Alterations of inhibitory synaptic responses in the dentate gyrus of temporal lobe epileptic patients

The number of orthodromically evoked population spikes was used to classify brain slice tissue from the dentate gyrus of temporal lobe epileptic patients as “more excitable” (multiple population spikes) or “less excitable” (a single population spike). During orthodromic stimulation, “more excitable” tissue exhibited less paired-pulse depression in comparison to “less excitable” tissue. During antidromic stimulaltion, both multiple population spikes and paired-pulse depression were observed in “more excitable” tissue. “Less excitable” tissue exhibited a single antidromic spike and often on antidromically evoked paired-pulse depression. The strength of antidromic paired-pulse depression was correlated positively with the number of antidromic spikes and was correlated negatively with orthodromic paired-pulse depression. Although orthodromic and antidromic paired-pulse depression were correlated to the number of orthodromically evoked populaltion spikes, this correlation was not as strong as that between orthodromic paired-pulse depression, antidromic paired-pulse depression, and number of antidromically evoked population spikes. The antidromic paired-pulse depression observed in tissue exhibiting antidromically evoked multiple population spikes was enhanced rather than blocked by bicuculline. In addition, the blockade of the antidromic paired-pulse depression by CNQX indicated that this inhibition is mediated by an AMPA-type glutamatergic synapse. We suggest that alterations in circuitry occur in the dentate gyrus of some temporal lobe epileptic patients and were manifested by both a loss of inhibitory input as well as an increase of inhibition, which was dependent on the pathway of stimulaltion. The results of pairing antidromic and orthodromic stimuli were consistent with these conclusions. © 1994 Wiley-Liss, Inc.     

Evidence for NMDA receptor involvement in environmentally induced dentate gyrus plasticity.

Research has demonstrated environmentally induced plasticity of hippocampal dentate gyrus-evoked potentials. Other research has shown a role of the NMDA receptor in dentate gyrus long-term potentiation (LTP). The authors tested the role of the NMDA receptor in one form of environmentally induced plasticity, in which transferring animals from their home cages to another environment results in significant excitatory postsynaptic potential (EPSP) enhancement and concomitant depression of the population spike. Rats were chronically implanted with stimulating electrodes in the perforant path and recording electrodes in the dentate gyrus bilaterally. Evoked potentials were recorded from freely behaving rats for four 20-minute sessions (1/wk), which took place immediately following an environmental transfer. Rats received 0.00, 0.05, 0.08, or 0.10 mg/kg MK-801 s.c. 30 minutes prior to recording sessions in either an ascending- or descending-dose series. Results showed that MK-801 produced a reduction of the EPSP enhancement, which takes place over the 20-minute session. The effects of MK-801 on spike depression varied as a function of dose series and time within a session, suggesting a long-term effect of MK-801 on spike depression. There was no detected effect of MK-801 on behavior. Results suggest a role of the NMDA receptor in this form of environmentally induced plasticity with different effects of NMDA receptor antagonism on EPSP enhancement and spike depression.     

Long-lasting potentiation and epileptiform activity produced by GABAB receptor activation in the dentate gyrus of rat hippocampal slice

Bath application of the GABAB receptor agonist baclofen produced a concentration-dependent long-lasting potentiation (LLP) of the evoked population spike in the dentate gyrus of rat hippocampal slices. A high concentration of baclofen (5 microM) also produced a loss of inhibition that was manifested as the appearance of epileptiform, multiple evoked population spikes and a decrease in paired-pulse inhibition. Both baclofen-induced potentiation and epileptiform activity could be blocked or significantly reduced in slices from pertussis toxin-treated animals (1 microgram, intradentate) or in slices pretreated with the NMDA receptor antagonist D-(-)-2-amino-5-phosphonovaleric acid (10 microM). At a concentration that had no significant effect on individual evoked responses (0.1 microM) but still produced a loss in paired-pulse inhibition, baclofen facilitated the induction of beta-adrenergic receptor-mediated LLP. LLP was induced in the dentate gyrus by bath application of 1 microM, but not 0.1 microM, isoproterenol. Coapplication of baclofen and isoproterenol, both at a concentration (0.1 microM) that individually had no effect on the population spike, produced a synergistic LLP of the population spike. We propose that baclofen produces a selective disinhibitory effect in the granule cell layer of the dentate gyrus by inhibiting the activity of GABAergic interneurons. At a low concentration, the subtle loss of inhibition can facilitate the induction of isoproterenol-induced LLP. At a high concentration, baclofen can produce an LLP that is probably induced by a loss of inhibition.     

