Hippocampal Spreading Depression Research Articles

Spreading depression and the clinical correlates of migraine

Migraine is the most common neurologic condition. One-third of migraineurs experience transient neurologic symptoms, the so-called aura. There is strong evidence that spreading depression (SD) is the electrophysiologic substrate of migraine aura. SD is an intense pan-depolarization wave that slowly propagates in gray matter by way of contiguity and transiently disrupts neuronal function. When induced subcortically, striatal SD causes hemiparesis, hippocampal SD can trigger seizures and impact cognition, and bilateral thalamic SD can diminish consciousness. Recent data show that transgenic mice expressing familial hemiplegic migraine (FHM) type 1 mutations in voltage-gated Ca2+ channels (Cav2.1) develop mutation-specific aura-like signs after a cortical SD similar to patients with the respective mutation. These signs are associated with facilitated subcortical SD propagation. As in FHM, mice with the R192Q mutation develop pure hemiplegia associated with cortical SDs propagating into caudoputamen. S218L mice display additional signs such as seizures and coma when SD propagates into hippocampus and thalamus. In hyperexcitable FHM brains, SD may propagate between cortex and subcortical structures via permissive gray matter bridges, or originate de novo in subcortical structures, to explain unusual and severe aura signs and symptoms. Reciprocal spread and reverberating waves can explain protracted attacks.

Is Spreading Depression Bad for You?Focus on “Repetitive Normoxic Spreading Depression-Like Events Result in Cell Damage in Juvenile Hippocampal Slice Cultures”

In this issue of the Journal of Neurophysiology (p. x), Pomper et al. report that repeated episodes of spreading depression-like events (SDLEs) caused irreversible injury in hippocampal slice cultures taken from immature brains. Although after the first four or five SDLEs, antidromic population

P/Q Ca2+ channel blockade stops spreading depression and related pyramidal neuronal Ca2+ rise in hippocampal organ culture.

Ca2+ channels and pyramidal cell Ca2+ are involved in hippocampal spreading depression (SD), but their roles remain elusive. Accordingly, we characterized Ca2+ changes during SD in CA3 pyramidal neurons and determined whether Ca2+ channel antagonists could prevent SD. SD was induced in hippocampal organotypic cultures (HOTCs), in which experimental conditions can be rigorously controlled. SD was triggered by transient exposure to sodium acetate (NaAc)-based Ringer's coupled to an electrical pulse in the dentate gyrus and its occurrence confirmed with interstitial DC recordings. Pyramidal cell Ca2+ was measured with fura-2 filled cells and was quantified at the soma, proximal and more distal apical dendrites. Regional Ca2+ changes began simultaneously with the triggering pulse of SD and reached three distinct peaks before returning to baseline concomitant with the interstitial DC potential of SD. The first peak occurred within 5 s of the triggering pulse, was smallest, and heralded the onset of SD. The second Ca2+ change was the greatest and reached a peak 6 s later, during the early phase of SD. The third was intermediate in size and occurred 18 s later, as SD reached its maximum interstitial DC change. SD was prevented by nonselective Ca2+ blockade (Ni2+ and Cd2+) but not by either L-Ca2+ channel (nifedipine) or N-Ca2+ channel inhibition (omega-conotoxin GVIA). Importantly, SD was blocked by P/Q Ca2+ channel antagonism (omega-agatoxin-IVA), which also prompted a significant reduction in pyramidal cell Ca2+ change and hyperexcitability. These results show that the spatiotemporal pattern of pyramidal cell Ca2+ change with SD is multiphasic; they provide further evidence that these changes begin before electrophysiologic evidence of SD. Furthermore, they show that P/Q Ca2+ channel antagonism can prevent SD in HOTCs and it appears to do so by preventing the NaAc-induced increased pyramidal cell excitability from NaAc exposure, which may involve altered GABAergic transmission.

