Adolescence alcohol exposure impairs fear extinction and alters medial prefrontal cortex plasticity.

After experiencing a traumatic event people often turn to alcohol to cope with symptoms. In those with post-traumatic stress disorder (PTSD) and a co-occurring alcohol use disorder (AUD), PTSD symptoms can worsen, suggesting that alcohol changes how traumatic memory is expressed. The objective of this series of experiments is to identify how alcohol drinking (EtOH), following cued fear conditioning and extinction, impacts fear expression in mice. Molecular (activity-regulated cytoskeleton-associated protein, Arc/arg3.1) and structural (dendrite and spine morphometry) markers of neuronal plasticity were measured following remote extinction retrieval. Mouse age (adolescent and adult) and sex were included as interacting variables in a full factorial design. Females drank more EtOH than males and adolescents drank more EtOH than adults. Adolescent females escalated EtOH intake across drinking days. Adolescent drinkers exhibited more conditioned freezing during extinction retrieval, an effect that persisted for at least 20 days. Heightened cued freezing in the adolescent group was associated with greater Arc/arg3.1 expression in layer (L) 2/3 prelimbic (PL) cortex, greater spine density, and reduced basal dendrite complexity. In adults, drinking was associated with reduced L2/3 infralimbic (IL) Arc expression but no behavioral differences. Few sex interactions were uncovered throughout. Overall, these data identify prolonged age-related differences in alcohol-induced fear extinction impairment and medial prefrontal cortex neuroadaptations.

Chemogenetic stimulation of the infralimbic cortex reverses alcohol-induced fear memory overgeneralization.

Post-traumatic stress disorder (PTSD) and alcohol use disorder (AUD) are often comorbid. Drinking tends to increase following trauma, which may exacerbate PTSD-related symptoms. Despite a clear relationship between excessive alcohol use and PTSD, how alcohol impacts the expression of traumatic fear remains unclear. This study aims to determine the neurobehavioral impact of chronic alcohol (ethanol; EtOH) on the expression of established fear memories in C57BL/6 N mice. We show that chronic EtOH selectively augments cued fear memory generalization and impairs fear extinction retrieval, leaving the expression of the original cued response intact. Immunohistochemistry for Arc/arg3.1 (Arc) revealed EtOH-induced decreases in Arc expression in the infralimbic cortex (IL) and basolateral amygdala complex (BLA) that were associated with cued fear memory overgeneralization. Chemogenetic stimulation of IL pyramidal neurons reversed EtOH-driven fear memory overgeneralization, identifying a role for the IL in cued fear memory precision. Considering the modulatory influence of the IL over conditioned fear expression, these data suggest a model whereby chronic EtOH-driven neuroadaptations in the IL promote fear memory overgeneralization. These findings provide new mechanistic insight into how excessive alcohol use, following exposure to a traumatic event, can exacerbate symptoms of traumatic fear.

Four weeks of high- versus low-load resistance training to failure on the rate of torque development, electromechanical delay, and contractile twitch properties.

The purpose of this study was to investigate the effects of 4-weeks of high- versus low-load resistance training to failure on rate of torque development (RTD), electromechanical delay (EMD), and contractile twitch characteristics. Fifteen men (mean±SD; age=21.7±2.4 yrs) were randomly assigned to either a high- (80% 1RM; n=7) or low-load (30% 1RM; n=8) training group and completed elbow flexion resistance training to failure 3 times per week for 4 weeks. The participants were tested at baseline, 2-, and 4-weeks of training. Peak RTD (pRTDV) and RTD at 0-30 (RTD30V), 0-50 (RTD50V), 0-100 (RTD100V), and 0-200 (RTD200V) ms, integrated EMG amplitude (iEMG) at 0-30, 0-50, and 0-100 ms, and EMD were quantified during maximal voluntary isometric muscle actions. Peak twitch torque, peak RTD, time to peak twitch, 1/2 relaxation time and the peak relaxation rate were quantified during evoked twitches. Four weeks of high-load, but not low-load resistance training, increased RTD200V. There were also increases in iEMG during the first 30 ms of muscle activation for the high- and low-load groups, which may have indirectly indicated increases in early phase motor unit recruitment and/or firing frequency. There were no significant training-induced adaptations in EMD or contractile twitch properties.

