c-fos proto-oncogene change in relation to REM sleep duration

Auditory stimulation has been shown to increase REM sleep periods in cats and humans. This effect has been attributed to an elevation of the level of excitability in a variety of brain stem neuronal groups. Fos-like immunostaining (FLI) has been useful in constructing maps of post-synaptic neuronal activity with single cell resolution, and has been suggested to be tightly correlated with ongoing neuronal activity. This study used FLI to quantify neurons from structures expressing c-fos in brain stem areas in animals with normal REMs and compared them with those showing extended REM periods. The results basically indicated that brain stem areas which in other studies have been described as having REM-ON cells, showed an increase in FLI, while no FLI changes occurred in areas described as having REM-OFF cells. These results are discussed in terms of the possibility that REM maintenance is related to a widespread increase in brain stem excitability.     

The effect of stimulus duration on noxious-stimulus induced c-fos expression in the rodent spinal cord.

C-fos is a proto-oncogene that is expressed within some neurons following depolarization. The protein product,fos, has been proposed as an anatomical marker for neuronal activity following noxious peripheral stimulation. However, the literature on noxious-stimulus induced fos expression contains several puzzling observations on the time course and laminar distribution of neuronal labeling within the spinal cord. This study has analyzed the effect of stimulus duration on the expression of fos-like immunoreactivity (FLI) within the spinal cord of anesthetized rats. In order to examine the time course of fos expression following brief periods of stimulation, we required a type of stimulus that was intense enough to activate nociceptors but that did not produce tissue damage. We have therefore employed pulsed, high intensity electrical stimulation, with stimulus durations ranging from 3 s to 24 h. The results indicate that stimulus duration has a profound effect upon the number of labeled cells, the intensity of neuronal labeling, the laminar pattern of FLI, and the time course of fos expression. Brief stimulation periods induce relatively few and relatively lightly labeled neurons, located predominantly within the most superficial laminae of the dorsal horn. Maximal immunoreactivity appears approximately 2 h after stimulation has ceased, and disappears within hours. Continuous stimulation produces many more labeled cells, darker labeling, and FLI within both dorsal and ventral laminar regions. Maximal FLI is seen after approximately 4.5 h of continuous stimulation, with reduction in the number of labeled cells thereafter. These data indicate that the results of any study employing c-fos as a marker for neuronal activity may be affected by the duration of the exciting stimulus.     

Seizures and Proto-Oncogene Expression offosin the Brain of Adult Genetically Epilepsy-Prone Rats

The mechanisms and brain circuitry that render genetically epilepsy-prone rats (GEPRs) susceptible to acoustically induced seizures are not completely known. The present study explores the neuroanatomy of acoustically induced seizures by immunohistochemical analysis of the proto-oncoproteinfosafter intense acoustic stimulation (AS) with and without seizures. Acoustic stimulation induced tonic convulsions in GEPR-9s, but not in control rats. Locations of brain nuclei showingfos-like immunoreactive (FLI) neurons following AS with and without seizures were mapped. Semiquantitative methods were used to compare FLI neuron numerical densities in AS control rats and GEPRs. Many brain areas exhibited profound FLI in AS control rats and GEPRs. Unexpectedly, the cochlear nuclei and the central nucleus of the inferior colliculi (ICc), both of which are requisite for AGS initiation, exhibited a diminishedfosexpression in animals having seizures compared to AS controls. In contrast, GEPRs displayed a significant increase in FLI neurons within the dorsal cortex of the IC (ICd) compared to AS controls. This finding may suggest a seizure-related amplification of the auditory signal between the ICc and the ICd. Other nuclei, known to be involved in auditory transmission (i.e., superior olivary complex; trapezoid nucleus; dorsal nucleus of the lateral lemniscus, DNLL), did not show differential FLI densities between seizure and AS control animals. In contrast, seizure-induced FLI was observed in many nonauditory brain nuclei. Of particular interest was the identification of an intensely labeled nucleus in the GEPR. This nucleus resides in the most posterior and dorsal–lateral part of the pedunculopontine tegmental nucleus–pars compacta (PPTn-pc) immediately adjacent to the DNLL and extends posteriorly into the superior lateral subnucleus of the lateral parabrachial area (SLPBn). Therefore, we have tentatively termed this nucleus the PPSLPBn. The PPSLPBn lies in a region previously described as a mesencephalic locomotor region and a suspected functional involvement of this nucleus in display of seizure activity is under investigation. Other brain stem nuclei showing differentialfosexpression between GEPRs and AS control rats are also described.     

