Unilateral cortical spreading depression in the rat: effects on feeding, drinking and other behaviors

Direct electrophysiological evidence that spreading depolarization-induced spreading depression is the pathophysiological correlate of the migraine aura and a review of the spreading depolarization continuum of acute neuronal mass injury

Spreading depolarization is observed as a large negative shift of the direct current potential, swelling of neuronal somas, and dendritic beading in the brain's gray matter and represents a state of a potentially reversible mass injury. Its hallmark is the abrupt, massive ion translocation between intraneuronal and extracellular compartment that causes water uptake (= cytotoxic edema) and massive glutamate release. Dependent on the tissue's energy status, spreading depolarization can co-occur with different depression or silencing patterns of spontaneous activity. In adequately supplied tissue, spreading depolarization induces spreading depression of activity. In severely ischemic tissue, nonspreading depression of activity precedes spreading depolarization. The depression pattern determines the neurological deficit which is either spreading such as in migraine aura or migraine stroke or nonspreading such as in transient ischemic attack or typical stroke. Although a clinical distinction between spreading and nonspreading focal neurological deficits is useful because they are associated with different probabilities of permanent damage, it is important to note that spreading depolarization, the neuronal injury potential, occurs in all of these conditions. Here, we first review the scientific basis of the continuum of spreading depolarizations. Second, we highlight the transition zone of the continuum from reversibility to irreversibility using clinical cases of aneurysmal subarachnoid hemorrhage and cerebral amyloid angiopathy. These illustrate how modern neuroimaging and neuromonitoring technologies increasingly bridge the gap between basic sciences and clinic. For example, we provide direct electrophysiological evidence for the first time that spreading depolarization-induced spreading depression is the pathophysiological correlate of the migraine aura.

Does single cortical spreading depression elicit pain behaviour in freely moving rats?

INTRODUCTION

Behavioural animal studies are critical, particularly to translate results to human beings. Cortical spreading depression (CSD) has been implicated in migraine pathogenesis. We aimed to investigate the effects of CSD on the behaviour of freely moving rats, since available CSD models do not include awake animals.

MATERIALS AND METHODS

We developed a new model to induce single CSD by applying topical N-methyl-D-aspartate (NMDA) and employed a combination of an automated behavioural analysis system, video camera and ultrasonic vocalisation (USV) calls for the first time. Electrocorticograms were also studied during CSD in freely moving rats. Behaviour associated with cephalic pain was assessed in a group of rats that received sumatriptan. Cortical c-fos immunoreactivity was performed in order to confirm CSD.

RESULTS

NMDA induced single CSD in ipsilateral cortex, evoked freezing behaviour (P < 0.01) and increased the number of wet dog shakes (WDS; P < 0.01). Grooming, locomotion, eating, drinking, and circling were not significantly altered among groups. Ultrasonic vocalisations compatible with pain calls (22-27 kHz) were only detected in 3 out of 25 rats. Sumatriptan did not significantly reduce the freezing behaviour. CSD induced significant c-fos expression in ipsilateral cerebral cortex and amygdala (P < 0.01).

CONCLUSIONS

CSD induces freezing behaviour by invoking anxiety/fear via amygdala activation in freely-moving rats. Single CSD is unlikely to lead to severe pain in freely-moving rats, though the development of mild or vague pain cannot be excluded. The relevance of rat behavioural responses triggered by CSD to migraine symptoms in humans needs further evaluation.

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.

