Adenosine suppresses GABAA receptor-mediated responses in rat sacral dorsal commissural neurons

The modulatory effect of adenosine on gamma-aminobutyric acid (GABA)-activated whole-cell currents were investigated in the neurons acutely dissociated from the rat sacral dorsal commissural nucleus (SDCN) using the nystatin perforated patch recording configuration under the voltage-clamp conditions. The results showed that: (1) GABA acted on GABAA receptor and elicited inward Cl- currents (IGABA) at a holding potential (VH) of -40 mV; (2) adenosine suppressed GABA-induced Cl- current without affecting the reversal potential of IGABA and the apparent affinity of GABA to its receptor; (3) N6-cyclohexyladenosine mimicked the suppression effect of adenosine on IGABA, whereas 8-cyclopentyl-1,3-dipropylxanthine blocked the suppression effect of adenosine; (4) adenosine fails to suppress IGABA on the neurons that were pretreated with bisindolylmaleimide I (BIM), while after pretreatment with H-89, the inhibitory effect of adenosine on IGABA were not affected; (5) the suppression effect of adenosine on IGABA remained in the presence of BAPTA-AM. The present results indicate that the suppression of adenosine on IGABA is mediated by adenosine A1 receptor and through a Ca2+-independent protein kinase C transduction pathway, and that the interactions between adenosine and GABA might participate in the modulation of nociceptive information transmission at the SDCN.     

Adenosine modulation of amino acid release in rat hippocampus during ischemia and veratridine depolarization

This study was undertaken to determine whether endogenous adenosine modulates ‘in vivo’ neurotransmitter amino acid release via its presynaptic receptors. Two conditions were compared: neuronal depolarization by local infusion of veratridine (600 μM), and transient global ischemia by four-vessel occlusion. Both stimuli were applied for 20 min. Extracellular amino acid (glutamate, taurine/GABA, glycine) variations in concentration were determined in the rat hippocampus by microdialysis and HPLC. Modulation of adenosine receptor activity was objectified by continuous local infusion of an adenosine agonist (R-phenylisopropyladenosine R-PIA) or an antagonist (theophylline), starting one hour before stimulation of amino acid release. R-PIA (100 μM) significantly decreased the glutamate release (50%) evoked by veratridine, whereas it did not significantly modify the ischemia-induced glutamate release. In contrast, theophylline did not significantly affect veratridine-induced glutamate release, but it significantly potentiated glutamate efflux (400%) under ischemic conditions. Neither treatment altered the release of the other amino acids. These data suggest that endogenous adenosine appearing in the extracellular space during veratridine-induced depolarization cannot control glutamate release. In contrast, ischemia-induced glutamate release was strongly inhibited by the concomitant increase in extracellular adenosine.     

Spatiotemporal specificity of GABAA receptor-mediated regulation of adult hippocampal neurogenesis

GABAergic transmission regulates adult neurogenesis by exerting negative feedback on cell proliferation and enabling dendrite formation and outgrowth. Further, GABAergic synapses target differentiating dentate gyrus granule cells prior to formation of glutamatergic connections. GABA(A) receptors (GABA(A) Rs) mediating tonic (extrasynaptic) and phasic (synaptic) transmission are molecularly and functionally distinct, but their specific role in regulating adult neurogenesis is unknown. Using global and single-cell targeted gene deletion of subunits contributing to the assembly of GABA(A) Rs mediating tonic (α4, δ) or phasic (α2) GABAergic transmission, we demonstrate here in the dentate gyrus of adult mice that GABA(A) Rs containing α4, but not δ, subunits mediate GABAergic effects on cell proliferation, initial migration and early dendritic development. In contrast, α2-GABA(A) Rs cell-autonomously signal to control positioning of newborn neurons and regulate late maturation of their dendritic tree. In particular, we observed pruning of distal dendrites in immature granule cells lacking the α2 subunit. This alteration could be prevented by pharmacological inhibition of thrombospondin signaling with chronic gabapentin treatment, shown previously to reduce glutamatergic synaptogenesis. These observations point to homeostatic regulation of inhibitory and excitatory inputs onto newborn granule cells under the control of α2-GABA(A) Rs. Taken together, the availability of distinct GABA(A) R subtypes provides a molecular mechanism endowing spatiotemporal specificity to GABAergic control of neuronal maturation in adult brain.     