Accelerated Hippocampal Spreading Depression and Enhanced Locomotory Activity in Mice with Astrocyte-Directed Inactivation of Connexin43

Using a human glial fibrillary acidic protein (hGFAP) promoter-driven cre transgene, we have achieved efficient inactivation of a floxed connexin43 (Cx43) gene in astrocytes of adult mice. The loss of Cx43 expression was monitored in a cell-autonomous manner via conditional replacement of the Cx43-coding region by a lacZ reporter gene. In this way, we bypassed the early postnatal lethality previously reported for Cx43 null mice and characterized the phenotypic consequences of Cx43 deficiency in the CNS. Mice lacking Cx43 in astrocytes were viable and showed no evidence of either neurodegeneration or astrogliosis. Spreading depression (SD) is a pathophysiological phenomenon observed in the CNS that is characterized by a propagating wave of depolarization followed by neuronal inactivation. Inhibitors of gap junctional communication have previously been shown to block initiation and propagation of SD. In contrast, we observed an increase in the velocity of hippocampal SD in the stratum radiatum of mice lacking Cx43 in astrocytes. In the same brain subregion, dye-coupling experiments revealed a reduction in overall astrocytic intercellular communication by approximately 50%. This strongly suggests separate and different neuronal and glial contributions of gap junctional intercellular communication to SD. Concomitant with increased velocity of spreading depression, we observed enhanced locomotory activity in mice lacking Cx43 in astrocytes.

Hippocampal spreading depression bilaterally activates the caudal trigeminal nucleus in rodents.

Spreading depression (SD) and migraine aura involve transiently altered (i.e., increased followed by decreased) electrophysiological activity that propagates at the distinctive rate of millimeters per minute (mm/min), leading to the suggestion that they (and perhaps pain from migraine) are causally related via changes in the same brain structure. Neocortex is considered the anatomical zone associated with migraine aura and is the sole area known to induce caudal trigeminal nucleus (TNC) activation from SD in rodents. However, classical evidence of SD in human neocortex is reported only with severe brain disease, while migraine is a common and comparatively benign disorder. Because SD occurs in human hippocampus, and memory dysfunction referable to hippocampus is seen in migraineurs, we determined whether recurrent SD confined to hippocampus in rat could induce TNC activation. Our work shows that recurrent hippocampal SD evoked a significant (P < 0.05-0.001) increase in bilateral c-fos immunostaining within TNC superficial laminae compared with sham controls. Furthermore, hippocampal SD occurred with a correlated and transient change in spontaneous activity and blood flow in the ipsilateral neocortex without spread of SD to that area. Thus, hippocampal SD may be a previously unrecognized, potential trigger for nociceptive activation of TNC perhaps associated with migraine.

Hippocampal damage induced by carbon monoxide poisoning and spreading depression is alleviated by chronic treatment with brain derived polypeptides

A model of acute carbon monoxide poisoning combined with spreading depression (SD) induced metabolic stress was used to examine the protective effects of cerebrolysin (CL) on the development of electrophysiological, behavioral and morphological signs of hypoxic damage. Capillary electrodes were implanted into the neocortex and hippocampus of anesthetized rats which were then exposed for 90 min to breathing of 0.8% to 0.5% CO, while 3 to 4 waves of cortical and hippocampal SD were elicited by microinjections of 5% KCl. Duration of SD-provoked depolarization of cerebral cortex and hippocampus was noted. Nine and 18 to 19 days later propagation of SD waves was recorded with the same electrodes and decrease of their amplitude was used as an index of brain damage which was significant in the hippocampus but not in the cortex. CL-treatment (2.5 ml/kg per day) started after CO administration and continued for 14 days significantly improved hippocampal recovery manifested by increased amplitude of SD waves. Behavioral tests performed 10 and 20 days after CO poisoning in the Morris water maze revealed better performance (escape latency 7 s) in the CL-treated than in untreated animals (14 s). Morphological analysis showed marked damage in the hippocampus consonant with electrophysiological and behavioral findings in the same animals. No apparent histological damage was found in rats exposed to CO inhalation alone without the additional SD-provoked depolarization. It is concluded that chronic CL-treatment enhances recovery of hippocampal tissue after hypoxic damage of intermediate severity.