Functional microstates within human REM sleep: first evidence from fMRI of a thalamocortical network specific for phasic REM periods

High thalamocortical neuronal activity characterizes both, wakefulness and rapid eye movement (REM) sleep, but apparently this network fulfills other roles than processing external information during REM sleep. To investigate thalamic and cortical reactivity during human REM sleep, we used functional magnetic resonance imaging with simultaneous polysomnographic recordings while applying acoustic stimulation. Our observations indicate two distinct functional substates within general REM sleep. Acoustic stimulation elicited a residual activation of the auditory cortex during tonic REM sleep background without rapid eye movements. By contrast, periods containing bursts of phasic activity such as rapid eye movements appear characterized by a lack of reactivity to sensory stimuli. We report a thalamocortical network including limbic and parahippocampal areas specifically active during phasic REM periods. Thus, REM sleep has to be subdivided into tonic REM sleep with residual alertness, and phasic REM sleep with the brain acting as a functionally isolated and closed intrinsic loop.     

The effect of stimulus duration on noxious-stimulus induced c-fos expression in the rodent spinal cord

C-fos is a proto-oncogene that is expressed within some neurons following depolarization. The protein product,fos, has been proposed as an anatomical marker for neuronal activity following noxious peripheral stimulation. However, the literature on noxious-stimulus induced fos expression contains several puzzling observations on the time course and laminar distribution of neuronal labeling within the spinal cord. This study has analyzed the effect of stimulus duration on the expression of fos-like immunoreactivity (FLI) within the spinal cord of anesthetized rats. In order to examine the time course of fos expression following brief periods of stimulation, we required a type of stimulus that was intense enough to activate nociceptors but that did not produce tissue damage. We have therefore employed pulsed, high intensity electrical stimulation, with stimulus durations ranging from 3 s to 24 h. The results indicate that stimulus duration has a profound effect upon the number of labeled cells, the intensity of neuronal labeling, the laminar pattern of FLI, and the time course of fos expression. Brief stimulation periods induce relatively few and relatively lightly labeled neurons, located predominantly within the most superficial laminae of the dorsal horn. Maximal immunoreactivity appears approximately 2 h after stimulation has ceased, and disappears within hours. Continuous stimulation produces many more labeled cells, darker labeling, and FLI within both dorsal and ventral laminar regions. Maximal FLI is seen after approximately 4.5 h of continuous stimulation, with reduction in the number of labeled cells thereafter. These data indicate that the results of any study employing c-fos as a marker for neuronal activity may be affected by the duration of the exciting stimulus.     

Studies on AMP deaminase and 5'-nucleotidase in rat brain under different experimental conditions

Adenosine monophosphate (AMP) deaminase and 5'-nucleotidase, the two enzymes involved in the disposal of AMP, have been detected in different regions of normal rat brain and in animals subjected to heightened neuronal activity (leptazol-induced convulsions) and to depression of the central nervous system (CNS) by the administration of barbiturates. They have also been estimated in the CNS of animals subjected to anoxia or treated with lithium and ammonium salts. The AMP deaminase activity was found to be highest in cerebellum and lowest in cerebral cortex, while the 5'-nucleotidase activity was found to be highest in brain stem and lowest in cerebellum. The AMP deaminase activity was elevated in all the regions of brain during the preconvulsive and convulsive periods. The activity returned to normal during recovery. The activity of 5'-nucleotidase was found to be depressed in the preconvulsive and post-convulsive periods. The enzyme was also found to be depressed in all the three regions after the administration of barbiturates. Administration of lithium or ammonium salts of induction of anoxic states resulted in an increase in the activity of AMP deaminase in all the three regions of brain. These results are discussed in relation to the probable production of cyclic AMP and cyclic guanosine monophosphate (GMP) which may have depressive and excitatory roles, respectively, in brain. It appears that increased AMP deaminase activity is associated with increased neuronal activity while depression of 5'-nucleotidase activity is associated with conditions of decreased CNS excitability.     