Calcium-induced calcium release in rod photoreceptor terminals boosts synaptic transmission during maintained depolarization

We examined the contribution of calcium-induced calcium release (CICR) to synaptic transmission from rod photoreceptor terminals. Whole-cell recording and confocal calcium imaging experiments were conducted on rods with intact synaptic terminals in a retinal slice preparation from salamander. Low concentrations of ryanodine stimulated calcium increases in rod terminals, consistent with the presence of ryanodine receptors. Application of strong depolarizing steps (-70 to -10 mV) exceeding 200 ms or longer in duration evoked a wave of calcium that spread across the synaptic terminals of voltage-clamped rods. This secondary calcium increase was blocked by high concentrations of ryanodine, indicating it was due to CICR. Ryanodine (50 microm) had no significant effect on rod calcium current (I(ca)) although it slightly diminished rod light-evoked voltage responses. Bath application of 50 microm ryanodine strongly inhibited light-evoked currents in horizontal cells. Whether applied extracellularly or delivered into the rod cell through the patch pipette, ryanodine (50 microm) also inhibited excitatory post-synaptic currents (EPSCs) evoked in horizontal cells by depolarizing steps applied to rods. Ryanodine caused a preferential reduction in the later portions of EPSCs evoked by depolarizing steps of 200 ms or longer. These results indicate that CICR enhances calcium increases in rod terminals evoked by sustained depolarization, which in turn acts to boost synaptic exocytosis from rods.     

Adenosine A1 receptor-mediated inhibition of dopamine release from rat striatal slices is modulated by D1 dopamine receptors

Dopamine release is regulated by presynaptic dopamine receptors and interactions between adenosine and dopamine receptors have been well documented. In the present study, dopamine release from isolated striatal slices from Wistar rats was measured using fast cyclic voltammetry. Single-pulse stimulation (0.1 ms, 10 V) was applied every 5 min over a 2-h period. Superfusion with the adenosine (A)(1) receptor agonist N(6)-cyclopentyladenosine (CPA), but not the A(2) receptor agonist 3-[4-[2-[[6-amino-9-[(2R,3R,4S,5S)-5-(ethylcarbamoyl)-3,4-dihydroxy-oxolan-2-yl]purin-2-yl]amino]ethyl] phenyl]propanoic acid (CGS 21680), inhibited dopamine release in a concentration-dependent manner (IC(50) 3.80 x 10(-7) m; n = 10). The dose-response curve to CPA was shifted to the right (IC(50) 6.57 x 10(-6) m; n = 6, P < 0.05 vs. control) by the A(1) receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX). Neither the D(1) agonist 6-chloro-APB nor the D(1) antagonist R-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3- benzazepine-7-ol (SCH 23390) altered dopamine release on their own. However, SCH 23390 (3 microm) significantly attenuated the response to CPA (IC(50) 1.44 x 10(-5) m; n = 6, P < 0.01 vs. control). Furthermore, the inhibitory effect of CPA was significantly increased in the presence of 6-chloro-APB (1 microm). In radioligand binding experiments, CPA interacted with high- and low-affinity states of [(3)H]DPCPX-lableled A(1) receptors. The high-affinity agonist binding to A(1) receptors was inhibited by the stable guanosine triphosphate analogue Gpp(NH)p. In contrast, neither the proportion nor the affinity of high-affinity A(1) receptors was altered by dopamine or SCH 23390. These results provide evidence that the inhibition of dopamine release by adenosine A(1) receptors is dependent, at least in part, on the simultaneous activation of D(1) dopamine receptors. While the mechanism underlying this interaction remains to be determined, it does not appear to involve an intramembrane interaction between A(1) and D(1) receptors.     

Ictal epileptiform activity is facilitated by hippocampal GABAA receptor-mediated oscillations.

The cellular and network mechanisms of the transition of brief interictal discharges to prolonged seizures are a crucial issue in epilepsy. Here we used hippocampal slices exposed to ACSF containing 0 Mg(2+) to explore mechanisms for the transition to prolonged (3-42 sec) seizure-like ("ictal") discharges. Epileptiform activity, evoked by Shaffer collateral stimulation, triggered prolonged bursts in CA1, in 50-60% of slices, from both adult and young (postnatal day 13-21) rats. In these cases the first component of the CA1 epileptiform burst was followed by a train of population spikes at frequencies in the gamma band and above (30-120 Hz, reminiscent of tetanically evoked gamma oscillations). The gamma burst in turn could be followed by slower repetitive "tertiary" bursts. Intracellular recordings from CA1 during the gamma phase revealed long depolarizations, action potentials rising from brief apparent hyperpolarizations, and a drop of input resistance. The CA1 gamma rhythm was completely blocked by bicuculline (10-50 microm), by ethoxyzolamide (100 microm), and strongly attenuated in hyperosmolar perfusate (50 mm sucrose). Subsequent tertiary bursts were also blocked by bicuculline, ethoxyzolamide, and in hyperosmolar perfusate. In all these cases intracellular recordings from CA3 revealed only short depolarizations. We conclude that under epileptogenic conditions, gamma band oscillations arise from GABA(A)ergic depolarizations and that this activity may lead to the generation of ictal discharges.     

