Students "News and Views" final papers
(Neuroplasticity and Neurobiology courses)
(Neuroplasticity and Neurobiology courses)
Sleep to remember
by Elena Iliadis
Though it may be hard to come by, sleep plays an essential role in key neural processes such as information processing and memory consolidation. Sleep deprivation has been firmly linked to diminished cognitive functions such as memory retention, however, the neural mechanisms that underlie sleep dependent memory consolidation are poorly understood. In a 2019 paper, Dag et. al. explored this question in Drosophila to find that reactivation of
dopaminergic neurons during sleep that were previously active during memory acquisition is linked to long-term memory storage. Particularly, they present evidence that sleep-promoting neurons in the fan-shaped body (FB) activate DANs-aSP13 neurons during post-learning sleep to induce long term memory (LTM). In previous research, dopaminergic aSP13 neurons (DAN-aSP13s) were identified as necessary and sufficient for STM acquisition (Keleman et.al., 2012). In a discrete time window of 7-10 hours after learning, DAN-aSP13s activate Kenyon Cells of the mushroom body, a neuropil critical for memory formation. Going off this discovery, Dag et. al., set out to determine how post-learning reactivation of these same DAN-aSP13s allows for memory consolidation
from STM to LTM. Drosophila were selected as the ideal model for this study because not only has sleep
been well documented in these animals, but the key neural processes that occur during mammal sleep are largely preserved in Drosophila. Courtship conditioning, in which male flies learn to associate the result of their own courtship behavior with cues presented by females, was utilized as the training protocol to examine memory retention in this study. After several genetic and behavioral studies to investigate the connection between sleep,
reactivation of DAN-aSP13s, and memory consolidation, several key findings emerged. Sleep increased as DAN-aSP13s were activated in the specific time window of 7-10 hours after learning, demonstrating that reactivation of these neurons is highly sleep-dependent. Additionally, sleep deprivation during this critical window was found to disrupt LTM. In tandem, these findings demonstrate how post-learning sleep and subsequent DAN-aSP13s reactivation is essential for LTM consolidation. Additionally, sleep promoting neurons in the ventral layer of the FB (vFB) were found to activate DAN-aSP13s during the discrete 7-10 hour post-learning window to mediate this courtship LTM. In their model for sleep-dependent LTM consolidation, Dag et. al. suggests that a learning-dependent sleep drive transmitted to vFB neurons in turn causes these neurons to reactivate DAN-aSP13s and enhance sleep. Therefore, as supported by experimental evidence, this dual role of vFB neurons to induce sleep and reactivate DAN-aSP13s demonstrates their critical role in mediating LTM consolidation. As they ventured into uncharted territory regarding the connection between sleep and memory in this study, Dag et. al successfully elucidated the causal relationship between post-learning activation of DAN-aSP13s by vFB neurons, and the consolidation of courtship LTM in Drosophila. Though much of the mechanisms behind learning-dependent sleep and LTM consolidation are still yet to be understood, this link between vFB neurons and the reactivation of DAN-aSP13s provides key insight as to where future studies are to focus. Does this pathway elucidated by courtship learning remain consistent when paired with other modes of learning, such as olfactory conditioning? To what extent does homeostatic sleep drive interfere with this learning-dependent sleep drive? These questions beg consideration as we build upon the foundational findings of this study to further explore the connection between DAN-aSP13s reactivation, sleep, and LTM consolidation.
References
Dag, U., Lei, Z., Le, J. Q., Wong, A., Bushey, D., & Keleman, K. (2019). Neuronal reactivation during post-learning sleep consolidates long-term memory in Drosophila. Elife, 8, e42786.