NMDA receptor activation induces glutamate release through nitric oxide synthesis in guinea pig dentate gyrus

We tested the hypothesis that the release of glutamate following activation of N-methyl-d-aspartate (NMDA) receptors is mediated by nitric oxide (NO) production, using slices of the guinea pig hippocampus. The NMDA-induced glutamate release from slices of dentate gyrus or CA1, which was both concentration-dependent and Ca²⁺-dependent, was also Mg²⁺-sensitive and abolished by MK-801, a selective non-competitive NMDA receptor antagonist. In dentate gyrus, the NMDA-induced glutamate release was inhibited non-significantly by tetrodotoxin, whereas the NO synthase (NOS) inhibitor N^G-nitro-l-arginine (l-NNA) blocked the NMDA-induced release of glutamate in a concentration-dependent manner, but not a high K⁺-evoked release of glutamate. In addition, the l-NNA blockade of NMDA-induced release of glutamate was recovered by pretreatment with l-arginine, the normal substrate for NOS. These results suggest that activation of NMDA receptors in dentate gyrus, as well as subsequent Ca²⁺ fluxes, is required for the neuronal glutamate release mediated by NO production. On the other hand, the NMDA-evoked glutamate release from CA1 region was tetrodotoxin-sensitive and was not inhibited by l-NNA, thereby suggesting that activation of NMDA receptors in CA1 results in increased glutamate release in an NO-independent manner. Taken together, the NMDA receptor-mediated neuronal release of glutamate from the guinea pig dentate gyrus likely involves the recruitment of NOS activity.     

Somatostatin receptor type 2 undergoes plastic changes in the human epileptic dentate gyrus

Temporal lobe epilepsy (TLE) is characterized by hippocampal sclerosis together with profound losses and phenotypic changes of different classes of interneurons, including those expressing somatostatin (SRIF). To understand the functional significance of the plasticity of SRIF transmission in TLE, unraveling the status of SRIF receptors is, however, a prerequisite. To address this issue, we characterized expression and distribution of the major SRIF receptor, the sst2 subtype, in hippocampal tissue resected in patients with TLE using complementary neuroanatomic approaches. In patients with hippocampal sclerosis, the number of cells expressing sst2 receptor mRNA as well as sst2 receptor-binding sites and immunoreactivity decreased significantly in the CA1-3, reflecting neuronal loss. By contrast, in the dentate gyrus, sst2 receptor mRNA expression was strongly increased in the granule cell layer, and sst2 receptor-binding sites and immunoreactivity was preserved in the inner but decreased significantly in the outer molecular layer. In this latter region, pronounced changes in SRIF terminal fields were observed. Decreased receptor density in the distal dendrites of granule cells is likely to reflect downregulation of sst2 receptors in response to physiopathologic release of SRIF. Because sst2 receptors have anticonvulsant and antiepileptogenic properties, this phenomenon may contribute to the etiology of TLE seizures.     

Contribution of NMDA receptor channels to the expression of LTP in the hippocampal dentate gyrus

The role of glutamatergic NMDA receptor channels (NMDARs) in the induction of long-term potentiation (LTP) has been well established. In contrast, whether or not NMDARs contribute to the expression of LTP has been an issue of debate. In this study, we investigated the contribution of NMDARs to LTP expression in the hippocampal dentate gyrus (DG) by stimulating perforant path afferents with short bursts of pulses delivered at a moderate frequency (40 Hz), instead of using the traditional protocol of a single stimulus at a low frequency (<0.1 Hz). The synaptic summation provided by the "burst" protocol enabled us to measure the NMDAR-mediated component of synaptic responses (NMDA component), defined as the NMDAR antagonist D-2-amino-5-phosphonovalerate (APV2+)-sensitive component, in the presence of physiological concentrations of Mg (1 mM). Intracellular recordings were obtained from DG granule cells of rabbit hippocampal slices, and excitatory postsynaptic potentials (EPSPs) were measured in terms of the integrated area of their profiles. At 40 Hz, frequency facilitation of the evoked EPSPs was observed. The NMDA component gradually increased during the five-pulse train and frequency facilitation was significantly reduced after the application of APV. We tested the hypothesis that NMDARs undergo potentiation in LTP by comparing the NMDA/non-NMDA ratio of the synaptic responses in control and LTP groups. An increase in the ratio was observed in the LTP group, strongly suggesting potentiation of NMDARs. To infer changes in conductance at individual synapses based on EPSPs recorded at the soma, we constructed a compartmental model of a morphologically reconstructed DG granule cell. The effect on the NMDA/non-NMDA ratio of changes in AMPA and NMDA component synaptic conductance, and of differences in the distribution of activated synapses, was studied with computer simulations. The results confirmed that NMDARs are potentiated after the induction of LTP and contribute significantly to the expression of potentiation under physiological conditions.     

