T. S. Park

Neuroprotection from ischemic brain injury by hypoxic preconditioning in the neonatal rat.

Very recent studies in adult gerbils and rats have shown that exposure to sublethal ischemia can confer neuroprotection from subsequent lethal ischemic episodes. To determine if a similar phenomenon can be elicited during the perinatal period, we have developed a preconditioning regimen that involves exposure to normothermic hypoxia (8% oxygen) 24 h prior to hypoxia-ischemia in the well-established post-natal-day 7 rat pup model [20]. Significant infarction, manifested as a 34 +/- 4% reduction in cerebral hemispheric weight ipsilateral to the carotid ligation, was noted in control animals (n = 24) one week after hypoxia-ischemia, whereas littermates preconditioned with 3 h hypoxia (n = 29) showed no evidence of hemispheric necrosis. Lack of injury in the latter animals was confirmed at the cellular level by histopathologic analyses of Nissl-stained coronal sections. Thus, pre-exposure to hypoxia induces endogenous adaptive mechanisms that can protect the perinatal brain from hypoxic-ischemic injury.

Increases in Cerebral Interstitial Fluid Adenosine Concentration during Hypoxia, Local Potassium Infusion, and Ischemia

This study used the brain dialysis technique to test the hypothesis that the adenosine concentration of cerebral interstitial fluid increases during situations in which cerebral oxygen supply is inadequate for oxygen demand. Sealed 300-μm hollow dialysis fibers were implanted in the caudate nucleus of pentobarbital-anesthetized rats and perfused at 2 μl/min with artificial cerebrospinal fluid. In vitro tests indicated the recovery of adenosine, inosine, and hypoxanthine from the external medium to be ∼20% at 2 μl/min and close to 100% at 0.1 μl/min. Three in vivo interventions were tested: hypoxia/hypotension (Pao2 = 41.9 mm Hg; MABP = 42.8 mm Hg; n = 9), local potassium infusion (n = 4), and cerebral anoxia/ischemia (n = 10). These interventions produced 10-, 4-, and 30-fold increases in perfusate adenosine concentration, respectively, as well as increases in perfusate concentrations of inosine and hypoxanthine. A separate group of rats (n = 9) perfused at 0.1 μl/min yielded estimates of cerebral interstitial fluid adenosine, inosine, and hypoxanthine concentrations of 1.26, 3.30, and 7.19 μM, respectively. These results are consistent with the adenosine hypothesis for the regulation of CBF.

Nitric oxide mediates cerebral ischemic tolerance in a neonatal rat model of hypoxic preconditioning.

Neuroprotection against cerebral ischemia can be realized if the brain is preconditioned by previous exposure to a brief period of sublethal ischemia. The present study was undertaken to test the hypothesis that nitric oxide (NO) produced from the neuronal isoform of NO synthase (NOS) serves as a necessary signal for establishing an ischemia-tolerant state in brain. A newborn rat model of hypoxic preconditioning was used, wherein exposure to sublethal hypoxia (8% oxygen) for 3 hours renders postnatal day (PND) 6 animals completely resistant to a cerebral hypoxic-ischemic insult imposed 24 hours later. Postnatal day 6 animals were treated 0.5 hour before preconditioning hypoxia with the nonselective NOS inhibitor L-nitroarginine (2 mg/kg intraperitoneally). This treatment, which resulted in a 67 to 81% inhibition of calcium-dependent constitutive NOS activity 0.5 to 3.5 hours after its administration, completely blocked preconditioning-induced protection. However, administration of the neuronal NOS inhibitor 7-nitroindazole (40 mg/kg intraperitoneally) before preconditioning hypoxia, which decreased constitutive brain NOS activity by 58 to 81%, was without effect on preconditioning-induced cerebroprotection, as was pretreatment with the inducible NOS inhibitor aminoguanidine (400 mg/kg intraperitoneally). The protective effects of preconditioning were also not blocked by treating animals with competitive [3-(2-carboxypiperazin-4-yl)propyl-1-phosphonate; 5 mg/kg intraperitoneally] or noncompetitive (MK-801; 1 mg/kg intraperitoneally) N-methyl-D-aspartate receptor antagonists prior to preconditioning hypoxia. These findings indicate that NO production and activity are critical to the induction of ischemic tolerance in this model. However, the results argue against the involvement of the neuronal NOS isoform, activated secondary to a hypoxia-induced stimulation of N-methyl-D-aspartate receptors, and against the involvement of the inducible NOS isoform, but rather suggest that NO produced by the endothelial NOS isoform is required to mediate this profound protective effect.