by Elena Iliadis
Though it may be hard to come by, sleep plays an essential role in key neural processes such as information processing and memory consolidation. Sleep deprivation has been firmly linked to diminished cognitive functions such as memory retention, however, the neural mechanisms that underlie sleep dependent memory consolidation are poorly understood. In a 2019 paper, Dag et. al. explored this question in Drosophila to find that reactivation of
dopaminergic neurons during sleep that were previously active during memory acquisition is linked to long-term memory storage. Particularly, they present evidence that sleep-promoting neurons in the fan-shaped body (FB) activate DANs-aSP13 neurons during post-learning sleep to induce long term memory (LTM). In previous research, dopaminergic aSP13 neurons (DAN-aSP13s) were identified as necessary and sufficient for STM acquisition (Keleman et.al., 2012). In a discrete time window of 7-10 hours after learning, DAN-aSP13s activate Kenyon Cells of the mushroom body, a neuropil critical for memory formation. Going off this discovery, Dag et. al., set out to determine how post-learning reactivation of these same DAN-aSP13s allows for memory consolidation
from STM to LTM. Drosophila were selected as the ideal model for this study because not only has sleep
been well documented in these animals, but the key neural processes that occur during mammal sleep are largely preserved in Drosophila. Courtship conditioning, in which male flies learn to associate the result of their own courtship behavior with cues presented by females, was utilized as the training protocol to examine memory retention in this study. After several genetic and behavioral studies to investigate the connection between sleep,
reactivation of DAN-aSP13s, and memory consolidation, several key findings emerged. Sleep increased as DAN-aSP13s were activated in the specific time window of 7-10 hours after learning, demonstrating that reactivation of these neurons is highly sleep-dependent. Additionally, sleep deprivation during this critical window was found to disrupt LTM. In tandem, these findings demonstrate how post-learning sleep and subsequent DAN-aSP13s reactivation is essential for LTM consolidation. Additionally, sleep promoting neurons in the ventral layer of the FB (vFB) were found to activate DAN-aSP13s during the discrete 7-10 hour post-learning window to mediate this courtship LTM. In their model for sleep-dependent LTM consolidation, Dag et. al. suggests that a learning-dependent sleep drive transmitted to vFB neurons in turn causes these neurons to reactivate DAN-aSP13s and enhance sleep. Therefore, as supported by experimental evidence, this dual role of vFB neurons to induce sleep and reactivate DAN-aSP13s demonstrates their critical role in mediating LTM consolidation. As they ventured into uncharted territory regarding the connection between sleep and memory in this study, Dag et. al successfully elucidated the causal relationship between post-learning activation of DAN-aSP13s by vFB neurons, and the consolidation of courtship LTM in Drosophila. Though much of the mechanisms behind learning-dependent sleep and LTM consolidation are still yet to be understood, this link between vFB neurons and the reactivation of DAN-aSP13s provides key insight as to where future studies are to focus. Does this pathway elucidated by courtship learning remain consistent when paired with other modes of learning, such as olfactory conditioning? To what extent does homeostatic sleep drive interfere with this learning-dependent sleep drive? These questions beg consideration as we build upon the foundational findings of this study to further explore the connection between DAN-aSP13s reactivation, sleep, and LTM consolidation.
References
Dag, U., Lei, Z., Le, J. Q., Wong, A., Bushey, D., & Keleman, K. (2019). Neuronal reactivation during post-learning sleep consolidates long-term memory in Drosophila. Elife, 8, e42786.
Adolescent nicotine use augments the risk for compulsive alcohol drinking during adulthood.
by Joseph Abergel
The biological foundations for the association of adolescent smoking leading to pathological drinking in adulthood were never studied. Thomas et al. (4) demonstrated nicotine-imbibed teenage rats had altered GABA receptor signaling in the ventral tegmental area, leading to long-lasting increase of ethanol consumption in adulthood.Using an agonist, CLP, they restored GABA function and corrected the increase in alcohol drinking.
In recent years, nicotine intake among high and middle school students has substantially increased 2.The dramatic increase in nicotine use is closely associated with the significant exercise of vaping devices among teenagers.A report by the U.S. Surgeon General revealed that vaping among teenagers increased by 900% between 2011 and 2015 (2). Studies further show an association between e-cigarette use, containing nicotine, during teenage years are more prone to alcohol consumption (3). Understanding the biological and neurological effects of nicotine on teenagers, leading to the extreme intake of alcohol, will help display a clearer picture of the harmful mechanisms induced by nicotine in teenagers, supporting, with scientific evidence, the campaign to stop the use of e-cigarettes among adolescence.the cellular alterations caused by nicotine, leading to a higher risk of alcohol consumption, in the neural circuitry (4). The researchers administered daily injections of nicotine in adolescent or adult rats compared to the control group, which were injected with saline, to ultimately measure self-administration of ethanol. After a month, permitting the teenage rats to reach adulthood, they found that the adolescent rats exposed to nicotine consumed more alcohol at a statistically significant rate higher relative to the rats who were injected with nicotine in adulthood. Once this causation link was established, Thomas et al.defined the biological footings for the increase in alcohol self-administration in adulthood, due to adolescent nicotine exposure.