Phenytoin reduces early acetylcholine release after depolarization

Phenytoin 10 μM inhibits the K-evoked release of acetylcholine (ACh) from synaptosomes, a process which is biphasic. Phenytoin acts only on the early phase of release. Replacement of external Na with Li does not modify phenytoin's effect. Phenytoin augments the spontaneous release of ACh from resting synaptosomes but this effect is eliminated in Li media. It is likely that phenytoin reduces K-evoked Ca uptake and the Na/Ca exchange by separate mechanisms.     

Adenosine release upon spinal cord injury

The hypothesis that release of adenosine following spinal cord injury (SCI) may provide neuroprotective feedback is explored. Consistent with this hypothesis, substantial release of adenosine, estimated to reach 100 microM in the extracellular space, was detected by microdialysis sampling immediately following contusion SCI. There is also considerable release of excitatory amino acids following SCI. The latter was not affected by administration of the general adenosine receptor antagonist theophylline and the A1 antagonist 8-cyclopentyl-1,3-dipropylxanthine, implying that the adenosine released following SCI does not significantly influence the release of neurotoxic amino acids. Administration of the concentration of glutamate released upon SCI into the spinal cord caused only about 1% as much release of adenosine as did injury, evidence that elevated excitatory amino acids do not elicit an appreciable fraction of the release of adenosine that follows SCI. Results obtained suggest that release of endogenous adenosine is not neuroprotective by blocking release of excitatory amino acids following SCI.     

Interleukin-6 attenuates hyperthermia-induced seizures in developing rats

Previous studies indicated that several cytokines influenced the seizure propensity in convulsive disorders and were the cause of encephalopathies in childhood. We studied the role of one inflammatory cytokine, interleukin-6 (IL-6), in hyperthermia-induced seizures in developing rats. Twenty-four male Lewis rats (23–28 days old) were divided into three groups (n = 8/IL-6 (500 ng), IL-6 (50 ng), and saline control groups). We applied human recombinant IL-6 intra-nasally to developing rats 1 h before seizures induced by moist heated air (50 °C). The seizure latency was defined as the time from hyperthermia onset until the appearance of continuous seizure discharges on electroencephalography (EEG), and the seizure duration as the duration of continuous spike and wave discharges on EEG. Five of the eight rats in the IL-6 (500 ng) group, two in the IL-6 (50 ng) group, and one in the control group exhibited no seizure discharges during the 360 s heating period. In these cases, the seizure latency time was regarded as 360 s and the seizure duration time as 0 s. The median seizure latency for the IL-6 (500 ng) group, 360 s (range: 256–360), was significantly longer than that for the control one, 249 (121–360) (P < 0.05). The seizure duration for the IL-6 (500 ng) group, 0 s (0–20), was significantly shorter than that for the control one, 33 (0–76) (P < 0.025). Also, the adenosine receptor antagonist, aminophylline, prevented these effects of IL-6 on hyperthermia-induced seizures. These results indicate that IL-6 plays an anti-convulsive role through the adenosine system in hyperthermia-induced seizures, which might be relevant as to human febrile seizures.     

Real-time monitoring of glutamate transmitter release with anoxic depolarization during anoxic insult in rat striatum

In vivo continuous real-time measurement of glutamate concentration was performed during anoxia using a dialysis electrode. By this method, the temporal resolution of the measurement of glutamate concentration was improved due to shortening of the time delay compared with the microdialysis method, and changes in the glutamate concentration were more clearly represented with greater reproducibility. After exposure to anoxia, the glutamate concentration showed biphasic changes. A relationship between the DC potential and release of glutamate was confirmed by the synchronization of anoxic depolarization (AD) with the 1st phase of glutamate release. Since the 1st phase disappeared and AD was delayed and suppressed by blocking Ca2+ influx, exocytosis is considered to play an important role in the construction of the 1st phase, which had a close relation with the occurrence of AD. Moreover, since blocking Ca2+ influx also had an effect on the glutamate release from the metabolic pool (2nd phase), reversed uptake may be involved with energy failure in the 1st phase, Ca2+ influx into the cell and rapid changes of the ionic environment associated with AD.     