Differential alteration of NMDA receptor subunits in the gerbil dentate gyrus and subiculum following seizure

In the present study, a chronological and comparative analysis of the immunoreactivities of N-methyl-D-aspartate (NMDA) receptor subunits in hippocampus of both seizure resistant (SR) and seizure sensitive (SS) gerbils was made in order to clarify the temporal and spatial alterations of NMDA receptor subunit expressions in the hippocampus complex. The changes in NMDA receptor immunoreactivity in the hippocampi of SS gerbils were restricted to both the dentate gyrus and the subiculum. At 30 min postictal, a decline in NMDA receptor subunit 1 (NR1) immunoreactivity in the suprablade of dentate gyrus was observed. This is in contrast to the enhancement of its immunodensity in the infrablade. At 3 h postictal the NR1 immunoreactivity in the infrablade also declined significantly. At 12 h postictal, its immunoreactivity in the hilar neurons was reduced. The NMDA receptor subunit 2A/B (NR2A/B) immunoreactivity did not alter until 12 h following seizure-onset, when it was slightly decreased in the granule cells and hilar neurons. In the subiculum, NR1 immunoreactivity was significantly decreased, and was almost undetectable in this region until 12 h postictal; in contrast the NR2A/B immunoreactivity in this region increased significantly in this time point. These results suggest that the altering NMDA receptor expression in both the dentate gyrus and subiculum may affect tissue excitability and have an important role in regulating seizure activity in SS gerbils.     

Microglia engulf viable newborn cells in the epileptic dentate gyrus

Microglia, which are the brain's resident immune cells, engulf dead neural progenitor cells during adult neurogenesis in the subgranular zone (SGZ) of the dentate gyrus (DG). The number of newborn cells in the SGZ increases significantly after status epilepticus (SE), but whether and how microglia regulate the number of newborn cells after SE remain unclear. Here, we show that microglia rapidly eliminate newborn cells after SE by primary phagocytosis, a process by which viable cells are engulfed, thereby regulating the number of newborn cells that are incorporated into the DG. The number of newborn cells in the DG was increased at 5 days after SE in the adult mouse brain but rapidly decreased to the control levels within a week. During this period, microglia in the DG were highly active and engulfed newborn cells. We found that the majority of engulfed newborn cells were caspase‐negative viable cells. Finally, inactivation of microglia with minocycline maintained the increase in the number of newborn cells after SE. Furthermore, minocycline treatment after SE induced the emergence of hilar ectopic granule cells. Thus, our findings suggest that microglia may contribute to homeostasis of the dentate neurogenic niche by eliminating excess newborn cells after SE via primary phagocytosis. GLIA 2016;64:1508–1517     

NMDA receptor antagonists block norepinephrine-induced long-lasting potentiation and long-term potentiation in rat dentate gyrus

In the in vitro rat dentate gyrus, norepinephrine-induced long-lasting potentiation (NELLP) and long-term potentiation (LTP) of responses to perforant path stimulation were blocked by the N-methyl-D-aspartate (NMDA) receptor antagonists, D(-)-2-amino-5-phosphonovaleric acid (D(-)APV) and 3-[(+/-)-2-carboxypiperazin-4-yl]propyl-1-phosphonic acid (CPP). CPP and D(-)APV, but not L(+)APV, also depressed the orthodromic population spike but not the antidromic spike, which suggests that these receptors may function in low-frequency evoked activity of granule cells. We conclude that NELLP, like LTP in the dentate gyrus, requires NMDA receptor activation.     

Osmolality and nonsynaptic epileptiform bursts in rat CA1 and dentate gyrus.