With the rats administered with nicotine as adolescents and not in adulthood, the research team revealed a modification in the generally inhibitory neural circuitry of GABA neurons in the ventral tegmental area(VTA)--the “reward-mediating center”. The GABA receptor reversal potential in the VTA GABA neuron was shown to be more depolarized, than the controls, due to the impairment of chloride extrusion in the VTA GABA neuron. Consequently, the GABA signals in response to alcohol changed from inhibitory to excitatory. Nicotine exposure at a young age therefore altered the reward-mediating center, which led to an excitatory shift of GABA signaling, facilitating along-lasting increase of alcohol self-administration.
The potency of GABAergic inhibition is usually controlled with the chloride gradient. Knowing this information, they further showed that the reduction in chloride extrusion growth capacity is mediated by the down regulation of the K+, Cl- co transporter, KCC24. The long-lasting changes in reward responses to alcohol were caused by the decreased efficiency of movement of chloride ions across the cell membrane. Their discoveries imply that glucocorticoid receptors guided the reduced activity of KCC2 by a dephosphorylation mechanism. Yet, future studies should determine the role glucocorticoid receptors’ signaling molecules relative to KCC2 defective expressions, as these processes can vary between adults and adolescents. The regulation in chloride concentration was negatively affected, due to the malfunction of the chloride transporter, KCC2, leading to the increased in alcohol administration. Furthermore, downstream of the VTA GABA neurons and KCC2 changes, the nicotine introduction to the adolescent rats attenuated in vivo the firing of VTA dopaminergic neurons in response to alcohol.
However, Thomas et al. (4) did not stop their research at that point. They discovered that the intracellular accumulation of chloride can be undone by using a KCC2 agonist, CLP, which will improve chloride extrusion capacity. Subsequently, using the agonist on adolescent nicotine- treated animals, the alterations in VTA GABA signaling were prevented, leading to normal alcohol consumption relative to the controls. Therefore, restoring KCC2 function stabilized VTA GABA signaling and alcohol self-administration. By taking their findings together, the research team has proven that adolescent nicotine use can increase the risk for pathological alcohol drinking later in life.
The restoration of the KCC2 transporter can be a key therapeutic approach to alleviate excessive alcohol consumption in the smoking population. This can be especially beneficial for combating alcoholism in both adult and adolescent populations, due to nicotine intake, which still needs to be studied in future human clinical trials.Moreover,CLP can most likely help with any neurological conditions with impaired GABA function due to a faulty chloride transport such as epilepsy and chronic pain.Future work should examine the phenotypic responses of the agonist CLP on these health conditions.With steady progress in our understanding of nicotine’s effect on alcohol consumption, the stage is set to further help people ruined by nicotine and alcoholism with novel therapies.
References
by Joseph Abergel
The biological foundations for the association of adolescent smoking leading to pathological drinking in adulthood were never studied. Thomas et al. (4) demonstrated nicotine-imbibed teenage rats had altered GABA receptor signaling in the ventral tegmental area, leading to long-lasting increase of ethanol consumption in adulthood.Using an agonist, CLP, they restored GABA function and corrected the increase in alcohol drinking.
In recent years, nicotine intake among high and middle school students has substantially increased 2.The dramatic increase in nicotine use is closely associated with the significant exercise of vaping devices among teenagers.A report by the U.S. Surgeon General revealed that vaping among teenagers increased by 900% between 2011 and 2015 (2). Studies further show an association between e-cigarette use, containing nicotine, during teenage years are more prone to alcohol consumption (3). Understanding the biological and neurological effects of nicotine on teenagers, leading to the extreme intake of alcohol, will help display a clearer picture of the harmful mechanisms induced by nicotine in teenagers, supporting, with scientific evidence, the campaign to stop the use of e-cigarettes among adolescence.the cellular alterations caused by nicotine, leading to a higher risk of alcohol consumption, in the neural circuitry (4). The researchers administered daily injections of nicotine in adolescent or adult rats compared to the control group, which were injected with saline, to ultimately measure self-administration of ethanol. After a month, permitting the teenage rats to reach adulthood, they found that the adolescent rats exposed to nicotine consumed more alcohol at a statistically significant rate higher relative to the rats who were injected with nicotine in adulthood. Once this causation link was established, Thomas et al.defined the biological footings for the increase in alcohol self-administration in adulthood, due to adolescent nicotine exposure.
