Adolescent Intermittent Alcohol Exposure: Dysregulation of Thrombospondins and Synapse Formation are Associated with Decreased Neuronal Density in the Adult Hippocampus.

BACKGROUND: Adolescent intermittent alcohol exposure (AIE) has profound effects on neuronal function. We have previously shown that AIE causes aberrant hippocampal structure and function that persists into adulthood. However, the possible contributions of astrocytes and their signaling factors remain largely unexplored. We investigated the acute and enduring effects of AIE on astrocytic reactivity and signaling on synaptic expression in the hippocampus, including the impact of the thrombospondin (TSP) family of astrocyte-secreted synaptogenic factors and their neuronal receptor, alpha2delta-1 (α2δ-1). Our hypothesis is that some of the influences of AIE on neuronal function may be secondary to direct effects on astrocytes. METHODS: We conducted Western blot analysis on TSPs 1 to 4 and α2δ-1 from whole hippocampal lysates 24 hours after the 4th and 10th doses of AIE, then 24 days after the last dose (in adulthood). We used immunohistochemistry to assess astrocyte reactivity (i.e., morphology) and synaptogenesis (i.e., colocalization of pre- and postsynaptic puncta). RESULTS: Adolescent AIE reduced α2δ-1 expression, and colocalized pre- and postsynaptic puncta after the fourth ethanol (EtOH) dose. By the 10th dose, increased TSP2 levels were accompanied by an increase in colocalized pre- and postsynaptic puncta, while α2δ-1 returned to control levels. Twenty-four days after the last EtOH dose (i.e., adulthood), TSP2, TSP4, and α2δ-1 expression were all elevated. Astrocyte reactivity, indicated by increased astrocytic volume and area, was also observed at that time. CONCLUSIONS: Repeated EtOH exposure during adolescence results in long-term changes in specific astrocyte signaling proteins and their neuronal synaptogenic receptor. Continued signaling by these traditionally developmental factors in adulthood may represent a compensatory mechanism whereby astrocytes reopen the synaptogenic window and repair lost connectivity, and consequently contribute to the enduring maladaptive structural and functional abnormalities previously observed in the hippocampus after AIE.

Adolescent intermittent alcohol exposure: persistence of structural and functional hippocampal abnormalities into adulthood.

BACKGROUND: Human adolescence is a crucial stage of neurological development during which ethanol (EtOH) consumption is often at its highest. Alcohol abuse during adolescence may render individuals at heightened risk for subsequent alcohol abuse disorders, cognitive dysfunction, or other neurological impairments by irreversibly altering long-term brain function. To test this possibility, we modeled adolescent alcohol abuse (i.e., intermittent EtOH exposure during adolescence [AIE]) in rats to determine whether adolescent exposure to alcohol leads to long-term structural and functional changes that are manifested in adult neuronal circuitry. METHODS: We specifically focused on hippocampal area CA1, a brain region associated with learning and memory. Using electrophysiological, immunohistochemical, and neuroanatomical approaches, we measured post-AIE changes in synaptic plasticity, dendritic spine morphology, and synaptic structure in adulthood. RESULTS: We found that AIE-pretreated adult rats manifest robust long-term potentiation, induced at stimulus intensities lower than those required in controls, suggesting a state of enhanced synaptic plasticity. Moreover, AIE resulted in an increased number of dendritic spines with characteristics typical of immaturity. Immunohistochemistry-based analysis of synaptic structures indicated a significant decrease in the number of co-localized pre- and postsynaptic puncta. This decrease is driven by an overall decrease in 2 postsynaptic density proteins, PSD-95 and SAP102. CONCLUSIONS: Taken together, these findings reveal that repeated alcohol exposure during adolescence results in enduring structural and functional abnormalities in the hippocampus. These synaptic changes in the hippocampal circuits may help to explain learning-related behavioral changes in adult animals preexposed to AIE.

Binge-pattern ethanol exposure during adolescence, but not adulthood, causes persistent changes in GABAA receptor-mediated tonic inhibition in dentate granule cells.