Adenosine A1 receptor-mediated inhibition of adenylate cyclase in rabbit retina

The purine adenosine has been postulated as playing a role in CNS neurotransmission or modulation. Evidence is now provided that inhibition of adenylate cyclase in rabbit retinal homogenates is mediated via adenosine A1 receptors. Nanomolar concentrations of the A1 receptor agonists, cyclohexyladenosine (CHA) and phenylisopropyladenosine (PIA), significantly inhibited the activity of forskolin-stimulated adenylate cyclase in preparations in which endogenous adenosine was destroyed by pretreatment with adenosine deaminase. With increasing concentrations of either agonist, biphasic effects on enzyme activity were observed. The effect of the mixed A1-A2 agonist, N-ethyl-carboxamidoadenosine (NECA), on forskolin-stimulated, as well as basal adenylate cyclase, was also investigated. At micromolar concentrations, NECA significantly increased the activity of adenylate cyclase. Isobutylmethylxanthine, a potent antagonist at extracellular adenosine receptors, blocked the effects observed with PIA, CHA, and NECA. The uptake of both 3H-CHA and 3H-adenosine into retinal cells was demonstrated autoradiographically. Both agonists labeled ganglion cell bodies and certain cell bodies located in the proximal portion of the inner nuclear layer.     

Pregnenolone sulfate antagonizes GABAA receptor-mediated currents via a reduction of channel opening frequency

Our previous study showed antagonism of GABAA receptor-mediated whole-cell currents by pregnenolone sulfate (PS). Here, the effects of PS, picrotoxin (PTX) and pentobarbital (PB) were tested on GABA-activated single Cl- channels recorded from membrane patches of rat cortical neurons in primary cultures. PS and PTX selectively decreased the opening frequency of the channels, while PB increased mean open time and burst duration without affecting opening frequency. It is suggested that PS and PTX may antagonize GABAA receptor function through the same mechanism and/or the same binding site.     

Status epilepticus in mice deficient for succinate semialdehyde dehydrogenase: GABAA receptor-mediated mechanisms

The epilepsy that occurs in SSADH deficiency has a seizure phenotype similar to that occurring in the SSADH(-/-) mouse. We examined the expression and function of the GABA(A) receptor (GABA(A)R) in SSADH-deficient mice. A selective decrease in binding of [(35)S]tert-butylbicyclophosphorothionate was observed in SSADH(-/-) mice at postnatal day 7 that was progressive until the third postnatal week of life when, at the nadir of the decreased [(35)S]tert-butylbicyclophosphorothionate binding, generalized convulsive seizures emerged that rapidly evolved into status epilepticus. We also observed a substantial downregulation of the beta(2) subunit of GABA(A)R, a reduction in GABA(A)-mediated inhibitory postsynaptic potentials, and augmented postsynaptic population spikes recorded from hippocampal slices. The SSADH(-/-) mouse model represents a powerful investigative tool for understanding the pathophysiology of the seizures associated with human SSADH deficiency. These data raise the possibility that progressive dysfunction of the GABA(A)R may be involved in the development of seizures in SSDAH-deficient mice. Elucidation of the precise fundamental mechanisms of the perturbation of the GABA(A)R-mediated function in SSADH(-/-) mice could lead to the development of novel treatment modalities designed to reduce the neurological morbidity in children with SSADH deficiency.     

Adenosine release and changes in pial arteriolar diameter during transient cerebral ischemia and reperfusion