With the rats administered with nicotine as adolescents and not in adulthood, the research team revealed a modification in the generally inhibitory neural circuitry of GABA neurons in the ventral tegmental area(VTA)--the “reward-mediating center”. The GABA receptor reversal potential in the VTA GABA neuron was shown to be more depolarized, than the controls, due to the impairment of chloride extrusion in the VTA GABA neuron. Consequently, the GABA signals in response to alcohol changed from inhibitory to excitatory. Nicotine exposure at a young age therefore altered the reward-mediating center, which led to an excitatory shift of GABA signaling, facilitating along-lasting increase of alcohol self-administration.
The potency of GABAergic inhibition is usually controlled with the chloride gradient. Knowing this information, they further showed that the reduction in chloride extrusion growth capacity is mediated by the down regulation of the K+, Cl- co transporter, KCC24. The long-lasting changes in reward responses to alcohol were caused by the decreased efficiency of movement of chloride ions across the cell membrane. Their discoveries imply that glucocorticoid receptors guided the reduced activity of KCC2 by a dephosphorylation mechanism. Yet, future studies should determine the role glucocorticoid receptors’ signaling molecules relative to KCC2 defective expressions, as these processes can vary between adults and adolescents. The regulation in chloride concentration was negatively affected, due to the malfunction of the chloride transporter, KCC2, leading to the increased in alcohol administration. Furthermore, downstream of the VTA GABA neurons and KCC2 changes, the nicotine introduction to the adolescent rats attenuated in vivo the firing of VTA dopaminergic neurons in response to alcohol.
However, Thomas et al. (4) did not stop their research at that point. They discovered that the intracellular accumulation of chloride can be undone by using a KCC2 agonist, CLP, which will improve chloride extrusion capacity. Subsequently, using the agonist on adolescent nicotine- treated animals, the alterations in VTA GABA signaling were prevented, leading to normal alcohol consumption relative to the controls. Therefore, restoring KCC2 function stabilized VTA GABA signaling and alcohol self-administration. By taking their findings together, the research team has proven that adolescent nicotine use can increase the risk for pathological alcohol drinking later in life.
The restoration of the KCC2 transporter can be a key therapeutic approach to alleviate excessive alcohol consumption in the smoking population. This can be especially beneficial for combating alcoholism in both adult and adolescent populations, due to nicotine intake, which still needs to be studied in future human clinical trials.Moreover,CLP can most likely help with any neurological conditions with impaired GABA function due to a faulty chloride transport such as epilepsy and chronic pain.Future work should examine the phenotypic responses of the agonist CLP on these health conditions.With steady progress in our understanding of nicotine’s effect on alcohol consumption, the stage is set to further help people ruined by nicotine and alcoholism with novel therapies.
References
- Hull, M. The Rise of Teen Vaping and Teen Vaping Addiction: The Recovery Village.https://www.therecoveryvillage.com/teen-addiction/drug/teen-vaping/
- US Department of Health and Human Services. E-cigarette Use Among Youth and Young Adults: A Report of the SurgeonGeneral. Atlanta, GA: US Department of Health and Human Services, CDC; 2016.
- Teens using vaping devices in record numbers. https://www.nih.gov/news- events/news-releases/teens-using-vaping-devices-record-numbers.
- Thomas, A. M.; Ostroumov, A.; Kimmey, B. A.; Taormina, M. B.; Holden, W. M.; Kim, K.; Brown-Mangum, T.; Dani, J. A. Adolescent Nicotine Exposure Alters GABAA Receptor Signaling in theVentral Tegmental Area and Increases Adult Ethanol Self-Administration.Cell Reports2018,23(1), 68–77.