Local cerebral glucose utilization non-selectively elevated in rapid eye movement sleep of the fetus

The [14C]deoxyglucose method for measuring local cerebral glucose utilization was employed in an effort to identify regions of the brain which participate in the increased neuronal activity of rapid eye movement (REM) sleep. The study was conducted in near term fetal sheep in which REM periods are of sufficient duration to obtain reliable data with this method. Neither the postulated executive centers of REM sleep nor those structures in the brainstem known to participate in the electrical activity peculiar to this sleep phase were found to have selectively elevated rates of glucose utilization. Rather, these regions shared equally with virtually all other structures in having rates higher than those which accompany non-REM sleep.     

Increased turnover of Na-K ATPase molecules in rat brain after rapid eye movement sleep deprivation

It has been shown that rapid eye movement (REM) sleep deprivation increases Na-K ATPase activity. Based on kinetic study, it was proposed that increased activity was due to enhanced turnover of enzyme molecules. To test this, anti-alpha1 Na-K ATPase monoclonal antibody (mAb 9A7) was used to label Na-K ATPase molecules. These labeled enzymes were quantified on neuronal membrane by two methods: histochemically on neurons in tissue sections from different brain areas, and by Western blot analysis in control and REM sleep-deprived rat brains. The specific enzyme activity was also estimated and found to be increased, as in previous studies. The results confirmed our hypothesis that after REM sleep deprivation, increased Na-K ATPase activity was at least partly due to increased turnover of Na-K ATPase molecules in the rat brain.     

Brain distribution of vasoactive intestinal peptide receptors following REM sleep deprivation

Vasoactive intestinal peptide (VIP) has been shown to increase rapid eye movement (REM) sleep in normal and insomniac animals, while the administration of anti-VIP antibodies or an antagonist of VIP receptors decreases REM sleep. In addition, recently, it has been suggested that a VIP-like substance accumulates in the CSF during waking and that it may be involved in the production of the REM rebound normally seen following REM sleep deprivation. This evidence suggests that VIP may be important in modulating REM sleep in normal conditions and during REM sleep rebound. To determine whether VIP is involved in REM sleep homeostasis, VIP receptors of discrete brain areas was determined by autoradiography after 24 and 72 h of REM sleep deprivation (REM SD) by the water tank technique. Since this procedure has been suggested to produce some stress, an additional group adapted for 7 days to the sleep deprivation situation was tested. The results showed that REM SD produces an increase in the density of VIP receptors in several brainstem and forebrain structures at 24 h of REM SD and more so at 72 h of REM SD. Interestingly, results showed that habituation to the REM SD procedure decreases the density of VIP receptors in some areas of the brain of the REM sleep-deprived rats. The results are discussed in terms of the possibility that waking induces an increase of VIP receptors in several structures, which in turn are responsible for modulating REM sleep, but that stress contributes in part to VIP receptor changes.     