We utilized the closed cranial window technique in the anesthetized rat to determine changes in CSF concentrations of adenosine, inosine, and hypoxanthine and pial arteriolar diameter during transient (20 min) forebrain ischemia and reperfusion. After mock CSF under the cranial window was allowed to equilibrate with cerebral interstitial fluid, endogenous adenosine concentration was found to be 0.16 +/- 0.05 microM, while inosine and hypoxanthine were 0.35 +/- 0.17 and 1.23 +/- 0.47 microM, respectively. The concentration of adenosine in CSF increased 4.2-fold during ischemia and 13.8-fold during the first 5 min of reperfusion. Inosine and hypoxanthine concentrations were also significantly increased during ischemia and reperfusion. After 1 h of reperfusion, CSF adenosine and inosine levels had decreased from peak value but remained significantly above preischemic values. In contrast, hypoxanthine remained at peak concentrations even after 60 min of reperfusion. Preischemic arteriolar diameter was 42.6 +/- 11.3 microns and was not significantly changed after 20 min of ischemia. However, during the first 5 min of reperfusion, arteriolar diameter increased significantly (p less than 0.05), coincident with peak adenosine concentrations. By 60 min of reperfusion, arteriolar diameter had returned to baseline. These results indicate that during the postischemic period, adenine nucleosides and hypoxanthine in CSF are elevated and could affect reperfusion.     

Enhancement of NMDA receptor-mediated neurotoxicity in the hippocampal slice by depolarization and ischemia

Evidence from animal stroke models suggests that the proximate cause of neuronal degeneration after ischemia is massive release of glutamate and activation of NMDA receptors. However, in the physiologic presence of oxygen and glucose in the rat hippocampal slice preparation, the neurotoxicity of glutamate, as measured by inhibition of protein synthesis, requires high concentrations and is not prevented by glutamate receptor antagonists. Thus, the NMDA receptor-mediated neurotoxic effects of extracellular glutamate accumulation during ischemia might depend on additional factors, such as neuronal depolarization. In the experiments reported here, slices were exposed to glutamate in a medium intended to mimic the ionic conditions found during ischemia, high potassium (128 mM) and low sodium (26 mM). This depolarizing medium itself inhibited protein synthesis in a manner which was partially mediated by NMDA receptor activation, since it was significantly reversed by the noncompetitive NMDA antagonist, MK-801. Furthermore, the effect of glutamate under depolarizing conditions was also significantly decreased by MK-801, suggesting that glutamate was acting at NMDA receptors. Thus, depolarization appears to enhance the sensitivity of neurons to toxic NMDA receptor activation by glutamate. Under conditions that mimic ischemia, hypoxia plus hypoglycemia, a similar protective effect of NMDA receptor antagonists was observed. Depolarization and ischemia both appeared to attenuate the neurotoxicity of non-NMDA receptor agonists. It appears that under conditions of normal glucose and oxygen, high concentrations of bath applied glutamate inhibit protein synthesis at sites other than the NMDA receptor. However, when the Na+ gradient is decreased, as occurs during ischemia, glutamate's NMDA effects predominate. These findings suggest that ionic shifts may play a central role in permitting NMDA receptor-mediated ischemic neuronal damage.     

Transient in vivo membrane depolarization and glutamate release before anoxic depolarization in rat striatum.

Increased extracellular glutamate ([GLU]e), under the condition of cerebral ischemia, anoxia or hypoxia, has been recognized as being associated with neuronal cell damage and death. We performed real-time monitoring of [GLU]e dynamics in vivo in the rat striatum during systemic acute anoxia or hypoxia, as well as monitoring the direct current potential (DC) and cerebral blood flow (CBF). Adult Wistar rats were orotracheally intubated and artificially ventilated with room air. A microdialysis electrode, temperature sensor probe, DC microelectrode and laser Doppler probe were then implanted. The inspired gas was changed to 100% N(2) (anoxia), or to 3, 5 or 8% O(2) (remainder N(2)) (hypoxia). With 100% N(2), distinct biphasic [GLU]e elevations were observed. With 3% O(2), a transient [GLU]e increase was seen before anoxic depolarization (AD). With 5% O(2), however, the start of the transient [GLU]e increase was significantly delayed. Anoxia-induced depolarization started at about 100 s. The 3% O(2)-induced transient depolarization and AD began at nearly the same time as the transient and AD-induced increase in [GLU]e. Similarly, the responses to 5% O(2) showed significant delays in the transient depolarization and AD-induced increase in [GLU]e. CBF during 3 or 5% O(2) hypoxic insult was consistently maintained above the control level, i.e., prior to cardiac arrest. Our new dialysis electrode method employing both GOX and ferrocene-conjugated bovine serum albumin allowed evaluation of transient [GLU]e dynamics in the early phase of severe hypoxia in vivo.     