Coexpression of c-fos and hsp70 mRNAs in gerbil brain after ischemia: Induction threshold, distribution and time course evaluated by in situ hybridization

Levels of mRNAs encoding the proto-oncogene, c- fos, and the 70 kDa stress protein, hsp70, were evaluated in gerbil brain following transient cerebral ischemia of varied duration by in situ and blot hybridization techniques. Blots of total hippocampal RNA obtained after 5 min ischemic insults confirmed a characteristic, transient time course of c- fos expression with a striking elevation within 1 h and a return to control levels by 3 h recirculation. Hsp70 hybridization was significant at 1 h and continued to increase until 3–6 h after the insult. Striking accumulation of c- fos mRNA was detected within 15 min recirculation in dentate granule cells, persisting through 1 h, and a weaker signal was evident in CA1 and CA3 pyramidal neurons of hippocampus, as well as in prepiriform/entorhinal cortex and neocortical regions, during the same interval. Hsp70 hybridization showed an identical distribution at 1 h recirculation. Ischemic insults of 1 min duration resulted in no detectable increase of either mRNA, while 2 min ischemia resulted in changes comparable to those seen after 5 min insults. This common threshold corresponds to the ischemic interval required for energy depletion and resultant failure of intracellular ion homeostasis. In contrast, expression of hsp70 mRNA was not observed under conditions of brief depolarization accompanying cortical or hippocampal spreading depression that were shown to induce c- fos. A delayed component of c- fos mRNA expression was not detected in this model, while persistent hsp70 hybridization, restricted to hippocampal CA1 neurons, was evident at 48 h after either 2 min or 5 min ischemic insults. The parallels in c- fos and hsp70 mRNA expression during early recirculation suggest that overlapping mechanisms triggered following postischemic depolarization contribute to their induction after transient ischemia.

Rats do not experience cortical or hippocampal spreading depression as aversive

Cortical spreading depression (SD) may produce some symptoms of the aura of classical migraine but it is less probable that it can account for the headache. The aversiveness of SD was examined in unanesthetized rats. In Exp. 1, rats with implanted cortical cannulae were confined in the dark compartment of the step-through apparatus and repeated waves of SD were elicited in one hemisphere. After two such training sessions the rats did not evince passive avoidance of the compartment associated with cortical SD. In Exp. 2, thirsty rats with implanted hippocampal electrodes were trained to drink from two different spouts A and B. Hippocampal SD was elicited when the animal was drinking from spout A but not from spout B. Drinking was interrupted shortly after appearance of the SD wave and gradually recovered over the subsequent 10 min, but up to ten spout A-SD pairings did not change the animal's preference for spout A. It is concluded that cortical or hippocampal SD has no immediate or delayed aversive consequences.

Effect of hippocampal lesions on rat shuttle responses in four different behavioral tests

Rats with lesions in subareas CA1 - CA2 of the dorsal hippocampus made more shuttle responses to a buzzer than sham-operated or intact control animals in four different shuttle-box situations using buzzers and footshocks as stimuli. These differences were much more marked in two of the tests, in which the buzzer-shock interval was varied at random (a pseudoconditioning situation and an avoidance paradigm without stimulus pairing), than in the other two tests, in which the stimuli were paired on all trials (a Pavlovian paradigm and a typical two-way avoidance situation). These data agree closely with those of a previous report on the effect of hippocampal spreading depression on the same four tests. The results suggest that the hippocampus plays a role both in the inhibition of nonassociative effects of the footshocks and in the establishment of stimulus-stimulus relations in the brain.