In several clinical situations, such as hyposmolar states and hypoxia-ischemia, reductions in the size of the extracellular space are associated with increased seizure susceptibility. Nonsynaptic interactions provide a likely means of mediating the effect of extracellular space on seizure susceptibility. Synchronous bursting of CA1 hippocampal neurons occurs via nonsynaptic mechanisms in solutions containing very low [Ca2+] and excitatory amino acid antagonists. We tested the hypothesis that lowering the osmolality of the extracellular medium could induce nonsynaptic bursting in the dentate gyrus, even though it is normally resistant to this treatment. Extracellular field potentials were recorded in the dentate gyrus and CA1 area of rat hippocampal slices. In the low-[Ca2+] solution with normal osmolality, bursts of population spikes were recorded from the dentate gyrus in only 7% of the slices, but solutions with decreased osmolality induced bursting in 63%. Corresponding values for the CA1 area were 60 and 73%, respectively. Mannitol, which reversed the hyposmolar state, abolished bursting in both regions. This study demonstrates that reducing the size of the extracellular space by lowering extracellular osmolality can transform a seizure-resistant area into one that exhibits robust epileptiform activity.     

Effects of bicuculline and baclofen on paired-pulse depression in the dentate gyrus of epileptic patients

Paired-pulse field responses were recorded from the granule cell layer of the dentate gyrus in brain slices from temporal lobe epileptic patients. Paired-pulse depression (PPD) was examined using perforant path stimulation of low to moderate intensity at an inter-stimulus interval (ISI) of 20 ms. The paired-pulse ratio (PS₂/PS₁) was expressed as the population spike amplitude of the second response (PS₂) relative to that of the first response (PS₁). Representative tissue responses from each patient biopsy were divided into two groups that were significantly different based on the magnitude of the highest paired-pulse ratio recorded for each biopsy specimen: the strong paired-pulse depression group (PS₂/PS₁ = 0.12 ± 0.03; n = 15) and the weak paired-pulse depression group (PS₂/PS₁ = 0.68 ± 0.06; n = 13). Paired-pulse ratios from the strong PPD group were relatively independent of stimulus intensity, whereas, PPD was dependent on stimulus intensity in the weak PPD group; i.e., PPD was greatest at the lowest intensity and reached a plateau at higher intensities. Bicuculline (20 μM) and low concentrations of baclofen (0.1–0.2 μM) reduced paired-pulse depression in the strong PPD group, but did not significantly change the paired-pulse ratio in the weak PPD group. Paired-pulse facilitation was observed in some cases after inhibition was blocked pharmacologically. The number of population spikes was increased in the presence of bicuculline but was unchanged by baclofen. In the strong PPD group, baclofen significantly altered the EPSP-population spike (E-S) relationship by increasing the slope of the relationship for the second response, without having an effect on the slope of the first response. Baclofen had no effect on the E-S relationship of either response in the weak PPD group. The data are consistent with (1) less inhibition in the weak PPD group compared to the strong PPD group, (2) reduction of feedback inhibition in the strong PPD group by bicuculline and by low concentrations of baclofen, and (3) the occurrence of paired-pulse facilitation when inhibition was pharmacologically reduced in the dentate gyrus of temporal lobe epileptic patients. The results are also consistent with the presence of GABA_B receptors on human inhibitory interneurons that, when activated by baclofen, result in disinhibition of granule cells through feedback circuits. Although inhibition may be compromised in some epileptic human biopsy specimens, the presence of strong inhibition in other patients' biopsy material suggests the re-evaluation of the role of inhibition in epilepsy.     

The functional relationship between antidromically evoked field responses of the dentate gyrus and mossy fiber reorganization in temporal lobe epileptic patients

Field recordings from the dentate granule cell layer of in vitro brain slices of temporal lobe epileptic patients were evoked by antidromic stimulation. Tissue from the same specimen was stained by the Timm-sulfide method to assess the pattern and degree of mossy fiber reorganization into the supragranular layer. A wide range of physiological responses and Timm staining patterns was present across patients. A significant correlation was observed between the abnormality of antidromic responses, reflected by multiple secondary population spikes, and the degree of Timm staining of the supragranular layer. This relationship lends support to the hypothesis that mossy fiber synapses located in the supragranular layer may have functional implications for granule cell excitability in human epileptic tissue.     