Metformin is the key to treatments for various neurodegenerative diseases
by Brittany R. Lew
Multiple sclerosis (MS) can often cause irreversible neuronal damage due to unpredictable lesions¹. Furthermore, oligodendrocytes enable the central nervous system to remyelinate axons after damage². However, as a result of aging and other diseases, oligodendrocyte precursor cells (OPCs) are less efficient at differentiating, and thus, are less efficient at remyelination². Methods are being studied that aim to create more effective treatments for MS. Specifically, Neumann et al. and his colleagues assessed the performance of metformin on the process of reversing the effects of neuronal deterioration². To begin, the authors cultured OPCs from young adult mice (2-3 months) and aged mice (20-24 months)². The differential capability of these isolated OPCs were then evaluated in mediums that lacked proliferation-maintaining growth factors². They discovered that 60% of young OPCs differentiated into oligodendrocytes, while only 20% of aged OPCs differentiated². Furthermore, when various promoters of differentiation (T3, 9-cis-retinoic acid, miconazole or benzatrophine) were introduced to the cultures, only young OPCs showed a significant increase in differentiation, while aged OPCs were unaffected². These findings suggest that aged OPCs not only have a slower internal capacity for differentiation, but also a lessened response to differentiation promoting factors. Figure 1² | Aged OPCs are unable to respond to differentiation promoting factors. This is a visual representation of the conclusions of the first experiment conducted by Neumann et al²
This was not all they discovered, however. When the aged OPCs were cultured for a longer period (4 weeks), a significant increase in growth was noted². Thus, aged OPCs don’t necessarily lose their ability to differentiate, but rather, changed intrinsic properties alter their rate of differentiation². Next, the authors proved that aged OPCs lack normal expression of OPC-specific genes and show the characteristic signs of aging. Aged OPCs were found to have increased levels of Cnp1, Sirt2, and Enpp6, contributing to the decline of stem cell quality². These specific genes were linked to stem cell aging processes, such as unfolded protein response, autophagy, mitochondrial malfunction, and inflammasome signaling². Interestingly, an increase of mTOR was noted, which is ultimately responsible for cellular and DNA deterioration². After these discoveries, Neumann et al. tested the effects of dietary restrictions on remyelination. 12-month old rats (aged OPCs) were subjected to alternate-day fasting (ADF) for 6 months, after which, demyelination was introduced (via focal injections of ethidium bromide into cerebral white matter)². Rats who underwent ADF were able to achieve full remyelination, while their non-ADF counterparts showed no significant increase². These results, combined with findings of less DNA damage, increased self-renewal genes, and increased rates of MBP+ oligodendrocytes differentiation, led to the hypothesis that fasting has intracellular effects on various cells required for remyelination². Thus, they proved that ADF promotes remyelination through the restoration of differentiation capabilities in aged OPCs. To continue, Neumann et al. and his colleagues assessed the effects of metformin, a fasting-mimicking drug². Metformin-treated cells expressed an increase in Pdgfra and Ascl1 and decreases in CDkn2a and DNA damage, suggesting that metformin is able to alleviate various detrimental effects of aging². Treatment with metformin on aged OPCs showed an increase of responsiveness to pro-differentiation factors². Additionally, metformin was also shown to increase ATP levels in aged OPCs, improving mitochondrial function². Together, these findings showed that metformin not only increases differentiation, but also counteracts the limitations of aged OPCs. After these conclusions, the authors were determined to prove that metformin application had equal remyelination results to that of ADF-treated rats. Successfully, this experiment showed a near approximate increase in growth, in both the metformin treated rats and the ADF rats (after lesion induction), proving that metformin acts as a near substitute to ADF². MS is often characterized by accumulative neurodegeneration, where rare cases may prove fatal¹. However, it is people like Neumann et al. and his colleagues that give hope to the creation of new and improved methods to treat this disease. Neumann et al. discovered the advantages of metformin on reversing the effects of demyelination and restoring capability to aged OPCs.
These experiments provide the next building block towards future in vivo research, ultimately leading to many treatment implications to not only MS, but also, countless other neurodegenerative diseases, such as Alzheimer's disease.