Effect of hippocampal and neocortical spreading depression on rat shuttle behavior in four different experimental paradigms

As shown in previous papers, rat shuttle responses to a buzzer (SBs) depend on the operation of three main factors: a state of drive (D) determined by the presence of footshocks in the experimental situation; the pairing (i.e., fixed temporal relation) of buzzers and shocks (P); the contingency (C) of shocks upon SBs. Four tests were studied in which these factors operate in various combinations: (a) D test: 50 buzzers and 25 shocks at random intervals and in random sequence; (b) DP test (Pavlovian conditioning): 50 buzzers paired (contiguous) to shocks on trials, regardless of whether SBs are performed or not; (c) DC test: 50 buzzers, each followed by a shock at a randomly variable interval unless there is an SB on that trial; (d) DPC test (two-way avoidance): 50 buzzers paired to shocks only on those trials in which there is no SB. The effect of hippocampal and neocortical spreading depression on these tests was studied. Spreading depression was induced by the application of KCl crystals through implanted guide cannulae, and was ascertained by EEG recording. Application of KCl on the hippocampus caused both hippocampal and neocortical spreading depression; whereas when it was applied on the neocortex there was only spreading depression in this structure. The following behavioral responses were measured: SBs, jumping to the buzzer, and intertial shuttling. Neocortical spreading depression had no effect on any of these parameters. Hippocampal spreading depression caused an increase of SBs and of intertrial crossings in all four tests, and a depression of jumping responses in the DP test. The increase of SBs was more marked in the D and DC tests. In fact, in the animals with hippocampal spreading depression differences in SB performance between DP and D, or between DPC and DC, were very small and not significant; this was not the case in any of the other groups. Since, as shown previously both DP - D and DPC - DC are a measure of the P factor, these data suggest that the hippocampus normally exerts a tonic inhibitory influence on the operation of D, and that at the same time it plays a role in the operation of P. The results are consistent both with hypotheses which attribute to the hippocampusa role in behavioral inhibition, and with those which consider that it processes stimulus-stimulus dependent information.

Pavlovian conditioning of eating induced by spreading depression in cortex, striatum and hippocampus of rats

A single wave of unilateral spreading depression in the cortex, hippocampus or caudate nucleus of rats elicits eating after 2–6 min. The present experiments provide evidence that such spreading depression-induced eating can be classically conditioned to a complex conditioned stimulus. A wave of spreading depression was triggered by injection of 0.5–2.0 μl of 25 percent KC1 solution. In a first experiment successful conditioning was demonstrated in 20 rats, involving 7 cortical, 5 caudate and 8 hippocampal spreading depression sites. Four animals failed to show any conditioned eating. A control group of 8 animals, in which cortical spreading depression did not induce eating, showed no increase in eating in the presence of the CS after conditioning trials. A second experiment, which included pseudoconditioning and NaCl control groups, confirmed the results obtained in Experiment 1. Classical conditioning was successful in 11 animals, involving 6 cortical and 5 caudate spreading depression sites. Neither the pseudoconditioning (14 animals, involving 8 cortical and 6 caudate spreading depression sites) nor the NaCl control group (8 animals, all with cortical sites), showed eating in the presence of the CS. In both experiments the conditioned eating underwent gradual extinction.

Selective recovery from retrograde amnesia produced by hippocampal spreading depression.

Injections of potassium chloride into the hippocampus after learning produce temporary disruption of neural activity and retrograde amnesia. Recovery from the amnesia is selective-rats recover from amnesia of events that occurred24 hours before injection but do not recover from amnesia of events that occurred 10 seconds before injection.

Retrograde amnesia produced by hippocampal spreading depression.

Injection of potassium chloride into the hippocampus produces a disruption of electrical activity; a concomitant of this disruption is a deficit in retention of conditioned suppression learned 24 hours before injection.

The effect of cortical and hippocampal spreading depression on activity of bulbopontine reticular units in the rat

The effect of cortical and hippocampal spreading depression on activity of bulbopontine reticular units in the rat