The suppressant effect of ethanol, delivered via intrahippocampal microdialysis, on the firing of local pyramidal cells in freely behaving rats

Ethanol enhances JWH-018-induced impairment of sensorimotor and memory functions in mice: From preclinical evidence to forensic implication in Driving Under the Influence of Drugs

BACKGROUND

Several new Synthetic Cannabinoids have appeared each year since their introduction into the illicit drug market as recreational drugs. Among these, naphtalen-1-yl-(1-pentylindol-3-yl) methanone (JWH-018) is one of the most detected compounds in biological samples from patients involved in intoxication or death cases. Furthermore, consumption of JWH-018 has been linked to several cases of Driving Under the Influence of Drugs (DUID) suggesting that effects induced by this compound can affect individuals' ability to drive.

METHODS

Given the high spread of polydrug consumption and the wide number of alcohol-related traffic accidents, this study aims to investigate the acute effects induced by co-administration of JWH-018 with ethanol on sensorimotor and motor responses, grip strength and memory functions in CD-1 male mice. Acute impairments induced by JWH-018 and ethanol alone have also been investigated, in order to compare their effects with that induced by their concurrent administration.

RESULTS

In vivo behavioral experiments revealed a worsening of the cognitive and sensorimotor disruption after the co-administration of JWH-018 with ethanol compared to single compounds.

CONCLUSIONS

These animal-based findings suggest a potential increased impairment on psychomotor performances which could be related to driving abilities posed by poly-drug consumption involving SCs and ethanol.

Acute Effects of Ethanol on Hippocampal Spatial Representation and Offline Reactivation

Acute alcohol exposure impairs hippocampus-dependent spatial memory. However, there is little evidence for the effects of ethanol on the spike patterns of hippocampal cell populations. Here, we examined how the spatial firing patterns of place cells, neurons that encode specific locations, were altered in rats that were intraperitoneally injected with 1.5 g/kg ethanol. Ethanol administration partly reduced or abolished place-selective spiking of a subset of place cells during running periods in a spatial task, whereas a subset of place fields newly emerged, suggesting a partial reorganization of hippocampal spatial maps by ethanol. On the other hand, ethanol administration did not significantly alter the frequency of hippocampal sharp-wave ripple (SWRs) and synchronous spike patterns during resting periods, suggesting that offline memory consolidation and retrieval mechanisms underpinned by hippocampal neuronal synchronization are not strongly affected by ethanol. These results indicate that acute ethanol intake mainly affects the encoding of external information but has little impact on internal memory processing.

Effect of Alcohol on Hippocampal-Dependent Plasticity and Behavior: Role of Glutamatergic Synaptic Transmission

Problematic alcohol drinking and alcohol dependence are an increasing health problem worldwide. Alcohol abuse is responsible for approximately 5% of the total deaths in the world, but addictive consumption of it has a substantial impact on neurological and memory disabilities throughout the population. One of the better-studied brain areas involved in cognitive functions is the hippocampus, which is also an essential brain region targeted by ethanol. Accumulated evidence in several rodent models has shown that ethanol treatment produces cognitive impairment in hippocampal-dependent tasks. These adverse effects may be related to the fact that ethanol impairs the cellular and synaptic plasticity mechanisms, including adverse changes in neuronal morphology, spine architecture, neuronal communication, and finally an increase in neuronal death. There is evidence that the damage that occurs in the different brain structures is varied according to the stage of development during which the subjects are exposed to ethanol, and even much earlier exposure to it would cause damage in the adult stage. Studies on the cellular and cognitive deficiencies produced by alcohol in the brain are needed in order to search for new strategies to reduce alcohol neuronal toxicity and to understand its consequences on memory and cognitive performance with emphasis on the crucial stages of development, including prenatal events to adulthood.

