The rewarding and locomotor-sensitizing effects of repeated cocaine administration are distinct and separable in mice

Repeated psychostimulant exposure progressively increases their potency to stimulate motor activity in rodents. This behavioral or locomotor sensitization is considered a model for some aspects of drug addiction in humans, particularly drug craving during abstinence. However, the role of increased motor behavior in drug reward remains incompletely understood. Intracranial self-stimulation (ICSS) was measured concurrently with locomotor activity to determine if acute intermittent cocaine administration had distinguishable effects on motor behavior and perception of brain stimulation-reward (BSR) in the same mice. Sensitization is associated with changes in neuronal activity and glutamatergic neurotransmission in brain reward circuitry. Expression of AMPA receptor subunits (GluR1 and GluR2) and CRE binding protein (CREB) was measured in the ventral tegmental area (VTA), dorsolateral striatum (STR) and nucleus accumbens (NAc) before and after a sensitizing regimen of cocaine, with and without ICSS. Repeated cocaine administration sensitized mice to its locomotor stimulating effects but not its ability to potentiate BSR. ICSS increased GluR1 in the VTA but not NAc or STR, demonstrating selective changes in protein expression with electrical stimulation of discrete brain structures. Repeated cocaine reduced GluR1, GluR2 and CREB expression in the NAc, and reductions of GluR1 and GluR2 but not CREB were further enhanced by ICSS. These data suggest that the effects of repeated cocaine exposure on reward and motor processes are dissociable in mice, and that reduction of excitatory neurotransmission in the NAc may predict altered motor function independently from changes in reward perception

Molecular mechanisms mediating a deficit in recall of fear extinction in adult mice exposed to cocaine in utero.

Prenatal cocaine exposure has been shown to alter cognitive processes of exposed individuals, presumed to be a result of long-lasting molecular alterations in the brain. In adult prenatal cocaine exposed (PCOC) mice we have identified a deficit in recall of fear extinction, a behavior that is dependent on the medial prefrontal cortex (mPFC) and the hippocampus. While we observed no change in the constitutive expression of brain derived neurotrophic factor (BDNF) protein and mRNA in the mPFC and hippocampus of adult PCOC mice, we observed blunted BDNF signaling in the mPFC of adult PCOC mice after fear extinction compared to the control animals. Specifically, during the consolidation phase of the extinction memory, we observed a decrease in BDNF protein and it's phospho-TrkB receptor expression. Interestingly, at this same time point there was a significant increase in total Bdnf mRNA levels in the mPFC of PCOC mice as compared with controls. In the Bdnf gene, we identified decreased constitutive binding of the transcription factors, MeCP2 and P-CREB at the promoters of Bdnf exons I and IV in the mPFC of PCOC mice, that unlike control mice remained unchanged when measured during the behavior. Finally, bilateral infusion of recombinant BDNF protein into the infralimbic subdivision of the mPFC during the consolidation phase of the extinction memory rescued the behavioral deficit in PCOC mice. In conclusion, these findings extend our knowledge of the neurobiologic impact of prenatal cocaine exposure on the mPFC of mice, which may lead to improved clinical recognition and treatment of exposed individuals

Cocaine exposure decreases GABA neuron migration from the ganglionic eminence to the cerebral cortex in embryonic mice

Recurrent exposure of the developing fetus to cocaine produces persistent alterations in structure and function of the cerebral cortex. Neurons of the cerebral cortex are derived from two sources: projection neurons from the neuroepithelium of the dorsal pallium and interneurons from the ganglionic eminence of the basal telencephalon. The interneurons are GABAergic and reach the cerebral cortex via a tangential migratory pathway. We found that recurrent, transplacental exposure of mouse embryos to cocaine from embryonic day 8 to 15 decreases tangential neuronal migration and results in deficits in GABAergic neuronal populations in the embryonic cerebral wall. GABAergic neurons of the olfactory bulb, which are derived from the ganglionic eminence via the rostral migratory pathway, are not affected by the cocaine exposure suggesting a degree of specificity in the effects of cocaine on neuronal migration. Thus, one mechanism by which prenatal cocaine exposure exerts deleterious effects on cerebral cortical development may be by decreasing GABAergic neuronal migration from the ganglionic eminence to the cerebral wall. The decreased GABA neuron migration may contribute to persistent structural and functional deficits observed in the exposed offspring

Exogenous infusion of BDNF protein into the IL of PCOC mice normalizes the deficit in recall of an extinguished cue-conditioned fear.