Cerebral hemodynamics during cortical spreading depression in rabbits

Effects of a single cortical spreading depression (CSD), elicited by KCl microinjection, on diameter of pial arterioles and venules in the parieto-occipital cortex were examined in urethane-anesthetized adult rabbits using a closed cranial window. The velocity of CSD propagation was 2.7 +/- 0.1 mm/min (mean +/- S.E.M.). All arterioles (n = 39) except for those in the retrosplenial region (n = 6) increased their diameter significantly during CSD. The arteriolar dilation lasted for 1.5 +/- 0.1 min. Location of dilating arteriole and propagating CSD showed that they were always closely associated temporally. As a percentage change, diameters of smaller arterioles significantly increased (from 60 +/- 1 to 103 +/- 2 microns, 71%, n = 12) more than those of larger ones (from 82 +/- 2 to 129 +/- 3 microns, 57%, n = 27). While venules with initial diameter of 85 +/- 4 microns (n = 5) did not dilate, those with initial diameter of 49 +/- 3 microns increased to 57 +/- 3 microns (16%, n = 8) for 1.4 +/- 0.2 min during CSD. The majority of the dilated venules started to increase their diameter after nearby arterioles had dilated maximally. Pial arterioles, which dilated during ipsilateral CSD, decreased their diameter significantly from 78 +/- 2 to 72 +/- 3 microns (8%, n = 11) during contralateral CSD for 13.8 +/- 3.6 min with similar onset latencies as those observed for the dilation. Indomethacin pretreatment significantly enhanced arteriolar dilation during CSD (from 73 +/- 4 to 138 +/- 6 microns, 89%, n = 4).(ABSTRACT TRUNCATED AT 250 WORDS)

Electroencephalographic spreading depression and concomitant behavioral changes induced by intrahippocampal injections of ACTH1-24 and D-Ala2-Met-enkephalinamide in the rat

ACTH1-24 (0.5 or 10 micrograms = 0.17 or 3.45 nmol) and D-Ala2-Met-enkephalinamide (DAME; 10 micrograms = 17.05 nmol) were injected unilaterally into the hippocampus of freely moving rats to examine their effects on EEG activity, DC potentials and behavior. In 85% of the rats DAME elicited spreading depression (SD) with epileptiform discharges preceding and following the wave of SD. The following behavioral changes were recorded. DAME- and KCl-induced SD were accompanied by an increase in locomotor activity and wet-dog shaking behavior, which occurred only during the period of SD. After a wave of SD induced by DAME a biphasic pattern of activity, consisting of an initial depression in locomotion followed by hyperactivity, appeared in 59% of the rats. ACTH1-24 elicited SD in 13% of the rats tested. Neither the dosage of ACTH1-24 nor the strain of rats influenced the occurrence of SD and the incidence of ACTH-induced grooming behavior. SD induced by KCl also resulted in excessive grooming comparable to that induced by ACTH1-24. In the case of KCl-induced SD, grooming began directly after the injection of KCl and was frequently interrupted by short periods of locomotion. ACTH-induced grooming had a later onset and episodes of stretching and yawning were observed. It can be concluded that the behavioral effects of the injection of DAME are unspecific responses to SD and seizure activity. However, ACTH-induced grooming is not solely a byproduct of SD, since it occurred also in the absence of SD.

Impairment of thermoregulatory cooling behavior by single cortical spreading depression in the rat

Effects of single waves of unilateral cortical spreading depression (CSD) on skin-cooling operant behavior were studied in the rat with and without unilateral lesion in the preoptic and anterior hypothalamus (PO/AH). The skin-cooling behavior was severely suppressed for 6 min, with a resulting rise in rectal temperature (Tre), when CSD entered the frontal cortex contralateral to the PO/AH lesion. However, CSD ipsilateral to the PO/AH lesion slightly suppressed the skin-cooling behavior for 4 min with small rise in Tre. In the PO/AH intact rat, while 0.9% NaCl did not affect the skin-cooling behavior, unilateral CSD slightly suppressed it for 3 min almost in the same way as that of the ipsilateral CSD trial in the PO/AH lesioned rat. The results add further evidence to support the involvement of the frontal cortex in the central control of thermoregulation.

Cortical spreading depression and conditioned taste aversion: an attempt to resolve a controversy

The claim (Winn, Todd, & Elias, Behav. Biol. 19, 55-63 (1977) ) that cortical spreading depression (CSD) can serve as US in the conditioned taste-aversion (CTA) paradigm was experimentally examined. Rats given 15-min access to novel 0.1% sodium saccharin (CS) followed by ip NaCl and bilateral or unilateral CSD (US) displayed similar saccharin preference (54%) as the sham-CSD-treated controls in a multiple-bottle retention test. Rats receiving ip LiCl (0.15 M, 2% body weight) and sham CSD as the US showed marked saccharin aversion. It is concluded that CSD does not elicit CTA and that some claims to the contrary can perhaps be ascribed to CSD-induced disruption of attenuation of neophobia.