Sleep modulates cortical connectivity and excitability in humans: Direct evidence from neural activity induced by single‐pulse electrical stimulation

Sleep‐induced changes in human brain connectivity/excitability and their physiologic basis remain unclear, especially in the frontal lobe. We investigated sleep‐induced connectivity and excitability changes in 11 patients who underwent chronic implantation of subdural electrodes for epilepsy surgery. Single‐pulse electrical stimuli were directly injected to a part of the cortices, and cortico‐cortical evoked potentials (CCEPs) and CCEP‐related high‐gamma activities (HGA: 100–200 Hz) were recorded from adjacent and remote cortices as proxies of effective connectivity and induced neuronal activity, respectively. HGA power during the initial CCEP component (N1) correlated with the N1 size itself across all states investigated. The degree of cortical connectivity and excitability changed during sleep depending on sleep stage, approximately showing dichotomy of awake vs. non‐rapid eye movement (REM) [NREM] sleep. On the other hand, REM sleep partly had properties of both awake and NREM sleep, placing itself in the intermediate state between them. Compared with the awake state, single‐pulse stimulation especially during NREM sleep induced increased connectivity (N1 size) and neuronal excitability (HGA increase at N1), which was immediately followed by intense inhibition (HGA decrease). The HGA decrease was temporally followed by the N2 peak (the second CCEP component), and then by HGA re‐increase during sleep across all lobes. This HGA rebound or re‐increase of neuronal synchrony was largest in the frontal lobe compared with the other lobes. These properties of sleep‐induced changes of the cortex may be related to unconsciousness during sleep and frequent nocturnal seizures in frontal lobe epilepsy. Hum Brain Mapp, 2015. © 2015 Wiley Periodicals, Inc .     

Blockade of NMDA receptors and nitric oxide synthesis in the dorsolateral periaqueductal gray attenuates behavioral and cellular responses of rats exposed to a live predator

Innate fear stimulus induces activation of neurons containing the neuronal nitric oxide synthase enzyme (nNOS) in defensive‐related brain regions such as the dorsolateral periaqueductal gray (dlPAG). Intra‐dlPAG administration of nitric oxide synthase (NOS) inhibitors and glutamate antagonists induce anxiolytic‐like responses. We investigated the involvement of nitric oxide (NO) and glutamate neurotransmission in defensive reactions modulated by dlPAG. We tested if intra‐dlPAG injections of the selective nNOS inhibitor, N‐propyl‐L ‐arginine (NP), or the glutamate antagonist, AP7 (2‐amino‐7‐phosphonoheptanoic acid), would attenuate behavioral responses and cellular activation induced by predator exposure (cat). Fos‐like immunoreactivity (FLI) was used as a marker of neuronal functional activation, whereas nNOS immunohistochemistry was used to identify NOS neurons. Cat exposure induced fear responses and an increase of FLI in the dlPAG and dorsal premammillary nucleus (PMd). NP and AP7 attenuated the cat‐induced behavioral responses. Whereas NP tended to attenuate FLI in the dlPAG, AP7 induced a significant reduction in cellular activation of this region. The latter drug, however, increased FLI and double‐labeled cells in the PMd. Cellular activation of this region was significantly correlated with time spent near the cat (r = 0.7597 and 0.6057 for FLI and double‐labeled cells). These results suggest that glutamate/NO‐mediated neurotransmission in the dlPAG plays an important role in responses elicit by predator exposure. Blocking these neurotransmitter systems in this brain area impairs defensive responses. The longer time spent near the predator that follows AP7 effect could lead to an increased cellular activation of the PMd, a more rostral brain area that has also been related to defensive responses. © 2009 Wiley‐Liss, Inc.     

Responses of preoptic neurons to stimulation of caudal and rostral brain stem reticular structures

Effect of stimulation (1 Hz) of rostral and caudal brain stem reticular formation was studied on 41 neurons of preoptic area in encéphale isolé cats. Primary excitation was seen on almost all the 25 neurons influenced by stimulation of either of the areas. Many of these influenced neurons received inputs from both areas and showed poststimulatory oscillations in excitability. The two brain stem reticular structures, which have antagonistic influence on cortical EEG, cortical and subcortical neuronal activity, had identical influence on preoptic area neurons when stimulated at 1 Hz.     

