that P50 suppression and acoustic startle prepulse inhibition measure distinct neural mechanisms. The implications of these findings for operationally defining the psychological construct of gating with these psychophysiological measures are discussed.

Clonogenic analysis reveals reserve stem cells in postnatal mammals. II. Pluripotent epiblastic-like stem cells.

Undifferentiated cells have been identified in the prenatal blastocyst, inner cell mass, and gonadal ridges of rodents and primates, including humans. After isolation these cells express molecular and immunological markers for embryonic cells, capabilities for extended self-renewal, and telomerase activity. When allowed to differentiate, embryonic stem cells express phenotypic markers for tissues of ectodermal, mesodermal, and endodermal origin. When implanted in vivo, undifferentiated noninduced embryonic stem cells formed teratomas. In this report we describe a cell clone isolated from postnatal rat skeletal muscle and derived by repetitive single-cell clonogenic analysis. In the undifferentiated state it consists of very small cells having a high ratio of nucleus to cytoplasm. The clone expresses molecular and immunological markers for embryonic stem cells. It exhibits telomerase activity, which is consistent with its extended capability for self-renewal. When induced to differentiate, it expressed phenotypic markers for tissues of ectodermal, mesodermal, and endodermal origin. The clone was designated as a postnatal pluripotent epiblastic-like stem cell (PPELSC). The undifferentiated clone was transfected with a genomic marker and assayed for alterations in stem cell characteristics. No alterations were noted. The labeled clone, when implanted into heart after injury, incorporated into myocardial tissues undergoing repair. The labeled clone was subjected to directed lineage induction in vitro, resulting in the formation of islet-like structures (ILSs) that secreted insulin in response to a glucose challenge. This study suggests that embryonic-like stem cells are retained within postnatal mammals and have the potential for use in gene therapy and tissue engineering.