Danielle Gulick

Exposure to Kynurenic Acid During Adolescence Produces Memory Deficits in Adulthood

The glia-derived molecule kynurenic acid (KYNA) is an antagonist of α7 nicotinic acetylcholine receptors and the glycine(B) binding site on n-methyl-d-aspartateglutamate receptors, both of which have critical roles in neural plasticity as well as learning and memory. KYNA levels are increased in the brains and cerebral spinal fluid of persons with schizophrenia, leading to the notion that changes in KYNA concentration might contribute to cognitive dysfunction associated with this disorder. Indeed, recent studies indicate that increasing endogenous KYNA concentration by administering l-kynurenine (L-KYN, the precursor of KYNA) impairs spatial as well as contextual learning and memory in adult rats. In the present study, rats were treated with L-KYN (100 mg/kg) throughout adolescence to increase endogenous KYNA concentration during this critical time in brain development. Rats were then tested drug-free as adults to test the hypothesis that exposure to elevated levels of KYNA during development may contribute to cognitive dysfunction later in life. Consistent with prior studies in which adult rats were treated acutely with L-KYN, juvenile rats exposed to increased KYNA concentration during adolescence exhibited deficits in contextual fear memory, but cue-specific fear memory was not impaired. In addition, rats treated with L-KYN as adolescents were impaired on a novel object recognition memory task when tested as adults. The memory deficits could not be explained by drug-induced changes in locomotor activity or shock sensitivity. Together, these findings add to the growing literature supporting the notion that exposure to increased concentration of KYNA may contribute to cognitive deficits typically observed in schizophrenia.

Nicotine Withdrawal Disrupts Both Foreground and Background Contextual Fear Conditioning but not Pre-Pulse Inhibition of the Acoustic Startle Response in C57BL/6 Mice

Nicotine withdrawal is associated with multiple symptoms such as anxiety, increased appetite, and disrupted cognition in humans. Although animal models have provided insights into the somatic and affective symptoms of nicotine withdrawal, less research has focused on the effects of nicotine withdrawal on cognition. Therefore, in this study, C57BL/6J mice were used to test the effects of withdrawal from chronic nicotine on foreground and background contextual fear conditioning, which present the context as a primary or secondary stimulus, respectively. Mice withdrawn from 12 days of chronic nicotine (6.3mg/kg/day) or saline were trained and tested in either foreground or background contextual fear conditioning; nicotine withdrawal-associated deficits in contextual fear conditioning were observed in both conditions. Mice were also tested for the effects of withdrawal on pre-pulse inhibition of the acoustic startle reflex (PPI), a measure of sensory gating, and on the acoustic startle reflex. Mice withdrawn from 12 days of chronic nicotine (6.3 or 12.6 mg/kg/day) or saline underwent one 30-min PPI and startle session; no effect of withdrawal from chronic nicotine on PPI or startle was observed for either dose at 24h after nicotine removal. Therefore, mice were tested at different time points following withdrawal from 12.6 mg/kg/day chronic nicotine (8, 24, and 48 h after nicotine removal). No effect of withdrawal from chronic nicotine was observed at any time point for PPI. Overall, these results demonstrate that nicotine withdrawal disrupts two methods of contextual learning but not sensory gating in C57BL/6J mice.

The circadian Per1 and Per2 genes influence alcohol intake, reinforcement, and blood alcohol levels.

BACKGROUND Perturbations in the function of core circadian clock components such as the Period (Per) family of genes are associated with alcohol use disorder, and disruptions in circadian cycles may contribute to alcohol abuse and relapse. This study tested ethanol consumption, reinforcement, and metabolism in mice containing functional mutations in Per1 and/or Per2 genes on an ethanol-preferring background, C57BL/6J mice. METHODS Mice were tested in: (A) free-access intake with ascending concentrations of ethanol (2-16%, v/v), (B) conditioned place preference using ethanol (2g/kg for males; 2.5g/kg for females) vs. saline injections, (C) recovery of the righting reflex following a 4g/kg bolus of ethanol, and (D) blood ethanol levels 1h after a 2g/kg bolus of ethanol. RESULTS All Per mutant (mPer) mice showed increased ethanol intake and condition place preference compared to controls. There were also genotypic differences in blood ethanol concentration: in males, only mPer1 mice showed a significantly higher blood ethanol concentration than WT mice, but in females, all mPer mice showed higher blood ethanol levels than WT mice. CONCLUSIONS Mutation of either Per1 or Per2, as well as mutations of both genes, increases ethanol intake and reinforcement in an ethanol-preferring mouse model. In addition, this increase in ethanol seeking behavior seems to result both from a change in ethanol metabolism and a change in reward responding to ethanol, but not from any change in sensitivity to ethanols sedating effects.

Effects of ethanol and caffeine on behavior in C57BL/6 mice in the plus-maze discriminative avoidance task.