Bio-electrochemical microelectrode arrays for glutamate and electrophysiology detection in hippocampus of temporal lobe epileptic rats

Temporal Lobe Epilepsy (TLE) is a chronic neurological disorder, characterized by sudden, repeated and transient central nervous system dysfunction. For better understanding of TLE, bio-nanomodified microelectrode arrays (MEA) are designed, for the achievement of high-quality simultaneous detection of glutamate signals (Glu) and multi-channel electrophysiological signals including action potentials (spikes) and local field potentials (LFPs). The MEA was fabricated by Micro-Electro-Mechanical System fabrication technology and all recording sites were modified with platinum black nano-particles, the average impedance decreased by nearly 90 times. Additionally, glutamate oxidase was also modified for the detection of Glu. The average sensitivity of the electrode in Glu solution was 1.999 ± 0.032 × 10^-2pA/μM·μm²(n = 3) and linearity was R = 0.9986, with a good selectivity of 97.82% for glutamate and effective blocking of other interferents. In the in-vivo experiments, the MEA was subjected in hippocampus to electrophysiology and Glu concentration detection. During seizures, the fire rate of spikes increases, and the interspike interval is concentrated within 30 ms. The amplitude of LFPs increases by 3 times and the power increases. The Glu level (4.22 μM, n = 4) was obviously higher than normal rats (2.24 μM, n = 4). The MEA probe provides an advanced tool for the detection of dual-mode signals in the research of neurological diseases.

Neural Firing in the Prefrontal Cortex During Alcohol Intake in Alcohol-Preferring "P" Versus Wistar Rats

BACKGROUND

Neural activity within the prefrontal cortex (PFC) is altered by alcohol and alcohol-associated stimuli and is mediated by genetic susceptibility to alcoholism. However, very little is known about how genetic risk of excessive drinking might mediate neural firing in the PFC during alcohol consumption.

METHODS

To determine how genetic risk influences alcohol seeking, intake, and neural activity, a Pavlovian alcohol consumption task was used-the 2-Way Cued Access Protocol (2CAP). Alcohol-preferring "P" rats and relatives of their (heterogeneous) founding Wistar population were used for these studies. After acquisition of 2CAP, extinction of responding for alcohol was evaluated by substituting water for alcohol. Following these experiments, in vivo electrophysiological recordings were obtained during 2CAP from the PFC in a separate cohort of Wistar and P rats implanted with moveable tetrode microdrives.

RESULTS

P and Wistar rats increased daily alcohol seeking and intake with P rats consuming roughly twice as much alcohol as Wistar. Both rat populations decreased seeking behavior during extinction. However, P rats displayed persistent increases in seeking after controlling for intake versus Wistar. Higher firing rates (FRs) were observed in P rats prior to 2CAP and throughout alcohol and water consumption compared with Wistars that were matched for alcohol-drinking history. Differences in FR were driven, in part, by a larger percentage of neurons in P rats versus Wistars that increased FR compared with those that decreased, or did not change.

CONCLUSIONS

These data provide additional evidence of increased alcohol consumption and persistent alcohol seeking in P versus Wistar rats. Differences in PFC neural firing observed in P rats prior to drinking could be heritable and/or related to an enhanced response to alcohol-associated contextual cues. FR differences observed during alcohol drinking might be related to an augmented sensitivity of PFC neurons to orally consumed alcohol.

Alcohol use across the lifespan: An analysis of adolescent and aged rodents and humans