References
1. Rolak, L. Clin Med Res1, 57–60 (2003).
2. Neumann et al., Cell Stem Cell25, 473–485 (2019).
by Brittany R. Lew
Multiple sclerosis (MS) can often cause irreversible neuronal damage due to unpredictable lesions¹. Furthermore, oligodendrocytes enable the central nervous system to remyelinate axons after damage². However, as a result of aging and other diseases, oligodendrocyte precursor cells (OPCs) are less efficient at differentiating, and thus, are less efficient at remyelination². Methods are being studied that aim to create more effective treatments for MS. Specifically, Neumann et al. and his colleagues assessed the performance of metformin on the process of reversing the effects of neuronal deterioration². To begin, the authors cultured OPCs from young adult mice (2-3 months) and aged mice (20-24 months)². The differential capability of these isolated OPCs were then evaluated in mediums that lacked proliferation-maintaining growth factors². They discovered that 60% of young OPCs differentiated into oligodendrocytes, while only 20% of aged OPCs differentiated². Furthermore, when various promoters of differentiation (T3, 9-cis-retinoic acid, miconazole or benzatrophine) were introduced to the cultures, only young OPCs showed a significant increase in differentiation, while aged OPCs were unaffected². These findings suggest that aged OPCs not only have a slower internal capacity for differentiation, but also a lessened response to differentiation promoting factors. Figure 1² | Aged OPCs are unable to respond to differentiation promoting factors. This is a visual representation of the conclusions of the first experiment conducted by Neumann et al²
This was not all they discovered, however. When the aged OPCs were cultured for a longer period (4 weeks), a significant increase in growth was noted². Thus, aged OPCs don’t necessarily lose their ability to differentiate, but rather, changed intrinsic properties alter their rate of differentiation². Next, the authors proved that aged OPCs lack normal expression of OPC-specific genes and show the characteristic signs of aging. Aged OPCs were found to have increased levels of Cnp1, Sirt2, and Enpp6, contributing to the decline of stem cell quality². These specific genes were linked to stem cell aging processes, such as unfolded protein response, autophagy, mitochondrial malfunction, and inflammasome signaling². Interestingly, an increase of mTOR was noted, which is ultimately responsible for cellular and DNA deterioration². After these discoveries, Neumann et al. tested the effects of dietary restrictions on remyelination. 12-month old rats (aged OPCs) were subjected to alternate-day fasting (ADF) for 6 months, after which, demyelination was introduced (via focal injections of ethidium bromide into cerebral white matter)². Rats who underwent ADF were able to achieve full remyelination, while their non-ADF counterparts showed no significant increase². These results, combined with findings of less DNA damage, increased self-renewal genes, and increased rates of MBP+ oligodendrocytes differentiation, led to the hypothesis that fasting has intracellular effects on various cells required for remyelination². Thus, they proved that ADF promotes remyelination through the restoration of differentiation capabilities in aged OPCs. To continue, Neumann et al. and his colleagues assessed the effects of metformin, a fasting-mimicking drug². Metformin-treated cells expressed an increase in Pdgfra and Ascl1 and decreases in CDkn2a and DNA damage, suggesting that metformin is able to alleviate various detrimental effects of aging². Treatment with metformin on aged OPCs showed an increase of responsiveness to pro-differentiation factors². Additionally, metformin was also shown to increase ATP levels in aged OPCs, improving mitochondrial function². Together, these findings showed that metformin not only increases differentiation, but also counteracts the limitations of aged OPCs. After these conclusions, the authors were determined to prove that metformin application had equal remyelination results to that of ADF-treated rats. Successfully, this experiment showed a near approximate increase in growth, in both the metformin treated rats and the ADF rats (after lesion induction), proving that metformin acts as a near substitute to ADF². MS is often characterized by accumulative neurodegeneration, where rare cases may prove fatal¹. However, it is people like Neumann et al. and his colleagues that give hope to the creation of new and improved methods to treat this disease. Neumann et al. discovered the advantages of metformin on reversing the effects of demyelination and restoring capability to aged OPCs.
These experiments provide the next building block towards future in vivo research, ultimately leading to many treatment implications to not only MS, but also, countless other neurodegenerative diseases, such as Alzheimer's disease.
References
1. Rolak, L. Clin Med Res1, 57–60 (2003).
2. Neumann et al., Cell Stem Cell25, 473–485 (2019).
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