Differences in vulnerability to permanent focal cerebral ischemia among 3 common mouse strains.

Background and Purpose Genetically engineered mice are used to study the role of single genes in cerebral ischemia, but inherent, strain-dependent differences in neuronal vulnerability may affect experimental end points. To examine this possibility, tissue injury resulting from focal ischemia and its relationship to cerebral hemodynamics were determined in 3 common mutant mouse strains. Methods Permanent middle cerebral artery ligation was performed in male C57BL/6J, Balb/C, and 129X1/SvJ mice. Mean arterial blood pressure, blood gases, basal and postischemic cortical blood flow ([14C]iodoantipyrine autoradiography and laser-Doppler flowmetry), posterior communicating artery patency, and infarct size were determined. Results Basal cortical blood flow did not differ among strains. Ten minutes after middle cerebral artery ligation, relative red cell flow in the ischemic cortex was 6% to 7% of preischemic flow in every strain. Despite similar hemodynamics, cortical infarcts in Balb/C mice were 3-fold larger than those in 129X1/SvJ and C57BL/6J mice; infarct size in the latter 2 strains was not significantly different. The posterior communicating artery was either poorly developed or absent in >90% of the Balb/C and C57BL/6J but in <50% of the 129X1/SvJ mice. Conclusions The extent of ischemic injury differed markedly between the 3 strains. The presence and patency of posterior communicating arteries, although variable among strains, did not affect preischemic or postischemic cortical blood flow or bear any relationship to ischemic injury. Therefore, intrinsic factors, other than hemodynamic variability, may contribute to the differences in ischemic vulnerability among strains. These findings underscore the importance of selecting genetically matched wild-type controls.

Cerebral protection by hypoxic preconditioning in a murine model of focal ischemia-reperfusion.

Sublethal periods of hypoxia or ischemia can induce adaptive mechanisms to protect against subsequent lethal ischemic insults in a process known as ischemic preconditioning. In the present study, we developed a murine model of cerebral preconditioning using several common strains of adult mice. Animals were exposed to sublethal hypoxia (11% oxygen for 2 h) 48 h prior to a 90 min period of transient focal middle cerebral artery occlusion, induced by an intraluminal filament; injury was assessed 24 h later by TTC staining. Infarct volume in hypoxia-preconditioned animals was reduced 46%, 58%, and 64% in C57Bl/6, 129SvEv, and Swiss-Webster ND4 mice relative to their respective untreated controls. This non-invasive murine model of ischemic tolerance should be useful for elucidating the molecular basis of this protection using transgenic and knockout mice.

Ankle spasticity and strength in children with spastic diplegic cerebral palsy

Ankle spasticity and strength in 27 children with spastic diplegic cerebral palsy (CP) (mean age 9 years, range 3 to 18 years) and a group of 12 children without CP (comparison group) (mean age 9 years, range 5 to 18 years) were observed. To measure spasticity, a KinCom dynamometer dorsiflexed the passive ankle at five different speeds and recorded the resistive plantarflexion torques. Work values for the torque‐angle data were calculated at each speed. Using this data, linear regression was used to measure spasticity. To measure strength, the dynamometer rotated the ankle from maximum dorsiflexion to maximum plantarflexion at a speed of 10°/s while the child performed a maximum plantarflexion concentric contraction. The movement was reversed to record maximum dorsiflexion. Maximum torques and work by the plantarflexors and dorsiflexors were calculated. The group with CP had significantly more spasticity in the plantarflexors and significantly less strength in the plantarflexors and dorsiflexors than the group without CP. Results provide objective information quantifying ankle spasticity and strength in children with CP.

Sagittal craniosynostosis outcome assessment for two methods and timings of intervention.

A retrospective quantitative analysis of 40 infants who underwent surgery for sagittal craniosynostosis was conducted to determine whether any difference in outcome, with respect to cranial index (cranial width/cranial length x 100), could be associated with either the age at surgery or the extent of the operation. Children < or = 13 months old at surgery and for whom there were archived computed tomography digital data preoperatively, perioperatively, and 1 year postoperatively were studied. For statistical analysis, the operation was classified as either extended strip craniectomy or subtotal calvarectomy, and the age at operation was either < or = 4 months or > 4 months. Twenty-eight patients underwent extended strip craniectomy at a mean age of 5.1 months. Their mean cranial index preoperatively was 67 versus 71 at 1 year postoperatively (p < 0.0001). Of extended strip craniectomy patients, 15 were operated on at age < or = 4 months (mean = 2.9 months) and 13 at age > 4 months (mean = 7.6 months). Mean cranial indices for age at operation groups did not achieve age-appropriate normal range values 1 year postoperatively for either group, and there was no significant difference between the mean percentages of improvement achieved (p = 0.143). Twelve patients underwent subtotal calvarectomy at a mean age of 5.2 months. Their mean cranial index preoperatively was 66 versus 74 at 1 year postoperatively (p < 0.0001). The mean cranial index in this group reached age-appropriate normal range values 1 year postoperatively. The percentage improvement in cranial index 1 year after subtotal calvarectomy was greater than after extended strip craniectomy (p = 0.003). Extended strip craniectomy for sagittal craniosynostosis does not achieve normal cranial width:length proportions, even when performed before 4 months of age. Subtotal calvarectomy for sagittal craniosynostosis does achieve normal cranial width:length proportions in the majority of the children, at least when performed within the first 13 months of life.