<p>(<b>a</b>) Overview of the experimental paradigm. Guide cannulae, targeting the infralimbic subdivision of the mPFC bilaterally were surgically implanted into the mice after which they were allowed to recover for 5-7 days before behavioral testing. Immediately after the animals went through extinction training session 2 on day 3 of the behavioral paradigm, vehicle (0.9% saline; VEH) or recombinant BDNF protein (BDNF) was infused into the infralimbic cortex and animals were tested 24 hours later for extinction recall. (<b>b</b>) Percent freezing to the tone. On day 1, both prenatal treatment groups showed significant levels of acquisition with no difference in freezing between PSAL and PCOC mice. On days 2 and 3, both prenatal treatment groups showed significant within-session extinction with no difference in freezing between PSAL and PCOC mice. Immediately after day 3, recombinant BDNF or VEH was infused into the IL bilaterally. On day 4, PCOC VEH mice showed significantly increased freezing compared to PSAL VEH mice demonstrating a deficit in extinction recall (*p<0.05). However, PCOC BDNF mice showed significantly decreased freezing compared to PCOC VEH mice indicating a rescue of the behavioral deficit (††p<0.01). Error bars represent the mean ± SEM (PSAL VEH n=11 from 11 litters, BDNF n=9 from 9 litters; PCOC VEH n=9 from 9 litters; BDNF n=11 from 11 litters). <b>c</b>) Schematic representation of the guide cannula placements in animals that were used for behavioral testing. (<b>d</b>) A representative image of guide cannulae targeting the IL bilaterally.</p

Decreased mature BDNF protein and phosphorylated TrkB protein levels in the mPFC of prenatal cocaine exposed mice during fear extinction.

<p>(<b>a</b>) In the mPFC, there was significantly decreased mBDNF protein in PCOC mice compared to PSAL mice on day 3 and day 4. (<b>b</b>) In the hippocampus, there was no change in mBDNF protein levels at baseline, day 3 or day 4. (<b>c</b>) In the mPFC of PCOC mice compared to PSAL mice there was no change in total TrkB levels at baseline. However, at day 3 there was a trend (p=0.08) towards decreased TrkB protein levels in the mPFC of PCOC mice compared to PSAL mice. (<b>d</b>) There was no change in total TrkB protein levels in the hippocampus of PCOC mice at baseline or at day 3. (<b>e</b>) In the mPFC of PCOC mice compared to PSAL mice there was no change in P-Tyrosine protein levels at baseline but significantly decreased P-Tyrosine levels on day 3. (<b>f</b>) There was no change in P-Tyrosine protein levels in the hippocampus of PCOC mice at baseline or day 3. (*p<0.05, **p<0.01, ***p<0.001 PCOC vs. PSAL). Error bars represent the mean ± SEM (mBDNF - Baseline: PSAL n=9 from 9 litters, PCOC n=11 from 11 litters; Day 3: PSAL n=8 from 8 litters, PCOC n=8 from 8 litters; Day 4: PSAL n=8 from 8 litters; PCOC n=8 from 8 litters; TrkB/ P-Tyrosine - Baseline: PSAL n=8 from 8 litters, PCOC n=8 from 8 litters; Day 3: PSAL n=9 from 9 litters, PCOC n=8 from 8 litters).</p

Altered <i>Bdnf</i> mRNA expression in the mPFC of prenatal cocaine exposed mice during fear extinction.

<p>(<b>a</b>) There was no change in <i>Bdnf</i> exon IX mRNA levels in the mPFC at baseline. However, at day 3 there was significantly increased BDNF exon IX mRNA levels in the mPFC of PCOC mice compared to PSAL mice. (<b>b</b>) There was no change in BDNF exon IX mRNA levels in the hippocampus at baseline or on day 3. (<b>c</b>) There was no change in BDNF exon I mRNA in the mPFC of PCOC mice at baseline or on day 3. (<b>d</b>) In the hippocampus of PSAL mice, there were higher levels of BDNF exon I mRNA levels on day 3 relative to their levels at baseline. (<b>e</b>) There was decreased BDNF exon IV mRNA levels in the mPFC of PSAL mice on day 3 compared to its levels at baseline. (<b>f</b>) There was no change in BDNF exon IV mRNA levels in the hippocampus at baseline or day 3. (*p<0.05, PCOC vs. PSAL; †p<0.05, ††p<0.01 vs. baseline of that prenatal treatment). Error bars represent the mean ± SEM (Baseline: PSAL n=12 from 12 litters, PCOC n=14 from 14 litters; Day 3: PSAL n=9 from 9 litters, PCOC n=10 from 10 litters).</p

Pediatric Neurology Research in the Twenty-First Century: Status, Challenges, and Future Directions Post-COVID-19.