Adenosine A1 receptor-mediated inhibition of evoked glutamate release is coupled to calcium influx decrease in goldfish brain synaptosomes

Binding of [³H]cyclohexyladenosine (CHA) to the cellular fractions and P₂ subfractions of the goldfish brain was studied. The A₁ receptor density was predominantly in synaptosomal membranes. In goldfish brain synaptosomes (P₂), 30 mM K⁺ stimulated glutamate, taurine and GABA release in a Ca²⁺-dependent fashion, whereas the aspartate release was Ca²⁺-independent. Adenosine, R-phenylisopropyladenosine (R-PIA) and CHA (100 μM) inhibited K⁺-stimulated glutamate release (31%, 34% and 45%, respectively). All of these effects were reversed by the selective adenosine A₁ receptor antagonist, 8-cyclopentyltheophylline (CPT). In the same synaptosomal preparation, K⁺ (30 mM) stimulated Ca²⁺ influx (46.8±6.8%) and this increase was completely abolished by pretreatment with 100 nM ω-conotoxin. Pretreatment with 100 μM R-PIA or 100 μM CHA, reduced the evoked increase of intra-synaptosomal Ca²⁺ concentration, respectively by 37.7±4.3% and 39.7±9.0%. A possible correlation between presynaptic A₁ receptor inhibition of glutamate release and inhibition of calcium influx is discussed.     

Serotonin depletion attenuates AY-9944-mediated atypical absence seizures

Summary: Purpose: To test the hypothesis that serotonin (5‐HT) plays a role in the modulation of experimental atypical absence seizures. Methods: Male Long‐Evans hooded rats were treated from postnatal day (P) 2 to P20 with the cholesterol inhibitor AY‐9944 (AY). Epidural electrodes were implanted for electrocorticography (ECoG) followed by serotonin depletion by using para‐cholorophenylalanine (PCPA). High‐performance liquid chromatography (HPLC) was used to measure the levels of serotonin and its metabolite (5‐HIAA) in various brain regions. Serotonin metabolism was computed by using the 5‐HIAA/5‐HT ratio and used to ascertain differences between groups. Results: PCPA treatment was associated with a significant decrease in the total slow spike‐and‐wave discharge (SSWD) duration in AY‐treated rats compared with controls (p < 0.01). HPLC data confirmed the PCPA depletion of 5‐HT and 5‐HIAA in cortex, thalamus, hippocampus, and brainstem compared with naïve rats. AY‐treated rats showed higher levels of 5‐HIAA and 5‐HT in the same brain regions, with a concomitant decrease in rates of serotonin turnover. Conclusions: The data indicate that serotonin depletion protects against experimental atypical absence seizures. The increased levels of 5‐HIAA and 5‐HT and altered rates of serotonin turnover suggest that the serotonergic neurotransmission may be perturbed in the AY rat.     

Hippocampal transection attenuates kainic acid-induced amygdalar seizures in rats

Since the dorsal and ventral hippocampus in the rat may act differently from one another in limbic seizures, we studied effects of orthogonal transection between the dorsal and ventral hippocampus upon kainic acid-induced amygdalar seizures. A total of 26 rats were divided into three groups. Ten rats underwent transection using a modified wire knife (transection group); 16 others were untransection group (n=10) and controls (n=6). All the rats then underwent stereotactic implantation of electrodes in the left amygdala (LA), left dorsal hippocampus (LdH), left ventral hippocampus (LvH), and the left sensorimotor cortex (LCx). A stainless steel cannula also was introduced into the LA. Rats except controls later received 1.0 microg of kainic acid (KA) via the cannula. Controls received phosphate buffer solution alone. In the untransection group, multiple spike discharges in the LA immediately propagated concurrently to the LvH and LdH. Propagation involved the LCx to become status epilepticus 1 to 2 h after KA injection. Seizures, characterized by mastication, salivation, facial twitching, forelimb clonus, and sometimes rearing and falling, lasted 1 to 2 days. Microscopic examination revealed severe neuronal cell damage in the LA, LvH, and LdH. In the transection group, multiple spike discharges initiated from the LA and were propagated to LvH, but LdH as well as LCx involvement was slight. Status epilepticus involved only the LA and LvH 1 to 2 h following KA injection. Seizures subsided within 24 h, showing no ictal manifestations except for aggressiveness. Overall, seizures were weak and transient compared with those in controls. Histologically, hippocampal neuronal damage was slight, but damage to amygdalar neurons was similar to that in untransection group. No electroclinical and histological changes were seen in controls. These results indicated that connections between the dorsal and ventral hippocampus are important for full development of KA-induced amygdalar seizures.