Experience with Surgical Decompression of the Arnold-Chiari Malformation in Young Infants with Myelomeningocele

Forty-five infants with myelomeningocele in whom hydrocephalus was absent or adequately controlled developed signs and symptoms of the Arnold-Chiari malformation before the age of 3 months. All of them underwent laminectomy and opening of the dura mater for hindbrain decompression. The clinical presentation included swallowing difficulty, apneic episodes, stridor, bronchial aspiration, arm weakness, and opisthotonos. Within 2 weeks of the initial clinical presentation, the neurological status of 14 patients (31%) deteriorated dramatically and culminated in irreversible neurological deficits. In all patients, compression of the brain stem occurred in the spinal canal. A transverse dural band constricting the dural sac at the C-1 level was noted in 41% of the patients, and a mild degree of arachnoidal adhesion was noted in 23%. The lowermost level of the cerebellar tongue or medullary kink was located at C-1 to C-4 in 28 cases and at C-5 to T-1 in 17 cases. Twenty-eight (62%) of the patients were alive and 17 (38%) had died at the last follow-up assessment. All survivors showed improvement of their overall neurological function. Twenty-four made a complete recovery. The majority of deaths were attributed to respiratory failure. Early recognition of symptoms and prompt decompressive laminectomy are essential for successful management of the Arnold-Chiari malformation in infants.

Subtemporal transparahippocampal amygdalohippocampectomy for surgical treatment of mesial temporal lobe epilepsy. Technical note.

Amygdalohippocampectomy (AH) is an accepted surgical option for treatment of medically refractory mesial temporal lobe epilepsy. Operative approaches to the amygdala and hippocampus that previously have been reported include: the sylvian fissure, the superior temporal sulcus, the middle temporal gyrus, and the fusiform gyrus. Regardless of the approach, AH permits not only extirpation of an epileptogenic focus in the amygdala and anterior hippocampus, but interruption of pathways of seizure spread via the entorhinal cortex and the parahippocampal gyrus. The authors report a modification of a surgical technique for AH via the parahippocampal gyrus, in which excision is limited to the anterior hippocampus, amygdala and parahippocampal gyrus while preserving the fusiform gyrus and the rest of the temporal lobe. Because transparahippocampal AH avoids injury to the fusiform gyrus and the lateral temporal lobe, it can be performed without intracarotid sodium amobarbital testing of language dominance and language mapping. Thus the operation would be particularly suitable for pediatric patients in whom intraoperative language mapping before resection is difficult.

Effects of Acute Bolus and Chronic Continuous Intrathecal Baclofen on Genitourinary Dysfunction Due to Spinal Cord Pathology

A prospective, blinded study was done to examine the effects of acute bolus and chronic continuous intrathecal baclofen on genitourinary function in 10 patients with severe spasticity due to spinal cord pathology. Genitourinary function was assessed by symptom questionnaires and urodynamic studies performed after a bolus dose of baclofen and 6 to 12 months after continuous intrathecal baclofen. Results were compared to placebo for acute bolus testing or to pre-continuous intrathecal baclofen values. In all patients with irritative voiding and urge incontinence uninhibited bladder contractions were eliminated. Of 3 patients with an indwelling urethral catheter for incontinence due to detrusor hyperreflexia 1 was converted to intermittent self-catheterization. Whereas bladder capacity, compliance, sensation and voiding pressures were not different after continuous intrathecal baclofen, when a mean of all patients was compiled, a 72% increase in capacity and 16% improvement in compliance were observed in subjects without cervical spinal cord pathology. Detrusor-sphincter dyssynergia was abolished in 40% of the patients. Continuous intrathecal baclofen may represent a novel approach to the management of patients with a neurogenic bladder who have decreased bladder compliance and detrusor hyperreflexia not controlled by oral medications.