Effects Of Sleep Deprivation On Spatial Memory And Neuron Functioning

Effects of Sleep Deprivation on Spatial Memory and Neural Functioning Daniel R. Atwood PDBIO 325 Tissue Biology Fall 2009

Abstract Sleep deprivation has a wide range of negative effects on human performance. One of these effects that has been under a recent widespread investigation is how sleep deprivation effects spatial memory. Many studies have shown a close relationship between spatial memory and neurons: those of which are mostly found within the hippocampus. Not only does sleep deprivation effect the current neurons that have already been proliferated for quite some time, but it also effects the normal functions of neurogenesis: from survival rate to ability to specialize and show a neural phenotype. While disruption of sleep for a period shorter than 24-hours has little effect on both proliferated neurons and neurogenesis alike, prolonged disruption shows major histological changes which could explain the compromising of spatial memory.

Introduction Only within the past decade or two, several in-depth investigations have looked into the complexities of transformations that occur within the brain at both mesoscopic and microscopic level during the time that which all human kind undergoes on average of 6-8hrs a day: the same hours spent while placing oneself carefully upon their bed to experience a natural suspension of consciousness during which the body (and mind) is rejuvenated. Because these studies are fairly recent, the majority of our society lives in ignorance of its grand importance. Perhaps that is why most have little regard for sleep, merely putting up with the fact that mammalians are required to sleep, that perhaps it’s an ‘illness’ that we can one day cure ourselves from. This train of thought, when combined with the high demands of school and work in today’s world, has turned several to having severe sleep disorders originating from short and infrequent periods of sleep deprivation. Besides the recent findings of changes that happen at a histological level within the human body, many effects of sleep deprivation on human performance have been well known to the general public for quite some time now. These include irritability, weakened immune system, and of course, cognitive impartment (Boonstra et al, 2007). However, thanks to many recent discoveries, many neurological transformations have been witnessed and can explain reasons for 1

the compromising of spatial memory during sleep deprivation. Proliferated Cortical & Hippocampal Dendrite Spines There have been studies suggesting that sleep deprivation can alter the dendrite portion of already proliferated neurons. The dendrite, being the receiving part of the neuron, is a dynamic structure that can change in response to the surrounding environment or stimuli. An example of this was produced by the research carried out by Neurner-Jehle and his assistants. They reported a 42% average decrease of cortical concentration of the dendritic protein, dendrin, after having several lab rats experience a 24-hour sleep deprivation (Neuner-Jehle et al, 1996). In a more recent study, J.-R Chen and his assistants had similar results. Through the use of intracellular dye injection, they were able to reveal a comparison of the changes of dendritic arbors and dendritic spines between a control group of rats that were well rested versus others

Fig. 1 Representative intracellular dye-filled corticospinal neurons from control (A) and 5-day fatigue rats (B). The photograph was taken from one of the serial sections, 60-

that were sleep deprived for 5 days total. The

µm-thick, of the injected slice in while the injected

densities of dendritic spines on both the distal

fluorescence dye was immunohistochemically converted to

and proximal parts of the dendrite were

non-fading DAB reaction product. (A1-A4, B1-B4) High magnifications of the corresponding dendritic segments

significantly reduced in rats following 5 days of

marked in A and B to show that dendritic spines are well-

fatigue by approximately 23%-32% (as seen in

labeled. Scale bar=100 µm for A and B and 10 µm for A1-

Fig. 1) and it took about 3-days of rest to restore

A4 and B1-B4.

the dendritic spine densities on the corticospinal neurons for the 5-day-fatigue rats to match that of the well rested control group (Chen et al, 2009).

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Moreover, in the same experiment that J.-R Chen and his assistants conducted, they also checked the output neurons of CA1 and CA3 hippocampal areas. These two areas are known to be closely associated with learning and spatial memory. Just like with the corticospinal neurons mentioned above, they used the same intracellular dye to compare the differences in CA1 and CA3 between the control and the 5day sleep deprived group. On the CA1 hippocampal neurons, the distal part of the apical dendrites were reduced by 31% after 5 days of sleep deprivation, while those on basal dendrites were reduced even more dramatically by 52% (as seen in Fig. 2). On the CA3 hippocampal neurons, spine densities on proximal apical dendrites were reduced by 20% and on distal apical dendrites by 35%, while those on basal dendrites were reduced by 32%. It again took roughly 3-days for the experimental group to restore their densities of dendritic spines of all segments found on both CA1 and CA3 hippocampal neurons to match Fig. 2 The effect of fatigue on the dendritic spines of hippocampal CA1 pyramidal neurons. (A) Representative dendritic segments of the CA1 pyramidal cells of control, 5-day fatigue and 5-day fatigue followed by 3-day rest rats.