Feed-forward and feed-back activation of the dentate gyrus in vivo during dentate spikes and sharp wave bursts

Intermittently occurring field events, dentate spikes (DS), and sharp waves (SPW) in the hippocampus reflect population synchrony of principal cells and interneurons along the entorhinal cortex-hippocampus axis. We have investigated the cellular-synaptic generation of DSs and SPWs by intracellular recording from granule cells, pyramidal cells, and interneurons in anesthetized rats. The recorded neurons were anatomically identified by intracellular injection of biocytin. Extracellular recording electrodes were placed in the hilus to record field DSs and multiple units and in the CA1 pyramidal cell layer to monitor SPW-associated fast field oscillations (ripples) and unit activity. DSs were associated with large depolarizing potentials in granule cells, but they rarely discharged action potentials. When they were depolarized slightly with intracellular current injection, bursts of action potentials occurred concurrently with extracellularly recorded DSs. Two interneurons in the hilar region were also found to discharge preferentially with DSs. In contrast, CA1 pyramidal cells, recorded extracellularly and intracellularly, were suppressed during DSs. In association with field SPWs, extracellular recordings from the CA1 pyramidal layer and the hilar region revealed synchronous bursting of these cell populations. Intracellular recordings from CA3 and CA1 pyramidal cells, granule cells, and from a single CA3 region interneuron revealed SPW-concurrent depolarizing potentials and action potentials. These findings suggest that granule cells may be discharged anterogradely by entorhinal input or retrogradely by the CA3-mossy cell feedback pathway during DSs and SPWs, respectively. Although both of these intermittent population patterns can activate granule cells, the impact of DSs and SPWs is diametrically opposite on the rest of the hippocampal circuitry. Entorhinal cortex activation of the granule cells during DSs induces a transient decrease in the hippocampal output, whereas during SPW bursts every principal cell population of the hippocampal formation may be recruited into the population event. Hippocampus 7:437–450, 1997. © 1997 Wiley-Liss, Inc.     

NMDA receptor antagonists block the induction of long-term depression in the hippocampal dentate gyrus of the anesthetized rat

The present study tested the effect of two non-competitive NMDA receptor antagonists, ketamine and phencyclidine, on the induction of long-term depression (LTD) in the dentate gyrus of urethane-anesthetized rats. Both drugs blocked the induction of LTD as well as long-term potentiation (LTP). NMDA receptor activation thus seems to be required for the induction of both LTD and LTP in the dentate gyrus. High-intensity conditioning stimulation did not overcome the phencyclidine block of LTD. Strong, but brief, postsynaptic depolarization is apparently not the only event needed to trigger LTD.     

Running increases neurogenesis without retinoic acid receptor activation in the adult mouse dentate gyrus

Both vitamin A deficiency and high doses of retinoids can result in learning and memory impairments, depression as well as decreases in cell proliferation, neurogenesis and cell survival. Physical activity enhances hippocampal neurogenesis and can also exert an antidepressant effect. Here we elucidate a putative link between running, retinoid signaling, and neurogenesis in hippocampus. Adult transgenic reporter mice designed to detect ligand-activated retinoic acid receptors (RAR) or retinoid X receptors (RXR) were used to localize the distribution of activated RAR or RXR at the single-cell level in the brain. Two months of voluntary wheel-running induced an increase in hippocampal neurogenesis as indicated by an almost two-fold increase in doublecortin-immunoreactive cells. Running activity was correlated with neurogenesis. Under basal conditions a distinct pattern of RAR-activated cells was detected in the granule cell layer of the dentate gyrus (DG), thalamus, and cerebral cortex layers 3-4 and to a lesser extent in hippocampal pyramidal cell layers CA1-CA3. Running did not change the number of RAR-activated cells in the DG. There was no correlation between running and RAR activation or between RAR activation and neurogenesis in the DG of hippocampus. Only a few scattered activated retinoid X receptors were found in the DG under basal conditions and after wheel-running, but RXR was detected in other areas such as in the hilus region of hippocampus and in layer VI of cortex cerebri. RAR agonists affect mood in humans and reduce neurogenesis, learning and memory in animal models. In our study, long-term running increased neurogenesis but did not alter RAR ligand activation in the DG in individually housed mice. Thus, our data suggest that the effects of exercise on neurogenesis and other plasticity changes in the hippocampal formation are mediated by mechanisms that do not involve retinoid receptor activation.     