Relation of pontine choline acetyltransferase immunoreactive neurons with cells which increase discharge during REM sleep

The purpose of this study was to determine whether neurons in the medial pontine reticular formation with high discharge rates during REM sleep could be localized in regions of the brainstem having neurons displaying choline acetyltransferase immunoreactivity. Six cats were implanted with sleep recording electrodes and microwires to record extracellular potentials of neurons in the pontine reticular formation. Single-units with a S:N ratio greater than 2:1 were recorded for at least two REM sleep cycles. A total of 49 units was recorded from the pontine reticular formation at medial-lateral planes ranging from 0.8 to 3.7 mm. The greatest proportion of the units (28.6%) showed highest discharge during active waking and phasic REM sleep compared to quiet waking, non-REM sleep, transition into REM sleep or quiet REM sleep periods. A percentage (20.4%) of the cells had high discharge associated with phasic REM sleep periods while 8.2% of the cells showed a progressive increase in discharge from waking to REM sleep. Subsequent examination of the distribution of choline acetyltransferase immunoreactive cells in the PRF revealed that cells showing high discharge during REM sleep were not localized near presumed cholinergic neurons. Indeed, we did not find any ChAT immunoreactive somata in the medial PRF, an area which has traditionally been implicated in the generation of REM sleep. These results suggest that while increased discharge of PRF cells may be instrumental to REM sleep generation, these cells are not cholinergic.     

Alterations in the expression of neuronal chloride transporters may contribute to schizophrenia

During brain development, neuronal stem cells and immature neurons express high and low levels of, respectively, the Cl⁻ transporters NKCC1 and KCC2, which results in high intracellular Cl⁻ concentrations. Under these circumstances chloride-flux through the GABA-A channel is from intracellular to extracellular and consequently GABA depolarizes rather than hyperpolarizes immature cells. This excitatory response is essential for neurodevelopment since it affects proliferation of the neuronal progenitor pool, neuronal differentiation, dendrite and synapse formation and integration into the existing neuronal network. In animal experiments, seizures were found to increase NKCC1 expression, lower the KCC2 expression and accelerate neuronal differentiation. An increased expression of NKCC1 and mutations of the gene have been associated with schizophrenia. Stimulation of nicotinic α-7 receptors on mouse hippocampal neurons increases the expression of KCC2. A microdeletion in the genomic area 15q13-14 containing the nicotine α7 receptor has been described in patients with mental retardation, schizophrenia and juvenile epilepsy. It is conceivable that haplotype-insufficiency of the nicotinic α7 receptor might lead to a reduction in KCC2 protein levels. The data indicate that all three schizophrenia risk factors, i.e. seizures, mutations in NKCC1 and nicotinic α-7 receptors haplotype-insufficiency contribute to higher intracellular Cl⁻ concentrations, increased neuronal excitability and accelerated neuronal differentiation. Since also several other genetic risk factors for schizophrenia seem to accelerate neuronal maturation, it is hypothesized that the structural, cognitive and behavioral deficits of schizophrenia are caused be a too fast brain maturation process.     

Cell-Type-Specific Dynamics of Calcium Activity in Cortical Circuits over the Course of Slow-Wave Sleep and Rapid Eye Movement Sleep

