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A single pair of neurons links sleep to memory consolidation in Drosophila melanogaster.

Haynes PR, Christmann BL, Griffith LC - Elife (2015)

Bottom Line: Downregulation of α'/β' GABAA and GABABR3 receptors results in sleep loss, suggesting these receptors are the sleep-relevant targets of DPM-mediated inhibition.Regulation of sleep by neurons necessary for consolidation suggests that these brain processes may be functionally interrelated via their shared anatomy.These findings have important implications for the mechanistic relationship between sleep and memory consolidation, arguing for a significant role of inhibitory neurotransmission in regulating these processes.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Volen Center for Complex Systems, National Center for Behavioral Genomics, Brandeis University, Waltham, United States.

ABSTRACT
Sleep promotes memory consolidation in humans and many other species, but the physiological and anatomical relationships between sleep and memory remain unclear. Here, we show the dorsal paired medial (DPM) neurons, which are required for memory consolidation in Drosophila, are sleep-promoting inhibitory neurons. DPMs increase sleep via release of GABA onto wake-promoting mushroom body (MB) α'/β' neurons. Functional imaging demonstrates that DPM activation evokes robust increases in chloride in MB neurons, but is unable to cause detectable increases in calcium or cAMP. Downregulation of α'/β' GABAA and GABABR3 receptors results in sleep loss, suggesting these receptors are the sleep-relevant targets of DPM-mediated inhibition. Regulation of sleep by neurons necessary for consolidation suggests that these brain processes may be functionally interrelated via their shared anatomy. These findings have important implications for the mechanistic relationship between sleep and memory consolidation, arguing for a significant role of inhibitory neurotransmission in regulating these processes.

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Sleep loss resulting from Rdl/GABABR3-RNAi is primarily due to MB α’β’ expression.MB-GAL80 restricted c305a-GAL4 was used to drive Rdl-RNAi (A) or GABABR3-RNAi (B) in the c305a expression pattern outside of the MB. Top: shows total sleep in 30-min bins averaged across 3 days. Middle and bottom plots: show 3 day means of total sleep, mean sleep episode duration and number of sleep episodes quantified in 12-hr day/night bins. Non-MB c305a driven Rdl-RNAi results in a lesser degree of sleep loss and fragmentation and non-MB GABABR3-RNAi results in no changes in sleep or sleep structure, indicating these phenotypes are primarily due to MB α’β’ expression of c305a-GAL4. Grey shading indicates the dark period/night. All data are presented as mean ± SEM where * represents p < 0.05, **p < 0.001 and ***p < 0.0001 using the Mann-Whitney-Wilcoxon rank sum test. Statistics are described in the ‘Materials and methods’ section.DOI:http://dx.doi.org/10.7554/eLife.03868.020
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fig7s1: Sleep loss resulting from Rdl/GABABR3-RNAi is primarily due to MB α’β’ expression.MB-GAL80 restricted c305a-GAL4 was used to drive Rdl-RNAi (A) or GABABR3-RNAi (B) in the c305a expression pattern outside of the MB. Top: shows total sleep in 30-min bins averaged across 3 days. Middle and bottom plots: show 3 day means of total sleep, mean sleep episode duration and number of sleep episodes quantified in 12-hr day/night bins. Non-MB c305a driven Rdl-RNAi results in a lesser degree of sleep loss and fragmentation and non-MB GABABR3-RNAi results in no changes in sleep or sleep structure, indicating these phenotypes are primarily due to MB α’β’ expression of c305a-GAL4. Grey shading indicates the dark period/night. All data are presented as mean ± SEM where * represents p < 0.05, **p < 0.001 and ***p < 0.0001 using the Mann-Whitney-Wilcoxon rank sum test. Statistics are described in the ‘Materials and methods’ section.DOI:http://dx.doi.org/10.7554/eLife.03868.020

Mentions: GCaMP, EPAC and Arclight experiments demonstrate a lack of excitatory transmission from DPM neurons to the MBs and SuperClomeleon experiments demonstrate that the DPMs are capable of inhibiting MB neurons. The wake-promoting phenotype of MB α’/β’ neurons as well as a shared temporal role in memory consolidation suggest these neurons could be the targets of sleep-promoting DPM GABA release. In order to test this possibility, we expressed RNAi against Drosophila GABA receptors in MB α’/β’ neurons. It has previously been shown that the Drosophila ionotropic GABAA receptor, Rdl, is highly expressed in all lobes of the MBs (Liu et al., 2007). Consistent with the phenotype of DPM VGAT knockdown, we observe decreased nighttime sleep with knockdown of either Rdl (Figure 7A), or GABAB-R3 (Figure 7B) in MB α’/β’ neurons. In both cases sleep loss is the result of a decrease in the duration of nighttime sleep episodes. Knockdown of Rdl results in less total sleep loss since an increase in the total number of nighttime sleep episodes partially compensates for the decrease in mean sleep episode duration. Importantly, concurrent expression of the MB-GAL80 transgene, which blocks GAL4-mediated expression of receptor RNAis, greatly suppresses sleep loss and fragmentation phenotypes showing that the effects are specific to the MB α’/β’ lobes (Figure 7—figure supplement 1). Interestingly, experiments to determine the lobe-specific role of 5HT1A receptors suggest that 5HT acts generally in the MB, not just on the α’/β’ lobes (data not shown), suggesting that these two transmitters may play somewhat different roles at the circuit level in sleep and memory consolidation.10.7554/eLife.03868.019Figure 7.MB α’β’ GABA receptors promote nighttime sleep.