INTRODUCTION Caffeine is frequently consumed concurrent to or immediately following ethanol consumption. Identifying how caffeine and ethanol interact to modulate behavior is essential to understanding the co-use of these drugs. The plus-maze discriminative avoidance task (PMDAT) allows within-subject measurement of learning, anxiety, and locomotion. METHODS For training, each mouse was placed in the center of the plus-maze for 5 min, and each time that the mouse entered the aversive enclosed arm, a light and white noise were turned on. At testing, each mouse was returned to the center of the maze for 3 min. No cues were turned on during testing. RESULTS Ethanol (1.0-1.4 g/kg) dose-dependently decreased anxiety and learning, and increased locomotion. Caffeine (5.0-40.0 mg/kg) dose-dependently increased anxiety and decreased locomotion and learning. Caffeine failed to reverse ethanol-induced learning deficits. However, 1.4 g/kg ethanol blocked the anxiogenic effect of caffeine. DISCUSSION Although caffeine and ethanol interact to modulate behavior in the PMDAT, caffeine does not reverse ethanol-induced learning deficits. Ethanol-induced anxiolysis may contribute to alcohol consumption, while ethanols blockade of caffeine-induced anxiogenesis may contribute to co-use.

Varenicline Ameliorates Ethanol-Induced Deficits in Learning in C57BL/6 Mice

Ethanol is a frequently abused drug that impairs cognitive processes such as learning. Varenicline, an alpha4beta2 nicotinic receptor partial agonist and alpha7 nicotinic receptor full agonist prescribed for smoking cessation, has been shown to decrease ethanol consumption. The current study investigated whether varenicline could ameliorate ethanol-induced deficits in learning and whether varenicline alters blood alcohol concentration in C57BL/6 mice. Conditioning consisted of two auditory conditioned stimulus (CS; 30s, 85dB white noise)-foot shock unconditioned stimulus (US; 2s, 0.57mA) pairings. For all studies, saline or ethanol (1.0, 1.5, 2.0g/kg i.p.) was administered 15min before training, and saline or varenicline (0.05, 0.1, 0.2mg/kg i.p.) was administered 60min before either training or testing. For blood alcohol analysis, saline or varenicline (0.1mg/kg) was administered 60min before collection, and saline or ethanol (1.0, 1.5, 2.0g/kg) was administered 15min before collection. Varenicline dose-dependently ameliorated ethanol-induced conditioning deficits for all three doses of ethanol when administered before training but not when administered 24h later, before testing. In addition, varenicline did not alter blood alcohol concentration. The smoking cessation aid varenicline may have therapeutic uses for treating ethanol-associated disruptions in cognitive processes.

Nicotine and extinction of fear conditioning.

Despite known health risks, nicotine use remains high, especially in populations diagnosed with mental illnesses, including anxiety disorders and Post-Traumatic Stress Disorder (PTSD). Smoking in these populations may relate to the effects of nicotine on emotional memories. The current study examined the effects of nicotine administration on the extinction of conditioned fear memories. C57BL/6J mice were trained with two white noise conditioned stimulus (CS; 30 s, 85 dB)-foot shock (2 s, 0.57 mA) pairings. Extinction sessions consisted of six presentations of the CS (60 s) across multiple days. Mice were either tested in an AAA design, in which all stages occurred in the same context, or in an ABA design to identify if context changes alter extinction. Saline or nicotine was administered 5 min before training and/or extinction. In the AAA design, nicotine administration before training did not alter extinction. Nicotine administered prior to extinction sessions enhanced extinction and nicotine administered before training and extinction decreased extinction. In the ABA design, nicotine administered before extinction enhanced extinction and blocked context renewal of conditioned fear, while nicotine administered during training and extinction did not alter extinction but enhanced the context renewal of conditioned fear. Nicotine has a differential effect on extinction of fear conditioning depending on when it is administered. Administration during extinction enhances extinction whereas administration during training and extinction may strengthen contextual fear memories and interfere with extinction.

Nicotine acts in the anterior cingulate, but not dorsal or ventral hippocampus, to reverse ethanol-induced learning impairments in the plus-maze discriminative avoidance task.

The current study examines the role of the dorsal and ventral hippocampus, and anterior cingulate in the interactive effects of ethanol and nicotine on learning, anxiety and locomotion in the plus‐maze discriminative avoidance task, which allows dissociation of drug effects on each behaviour. At training, time spent in each of the arms of the elevated plus‐maze was recorded for 5 minutes. Each time that the mouse entered the aversive enclosed arm, a light and white noise were turned on. At testing, no cues were turned on and time spent in each arm was recorded for 3 minutes. The effects of systemic ethanol (1.0 or 1.4 g/kg) and nicotine (0.35 µg/0.50 µl/side) infused into the anterior cingulate, dorsal and ventral hippocampus were examined, as were the interactive effects of systemic ethanol (1.0 g/kg) and nicotine (0.09 mg/kg) with the high‐affinity nicotinic receptor antagonist dihydro‐beta‐erythroidine (DHβE) (18.0 µg/0.50 µl/side) infused into the anterior cingulate. Ethanol dose dependently decreased anxiety, increased locomotion, and decreased learning. Anterior cingulate‐infused nicotine decreased anxiety and reversed ethanol‐associated learning deficits. Anterior cingulate‐infused DHβE blocked reversal of ethanol‐induced learning deficits by systemic nicotine. Dorsal hippocampus‐infused nicotine reversed ethanol‐induced anxiolysis and hyper‐locomotion (1.4 g/kg) but produced no behavioural changes in ethanol‐naïve mice. Ventral hippocampus‐infused nicotine enhanced anxiolysis associated with 1.4 g/kg ethanol, but had no other effects. The anterior cingulate is necessary and sufficient for nicotine reversal of ethanol‐induced learning deficits. In addition, the anterior cingulate, dorsal hippocampus and ventral hippocampus may mediate drug‐induced changes in anxiety.