Sleep shapes cortical network activity, fostering global homeostatic downregulation of excitability while maintaining or even upregulating excitability in selected networks in a manner that supports memory consolidation. Here, we used two-photon calcium imaging of cortical layer 2/3 neurons in sleeping male mice to examine how these seemingly opposing dynamics are balanced in cortical networks. During slow-wave sleep (SWS) episodes, mean calcium activity of excitatory pyramidal (Pyr) cells decreased. Simultaneously, however, variance in Pyr population calcium activity increased, contradicting the notion of a homogenous downregulation of network activity. Indeed, we identified a subpopulation of Pyr cells distinctly upregulating calcium activity during SWS, which were highly active during sleep spindles known to support mnemonic processing. Rapid eye movement (REM) episodes following SWS were associated with a general downregulation of Pyr cells, including the subpopulation of Pyr cells active during spindles, which persisted into following stages of sleep and wakefulness. Parvalbumin-positive inhibitory interneurons (PV-In) showed an increase in calcium activity during SWS episodes, while activity remained unchanged during REM sleep episodes. This supports the view that downregulation of Pyr calcium activity during SWS results from increased somatic inhibition via PV-In, whereas downregulation during REM sleep is achieved independently of such inhibitory activity. Overall, our findings show that SWS enables upregulation of select cortical circuits (likely those which were involved in mnemonic processing) through a spindle-related process, whereas REM sleep mediates general downregulation, possibly through synaptic re-normalization.SIGNIFICANCE STATEMENT Sleep is thought to globally downregulate cortical excitability and, concurrently, to upregulate synaptic connections in neuron ensembles with newly encoded memory, with upregulation representing a function of sleep spindles. Using in vivo two-photon calcium imaging in combination with surface EEG recordings, we classified cells based on their calcium activity during sleep spindles. Spindle-active pyramidal (Pyr) cells persistently increased calcium activity during slow-wave sleep (SWS) episodes while spindle-inactive cells decreased calcium activity. Subsequent rapid eye movement (REM) sleep episodes profoundly reduced calcium activity in both cell clusters. Results indicate that SWS allows for a spindle-related differential upregulation of ensembles whereas REM sleep functions to globally downregulate networks.     

Immunocytochemical detection of fos protein combined with anterograde tract-tracing using biotinylated dextran

The present report deals with an axonal tract-tracing procedure in rat enabling visualization of anterogradely transported biotinylated dextran amine (BDA) combined with immnunocytochemical detection of Fos protein following electrical stimulation of the brain. This method allows us to evaluate whether a given structure, receiving both injection of BDA and electrical stimulation, elicits neuronal activation in another part of the brain via direct or indirect projections. We have used the method at the light microscopic level to determine the connectivity of the sensorimotor cortex in the rat. In various parts of the forebrain and brainstem, BDA-labeled fibers originating from the cortex were observed in close apposition to Fos-like immunoreactive cells (FLI) activated by stimulation. This result suggests a direct (probably monosynaptic) projection. On the contrary, FLI neurons were observed in areas devoid of direct afferents, indicating a cascade of activations. The method described in this protocol is applicable for functional anatomy purposes elsewhere within the central nervous system. It constitutes a preliminary step in identifying the validity of a pathway before examination of the reality of the monosynaptic relationship at the electron microscopic level.     

Influence of hypnogenic brain areas on wakefulness- and rapid-eye-movement sleep-related neurons in the brainstem of freely moving cats

Rapid-eye-movement (REM) sleep is normally preceded by non-REM sleep; however, every non-REM sleep episode is not followed by REM sleep. It has been proposed that, for the regulation of REM sleep, the brain areas modulating waking and non-REM sleep are likely to communicate with neurons promoting REM sleep. The former has been reported earlier, and in this study the latter has been investigated. Under surgical anaesthesia, cats were prepared for electrophysiological recording of sleep-wakefulness and electrical stimulation of caudal brainstem as well as preopticoanterior hypothalamic hypnogenic areas. Insulated microwires of 25-32 microm were used to record 52 single neuronal activities from the brainstem along with bipolar electroencephalogram, electromyogram, electrooculogram, and pontogeniculooccipital waves in freely moving, normally behaving cats. The neurons were classified into five groups based on changes in firing rates associated with different sleep-waking states compared with quiet wakefulness. Thereafter, the responses of these neurons to 1-Hz stimulation of the two non-REM sleep-promoting areas were studied. At the end of experiment, the stimulating and recording sites were histologically identified. It was observed that, among the affected neurons, the caudal brainstem non-REM sleep-promoting area excited more REM-on neurons, whereas the preopticoanterior hypothalamus hypnogenic area inhibited more awake-active neurons. Thus, the results suggest that, at the single neuronal level, the caudal brainstem non-REM sleep-modulating area, rather than the preopticoanterior hypothalamic hypnogenic area in the brain, plays a modulatory role in triggering REM sleep initiation at a certain depth of sleep.     