Electromyographic Responses from the Vastus Medialis during Isometric Muscle Actions.

This study examined the electromyographic (EMG) responses from the vastus medialis (VM) for electrodes placed over and away from the innervation zone (IZ) during a maximal voluntary isometric contraction (MVIC) and sustained, submaximal isometric muscle action. A linear electrode array was placed on the VM to identify the IZ and muscle fiber pennation angle during an MVIC and sustained isometric muscle action at 50% MVIC. EMG amplitude and frequency parameters were determined from 7 bipolar channels of the electrode array, including over the IZ, as well as 10 mm, 20 mm and 30 mm proximal and distal to the IZ. There were no differences between the channels for the patterns of responses for EMG amplitude or mean power frequency during the sustained, submaximal isometric muscle action; however, there were differences between channels during the MVIC. The results of the present study supported the need to standardize the placement of electrodes on the VM for the assessment of EMG amplitude and mean power frequency. Based on the current findings, it is recommended that electrode placements be distal to the IZ and aligned with the muscle fiber pennation angle during MVICs, as well as sustained, submaximal isometric muscle actions.

Adolescent nicotine-induced dendrite remodeling in the nucleus accumbens is rapid, persistent, and D1-dopamine receptor dependent.

Chronic nicotine exposure during adolescence induces dendritic remodeling of medium spiny neurons (MSNs) in the nucleus accumbens (NAcc) shell. While nicotine-induced dendritic remodeling has frequently been described as persistent, the trajectory of dendrite remodeling is unknown. Specifically, no study to date has characterized the structural plasticity of dendrites in the NAcc immediately following chronic nicotine, leaving open the possibility that dendrite remodeling emerges gradually over time. Further, the neuropharmacological mechanisms through which nicotine induces dendrite remodeling are not well understood. To address these questions, rats were co-administered chronic nicotine (0.5 mg/kg) and the D1-dopamine receptor (D1DR) antagonist SCH-23390 (0.05 mg/kg) subcutaneously every other day during adolescence. Brains were then processed for Golgi-Cox staining either 1 day or 21 days following drug exposure and dendrites from MSNs in the NAcc shell digitally reconstructed in 3D. Spine density was also measured at both time points. Our morphometric results show (1) the formation of new dendritic branches and spines 1 day following nicotine exposure, (2) new dendritic branches, but not spine density, remains relatively stable for at least 21 days, (3) the co-administration of SCH-23390 completely blocked nicotine-induced dendritic remodeling of MSNs at both early and late time points, suggesting the formation of new dendritic branches in response to nicotine is D1DR-dependent, and (4) SCH-23390 failed to block nicotine-induced increases in spine density. Overall this study provides new insight into how nicotine influences the normal trajectory of adolescent brain development and demonstrates a persistent form of nicotine-induced neuroplasticity in the NAcc shell that develops rapidly and is D1DR dependent.

Physiological Responses during Cycle Ergometry at a Constant Perception of Effort.

13 subjects performed an incremental test to exhaustion, 4, 8-min submaximal rides, and a 1-h ride at the rating of perceived exertion (RPE) that corresponded to the physical working capacity at the OMNI threshold (PWC(OMNI)) to examine: 1) the oxygen consumption (V̇O2), heart rate (HR), minute ventilation (+V̇(E)), respiratory frequency (FR), and power output responses during 1-h work bouts at a constant RPE that corresponded to the PWC(OMNI); and 2) the ability of current models to explain the responses for physiological and perceptual parameters during the 1-h work bouts. The RPE that corresponded to the PWC(OMNI) represented a sustainable exercise intensity (56±5% (V̇O(2Peak)) within the moderate-intensity domain. The mean, normalized slope coefficients for the V̇O2, +V̇(E), and power output vs. time relationships during the 1-h rides were significantly less than zero. The mean, normalized slope coefficient for the FR vs. time relationship during the 1-h rides, however, was not significantly different from zero. Thus, RPE most clearly tracked FR responses during the 1-h rides. It was hypothesized that afferent feedback from respiratory muscles may have mediated the perception of effort during cycle ergometry at a constant RPE in the moderate-intensity domain.