those within the control group. In this experiment, both the reduction of the rats cortical and hippocampal dendrite spines

Changes of spine densities were analyzed in B. Number of

resulted in reduced spatial memory

basal, proximal apical and distal apical dendritic segments

performances. However, after the sleep deprived

analyzed was 31, 24, and 33 for control, 27, 28, and 36 for 5 day-fatigue and 36, 47, and 50 for 5-day fatigue and 3day rest group. Scaled bar=10 µm.

experimental group had 3 days of rest, no longterm effects were demonstrated within their

neurological functions.

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Hippocampal SIRT1/COX Expression & Melatonin Other than temporary hippocampal dendrite density transformations mentioned above, these same neurons have been documented to experience another physiological metamorphosis closely associated with impaired performance in spatial learning and memory. In a recent experiment, Chang is his assistants used a SIRT1 immunohistochemistry stain to measure the differences in SIRT1 and COX expression in hippocampal neurons. This time around there four different experimental rat groups: a control group that was subjected to a normal circadian resting phase; a 5day sleep deprived group; and two additional 5-day sleep deprived groups with a dose of melatonin (one group given 25mg/kg and the other 100mg/kg). After dissection of the hippocampi, the rats subjected to 5-day sleep deprivation without melatonin dosage experienced a significant reduction of hippocampal SIRT1 and COX expression, both of which were demonstrated by impaired performance in spatial memory (as seen in Fig. 3). This conclusion was further solidified by a

Fig. 3 Light photomicrographs showing hippocampal sirtuin (SIRT1) immunoreactivity in normal untreated (A), total 5-day sleep deprived (TSD) (B), and total 5-day sleep deprived with different doses of melatonin treated rats (C-F). Note that in normal untreated rats, numerous SIRT1 immunoreactive neurons were observed in hippocampal pyramidal cell layers (A). However, following 5-days of TSD, the SIRT1 immunoreactivity was drastically decreased (B). Also note that in rats receiving different doses of melatonin, the expression of SIRT1 was gradually returned to normal levels (C-F). Scale bar = 100 µm.

water maze analysis, which revealed that the 5-day sleep deprived rats without melatonin dosage struggled to successfully complete the maze, taking more time than the other 3 groups. It must 4

also be noted that the group of 5-day sleep deprived rats that received doses of melatonin showed darker SIRT1 immunohistochemistry stains that those of the sleep deprived group without melatonin intake (Chang et al, 2009). Because of this, melatonin proved to combat the compromising effects of SIRT1 and COX expressions and therefore leading to a greater spatial memory performance, similar to the group of rats that were well rested. N1 Amplitude Two modern neuroimaging techniques that are commonly used to today to measure and record neural functions within the brain are functional magnetic resonance imaging (fMRI) and positron emission tomography (PET). The former measures the blood oxygenation leveldependent contrast while the latter measures hemodynamic changes by marking blood with a radioactive tracer (Cabeza & Nyberg, 2000). With respect to sleep deprivation, and through the use of either of these two neuroimaging techniques, significant alterations in the component N1 have been witnessed within the brain. N1 is a component that is closely associated with the responsibility of processing visual, auditory, and tactile stimuli that are located in the primary sensory areas found within the brain. Several experiments have been carried out showing a pronounced reduction of N1 amplitude in participants that had suffered either a night of sleep fragmentation or deprivation (Cote et al, 2006). This reduction of N1 amplitude reflected a decrease of the participants’ response to not only motor stimuli, but also visual and auditory stimuli. Because of this, spatial memory (that is, the ability to intake new information and recall it shortly afterwards) was also reduced because of the inability to successfully intake the same amount of peripheral stimuli that a well-rested individual would be able to process. However, after having a small dose of caffeine, it has been shown that a sleep-deprived individual can increase the once reduced N1 amplitude, which means processing of peripheral stimuli can once again increase (Lorist et al, 1994). It must be noted though, that the substitution of a good night’s rest with caffeine can only produce the same amplitude of the component of N1 for a short period of time, usually for only a couple of hours. Adenosine Adenosine is a neuromodulator that has been studied quite heavily. In the brain, adenosine primarily acts as an intercellular messenger that has been shown to be involved in 5