Seizure-induced neurogenesis in the adult brain

It is well established that seizures increase adult neurogenesis in the subventricular and subgranular zones, the most neurogenic regions of the adult rodent and apparently human brain. However, the role of increased neurogenesis in these areas in seizure generation (ictogenesis) and epileptogenesis remains elusive. It is of utmost importance to explore how the cells that are born in response to epileptic seizures are functionally integrated into the existing neuronal networks, and how this integration would contribute to the excitability of this network. This will determine whether increased neurogenesis is beneficial or counteractive to ictogenesis and epileptogenesis. Some of the crucial factors affecting the functional integration of newborn cells seem to be excessive neuronal activity and/or inflammatory microenvironment, both associated with acute, as well as chronic, epileptic conditions. This review will focus on aspects of the functional integration of newborn cells in animal models of epilepsy with various degrees of seizure severity and associated microenvironmental alterations in the brain tissue.     

The cholinergic rapid eye movement sleep induction test with RS-86. State or trait marker of depression?

Rapid eye movement (REM) sleep disinhibition at the beginning of the night is one of the most frequently described biologic abnormalities in depression. As REM sleep in animals and humans seems to be facilitated by cholinergic neuronal activity, it has been postulated that REM sleep disinhibition in depression is a consequence of cholinergic neuronal overactivity. The current study with the newly available cholinergic agonist RS-86, which is orally active, has a half-life of six to eight hours, and exhibits only minor peripheral side effects, supports this assumption. The application of this compound before sleep led to a significantly faster induction of REM sleep at the beginning of the night in patients with major depressive disorders compared with healthy subjects and patients with other nondepressive psychiatric diseases, such as eating disorders. Whereas 14 of 16 depressed patients displayed sleep-onset REM periods after the administration of RS-86, this happened only in three of the 16 healthy controls and in one of the 20 patients with other diagnoses. The increased susceptibility of REM sleep to cholinergic stimulation was limited to the state of depression and was not observed in a group of remitted depressed patients.     

Monday July 3, 200612:00–13:30Hall 3DPlatform SessionBasic Science I: Molecules and Networks for Epileptogenesis

¹ M. Kokaia (   ¹ Wallenberg Neuroscience Center, Lund University Hospital, Sweden )
Purpose: Neural stem cells in the adult mammalian brain (including humans) continue to produce new functional granule cells in the dentate gyrus subgranular zone and new olfactory bulb neurons in the subventricular zone during an entire life. In the hippocampus, neurogenesis has been proposed to play a role in learning and memory and mood regulation. The new cells develop electrophysiological characteristics and synaptic inputs very similar to those of the rest of the cell population. The purpose of the study was to explore whether tissue environment in an epileptic brain influences properties of afferent synapses formed on newborn granule cells.
Method: Rats were exposed to either a physiological stimulus, i.e., running, or status epilepticus, which gives rise to neuronal death, inflammation, increased network excitability and recurrent spontaneous seizures. Both treatments increase neurogenesis in the dentate gyrus. We labelled newborn cells by GFP-retroviral vector injections right after these treatments to identify the cells and apply whole-cell patch-clamp recordings in live hippocampal slices.
Results: Granule cells formed after running and status epilepticus exhibited similar intrinsic membrane properties. However, new neurons born into the epileptic environment differed with respect to tonic drive and short-term plasticity of both excitatory and inhibitory afferent synapses. The new granule cells formed after status epilepticus exhibited functional connectivity consistent with reduced synaptic network excitability of the dentate gyrus, i.e., decreased excitatory and increased inhibitory input activity.
Conclusion: We demonstrate for the first time a high degree of plasticity in synaptic inputs to the new neurons, which could mitigate pathological activity in the epileptic brain.