BACKGROUND: In recent years, it has become clear that acute ethanol (EtOH) affects various neurobiological and behavioral functions differently in adolescent animals than in adults. However, less is known about the long-term neural consequences of chronic EtOH exposure during adolescence, and most importantly whether adolescence represents a developmental period of enhanced vulnerability to such effects. METHODS: We made whole-cell recordings of GABAA receptor-mediated tonic inhibitory currents from dentate gyrus granule cells (DGGCs) in hippocampal slices from adult rats that had been treated with chronic intermittent ethanol (CIE) or saline during adolescence, young adulthood, or adulthood. RESULTS: CIE reduced baseline tonic current amplitude in DGGCs from animals pretreated with EtOH during adolescence, but not in GCs from those pretreated with EtOH during young adulthood or adulthood. Similarly, the enhancement of tonic currents by acute EtOH exposure ex vivo was increased in GCs from animals pretreated with EtOH during adolescence, but not in those from animals pretreated during either of the other 2 developmental periods. CONCLUSIONS: These findings underscore our recent report that CIE during adolescence results in enduring alterations in tonic current and its acute EtOH sensitivity and establish that adolescence is a developmental period during which the hippocampal formation is distinctively vulnerable to long-term alteration by chronic EtOH exposure.

Long-term modulation of A-type K(+) conductances in hippocampal CA1 interneurons in rats after chronic intermittent ethanol exposure during adolescence or adulthood.

BACKGROUND: Chronic alcohol use, especially exposure to alcohol during adolescence or young adulthood, is closely associated with cognitive deficits that may persist into adulthood. Therefore, it is essential to identify possible neuronal mechanisms underlying the observed deficits in learning and memory. Hippocampal interneurons play a pivotal role in regulating hippocampus-dependent learning and memory by exerting strong inhibition on excitatory pyramidal cells. The function of these interneurons is regulated not only by synaptic inputs from other types of neurons but is also precisely governed by their own intrinsic membrane ionic conductances. The voltage-gated A-type potassium current (IA ) regulates the intrinsic membrane properties of neurons, and disruption of IA is responsible for many neuropathological processes including learning and memory deficits. Thus, it represents a previously unexplored cellular mechanism whereby chronic ethanol (EtOH) may alter hippocampal memory-related functioning. METHODS: Using whole-cell electrophysiological recording methods, we investigated the enduring effects of chronic intermittent ethanol (CIE) exposure during adolescence or adulthood on IA in rat CA1 interneurons. RESULTS: We found that the mean peak amplitude of IA was significantly reduced after CIE in either adolescence or adulthood, but IA density was attenuated after CIE in adolescence but not after CIE in adulthood. In addition, the voltage-dependent steady-state activation and inactivation of IA were altered in interneurons after CIE. CONCLUSIONS: These findings suggest that CIE can cause long-term changes in IA channels in interneurons and thus may alter their inhibitory influences on memory-related local hippocampal circuits, which could be, in turn, responsible for learning and memory impairments observed after chronic EtOH exposure.

In the rat, chronic intermittent ethanol exposure during adolescence alters the ethanol sensitivity of tonic inhibition in adulthood.