Adolescence and old age are unique periods of the lifespan characterized by differential sensitivity to the effects of alcohol. Adolescents and the elderly appear to be more vulnerable to many of alcohol's physiological and behavioral effects compared to adults. The current review explores the differential effects of acute alcohol, predominantly in terms of motor function and cognition, in adolescent and aged humans and rodents. Adolescents are less sensitive to the sedative-hypnotic, anxiolytic, and motor-impairing effects of acute alcohol, but research results are less consistent as it relates to alcohol's effects on cognition. Specifically, previous research has shown adolescents to be more, less, and similarly sensitive to alcohol-induced cognitive deficits compared to adults. These equivocal findings suggest that learning acquisition may be differentially affected by ethanol compared to memory, or that ethanol-induced cognitive deficits are task-dependent. Older rodents appear to be particularly vulnerable to the motor- and cognitive-impairing effects of acute alcohol relative to younger adults. Given that alcohol consumption and abuse is prevalent throughout the lifespan, it is important to recognize age-related differences in response to acute and long-term alcohol. Unfortunately, diagnostic measures and treatment options for alcohol dependence are rarely dedicated to adolescent and aging populations. As discussed, although much scientific advancement has been made regarding the differential effects of alcohol between adolescents and adults, research with the aged is underrepresented. Future researchers should be aware that adolescents and the aged are uniquely affected by alcohol and should continue to investigate alcohol's effects at different stages of maturation.

Confounding effects of volatile anesthesia on CBV assessment in rodent forebrain following ethanol challenge

PURPOSE

To compare and contrast the pattern and characteristics of the cerebral blood volume (CBV) response to ethanol (EtOH) in rats under awake and anesthetized conditions.

MATERIALS AND METHODS

Acute EtOH (0.75 g/kg) challenge-induced CBV changes were measured using a contrast-enhanced functional MRI CBV method in 15 male Sprague Dawley rats under three experimental conditions: 1.0% to 1.2% isoflurane (N = 5); 0.8% halothane (N = 5); and awake with no anesthetic (N = 5). Physiological parameters were collected from bench settings in nine rats from the above different conditions. Four parameters: 1) area under the curve (AUC%); 2) the maximum signal change (Max%); 3) EtOH absorption rate (alpha(2)); and 4) EtOH elimination rate (alpha(1)) were employed to compare EtOH-induced MRI signals between the awake and anesthetized groups.

RESULTS

Both awake and anesthetized animals responded with an increase in CBV to EtOH challenge. However, the presence of anesthesia promoted a significant preferential flow to subcortical areas not seen in the awake condition.

CONCLUSION

Unclear mechanisms of anesthesia add a layer of uncertainty to the already complex interpretation of EtOH's influence on neuronal activity, cellular metabolism, and hemodynamic coupling.

Ethanol effects on dentate granule cell LTP

In previous studies we identified a lateral hypothalamic area (LHA) sensitive to ethanol, < 5.0 mM, when the perifornical region of the area is perfused with different concentrations of ethanol. Some of these perifornical neurons contain angiotensin (Ang) and project directly to the dentate gyrus where angiotensin is released and inhibits LTP in medial perforant path-dentate granule cell synapses. The AT1 subtype receptor is involved because pretreatment with losartan, an AT1 antagonist, prevents Ang II, diazepam, and ethanol impairment of LTP as well as their effects on behavior. There is a possibility that these effects were not specific to the LHA; but might be attributable to direct effects of ethanol on postsynaptic granule cells due to diffusion of the ethanol in the extracellular space or by the circulatory system. The purpose of the present study was to determine a dose effect of ethanol on LTP in these same synapses when the dentate gyrus was perfused with several different concentrations of ethanol under the same conditions in urethane anesthetized rats. Ethanol was administered directly into the dentate gyrus by means of a fine stainless steel cannula attached approximately 1.0 mm from the tip of the glass capillary recording electrode. Results show that the threshold for ethanol in the dentate is higher by a factor of ten, > 30 mM and < 50 mM; and that at higher doses ethanol can have a direct effect on the LHA; and possibly toxic due to increasing ethanol in the blood circulatory system.

