Excitatory and inhibitory amino acid changes in ischemic brain regions in spontaneously hypertensive rats

Amino acid transmitters in patients with headache during the acute phase of cerebrovascular ischemic disease

BACKGROUND AND PURPOSE

The pathophysiology of headache occurring at stroke onset is unknown. Migraine and ischemia share an excessive release of neuroexcitatory amino acids. Inhibitory amino acids also may be implicated in both diseases. We investigated whether fluctuations of these amino acids occur in headache accompanying cerebral infarction.

METHODS

We studied 100 patients with infarction in the territory of the middle cerebral artery. Neurological impairment was assessed using the Canadian Neurological Scale and Barthel Index. Size of infarction was determined with CT. Twenty-eight patients developed headache. Glutamate, aspartate, and taurine were quantified in blood and cerebrospinal fluid (CSF) within 24 hours of stroke onset with cationic exchange chromatography.

RESULTS

Stroke subtypes, size of infarct on CT, and clinical scales were similar in patients with and without headache. Plasma glutamate level was 321.14 +/- 149.53 mumol/L in patients with headache and 233 +/- 107.23 mumol/L in those without headache (P < .005). Glutamate in CSF was higher in patients with headache (4.6 +/- 1.49 mumol/L) than in patients without headache (3.11 +/- 1.18 mumol/L) (P < .001). Aspartate concentrations in plasma and CSF were similar in both groups. Taurine concentrations in plasma were 103.10 +/- 52.82 mumol/L and 177.49 +/- 90.92 mumol/L in headache and nonheadache patients, respectively (P < .001). Taurine levels in CSF were 5.42 +/- 2.42 mumol/L in patients with headache and 9.27 +/- 5.31 mumol/L in those without headache (P < .001). No significant correlation was found between amino acid levels in plasma or CSF and size of infarction.

CONCLUSIONS

Amino acid neurotransmitters play a role in the pathophysiology of headache that occurs at the onset of stroke. The ischemic penumbral area, more than the infarction itself, may cause a state of cortical hyperexcitability that would be responsible for the cortical release of amino acids and the induction of headache by altering pain perception mechanisms.

Effects of GABAergic drugs on the recovery of reflex potentials after spinal cord ischemia in cats

Effects of GABAergic drugs on the recovery of reflex potentials after spinal cord ischemia were examined in anesthethized spinal cats. Monosynaptic reflex (MSR) and polysynaptic reflex (PSR) potentials, elicited by electrical stimulation of the tibial nerve in spinal cats, were recorded from the lumbo-sacral ventral root. The spinal reflex potentials were immediately depressed by occlusion of the thoracic aorta and the bilateral mammary arteries for 10 min. The potentials recovered gradually to the control level within 90 min after reperfusion. Pretreatment with bicuculline (0.3 mg/kg, i.v.), a GABA antagonist, or semicarbazide (200 mg/kg, i.v.), an inhibitor of GABA synthesis, accelerated the recovery of PSR potentials after the removal of the arterial occlusion. In contrast, pretreatment with aminooxyacetic acid (10 mg/kg, i.v.), an inhibitor of GABA degradation, retarded the recovery of PSR potentials, and this effect was overcome by the addition of the opioid antagonist naloxone (10 mg/kg, i.v.). These results suggest that the GABAergic system retards the recovery of PSR potentials after a brief spinal cord ischemia, which can be antagonized by naloxone.

Ischemia-induced release of amino acids in the hippocampus of aged hypertensive rats

We have recently demonstrated the age-related vulnerability of hippocampal neurons to 20-min forebrain ischemia in spontaneously hypertensive rats (SHR). In the present study, we investigated the effect of aging on the release of amino acids in the hippocampus during transient cerebral ischemia for 20 min. Concentrations of extracellular amino acids and cerebral blood flow in the CA1 subfield were examined by an in vivo brain dialysis technique and a hydrogen clearance method, respectively, in adult (5-7 month) and aged (19-23 month) female SHR. During cerebral ischemia by bilateral carotid artery occlusion, cerebral blood flow to the hippocampus decreased to 20% of the resting values in both groups. After recirculation, both groups showed delayed hypoperfusion which was more prominent in the aged SHR. In the adult rats, concentrations of both aspartate and glutamate increased to approximately 8-fold of the resting values during ischemia. The elevation of these excitatory amino acids in the adult SHR was not significantly different from that in the aged rats. In contrast, the concentration of taurine increased 26-fold in the adult SHR but only 16-fold in the aged rats. Changes in other amino acids were not different between the two groups. These results indicate that an imbalance of excitatory and inhibitory amino acids, e.g., smaller release of taurine, during ischemia may, at least in part, contribute to the age-related vulnerability of hippocampal neurons to transient cerebral ischemia in SHR.