BackgroundThe year 2020 marked a fundamental shift in the pediatric neurology field. An impressive positive trajectory of advances in patient care and research faced sudden global disruptions by the coronavirus disease 2019 pandemic and by an international movement protesting racial, socioeconomic, and health disparities. The disruptions revealed obstacles and fragility within the pediatric neurology research mission. However, renewed commitment offers unique opportunities for the pediatric neurology research community to enhance and prioritize research directions for the coming decades.MethodsThe Research Committee of the Child Neurology Society evaluated the challenges and opportunities facing the pediatric neurology research field, including reviewing published literature, synthesizing publically available data, and conducting a survey of pediatric neurologists.ResultsWe identified three priority domains for the research mission: funding levels, active guidance, and reducing disparities. Funding levels: to increase funding to match the burden of pediatric neurological disease; to tailor funding mechanisms and strategies to support clinical trial efforts unique to pediatric neurology; and to support investigators across their career trajectory. Active guidance: to optimize infrastructure and strategies, to leverage novel therapeutics, enhance data collection, and improve inclusion of children in clinical trials. Reducing disparities: to reduce health disparities in children with neurological disease, to develop proactive measures to enhance workforce diversity and inclusion, and increase avenues to balance work-life obligations for investigators.ConclusionsIn this uniquely challenging epoch, the pediatric neurology research community has a timely and important mission to re-engage the public and government, advancing the health of children with neurological conditions

Lentiviral-mediated gene transfer of brain-derived neurotrophic factor is neuroprotective in a mouse model of neonatal excitotoxic challenge

Excitotoxicity may be a critical factor in the formation of brain lesions associated with cerebral palsy. When injected into the murine neopallium at postnatal day 5, the glutamatergic analog N-methyl-D-aspartate (NMDA) produces transcortical neuronal death and periventricular white matter cysts, which mimic brain damage observed in human term and preterm neonates at risk for developing cerebral palsy. We previously showed that intracerebral injection of brain-derived neurotrophic factor (BDNF) was neuroprotective in this model. Because BDNF does not easily cross the blood-brain barrier, alternative strategies to avoid repeated intracerebral injections of BDNF should be tested, particularly when the goal of such translational research is ultimately to achieve clinical application. The goal of the present study was to assess the protective role of lentiviral-mediated gene transfer of BDNF against excitotoxic lesions induced by NMDA in newborn mice. We first assessed the biological activity of BDNF gene transfer in vitro and determined the efficiency of gene transfer in our in vivo model. We next administered the BDNF-expressing vector by intracerebral injection in neonatal mice, 3 days before inducing NMDA lesions. When compared with a control green fluorescent protein-expressing lentiviral vector, administration of BDNF-expressing vector induced a significant protection of the periventricular white matter and cortical plate against the NMDA-mediated insult. Intraventricular delivery of the BDNF-expressing lentiviral vector was more efficient in terms of neuroprotection than the intraparenchymal route. Altogether, the present study shows that viral-mediated gene transfer of BDNF to newborn mouse brain is feasible and affords significant neuroprotection against an excitotoxic insult

Deficit in recall of an extinguished cue-conditioned fear in prenatal cocaine exposed mice.

<p>(<b>a</b>) Percent freezing to the tone. On day 1, mice were fear conditioned with five 30 sec tones that co-terminated with a 1 sec 0.7mA shock. On days 2 and 3, mice received extinction training in a novel environment and on day 4 were tested for extinction recall. Both prenatal treatment groups showed significant levels of acquisition on day 1. On days 2 and 3, all animals showed significant within-session extinction with no difference in freezing between PSAL and PCOC mice. At extinction testing on day 4, PCOC mice showed a deficit in recall of fear extinction (*p<0.05). Error bars represent the mean ± SEM (PSAL n=9 from 9 litters; PCOC n=9 from 9 litters). (<b>b</b>) Overview of the experimental paradigm. Brain tissue for molecular experiments was collected at three different time points from separate cohorts of animals. For analysis of constitutive levels of MeCP2 and P-CREB binding, Bdnf mRNA and protein expression, and phosphorylated TrkB analyses, tissue was collected in adult PSAL and PCOC animals that were not subjected to any behavioral testing (baseline). For molecular analyses during the consolidation phase of the extinction memory, tissue was collected immediately after extinction training on day 3 (Day 3) or immediately after the test for extinction recall on day 4 (Day 4).</p