Effects of exercise on NMDA receptor subunit contributions to bidirectional synaptic plasticity in the mouse dentate gyrus

We examined synaptic plasticity in the dentate gyrus (DG) of the hippocampus in vitro in juvenile C57Bl6 mice (28-40 days of age), housed in control conditions with minimal enrichment (Controls) or with access to an exercise wheel (Runners). LTP expression was significantly greater in slices from Runners than in those from Controls, but could be blocked by APV in both groups. LTP was significantly reduced by NR2B subunit antagonists in both groups. NVP-AAM077, an antagonist with a higher preference for NR2A subunits over NR2B subunits, blocked LTP in slices from Runners and produced a slight depression in Control animals. LTD in the DG was also blocked by APV, but not by either of the NR2B specific antagonists. Strikingly, NVP-AAM077 prevented LTD in Runners, but not in Control animals, suggesting an increased involvement of NR2A subunits in LTD in animals that exercise. NVP-AAM077 did not block LTD in NR2A Knock Out (KO) animals that exercised, as expected. In an attempt to discern whether NMDA receptors located at extrasynaptic sites could play a role in the induction of LTD, DL-TBOA was used to block excitatory amino acid transport and increase extracellular glutamate levels. Under these conditions, LTD was not blocked by the co-application of a specific NR2B subunit antagonist in either group, but NVP-AAM077 again blocked LTD selectively in Runners. These results indicate that NR2A and NR2B subunits play a significant role in LTP in the DG, and that exercise can significantly alter the contribution of NMDA NR2A subunits to LTD.     

Structural and functional asymmetry in the normal and epileptic rat dentate gyrus

The rat dentate gyrus is usually described as relatively homogeneous. Here, we present anatomic and physiological data which demonstrate that there are striking differences between the supra- and infrapyramidal blades after status epilepticus and recurrent seizures. These differences appear to be an accentuation of a subtle asymmetry present in normal rats. In both pilocarpine and kainic acid models, there was greater mossy fiber sprouting in the infrapyramidal blade. This occurred primarily in the middle third of the hippocampus. Asymmetric sprouting was evident both with Timm stain as well as antisera to brain-derived neurotrophic factor (BDNF) or neuropeptide Y (NPY). In addition, surviving NPY-immunoreactive hilar neurons were distributed preferentially in the suprapyramidal region of the hilus. Extracellular recordings from infrapyramidal sites in hippocampal slices of pilocarpine-treated rats showed larger population spikes and weaker paired-pulse inhibition in response to perforant path stimulation relative to suprapyramidal recordings. A single stimulus could evoke burst discharges in infrapyramidal granule cells but not suprapyramidal blade neurons. BDNF exposure led to spontaneous epileptiform discharges that were larger in amplitude and longer lasting in the infrapyramidal blade. Stimulation of the infrapyramidal molecular layer evoked larger responses in area CA3 than suprapyramidal stimulation. In slices from the temporal pole, in which anatomic evidence of asymmetry waned, there was little evidence of physiological asymmetry either. Of interest, some normal rats also showed signs of greater evoked responses in the infrapyramidal blade, and this could be detected with both microelectrode recording and optical imaging techniques. Although there were no signs of hyperexcitability in normal rats, the data suggest that there is some asymmetry in the normal dentate gyrus and this asymmetry is enhanced by seizures. Taken together, the results suggest that supra- and infrapyramidal blades of the dentate gyrus could have different circuit functions and that the infrapyramidal blade may play a greater role in activating the hippocampus.     

Deficit of Kcnma1 mRNA expression in the dentate gyrus of epileptic rats

Epileptogenesis in mesial temporal lobe epilepsy is determined by several factors including abnormalities in the expression and function of ion channels. Here, we report a long-lasting deficit in gene expression of Kcnma1 coding for the large-conductance calcium-activated potassium (BK, MaxiK) channel alpha-subunits after pilocarpine-induced status epilepticus. By using comparative real-time PCR, Taqman gene expression assays, and the delta-delta comparative threshold method we detected a significant reduction in Kcnma1 expression in microdissected dentate gyrus at different intervals after status epilepticus (24 h, 10 days, 1 month, and more than 2 months). BK channels are key regulators of neuronal excitability and transmitter release. Hence, defective Kcnma1 expression may play a critical role in the pathogenesis of mesial temporal lobe epilepsy.