BACKGROUND: Alcohol drinking by adolescents is a major public health concern. Adolescents tend to drink in a chronic, intermittent, that is, "binge," pattern, and such patterns of ethanol exposure are associated with increased risk of neurotoxicity and the development of alcohol use disorders (Crews et al., 2000; Hunt, 1993). Both adolescent humans and rats are more sensitive to acute ethanol-induced memory impairment than adults (Acheson et al., 1998; Markwiese et al., 1998). Furthermore, in rats, chronic intermittent ethanol (CIE) exposure during adolescence produces a long-lasting, perhaps permanent, maintenance of the adolescent high sensitivity to ethanol's amnestic effects (White et al., 2000a). We have previously shown that acute ethanol increases tonic inhibitory current mediated by extrasynaptic GABA(A) receptors more efficaciously in dentate granule cells (DGCs) from adolescent than adult rats (Fleming et al., 2007). In this study, we determined if CIE during adolescence produced long-lasting changes in this tonic current. METHODS: Adolescent rats were subjected to a CIE exposure regimen and allowed to mature to full adulthood. Whole-cell voltage-clamp measurements of tonic inhibitory current and mean phasic current were made in vitro in hippocampal brain slices. RESULTS: CIE exposure during adolescence increased the ethanol sensitivity of tonic inhibitory current mediated by extrasynaptic GABA(A) receptors and decreased the ethanol sensitivity of phasic, synaptic GABA(A) receptor-mediated current in adult DGCs. CONCLUSIONS: CIE exposure during adolescence produces long-lasting changes in the function and ethanol sensitivity of extrasynaptic GABA(A) receptors in DGCs. These changes appear to "lock-in" and maintain the high adolescent sensitivity to ethanol in these cells. Furthermore, greater ethanol enhancement of tonic inhibition in the hippocampal formation after CIE is consistent with the greater sensitivity to ethanol-induced memory impairment after adolescent CIE. This finding represents the first demonstration of a long-term, memory-related cellular effect of CIE during adolescence, and the "lock-in" of adolescent ethanol sensitivity that these results suggest could represent a conceptual step forward in understanding the vulnerability of the adolescent brain to alcohol.

Dopamine attenuates evoked inhibitory synaptic currents in central amygdala neurons.

The central nucleus of the amygdala (CeA) plays a critical role in regulating the behavioral, autonomic and endocrine response to stress. Dopamine (DA) participates in mediating the stress response and DA release is enhanced in the CeA during stressful events. However, the electrophysiological effects of DA on CeA neurons have not yet been characterized. Therefore, the purpose of this study was to identify and characterize the effect of DA application on electrophysiological responses of CeA neurons in coronal brain sections of male Sprague-Dawley rats. We used whole-cell patch-clamp electrophysiological techniques to record evoked synaptic responses and to determine basic membrane properties of CeA neurons both before and after DA superfusion. DA (20-250 µM) did not significantly alter membrane conductance over the voltage range tested. However, DA significantly reduced the peak amplitude of evoked inhibitory synaptic currents in CeA neurons. Pretreatment with the D(2) receptor antagonist eticlopride failed to significantly block the inhibitory effects of DA. In contrast, pretreatment with the D(1) receptor antagonist SCH-23390 significantly reduced the effects of DA on evoked inhibitory neurotransmission in these neurons. Moreover, bath superfusion of the specific D(1) receptor agonist SKF-39393, but not the D(2) receptor agonist quinpirole, significantly reduced peak amplitude of evoked inhibitory synaptic events. DA reduced the frequency of miniature IPSCs without altering the amplitude, while having no effect on the amplitude of IPSCs elicited by pressure application of GABA. These results suggest that DA may modulate inhibitory synaptic transmission in CeA through D(1) receptor activation primarily by a presynaptic mechanism.

Differential sensitivity of hippocampal interneurons to ethanol in adolescent and adult rats.

Ethanol (EtOH) promotes GABAergic synaptic transmission in the central nervous system. We have shown that EtOH enhances the frequency of GABA(A) receptor-mediated spontaneous inhibitory postsynaptic currents less powerfully in hippocampal CA1 pyramidal neurons from adolescent animals compared with those from adults. However, we have also shown that EtOH promotes the firing of hippocampal interneurons, located in stratum lacunosum moleculare (SLM), from adolescent animals more potently than in those from adults. Thus the latter finding would seem to be inconsistent with the former. To understand this apparent inconsistency, we have now assessed the effects of EtOH on a different subpopulation of hippocampal interneurons, those with somata located in the stratum oriens (SO). We found that EtOH-induced enhancement of the frequency of spontaneous action potentials (sAPs) was less in interneurons from adolescent rats compared with those from adults. In addition, EtOH-induced reduction of the afterhyperpolarization decay time constant (τ(slow)) was less pronounced in interneurons from adolescent rats, as was the EtOH-induced increase in the amplitude of the hyperpolarization-activated cation current, I(h). The effect of EtOH on sAP firing frequency was blocked by application of the I(h) antagonist 4-ethylphenylamino-1,2-dimethyl-6-methylaminopyrimidinium chloride (ZD7288). These results indicate that although EtOH promotes the firing of hippocampal interneurons, through promotion of I(h), the developmental expression of this effect differs between interneurons with somata located in the SO and SLM.

