Spindle-slow wave coupling and problem-solving skills: Impact of age

We examined how aging affects the role of sleep in the consolidation of newly learned cognitive strategies. Forty healthy young adults (20-35 years) and 30 healthy older adults (60-85 years) were included. Participants were trained on the Tower of Hanoi (ToH) task, then, half of each age group were assigned to either the 90-minute nap condition, or stayed awake, before retesting. The temporal co-occurrence between slow-waves (SW) and sleep spindles (SP) during NREM sleep was examined as a function of age in relation to memory consolidation of problem-solving skills. We found that despite intact learning, older adults derived a reduced benefit of sleep for problem-solving skills relative to younger adults. As expected, the percentage of coupled spindles was lower in older compared to younger individuals from control to testing sessions. Furthermore, coupled spindles in young adults were more strongly coupled to the SW upstate compared to older individuals. Coupled spindles in older individuals were lower in amplitude (mean area under curve; μV) compared to the young group. Lastly, there was a significant relationship between offline gains in accuracy on the ToH and percent change of spindles coupled to the upstate of the slow wave in older, but not younger adults. Multiple regression revealed that age accounted for differences in offline gains in accuracy, as did spindle coupling during the upstate. These results suggest that with aging, spindle-slow wave coupling decreases. However, the degree of the preservation of coupling with age correlates with the extent of problem-solving skill consolidation during sleep.

Sleep spindles in adolescents with major depressive disorder

Sleep spindle differences in adolescents with major depressive disorder (MDD) compared to healthy adolescents is an ongoing debate. Results mostly indicate decreased sleep spindle activity in adolescents with MDD. Given that sleep spindles predominate NREM and that acutely delaying the sleep period via a "sleep delay challenge" (SDC) increases non-rapid eye movement (NREM) sleep duration, it may be possible to increase spindle density in adolescents with MDD, which may provide a therapeutic benefit to depression symptoms. Here, we examined the impact of a SDC on spindle density and depression symptomology in adolescents with MDD (n = 66) and healthy controls (n = 62) tested across three nights: adaptation, normal sleep, and a SDC night which delayed bedtime by three hours. The results showed that; (1) there was no difference in spindle density between groups on the normal sleep night, (2) following the SDC, both males and females with MDD had a decrease in the frequency of slow spindles, while only females with MDD had an increase in the frequency of fast spindles, (3) acute SDC reduced depression symptoms in both groups, and (4) light sleep on the normal sleep night and slow spindle frequency at SDC predicted an 8 % improvement in depression symptoms, regardless of sex or MDD diagnosis. Taken together, these results suggest that; (a) spindles may be a useful biological marker of depression symptomatology regardless of clinical MDD diagnosis, and (b) that acute SDC may help alleviate depression symptoms in adolescents with MDD.

Sleep Enhances Consolidation of Memory Traces for Complex Problem-Solving Skills

Sleep consolidates memory for procedural motor skills, reflected by sleep-dependent changes in the hippocampal-striatal-cortical network. Other forms of procedural skills require the acquisition of a novel strategy to solve a problem, which recruit overlapping brain regions and specialized areas including the caudate and prefrontal cortex. Sleep preferentially benefits strategy and problem-solving skills over the accompanying motor execution movements. However, it is unclear how acquiring new strategies benefit from sleep. Here, participants performed a task requiring the execution of a sequence of movements to learn a novel cognitive strategy. Participants performed this task while undergoing fMRI before and after an interval of either a full night sleep, a daytime nap, or wakefulness. Participants also performed a motor control task, which precluded the opportunity to learn the strategy. In this way, we subtracted motor execution-related brain activations from activations specific to the strategy. The sleep and nap groups experienced greater behavioral performance improvements compared to the wake group on the strategy-based task. Following sleep, we observed enhanced activation of the caudate in addition to other regions in the hippocampal-striatal-cortical network, compared to wakefulness. This study demonstrates that sleep is a privileged time to enhance newly acquired cognitive strategies needed to solve problems.

Effects of dietary linoleic acid on rat platelet ADP-induced aggregation and binding of 125I-fibrinogen

Platelets from rats fed a diet high in linoleic acid (6%) bound increased amounts of fibrinogen on stimulation with ADP, compared to those from rats fed diets with low (2%) or no linoleic acid. However, this increased fibrinogen binding was associated with a decrease in platelet aggregation induced by ADP. Changes in the linoleic acid concentration in platelet membranes may cause changes in this relationship.

Effects of oral contraceptives, or lanosterol, on ADP-induced aggregation and binding of 125I-fibrinogen to rat platelets

The aggregation to ADP and the binding of 125I-fibrinogen to platelets from rats treated with oral contraceptives or normal platelets treated in vitro with lanosterol were compared to their respective controls. Both types of platelets showed a significant increase in ADP-induced aggregation and in binding of fibrinogen, indicating that the effect of oral contraceptives could be partly due to increased levels of lanosterol in platelet membrane.

The effect of oral contraceptives on rat platelet membrane glycoproteins

Female rats were administered oral contraceptives and the levels of sialic acid on platelet membrane and granule glycoproteins were compared to controls using a sialic acid assay and a fluorescein-conjugated wheat germ agglutinin binding assay and also by measuring the binding of 125I-labelled wheat germ agglutinin to glycoprotein bands from platelets separated by polyacrylamide electrophoresis. The contraceptive-treated rats showed increased levels of glycoprotein sialylation which may partly explain the altered physiological function of the platelets.

Comparison of the major membrane glycoproteins and proteins of human, rabbit and rat blood platelets

Rabbit and rat blood platelets behave differently from human platelets in response to a number of aggregating agents. The aim of this work was to compare platelet membrane glycoproteins (GP) and proteins of these 3 species and relate these results to physiological functions. Washed platelets were surface labelled by techniques specific for their oligosaccharide (sialic acid, galactose/N-acetyl galactosamine) or protein moieties, and separated on a high resolution Laemmli SDS polyacrylamide gel. Higher labelling of terminal galactose/N-acetyl galactosamine residues was obtained for rat and rabbit platelets as compared to human. Glycoproteins of rabbit and rat platelets migrating at the same position as the most sialylated human platelet GP (Ib), were insignificantly labelled. However, in rabbit and rat platelets, the most sialylated GP were located at an apparent molecular weight (Mr) similar to and above human Ia, and part of this GP was lost in the supernatant in the presence of 0.002 M Ca++. Rat membrane proteins having a similar Mr to iodinated human platelet membrane proteins (IIb, IIIa) were weakly labelled in contrast to rabbit membrane proteins. These studies demonstrate differences between the platelet membrane protein and GP composition of rabbit, rat and human platelets, which may explain some of the differences observed in vitro with aggregation responses in these species.