Durable fear memories require PSD-95.

Traumatic fear memories are highly durable but also dynamic, undergoing repeated reactivation and rehearsal over time. Although overly persistent fear memories underlie anxiety disorders, such as posttraumatic stress disorder, the key neural and molecular mechanisms underlying fear memory durability remain unclear. Postsynaptic density 95 (PSD-95) is a synaptic protein regulating glutamate receptor anchoring, synaptic stability and certain types of memory. Using a loss-of-function mutant mouse lacking the guanylate kinase domain of PSD-95 (PSD-95(GK)), we analyzed the contribution of PSD-95 to fear memory formation and retrieval, and sought to identify the neural basis of PSD-95-mediated memory maintenance using ex vivo immediate-early gene mapping, in vivo neuronal recordings and viral-mediated knockdown (KD) approaches. We show that PSD-95 is dispensable for the formation and expression of recent fear memories, but essential for the formation of precise and flexible fear memories and for the maintenance of memories at remote time points. The failure of PSD-95(GK) mice to retrieve remote cued fear memory was associated with hypoactivation of the infralimbic (IL) cortex (but not the anterior cingulate cortex (ACC) or prelimbic cortex), reduced IL single-unit firing and bursting, and attenuated IL gamma and theta oscillations. Adeno-associated virus-mediated PSD-95 KD in the IL, but not the ACC, was sufficient to impair recent fear extinction and remote fear memory, and remodel IL dendritic spines. Collectively, these data identify PSD-95 in the IL as a critical mechanism supporting the durability of fear memories over time. These preclinical findings have implications for developing novel approaches to treating trauma-based anxiety disorders that target the weakening of overly persistent fear memories.

The rate of torque development: a unique, non-invasive indicator of eccentric-induced muscle damage?

This study examined the time courses of recovery for isometric peak torque and rate of torque development (RTD) after eccentric-induced muscle damage. 18 men completed 6 sets of 10 maximal eccentric isokinetic muscle actions at 30° · s(-1). Peak torque, peak RTD and RTD at 10 (RTD10), 50 (RTD50), 100 (RTD100) and 200 ms (RTD200), serum creatine kinase and lactate dehydrogenase were measured before (PRE), immediately after (POST), 24, 48 and 72 h after eccentric exercise. Creatine kinase and lactate dehydrogenase increased from 139 to 6 457 and from 116 to 199 IU · L(-1) from PRE to 72 h, respectively. Peak torque and all RTDs decreased at POST. Peak torque and RTD200 remained lower than PRE through 72 h. Peak RTD remained lower than PRE through 48 h, but was not different from PRE at 72 h. RTD10 and RTD100 were lower than PRE through 24 h, but were not different from PRE at 48 and 72 h. RTD50 decreased at POST, but was not different from PRE at 24 h. Early phase RTDs recovered more quickly than PT and RTD200. Early phase RTDs may reflect neural mechanisms underlying eccentric-induced force decrements, while late RTDs may describe the same physiological mechanisms as PT.

Persisting changes in basolateral amygdala mRNAs after chronic ethanol consumption.

Adolescent alcohol use is common and evidence suggests that early use may lead to an increased risk of later dependence. Persisting neuroadaptions in the amygdala as a result of chronic alcohol use have been associated with negative emotional states that may lead to increased alcohol intake. This study assessed the long-term impact of ethanol consumption on levels of several basolateral amygdala mRNAs in rats that consumed ethanol in adolescence or adulthood. Male Long-Evans rats were allowed restricted access to ethanol or water during adolescence (P28, n=11, controls=11) or adulthood (P80, n=8, controls=10) for 18 days. After a sixty day abstinent period, the brain was removed and sections containing the basolateral amygdala were taken. In situ hybridization was performed for GABA(A) alpha(1), glutamic acid decarboxylase (GAD(67)), corticotropin releasing factor (CRF), and N-methyl-D-aspartate (NMDA) NR2A mRNAs. A significant decrease was observed in GABA(A) alpha(1), GAD(67), and CRF, but not NR2A, mRNAs in adult rats that consumed ethanol in comparison to controls. No significant changes were seen in adolescent consumers of ethanol for any of the probes tested. A separate analysis for each probe in the piriform cortex ascertained that the changes after ethanol consumption were specific to the basolateral amygdala. These results indicate that chronic ethanol consumption induces age-dependent alterations in basolateral amygdala neurochemistry.