The Hippocampus and Cingulate Cortex Differentially Mediate the Effects of Nicotine on Learning Versus on Ethanol-Induced Learning Deficits Through Different Effects at Nicotinic Receptors

The current study examined the effects of nicotine infusion into the dorsal hippocampus or anterior cingulate on fear conditioning and on ethanol-induced deficits in fear conditioning, and whether these effects involved receptor activation or inactivation. Conditioning consisted of two white noise (30 s, 85 dB)–foot-shock (2 s, 0.57 mA) pairings. Saline or ethanol was administered to C57BL/6 mice 15 min before training and saline or nicotine was administered 5 min before training or before training and testing. The ability of the high-affinity nicotinic acetylcholinergic receptor (nAChR) antagonist dihydro-β-erythroidine (DHβE) to modulate the effects of ethanol and nicotine was also tested; saline or DHβE was administered 25 (injection) or 15 (infusion) minutes before training or before training and testing. Infusion of nicotine into the hippocampus enhanced contextual fear conditioning but had no effect on ethanol-induced learning deficits. Infusion of nicotine into the anterior cingulate ameliorated ethanol-induced deficits in contextual and cued fear conditioning but had no effect on learning in ethanol-naive mice. DHβE blocked the effects of nicotine on ethanol-induced deficits; interestingly, DHβE alone and co-administration of subthreshold doses of DHβE and nicotine also ameliorated ethanol-induced deficits but failed to enhance learning. Finally, DHβE failed to ameliorate ethanol-induced deficits in β2 nAChR subunit knockout mice. These results suggest that nicotine acts in the hippocampus to enhance contextual learning, but acts in the cingulate to ameliorate ethanol-induced learning deficits through inactivation of high-affinity β2 subunit-containing nAChRs.

Interactive effects of ethanol and nicotine on learning, anxiety, and locomotion in C57BL/6 mice in the plus-maze discriminative avoidance task.

INTRODUCTION Alcohol and nicotine both alter learning, locomotion, and anxiety, yet no study has directly examined the interactive effects of these drugs across these behaviors within subjects. Such a comparison would determine if the drugs produce independent effects on each behavior. The plus-maze discriminative avoidance task (PMDAT) allows within-subject measurement of these behaviors. METHODS For training, each mouse explored the elevated plus-maze for 5 min and each time a mouse entered the aversive enclosed arm, a light and white noise were turned on. For testing, each mouse was returned to the center of the maze and, for 3 min, the time in each arm or in the center area was recorded. No cues were turned on during testing. The effects of ethanol (0.6-2.6 g/kg 15 min before training) and nicotine (0.045-0.18 mg/kg 5 min before training), alone or in combination, on behavior were examined. RESULTS Ethanol dose-dependently decreased anxiety, increased locomotion, and decreased learning but different doses altered each behavior. Nicotine dose-dependently increased anxiety and locomotion and decreased learning but different doses altered each behavior. Nicotine (0.09 mg/kg) reversed ethanol-associated changes in learning (1.0 and 1.4 g/kg), locomotion (1.4 g/kg), and anxiety (1.4 g/kg). CONCLUSIONS The effects of nicotine or ethanol on learning occurred at different doses than those that altered anxiety or locomotion, suggesting that the drug effects on learning are independent of the effects on anxiety and locomotion. With combined administration, nicotine reduced ethanol-associated deficits in learning and changes in anxiety and locomotion.

Reelin supplementation recovers synaptic plasticity and cognitive deficits in a mouse model for Angelman syndrome

The Reelin signaling pathway is implicated in processes controlling synaptic plasticity and hippocampus‐dependent learning and memory. A single direct in vivo application of Reelin enhances long‐term potentiation, increases dendritic spine density and improves associative and spatial learning and memory. Angelman syndrome (AS) is a neurological disorder that presents with an overall defect in synaptic function, including decreased long‐term potentiation, reduced dendritic spine density, and deficits in learning and memory, making it an attractive model in which to examine the ability of Reelin to recover synaptic function and cognitive deficits. In this study, we investigated the effects of Reelin administration on synaptic plasticity and cognitive function in a mouse model of AS and demonstrated that bilateral, intraventricular injections of Reelin recover synaptic function and corresponding hippocampus‐dependent associative and spatial learning and memory. Additionally, we describe alteration of the Reelin profile in tissue from both the AS mouse and post‐mortem human brain.