Prolonged neurophysiological effects of cumulative wine drinking

The effects of a single, large dose of alcohol have been studied extensively, but how alcohol affects the brain under more realistic social drinking situations has received scant attention. The neurophysiological effects of a cumulative dose of alcohol were investigated as subjects drank three glasses of alcoholic or placebo red wine, 1 h apart. In a double-blind procedure, electroencephalographic (EEG) activity was recorded for social drinkers during rest and performance of a working memory task at two levels of difficulty. Background EEG power in the theta, slow alpha, and beta bands increased with alcohol consumption. Along with this systemic increase in background cortical resonant activity, event-related potential (ERP) amplitudes decreased between 200 and 350 ms poststimulus and P300 latency increased, effects that occurred while relevant stimulus factors were being evaluated. These neurophysiological effects endured 3 h after drinking, whereas blood/breath alcohol concentration had decreased considerably and cognitive performance returned to normal. These findings seem to indicate that moderate social alcohol consumption has cumulative effects on brain function that persist for hours after chemical and behavioral indicators of intoxication have diminished. The results seem to indicate that neuronal populations needed for stimulus processing were less available after wine consumption (as evidenced by reduced ERP amplitudes) because of increased background oscillatory activity (as evidenced by increased background EEG power).

Evidence for the ability of hippocampal neurons to develop acute tolerance to ethanol in behaving rats

BACKGROUND

The cellular mechanisms underlying acute tolerance to alcohol are unclear. This study aimed to determine whether hippocampal neurons have the ability to develop acute tolerance to alcohol in behaving rats.

METHODS

Intrahippocampal microdialysis was performed in freely behaving rats, and the firing of single neurons in the dialysis area was recorded. The control microdialysis fluid, artificial cerebrospinal fluid (ACSF), was replaced with 1 M ethanol in ACSF for a 30 min period. One hour later, the ethanol perfusion was repeated. To test the functional integrity of the microdialysis probe in situ, each microdialysis session was completed with recording the effect of a 10-20 min perfusion of 500 microM N-methyl-D-aspartate (NMDA). The extracellular concentration profile of ethanol during intrahippocampal microdialysis with 1 M ethanol was estimated in a separate study in anesthetized rats. The ethanol content was measured in tissue slices surrounding the probe with gas chromatography (GC), and the generated data were analyzed with a mathematical model for microdialysis to estimate the concentration of ethanol at the recording site.

RESULTS

The predominant effect of the first intrahippocampal microdialysis with ethanol was a decrease in firing rate in both pyramidal cells and interneurons. In contrast, such firing rate decrease did not develop during the second ethanol perfusion. Subsequent NMDA perfusion still induced robust changes in the electrical activity of the neurons. The estimated extracellular ethanol concentration at the recording site was 45-70 mM.

CONCLUSION

This study revealed that hippocampal neurons have the ability to develop acute tolerance to a single exposure of clinically relevant concentrations of ethanol in behaving rats, without influences from the rest of the body.

Neuronal subserving of behavior before and after chronic ethanol treatment

We have previously shown that an acute ethanol dose (1 g/kg), sufficient to impair the performance of a healthy rabbit, also reversibly depresses the activity of those limbic-cortex neurons that are specifically activated during recently learned behavioral acts. Our new morphological and neurophysiological data suggest a death of such neurons after 9-month chronic ethanol treatment. The effect of acute ethanol administration on neurons and performance speed in alcoholic rabbits was opposite to that found in healthy animals. Our results help to understand why neurocognition of alcoholics changes and why acute low-level alcohol ingestion influences them differently than healthy individuals.