Role of cannabinoid receptor type 1 desensitization in greater tetrahydrocannabinol impairment of memory in adolescent rats.

Adolescence is a well defined developmental period during which marijuana use is common. However, little is known about the response to marijuana in adolescents compared with adults. We have shown previously that adolescent rats are more impaired than adults by Δ(9)-tetrahydrocannabinol (THC), the main psychoactive compound in marijuana, in a spatial learning task, but the mechanism responsible for this differential impairment is not understood. We determined the role of THC tolerance and cannabinoid receptor type 1 (CB1) regulation in THC-induced spatial learning impairment in adolescent and adult rats. We measured the development of tolerance to THC-induced learning impairment in adolescent (postnatal days 30-35) and adult (postnatal days 70-75) rats. We pretreated them for 5 days with 10 mg/kg THC, and then evaluated the effects of vehicle or THC treatment on learning during training in the Morris water maze. We also determined CB1 number and functional coupling in the hippocampus of adolescents and adults. Finally, we measured the time course of hippocampal CB1 desensitization in adolescents and adults during treatment with 10 mg/kg THC or vehicle. Our results indicate that adults, but not adolescents, become tolerant to the effects of THC during water maze training after 5 days of pretreatment. CB1s in adolescent hippocampus are less functionally coupled to G proteins and desensitize more slowly in response to THC treatment than those of adults. THC may impair learning in adolescents more than in adults because of delayed activation of cellular homeostatic adaptive mechanisms underlying cannabinoid tolerance in the hippocampus.

The novel micro-opioid receptor antagonist, [N-allyl-Dmt(1)]endomorphin-2, attenuates the enhancement of GABAergic neurotransmission by ethanol.

AIMS: We investigated the effects of [N-allyl-Dmt(1)]endomorphin-2 (TL-319), a novel and highly potent micro-opioid receptor antagonist, on ethanol (EtOH)-induced enhancement of GABA(A) receptor-mediated synaptic activity in the hippocampus. METHODS: Evoked and spontaneous inhibitory postsynaptic currents (eIPSCs and sIPSCs) were isolated from CA1 pyramidal cells from brain slices of male rats using whole-cell patch-clamp techniques. RESULTS: TL-319 had no effect on the baseline amplitude of eIPSCs or the frequency of sIPSCs. However, it induced a dose-dependent suppression of an ethanol-induced increase of sIPSC frequency with full reversal at concentrations of 500 nM and higher. The non-specific competitive opioid receptor antagonist naltrexone also suppressed EtOH-induced increases in sIPSC frequency but only at a concentration of 60 microM. CONCLUSION: These data indicate that blockade of micro-opioid receptors by low concentrations of [N-allyl-Dmt(1)]endomorphin-2 can reverse ethanol-induced increases in GABAergic neurotransmission and possibly alter its anxiolytic or sedative effects. This suggests the possibility that high potency opioid antagonists may emerge as possible candidate compounds for the treatment of ethanol addiction.

Impact of a Neuroscience-Based Health Education Course on High School Students' Health Knowledge, Beliefs, and Behaviors.