A single pair of neurons links sleep to memory consolidation in Drosophila melanogaster.

Haynes PR, Christmann BL, Griffith LC - Elife (2015)

Sleep loss resulting from Rdl/GABABR3-RNAi is primarily due to MB α’β’ expression.MB-GAL80 restricted c305a-GAL4 was used to drive Rdl-RNAi (A) or GABABR3-RNAi (B) in the c305a expression pattern outside of the MB. Top: shows total sleep in 30-min bins averaged across 3 days. Middle and bottom plots: show 3 day means of total sleep, mean sleep episode duration and number of sleep episodes quantified in 12-hr day/night bins. Non-MB c305a driven Rdl-RNAi results in a lesser degree of sleep loss and fragmentation and non-MB GABABR3-RNAi results in no changes in sleep or sleep structure, indicating these phenotypes are primarily due to MB α’β’ expression of c305a-GAL4. Grey shading indicates the dark period/night. All data are presented as mean ± SEM where * represents p < 0.05, **p < 0.001 and ***p < 0.0001 using the Mann-Whitney-Wilcoxon rank sum test. Statistics are described in the ‘Materials and methods’ section.DOI:http://dx.doi.org/10.7554/eLife.03868.020
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4305081&req=5

fig7s1: Sleep loss resulting from Rdl/GABABR3-RNAi is primarily due to MB α’β’ expression.MB-GAL80 restricted c305a-GAL4 was used to drive Rdl-RNAi (A) or GABABR3-RNAi (B) in the c305a expression pattern outside of the MB. Top: shows total sleep in 30-min bins averaged across 3 days. Middle and bottom plots: show 3 day means of total sleep, mean sleep episode duration and number of sleep episodes quantified in 12-hr day/night bins. Non-MB c305a driven Rdl-RNAi results in a lesser degree of sleep loss and fragmentation and non-MB GABABR3-RNAi results in no changes in sleep or sleep structure, indicating these phenotypes are primarily due to MB α’β’ expression of c305a-GAL4. Grey shading indicates the dark period/night. All data are presented as mean ± SEM where * represents p < 0.05, **p < 0.001 and ***p < 0.0001 using the Mann-Whitney-Wilcoxon rank sum test. Statistics are described in the ‘Materials and methods’ section.DOI:http://dx.doi.org/10.7554/eLife.03868.020
Mentions: GCaMP, EPAC and Arclight experiments demonstrate a lack of excitatory transmission from DPM neurons to the MBs and SuperClomeleon experiments demonstrate that the DPMs are capable of inhibiting MB neurons. The wake-promoting phenotype of MB α’/β’ neurons as well as a shared temporal role in memory consolidation suggest these neurons could be the targets of sleep-promoting DPM GABA release. In order to test this possibility, we expressed RNAi against Drosophila GABA receptors in MB α’/β’ neurons. It has previously been shown that the Drosophila ionotropic GABAA receptor, Rdl, is highly expressed in all lobes of the MBs (Liu et al., 2007). Consistent with the phenotype of DPM VGAT knockdown, we observe decreased nighttime sleep with knockdown of either Rdl (Figure 7A), or GABAB-R3 (Figure 7B) in MB α’/β’ neurons. In both cases sleep loss is the result of a decrease in the duration of nighttime sleep episodes. Knockdown of Rdl results in less total sleep loss since an increase in the total number of nighttime sleep episodes partially compensates for the decrease in mean sleep episode duration. Importantly, concurrent expression of the MB-GAL80 transgene, which blocks GAL4-mediated expression of receptor RNAis, greatly suppresses sleep loss and fragmentation phenotypes showing that the effects are specific to the MB α’/β’ lobes (Figure 7—figure supplement 1). Interestingly, experiments to determine the lobe-specific role of 5HT1A receptors suggest that 5HT acts generally in the MB, not just on the α’/β’ lobes (data not shown), suggesting that these two transmitters may play somewhat different roles at the circuit level in sleep and memory consolidation.10.7554/eLife.03868.019Figure 7.MB α’β’ GABA receptors promote nighttime sleep.

Bottom Line: Downregulation of α'/β' GABAA and GABABR3 receptors results in sleep loss, suggesting these receptors are the sleep-relevant targets of DPM-mediated inhibition.Regulation of sleep by neurons necessary for consolidation suggests that these brain processes may be functionally interrelated via their shared anatomy.These findings have important implications for the mechanistic relationship between sleep and memory consolidation, arguing for a significant role of inhibitory neurotransmission in regulating these processes.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Volen Center for Complex Systems, National Center for Behavioral Genomics, Brandeis University, Waltham, United States.

ABSTRACT
Sleep promotes memory consolidation in humans and many other species, but the physiological and anatomical relationships between sleep and memory remain unclear. Here, we show the dorsal paired medial (DPM) neurons, which are required for memory consolidation in Drosophila, are sleep-promoting inhibitory neurons. DPMs increase sleep via release of GABA onto wake-promoting mushroom body (MB) α'/β' neurons. Functional imaging demonstrates that DPM activation evokes robust increases in chloride in MB neurons, but is unable to cause detectable increases in calcium or cAMP. Downregulation of α'/β' GABAA and GABABR3 receptors results in sleep loss, suggesting these receptors are the sleep-relevant targets of DPM-mediated inhibition. Regulation of sleep by neurons necessary for consolidation suggests that these brain processes may be functionally interrelated via their shared anatomy. These findings have important implications for the mechanistic relationship between sleep and memory consolidation, arguing for a significant role of inhibitory neurotransmission in regulating these processes.

Show MeSH
Related in: MedlinePlus