Evidence for elevated nicotine-induced structural plasticity in nucleus accumbens of adolescent rats.

Male Long-Evans rats were administered nicotine bitartrate or sodium tartrate either during adolescence (p29-43) or adulthood (p80-94). Route of administration was via subcutaneously implanted osmotic pump (initial dose 2.0 mg/kg/day, free base). Five weeks following nicotine administration, brains were processed for Golgi-Cox staining. Medium spiny neurons from nucleus accumbens (NAc) shell were digitally reconstructed for morphometric analysis. Total dendritic length and branch number were greater in medium spiny neurons from animals pretreated with nicotine during adolescence. A branch order analysis indicated that increased branch number was specific to higher order branches. Mean branch lengths did not differ with respect to treatment as a function of branch order. Thus, nicotine-induced increases in total dendritic length were a function of greater numbers of branches, not increased segment length. In contrast, adult nicotine exposure did not significantly alter total dendritic length or branch number of medium spiny neurons. Total dendritic length and branch number of a second morphological type, the large aspiny neuron, did not differ following either adolescent or adult pretreatment. The age-dependent alteration of accumbal structure was associated with qualitatively different behavioral responses to drug challenge. These data provide evidence that drug-induced structural plasticity in nucleus accumbens is considerably more pronounced during adolescence.

Ventral tegmental area region governs GABA(B) receptor modulation of ethanol-stimulated activity in mice.

Locomotor stimulation in response to ethanol in mice may model human ethanol-induced euphoria. The associated neural substrates, possibly relevant to alcoholism, have not been fully elucidated. Systemic injection of baclofen, a GABA(B) receptor agonist, attenuates ethanol's stimulant effects. GABA(B) receptors on dopamine cell bodies in the ventral tegmental area (VTA) may modulate ethanol-induced dopamine release, a postulated mechanism for ethanol's stimulant effects. However, baclofen's attenuating effects could be associated with peripheral receptor actions. Baclofen was injected i.c.v. or into the VTA of FAST mice, bred for extreme sensitivity to ethanol-induced locomotor stimulation, to test the hypotheses that (1) central GABA(B) receptors influence baclofen's effects on ethanol-stimulated activity, and (2) VTA GABA(B) receptors specifically modulate ethanol's stimulant effects. I.c.v. baclofen dose-dependently attenuated ethanol stimulation, supporting a central locus for baclofen's effects. Anterior VTA baclofen also attenuated ethanol stimulation. However, more posterior VTA infusions unexpectedly potentiated ethanol stimulation. In SLOW mice, bred for resistance to ethanol stimulation, posterior intra-VTA baclofen did not alter EtOH response. However, anterior VTA baclofen alone produced a locomotor depressant effect in SLOW mice, not seen in FAST mice. GABA(B) receptor autoradiography using [(3)H]CGP 54626, a potent GABA(B) receptor antagonist, did not reveal line differences in binding density in the VTA, or in the substantia nigra pars compacta, a nearby brain structure associated with motor control. These results suggest that anterior VTA GABA(B) receptors play a role in baclofen's attenuation of ethanol's stimulant effects, and that posterior VTA GABA(B) receptors serve an opposite role that is normally masked. Selection for differential ethanol stimulant sensitivity has altered VTA GABA(B) systems that influence locomotor behavior. However, differences in GABA(B) receptor densities in the VTA or substantia nigra pars compacta cannot explain the selected line difference.