PURPOSE: The purpose of this pilot study was to evaluate the potential of an innovative high school neuroscience-based health course for implementation feasibility and impact on student outcomes. METHODS: Thirteen teachers from two high schools participated in this quasi-experimental pilot study including 395 students (202 in the intervention classes and 193 in the comparison classes). Students completed pre/post online surveys assessing their knowledge, beliefs, and behaviors. Our analysis strategy for multi-item measures was to estimate the effects of the intervention on latent change scores in structural equation models. RESULTS: Students in the neuroscience health classes showed a significant increase in neuroscience knowledge as compared to students in the comparison group (difference estimate in proportion correct metric, adjusted for covariates = .04; 95% confidence interval [.01, .06]). However, none of the other primary outcomes showed a significant difference between conditions. Teachers in the intervention group were observed implementing the neuroscience and health components more often than the self-regulation and growth mindset components. Students in the neuroscience group were more likely to mention the importance of caring for their brain and its link to health behaviors. CONCLUSIONS: Findings demonstrate that information about the link between health behaviors and brain functioning can be successfully integrated into a high school health education course, although effects on student health beliefs and behaviors were not observed. Additional development work should focus on clarifying the theoretical mechanisms of change, integrating the neuroscience content with self-regulation and growth mindset, and providing additional professional development for teachers.

Differential anxiogenic, aversive, and locomotor effects of THC in adolescent and adult rats.

RATIONALE: Unpleasant side effects of drugs of abuse often limit their repeated use; however, such effects may be attenuated in adolescents compared to adults. OBJECTIVES: We investigated whether the anxiogenic, aversive, or locomotor effects of delta-9-tetrahydrocannabinol (THC) differ between adolescent and adult rats. METHODS: We used the elevated plus maze (EPM) and light-dark tests of anxiety, the conditioned taste aversion and conditioned place aversion (CPA) tests of generalized aversion, and measures of stress hormone levels in serum to examine effects of THC in adolescent and adult rats. Locomotor activity was also recorded in the EPM, light-dark task, and CPA association sessions. RESULTS: In the EPM and light-dark tasks, THC was anxiogenic in both age groups, but the drug was more anxiogenic in adults than in adolescents. In the place and taste aversion tasks, THC was aversive in both ages, and at 1.25 and 5 mg/kg, was more aversive in adults than in adolescents. The locomotor response to THC, as measured in the anxiety tasks and CPA, affected adults more than adolescents. Multiple measures revealed a locomotor-decreasing effect in adults, whereas some measures suggested a small locomotor-increasing effect in adolescent rats. CONCLUSIONS: These results suggest that THC can have greater anxiogenic, aversive, and locomotor-reducing effects in adult rats than in adolescent rats. These findings suggest an explanation for reduced marijuana use in adult humans compared to teenagers.

Neurosteroid modulation of GABAergic neurotransmission in the central amygdala: a role for NMDA receptors.

The neurosteroid 3alpha-hydroxy-5alpha-pregnan-20-one (allopregnanolone or ALLO) positively modulates GABA(A) receptors, an action that may contribute to the anxiolytic effects of ALLO. Recent evidence suggests that ALLO's anxiolytic effects appear to be mediated by the amygdala, a key neural structure for emotional and cognitive behaviors. However, little is known regarding ALLO effects on amygdala physiology. We therefore explored ALLO effects on GABA neurotransmission in the central nucleus (Ce) of the amygdala, a major output nucleus involved in fear and anxiety. We recorded evoked GABA(A) receptor-mediated inhibitory postsynaptic currents (IPSCs) in Ce neurons using whole-cell patch clamp techniques. We observed that ALLO significantly reduced the amplitude of evoked GABA(A) receptor-mediated IPSCs. However, the effect of ALLO was occluded by the NMDA receptor antagonist D-APV. D-APV alone also reduced evoked IPSCs in Ce neurons. These results suggest that ALLO-induced reduction of GABAergic transmission in Ce appears to depend on neural network activity, possibly involving an NMDA receptor-mediated mechanism. These ALLO effects on GABAergic transmission in the central amygdala may play a role in mediating its anxiolytic actions.

Differential effects of delta9-THC on learning in adolescent and adult rats.

