Endothelin-1 (ET-1), a vasoconstrictor, has recently been used to induce focal ischemia in rodents and marmoset monkeys. The rhesus monkey, however, has numerous advantages to the rodent and marmoset that make it a superior and irreplaceable animal model for studying stroke in the brain. In the present study, after mapping the preferred hand representation in two healthy male monkeys with intracortical micro-stimulation, ET-1 was microinjected into the contralateral motor cortex (M1) to its preferred hand. The monkeys had been trained in three manual dexterity tasks before the microinjection and were tested for these tasks following the ET-1 injection. Brain Magnetic Resonance Imaging scans were performed 1, 7, 14 and 28 days post ischemia. It was found that ET-1 impaired the manual dexterity of the monkeys in the vertical slot and rotating Brinkman board tasks 3–8 days after the injection.
Brain imaging found that severe edema was present 7 days after the focal ischemia. This data suggest that ET-1 can induce transient ischemic stroke in rhesus monkey and that ET-1 induced focal ischemia in non-human primates is a potential model to study the mechanism of stroke and brain repair after stroke. Effect of ET-1 on manual dexterity in the vertical slot taskThe number of successful food retrieval movements in the vertical slot task was decreased on D3 (P = 0.004) and D8 (P = 0.02) after ET-1 injection in comparison to performances before the injection.
However, the monkeys’ ability to retrieve the food pellets had recovered at 15 days (P = 0.014) and 29 days (P = 0.016) after the ET-1 injection. This was reflected by increased successful retrievals of the food in comparison with the number of retrievals on D3.
Archer 15 1263 Manual Dexterity 1
Brain imaging analysisTo investigate the effect of ET-1 induced ischemic damage in the brain, the volume of edema and infarct were assessed with an MRI scan.The ET-1 induced edema and infarct in the M1 cortex were dependent on the day after injection. The infarct was seen in the ET-1 treated group on D1.
In monkey #08389, the volume of the edema was severely increased in the T2W image 7 days after the ET-1 injection. On D14, the edema volume slowly decreased and on day 28, the edema was almost unobservable in the T2W image.
Similarly, the infarct volume was large in monkey #06023 on D1. The infarct became severe on D7 after the ET-1 injection. A decrease in edema was slowly seen on day 14 and the edema in monkey #06023 had been repaired on D28 in the T2W image. However, there was no significant difference between the volumes of the edema on days 7 and those calculated on days 1, 14 or 28. AnimalsTwo adult healthy rhesus monkeys ( Macaca mulatta) weighing 8–9 kg (7–9 years old) from breeding colonies at the Kunming Institute of Zoology (KIZ) were used in these experiments. Their ID numbers were #06023 and #08389, respectively.
The monkeys were housed under standard conditions (12 h light/dark cycle with light on from 07:00 to 19:00; humidity at 60% and temperature at 21 ± 2 °C). Monkeys had free access to tap water and were punctually supplied food three times a day. Experiments were performed between 8:00 and 17:00 h. All experimental procedures involving animals were performed in accordance with the guidelines for the National Care and Use of Animals approved by National Animal Research Authority of P. All efforts were made to minimize animal suffering and to reduce the number of animals required. Surgery and intracortical microstimulationAll surgical procedures were conducted on monkeys anesthetized with hydrochloric acidulated ketamine (He Nan Run Hong Pharmaceutical Company, 10 mg/kg, i.m.) and maintained with sodium pentobarbital (Shang Hai Westang Bio-Tech Company, 20 mg/kg, i.m.). Atropine (0.05 mg/kg, i.m.) was used to reduce salivation and other secretions.
Body temperature was maintained at normal levels using a heating pad during surgery. The monkey’s head was fixed on the stereotaxic apparatus after anesthesia.A 2 cm × 3 cm portion of skull over the precentral gyrus containing the hand representation of M1 was removed contralaterally to the dominant hand. A map of the hand representation area in primary motor cortex M1 was constructed using intracortical microstimulation (ICSM) with a HuaTuo electroacupuncture therapeutic apparatus (SDZ-V, Su Zhou Medical Instrument Co., Ltd.). Two electrode (acupuncture needles) penetrations were spaced at 2 mm intervals. One electrode was placed on the surface of the brain and the other one was placed into the cortex at a depth of 3 mm. A conventional electric stimulus (10–30 Hz, 5–25 μA) was used to evoke movement at each electrode penetration site.
The region of the M1 cortex corresponding to a digit within a 2 mm square of cortical surface was carefully defined by digit movement during the stimulus.