processes such as sleep regulation and arousal, as well as inhibition of most other neurotransmitters (Dunwiddie & Masino, 2001). Because of adenosine’s inhibition effect of neurotransmitter’s firing rate, it essentially has the ability to reduce excitability throughout the entire brain (as seen in Fig. 4). During sleep deprivation, adenosine levels have been recorded accumulating in select parts throughout the brain, thereby promoting the macroscopic symptom Fig. 4 Dose-response curve for depression of neuronal firing rate by adenosine (n=4–6 trials per dose). The firing rate was initially set at 2 Hz by injection of a depolarizing

is drowsiness (Arrigoni et al, 2006). With the decrease in amplitude of component N1, along

holding current (+50.3±13.3 pA; n=15 neurons). Data are

with the accumulation of adenosine, a profound

fit (line) using a sigmoid equation, max

compromising effect on spatial memory occurs

inhibition=100±13.7%; IC50=8.8±1.3 μM; and k=2.5±0.3 nM.

because of the temporary neurological changes that take place.

Neurogenesis Neurogenesis, the process by which an organism obtains new neurons, was traditionally believed to occur only during the embryonic stages in the CNS of mammalians. However, many recent studies within the past few decades have shown that the adult brain contains many unspecialized progenitor cells that give rise to new neurons (Ming & Song, 2005). These new neurons are generated in select areas throughout the adult brain, most notably the dentate gyrus of hippocampal formation. The hippocampus is one of the most important parts of the cognitive system that plays a crucial role in the maintenance of memories and emotions. Neurogenic Proliferation Several studies on laboratory mice have reported that while under baseline conditions, short sleep deprivation (<1 day) during the normal circadian resting phase did not affect neural cell proliferation in mice, as seen in Fig. 5 (Van der Borght et al, 2006). This trend seems to closely follow the same outcome that previous proliferated neurons experienced mentioned above. However, cell proliferation is significantly suppressed when sleep 6

deprivation (or disruption of sleep) is prolonged and last for several days or more (Roman et al, 2005). In order to further solidify this hypothesis, a number of experiments have directly compared the effect of short sleep deprivation (<1 day) with

Fig. 5 Effect of sleep deprivation on hippocampal cell proliferation. (B) The sleep deprivation procedure had no effect on the number of Ki-67 positive cells. (E) BrdU, which had been injected 2 h prior to sacrificing the mice, was incorporated in the same number of cells in sleep-deprived and control mice.

the effects of prolonged sleep restriction ( >3 days) and have confirmed that a reduction in hippocampal cell proliferation is only found with prolonged sleep restriction or disruption (Meerlo et al, 2009). Neurogenic Maturation & Differentiation Besides the dramatic decline in neurogenic proliferation, sleep deprivation also has a negative impact on neurogenic maturation and differentiation. Several experiments have been conducted that have showed a decreased amount of progenitor cells that later express a functional Fig. 6 Effect of sleep deprivation on phenotype expression of surviving cells, with the white columns

phenotype that matches already proliferated

pertaining to the well-rested control group and the black

neurons. One example can be found in a

columns pertaining to the experimental group. Phenotype

experiment that Guzman-Marin conducted. Oddly

of surviving cells were determined by immunofluorescent triple labeling for BrdU.

enough, his data showed that the neurogenic maturation to a neuronal phenotype was at its

lowest percentage only after 4 days of complete sleep deprivation, instead of an anticipated 7 days, as seen in Fig. 6 (Guzman-Marin et al, 2007). Because sleep deprivation has an overall same result on all the steps of neurogenesis, from neural proliferation to maturation and differentiation, they all equally compromise spatial memory by decreasing the amount of functional neurons within the brain.

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Conclusion & Summary After close analysis of the cumulative experiments, a solid understanding can be achieved that sleep deprivation (whether in form of limited hours of sleep or fragmentation) leads to an overall negative effect on neurons, both previously proliferated and those currently going through one of the many stages of neurogenesis. Neurons present in the hippocampus and cortex (both of which are closely associated with spatial memory) experienced a range of degrading histological transformations, ranging from less dense dendritic spines to decreased expressions of SITR1 and COX. However, after a short period of rest (usually around 3-days), the brain showed the ability to rejuvenate itself and experience no long-term effects. On top of that, both caffeine and melatonin doses proved to combat some of the negative effects of sleep deprivation. Besides directly dealing with neural function, another experiment that proved to provide another indictor of compromised spatial memory was a decrease in the amplitude of N1, which can be read by either a PET or fMRI, two modern neuroimaging techniques used today. Despite all of these discoveries, the general study of neurological transformations that occur due to sleep deprivation is still a relatively new field of science. At the very least though, with this more profound understanding on the importance of sleep, perhaps society as a whole would come to a deeper appreciation for it, thereby leading to a closer adherence to an adequate daily sleep schedule.