Marijuana use remains strikingly high among young users in the U.S., and yet few studies have assessed the effects of delta9-tetrahydrocannabinol (THC) in adolescents compared to adults. This study measured the effects of THC on male adolescent and adult rats in the Morris water maze. In Experiment 1, adolescent (PD=30-32) and adult (PD=65-70) rats were treated acutely with 5.0 mg/kg THC or vehicle while trained on the spatial version of the water maze on five consecutive days. In Experiment 2, adolescent and adult rats were treated acutely with 2.5 or 10.0 mg/kg THC or vehicle while trained on either the spatial and non-spatial versions of the water maze. In Experiment 3, adolescent and adult rats were treated with 5.0 mg/kg THC or vehicle daily for 21 days, and were trained on the spatial and then the non-spatial versions of the water maze task four weeks later in the absence of THC. THC impaired both spatial and nonspatial learning more in adolescents than in adults at all doses tested. However, there were no long-lasting significant effects on either spatial or non-spatial learning in rats that had been previously exposed to THC for 21 days. This developmental sensitivity is analogous to the effects of ethanol, another commonly used recreational drug.

NMDA receptor antagonists disinhibit rat posterior cingulate and retrosplenial cortices: a potential mechanism of neurotoxicity.

NMDA receptor antagonists produce region-specific neurodegeneration by an undetermined mechanism, but one proposed mechanism involves disinhibition. In certain areas of the brain, NMDA receptors mediate excitatory drive onto inhibitory interneurons. Thus, NMDA receptor/channel antagonists may reduce inhibition (i.e., produce "disinhibition"). If a sufficient level of disinhibition is produced, enhanced vulnerability to excitotoxicity may result. Furthermore, if there are region-specific differences in NMDA antagonist-induced disinhibition, this could underlie region-specific NMDA antagonist-induced neurotoxicity. In the present study, we tested this hypothesis by exposing rat brain slices to the NMDA receptor antagonist dizocilpine maleate (MK-801) and measuring MK-801-induced disinhibition in areas of higher and lower vulnerability to neurodegeneration [posterior cingulate/retrosplenial cortices (PCC/RSC) and parietal cortex, respectively]. Using whole-cell patch-clamp techniques, bicuculline-sensitive GABA(A) receptor-mediated IPSCs were measured in biocytin-labeled pyramidal neurons in the PCC/RSC and parietal cortex. In the PCC/RSC, bath-applied MK-801 (10-40 microm) produced disinhibition, shown as a concentration-dependent decrease in spontaneous IPSC frequency and amplitude; MK-801 (40 microm) also reduced evoked IPSC amplitudes. In parietal cortex, MK-801 produced significantly less disinhibition. To determine whether disinhibition is caused by presynaptic or postsynaptic mechanisms, we tested the effects of MK-801 (40 microm) against miniature IPSC (mIPSC) frequency and amplitude in tetrodotoxin (TTX; 0.5 microm)-treated slices and found that MK-801 did not alter mIPSC frequency or amplitude. Taken together, these results suggest that NMDA receptors regulate activity of inhibitory interneurons and, consequently, GABA release in certain cortical areas. This region-specific reduction in inhibitory input to pyramidal cells could underlie the region-specific neurotoxicity of NMDA antagonists.

Prenatal choline supplementation protects against postnatal neurotoxicity.

Choline, a dietary compound present in many foods, has recently been classified as an essential nutrient for humans. There is evidence from animal models that the availability of choline during the prenatal period influences neural and cognitive development. Here we report that choline supplementation during a 6 d gestational period protects against neurodegeneration in the posterior cingulate and retrosplenial cortices of female adolescent rats produced by peripheral administration of the NMDA receptor antagonist dizocilpine (MK-801). These data show that availability of a single nutrient, choline, during a brief period of prenatal development diminishes vulnerability to neurotoxicity in adolescent offspring.

Prenatal dietary choline availability alters postnatal neurotoxic vulnerability in the adult rat.

The availability of choline during the prenatal period influences neural and cognitive development. Here we report that choline supplementation during a six-day gestational period protects against neurodegeneration in the posterior cingulate and retrosplenial cortices of adult female rats produced by systemic administration of the N-methyl-D-aspartate receptor antagonist dizocilpine (MK-801). These data show that availability of choline during a brief prenatal period diminishes vulnerability to neurotoxicity in adult offspring.