Effects of ethanol on hippocampal place-cell and interneuron activity

Mounting evidence suggests that ethanol exerts effects on learning and memory by altering cellular activity in the hippocampus and related structures. However, little is actually known regarding ethanol's effects on hippocampal function in awake, freely-behaving animals. The present study examines the effects of ethanol on hippocampal place-cell and interneuron activity in freely-behaving rats. Signals from individual hippocampal neurons were isolated while subjects traversed a symmetric Y-maze for food reward. Following 15 min of baseline recording, subjects were injected with one of four doses of ethanol (0.0, 0.5, 1.0 and 1.5 g/kg), and cellular activity was monitored for a 1-h time period. Following sufficient time for recovery (minimum of 3 h post injection), cellular activity was monitored for an additional 15-min period. Both 1.0 and 1.5 g/kg ethanol potently suppressed the firing of hippocampal place-cells without altering place-field locations. Ethanol did not significantly suppress out-of-field firing rates, leading to a decrease in spatial specificity (i.e. the ratio of in-field/out-of-field firing rates). Interneuron activity was not altered by 1.0 g/kg ethanol, but was occasionally suppressed by 1.5 g/kg ethanol. Results are interpreted in light of recent behavioral and electrophysiological studies examining the effects of ethanol on hippocampal function.

Ethanol, memory, and hippocampal function: a review of recent findings

For well over a century, ethanol was believed to exert its effects on cognition and behavior by producing a ubiquitous depression of central nervous system activity. A general disruption in brain function was consistent with the belief that ethanol's effects on cognition and behavior were also quite general. Substantial evidence now indicates that ethanol produces a host of selective effects on neural activity, resulting in regional differences in ethanol's effects in the brain. Consistent with such evidence, recent research suggests that ethanol's effects on cognition and behavior are not as global as previously assumed. The present paper discusses evidence that many of ethanol's effects on learning and memory stem from altered cellular activity in the hippocampus and related structures. Potential mechanisms for ethanol's disruption of hippocampal function are reviewed. Evidence suggests that ethanol disrupts activity in the hippocampus by interacting directly with hippocampal neurons and by interacting with critical hippocampal afferents.

Microdialysis-coupled place cell detection in the hippocampus: a new strategy for the search for cognition enhancer drugs

1. The MPCD method in freely moving rats is a new neuroscience technique. It is able to detect the location-specific firing of hippocampal place cells, and to deliver, via microdialysis, various drug solutions into the extracellular environment of the detected neurons. Place cells are critical elements of the neural system in brain which governs cognitive processes. It is emphasized in this article that effective cognition enhancer drugs must selectively and significantly affect the firing of these cells. 2. By using MPCD, it is possible to recognize drug combinations which can increase the location-specific firing of place cells to an optimal level. This paper proposes that such pharmacological action facilitates engram-creation in extrahippocampal cortical areas, improving cognitive functions. Thus, an MPCD-based research strategy may lead to the rational development of a new generation of cognition enhancer drugs for the treatment of learning and memory disorders, including Alzheimer's disease (AD).

Manipulation of pyramidal cell firing in the hippocampus of freely behaving rats by local application of K+ via microdialysis

In this study, microdialysis was performed in the hippocampus of freely behaving rats, and the firing of pyramidal cells, including place cells, was recorded at the site of the microdialysis probe. For 10-min periods, the artificial cerebrospinal fluid (ACSF) in the microdialysis system was replaced with ACSF containing 50 mM K+ (high K+ solution). Complementary in vitro tests determined that microdialysis with such high K+ solution produced an outflow of 5% of the perfused K+ from the microdialysis probe. Application of K+ with this method into the CA1 region significantly increased the firing of the local pyramidal cells, including place cells, during both movement and sleep. On average, K+ exposures increased the firing rate of the neurons to 306% and 448% of the control firing rate during movement and sleep, respectively. After the termination of the K+ outflow, the cells continued to discharge for 5-30 min with a significantly higher frequency than before the K+ challenge. This phenomenon also occurred in both behavioral states. During the period of enhanced firing, the out-of-field firing rate of the recorded place cells was dramatically increased. It was also found that during the K+ applications, otherwise silent pyramidal cells often became electrically active. The K(+)-induced firing modifications were usually not accompanied by behavioral or EEG changes. The data raise the possibility that transient elevations in the extracellular K+ concentration contribute to the ionic/molecular processes which are responsible for plastic firing pattern modifications in hippocampus. Pharmacological manipulation of place cells with the described method offers a new strategy to understand the molecular bases of spatial memory.