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Works Cited Primary Sources: 1) Neuner-Jehle, M., et al. "Characterization and Sleep Deprivation-Induced Expression Modulation of Dendrin, a Novel Dendritic Protein in Rat Brain Neurons." Journal of neuroscience research 46.2 (1996): 138-51. Print. 2) Chen, J. -R, et al. "Fatigue Reversibly Reduced Cortical and Hippocampal Dendritic Spines Concurrent with Compromise of Motor Endurance and Spatial Memory." Neuroscience 161.4 (2009): 1104-13. Print. 3) Chang, Hung-Ming, Un-In Wu, and Chyn-Tair Lan. "Melatonin Preserves Longevity Protein (Sirtuin 1) Expression in the Hippocampus of Total Sleep-Deprived Rats." Journal of pineal research 47.3 (2009): 211-20. Print. 4) Cote, K. A., et al. "Waking Quantitative Electroencephalogram and Auditory Event-Related Potentials Following Experimentally Induced Sleep Fragmentation." Sleep 26.6 (2003): 687-94. Print. 5) Lorist, M. M., et al. "Influence of Caffeine on Selective Attention in Well-Rested and Fatigued Subjects." Psychophysiology 31.6 (1994): 525-34. Print. 6) Arrigoni, E., et al. "Adenosine Inhibits Basal Forebrain Cholinergic and Noncholinergic Neurons in Vitro." Neuroscience 140.2 (2006): 403-13. Print. 7) Van der Borght, K., et al. "Hippocampal Cell Proliferation Across the Day: Increase by Running Wheel Activity, but no Effect of Sleep and Wakefulness." Behavioural brain research 167.1 (2006): 36-41. Print.

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8) Roman, V., et al. "Sleep Restriction by Forced Activity Reduces Hippocampal Cell Proliferation." Brain research 1065.1-2 (2005): 53-9. Print. 9) Guzman-Marin, R., et al. "Hippocampal Neurogenesis is Reduced by Sleep Fragmentation in the Adult Rat." Neuroscience 148.1 (2007): 325-33. Print.

Secondary Sources: 10) Boonstra, T. W., et al. "Effects of Sleep Deprivation on Neural Functioning: An Integrative Review." Cellular and Molecular Life Sciences 64.7-8 (2007): 934-46. Print. 11) Cabeza, R., and L. Nyberg. "Imaging Cognition II: An Empirical Review of 275 PET and fMRI Studies." Journal of cognitive neuroscience 12.1 (2000): 1-47. Print. 12) Dunwiddie, T. V., and S. A. Masino. "The Role and Regulation of Adenosine in the Central Nervous System." Annual Review of Neuroscience 24 (2001): 31-55. Print. 13) Ming, G. L., and H. J. Song. "Adult Neurogenesis in the Mammalian Central Nervous System." Annual Review of Neuroscience 28 (2005): 223-50. Print. 14) Meerlo, Peter, et al. "New Neurons in the Adult Brain: The Role of Sleep and Consequences of Sleep Loss." Sleep Medicine Reviews 13.3 (2009): 187-94. Print.

Diagrams: Fig. 1) Neuner-Jehle, M., et al. "Characterization and Sleep Deprivation-Induced Expression Modulation of Dendrin, a Novel Dendritic Protein in Rat Brain Neurons." Journal of neuroscience research 46.2 (1996): 138-51. Print. 10

Fig. 2) Chen, J. -R, et al. "Fatigue Reversibly Reduced Cortical and Hippocampal Dendritic Spines Concurrent with Compromise of Motor Endurance and Spatial Memory." Neuroscience 161.4 (2009): 1104-13. Print. Fig. 3) Chang, Hung-Ming, Un-In Wu, and Chyn-Tair Lan. "Melatonin Preserves Longevity Protein (Sirtuin 1) Expression in the Hippocampus of Total Sleep-Deprived Rats." Journal of pineal research 47.3 (2009): 211-20. Print. Fig. 4) Arrigoni, E., et al. "Adenosine Inhibits Basal Forebrain Cholinergic and Noncholinergic Neurons in Vitro." Neuroscience 140.2 (2006): 403-13. Print. Fig. 5) Van der Borght, K., et al. "Hippocampal Cell Proliferation Across the Day: Increase by Running Wheel Activity, but no Effect of Sleep and Wakefulness." Behavioural brain research 167.1 (2006): 36-41. Print. Fig. 6) Guzman-Marin, R., et al. "Hippocampal Neurogenesis is Reduced by Sleep Fragmentation in the Adult Rat." Neuroscience 148.1 (2007): 325-33. Print.

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