Differential effects of ethanol on motor coordination in adolescent and adult rats.

Recent evidence suggests that adolescence represents a unique period of sensitivity to the effects of ethanol. Adolescent animals are more sensitive than adults to many of the effects of ethanol, including ethanol-induced learning and memory impairments, while being less sensitive to others, including ethanol-induced sedation. It is well known that ethanol produces dramatic impairments in balance and motor coordination. While previous research suggests that adolescents and adults do not differ in their sensitivity to the effects of relatively low doses of ethanol on motor coordination, it is not known whether differences in performance would emerge at higher doses. The present study compared the impact of a range of ethanol doses (1.0, 2.0 and 3.0 g/kg) on motor coordination in adolescent [postnatal day (PD) 35-40] and adult (PD 70-75) rats. Motor coordination was assessed using the tilting plane test before ethanol administration (baseline) and at 15, 30, 60, 120 and 180 min after ethanol administration. Performance was not affected by 1.0 g/kg ethanol in either age group. However, adults were more impaired than adolescents at nearly every time point following administration of both 2.0 and 3.0 g/kg ethanol. The results provide further evidence that adolescents and adults are differentially sensitive to the behavioral effects of ethanol. Given the critical role of motor coordination in the ability to operate motor vehicles and the central role of balance and coordination in field sobriety tests, these data could have important implications if extended to human subjects.

In vitro electrophoresis and in vivo electrophysiology of peripheral nerve using DC field stimulation.

BACKGROUND: Given the movement of molecules within tissue that occurs naturally by endogenous electric fields, we examined the possibility of using a low-voltage DC field to move charged substances in rodent peripheral nerve in vitro. NEW METHOD: Labeled sugar- and protein-based markers were applied to a rodent peroneal nerve and then a 5-10 V/cm field was used to move the molecules within the extra- and intraneural compartments. Physiological and anatomical nerve properties were also assessed using the same stimulation in vivo. RESULTS: We demonstrate in vitro that charged and labeled compounds are capable of moving in a DC field along a nerve, and that the same field applied in vivo changes the excitability of the nerve, but without damage. CONCLUSIONS: The results suggest that low-voltage electrophoresis could be used to move charged molecules, perhaps therapeutically, safely along peripheral nerves.

Effect of sub-chronic intermittent ethanol exposure on spatial learning and ethanol sensitivity in adolescent and adult rats.

It has become clear that adolescence is a period of distinct responsiveness to the acute effects of ethanol on learning and other cognitive functions. However, the effects of repeated intermittent ethanol exposure during adolescence on learning and cognition are less well studied, and other effects of repeated ethanol exposure such as withdrawal and chronic tolerance complicate such experiments. Moreover, few studies have compared the effects of repeated ethanol exposure during adolescence and adulthood, and they have yielded mixed outcomes that may be related to methodological differences and/or secondary effects of ethanol on behavioral performance. One emerging question is whether relatively brief intermittent ethanol exposure (i.e., sub-chronic exposure) during adolescence or adulthood might alter learning at a time after exposure when chronic tolerance would be expected, and whether tolerance to the cognitive effects of ethanol might influence the effect of ethanol on learning at that time. To address this, male adolescent and adult rats were pre-treated with sub-chronic daily ethanol (five doses [4.0 g/kg, i.p.] or saline at 24-h intervals, across 5 days). Two days after the last pre-exposure, spatial learning was assessed on 4 consecutive days using the Morris water maze. Half of the animals from each treatment cell received ethanol (2.0 g/kg, i.p.) 30 min prior to each testing session and half of the animals received saline. Ethanol pre-exposure altered water maze performance in adult animals but not in adolescents, and acute ethanol exposure impaired learning in animals of both ages independent of pre-exposure condition. There was no evidence of cognitive tolerance in animals of either age group. These results indicate that a relatively short period of intermittent ethanol exposure during adulthood, but not adolescence, promotes thigmotaxis in the water maze shortly after pre-exposure but does not induce cognitive tolerance to the effects of ethanol in either age group.