Dorsal subcoeruleus nucleus (SubCD) involvement in context-associated fear memory consolidation.

The neurobiological mechanisms of emotional memory processing can be investigated using classical fear conditioning as a model system, and evidence from multiple lines of research suggests that sleep influences consolidation of emotional memory. In rodents, some of this evidence comes from a common finding that sleep deprivation from 0 to 6 h after fear conditioning training impairs processing of conditioned fear memory. Here, we show that during a 6-h session of sleep-wake (S-W) recording, immediately after a session of context-associated fear conditioning training, rats spent more time in wakefulness (W) and less time in slow-wave sleep (SWS) and rapid eye movement (REM) sleep. This context-associated fear conditioning training-induced reduction in SWS lasts for 2 h, and the REM sleep reduction lasts throughout the entire 6-h post-training S-W recording period. Interestingly, these reductions in SWS and REM sleep during this 6-h period did not impair memory consolidation for context-associated fear conditioning. The results of this study show, for the first time, that lesions within the dorsal part of the subcoeruleus nucleus (SubCD), which were unintentionally caused by the implantation of bipolar recording electrodes, impair consolidation of context-associated fear conditioning memory. Together, the results of these experiments suggest that emotional memory processing associated with fear conditioning can be completed successfully within less than a normal amount of sleep, but it requires a structurally and functionally intact SubCD, an area in the brain stem where phasic pontine wave (P-wave) generating cells are located.

A novel role for calcium/calmodulin kinase II within the brainstem pedunculopontine tegmentum for the regulation of wakefulness and rapid eye movement sleep.

Considerable evidence suggests that the brainstem pedunculopontine tegmentum (PPT) neurons are critically involved in the regulation of rapid eye movement (REM) sleep and wakefulness (W); however, the molecular mechanisms operating within the PPT to regulate these two behavioral states remain relatively unknown. Here we demonstrate that the levels of calcium/calmodulin kinase II (CaMKII) and phosphorylated CaMKII expression in the PPT decreased and increased with 'low W with high REM sleep' and 'high W/low REM sleep' periods, respectively. These state-specific expression changes were not observed in the cortex, or in the immediately adjacent medial pontine reticular formation. Next, we demonstrate that CaMKII activity in the PPT is negatively and positively correlated with the 'low W with high REM sleep' and 'high W/low REM sleep' periods, respectively. These differences in correlations were not seen in the medial pontine reticular formation CaMKII activity. Finally, we demonstrate that with increased PPT CaMKII activity observed during high W/low REM sleep, there were marked shifts in the expression of genes that are involved in components of various signal transduction pathways. Collectively, these results for the first time suggest that the increased CaMKII activity within PPT neurons is associated with increased W at the expense of REM sleep, and this process is accomplished through the activation of a specific gene expression profile.

Improvement of two-way active avoidance memory requires protein kinase a activation and brain-derived neurotrophic factor expression in the dorsal hippocampus.

Previous studies have shown that two-way active avoidance (TWAA) memory processing involves a functional interaction between the pontine wave (P wave) generator and the CA3 region of the dorsal hippocampus (DH-CA3). The present experiments examined whether the interaction between P wave generator activity and the DH-CA3 involves the intracellular protein kinase A (PKA) signaling system. In the first series of experiments, rats were subjected to a session of TWAA training followed immediately by bilateral microinjection of either the PKA activation inhibitor (KT-5720) or vehicle control into the DH-CA3 and tested for TWAA memory 24 h later. The results indicated that immediate KT-5720 infusion impaired improvement of TWAA performance. Additional experiments showed that KT-5720 infusion also blocked TWAA training-induced BDNF expression in the DH-CA3. Together, these findings suggest that the PKA activation and BDNF expression in the DH-CA3 is essential for the improvement of TWAA memory.

Spontaneous REM sleep is modulated by the activation of the pedunculopontine tegmental GABAB receptors in the freely moving rat.

Considerable evidence suggests that the neurotransmitter gamma-aminobutyric acid (GABA)-ergic system and pedunculopontine tegmentum (PPT) in the brain stem are critically involved in the regulation of rapid-eye-movement (REM) sleep. GABA and its various receptors are normally present in the PPT cholinergic cell compartment. The aim of this study was to identify the role of GABA and its receptors in the regulation of REM sleep. To achieve this aim, specific receptors were activated differentially by local microinjection of selective GABA receptor agonists into the PPT while quantifying its effects on REM sleep in freely moving chronically instrumented rats (n = 21). The results demonstrated that when GABAB receptors were activated by local microinjection of a GABAB receptor selective agonist, baclofen, spontaneous REM sleep was suppressed in a dose-dependent manner. The optimum dose for REM sleep reduction was 1.5 nmol. In contrast, when GABAA and GABAC receptors were activated by microinjecting their receptor selective agonists, isoguvacine (ISGV) and cis-4-aminocrotonic acid (CACA), respectively, the total percentages of REM sleep did not change compared with the control values. In another eight freely moving rats, effects of baclofen application was tested on firing rates of REM-on cells (n = 12). Of those 12 neurons, 11 stopped firing immediately after application of baclofen [latency: 50 +/- 14 s (SD)] and remained almost silent for 130 +/- 12 min. Findings of the present study provide direct evidence that the PPT GABAB receptors and REM-on cells are involved in the regulation of REM sleep.

Effects of passive-avoidance training on sleep-wake state-specific activity in the basolateral and central nuclei of the amygdala.

This study examined the effects of intense emotional learning on the sleep-wake state-specific electroencephalographic (EEG) activities of the basolateral (BLA) and central (CeA) nuclei of the amygdala. Rats were trained on a passive-avoidance learning (PAL) protocol that was followed by 6 hr of undisturbed polygraphic recording and a PAL test. After PAL training, the total amount of REM sleep decreased: high-frequency EEG power decreased in the CeA during REM sleep and increased in the BLA during all sleep-wake stages. These results suggest that there is no homeostatic demand for REM sleep after intense emotional learning. However, the PAL-specific changes in the local EEG suggest that some form of memory processing may occur within the amygdala during REM sleep.

Choline availability during embryonic development alters the localization of calretinin in developing and aging mouse hippocampus.

Choline availability in the diet during pregnancy alters fetal brain biochemistry with resulting behavioral changes that persist throughout the lifetime of the offspring. In the present study, the effects of dietary choline on the onset of GABAergic neuronal differentiation in developing fetal brain, as demarcated by the expression of calcium binding protein calretinin, are described. In these studies, timed-pregnant mice were fed choline supplemented, control or choline deficient AIN-76 diet from day 12-17 of pregnancy and the brains of their fetuses were studied on day 17 of gestation. In the primordial dentate gyrus, we found that pups from choline deficient-dams had more calretinin protein (330% increase), and pups from choline supplemented-dams had less calretinin protein (70% decrease), than did pups from control-dams. Importantly, decreased calretinin protein was still detectable in hippocampus in aged, 24-month-old mice, born of choline supplemented-dams and maintained since birth on a control diet. Thus, alterations in the level of calretinin protein in fetal brain hippocampus could underlie the known, life long effects of maternal dietary choline availability on brain development and behavior.

Single cell activity patterns of pedunculopontine tegmentum neurons across the sleep-wake cycle in the freely moving rats.

Microinjections of the excitatory amino acid, L-glutamate into the cholinergic cell compartment of the pedunculopontine tegmentum (PPT) of the rat induces both wakefulness and/or rapid eye movement (REM) sleep depending on the glutamate dosage. However, no studies have systematically recorded the electrical activity of these cells in the freely moving rat across the sleep-wake cycle. In this study, we have recorded the spontaneous activity patterns of single PPT cells (n = 70) in the freely moving rat across the sleep-wake cycle. PPT neurons were classified into three groups based on patterns in their spontaneous activity. The first group of cells (12.86%) was more active during REM sleep than they were during wakefulness or slow-wave sleep (SWS). The second group of cells (60.0%) was more active during REM and wakefulness than during SWS. The firing rate of the third group of cells (27.14%) did not change as a function of behavioral state. This study also demonstrated that the level of activity within the cholinergic cell compartment of the PPT during SWS drops to 7.4% of that observed during wakefulness and that during REM sleep it changes to 65.5% of wakefulness levels. These findings indicate that in the freely moving rat, the discharging of PPT neurons correlates with wakefulness and REM sleep. Additionally, these neurons may be an integral part of the brainstem wakefulness and REM sleep-generating mechanisms in the rat.