Stimulant therapy and seizure risk in children with ADHD.

Stimulants are an effective treatment frequently prescribed for attention-deficit-hyperactivity disorder (ADHD), but they commonly are believed to lower the threshold for seizures. Although several studies have revealed that stimulants do not exacerbate well-controlled epilepsy, there is a paucity of data about seizure risk in nonepileptic children treated with stimulants. Two hundred thirty-four children (179 males, 9.1 +/- 3.6 years of age; 55 females, 9.6 +/- 3.9 years of age) with uncomplicated ADHD received electroencephalograms (EEGs) performed in our institution. Thirty-six patients (15.4%) demonstrated epileptiform abnormalities, and 198 (84.6%) demonstrated normal or nonepileptiform EEGs. Rolandic spikes accounted for 40% of the abnormal EEGs and 60% of those with focal abnormalities. Stimulant therapy was elected by 205 of 234 patients (87.6%). Seizures occurred only in the treated group, in one of 175 patients with a normal EEG (incidence 0.6%, 95% confidence intervals 0%-1.7%) and three of 30 treated patients with epileptiform EEGs (incidence 10%, 95% confidence interval 0%-20.7%). Seizures occurred in two of 12 children (16.7%) with rolandic spikes. These data suggest that a normal EEG can be used to assign children with ADHD to a category of minimal risk for seizure. In contrast, an epileptiform EEG in neurologically normal children with ADHD predicts considerable risk for the eventual occurrence of seizure. The risk, however, is not necessarily attributable to stimulant use.

Maturation of glutamatergic neurotransmission in dentate gyrus granule cells.

We studied the development of glutamatergic neurotransmission in dentate gyrus granule cells (GCs) in hippocampal slices from 5 to 12-day-old rats. The active postnatal neuronogenesis in dentate permits GCs with staggered birthdates to be studied in situ in a single preparation. We recorded evoked responses to medial perforant path stimulation using visually-guided whole-cell patch clamping to select immature GCs, and biocytin filling to correlate electrophysiologic responses with maturational stage. Even within this immature cell population we found four distinct electrophysiologic patterns. Type 1 cells had no glutamatergic current; Type 2 cells had only N-methyl-D-aspartate receptor (NMDA) current; Type 3 cells had both NMDA and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) current although the NMDA component could be isolated at low stimulus intensity (NMDA threshold/=AMPA threshold. Type 1 cells were least mature, and Type 4 cells most mature as assessed by cell properties, dendritic arborization, and penetration of dendrites into the molecular layer. Thus NMDA-mediated currents predominate early in GC development as is consistent with their role in processes that determine dentate architecture - neuronal migration, dendritic outgrowth and regression, and synapse stabilization. By analogy with 'silent synapses' (i.e. synapses that contain only NMDA receptors), Type 2 cells are candidate 'silent cells' that may undergo activity-dependent acquisition of functional fast-conducting AMPA receptors with maturation.

Morphologic and electrophysiologic maturation in developing dentate gyrus granule cells.

Dentate gyrus granule cells from immature (7-28 days) Sprague-Dawley rats were examined with whole cell patch clamp recordings and biocytin filling in in vitro hippocampal slice preparations. Although recordings were confined to the middle third of the suprapyramidal limb of the dentate, the granule cells exhibited marked variability in their physiologic properties: input resistance (IR) ranged from 250 MOmega to 3 GOmega, and resting membrane potential (RMP) from -82 to -41 mV. Both IR and RMP were inversely correlated with dendritic length, a morphometric indicator of cell maturity. Thus the highest IR cells were the youngest, and maturation was characterized by a progressive decrease in IR, hyperpolarization of RMP, and elongation of the dendritic arbor. When cells were grouped by IR, significant intergroup differences were found in RMP, dendritic length, and number of dendritic terminal branches. Although cells of all IR categories were examined throughout the age spectrum under study, none of the inter-IR group differences was age-dependent. These data suggest that IR provides a reasonable estimate of granule cell maturity and that maturation entails predictable changes in cell properties and morphology. These aspects of maturation correlate with each other, are independent of animal age, and most likely proceed according to a program related to cell birth.

Joubert's syndrome and prenatal hydrocephalus.

Joubert's syndrome is an autosomal-recessive condition characterized by dysgenesis of the cerebellar vermis, hypotonia, developmental delay, a respiratory pattern of alternating tachypnea and apnea, and abnormal eye movements. Radiologic findings include a midline cerebellar cleft in place of the vermis and a characteristic shape of the fourth ventricle. Prenatal hydrocephalus has been proposed as a possible etiology for the cerebellar abnormalities but has not previously been described in association with this syndrome. The authors report a patient with clinical and radiographic features consistent with Joubert's syndrome who presented with congenital hydrocephalus.

GABAA currents in immature dentate gyrus granule cells.

We used whole cell patch clamp and gramicidin perforated patch recordings in hippocampal slices to study gamma-aminobutyric acid (GABA) currents in granule cells (GCs) from juvenile rat dentate gyrus (DG). GCs are generated postnatally and asynchronously such that they can be detected at different stages of their maturation in DG within the first month. In contrast, inhibitory interneurons are generated embryonically, and their circuitry is well developed even as their target GCs and GC excitatory connections are still being formed. In this study, two GABA currents evoked in GCs by medial perforant path stimulation are compared. The first, pharmacologically isolated by glutamate receptor blockade, is the product of direct activation of GABA interneurons with monosynaptic input to the recorded GC (monosynaptic GABAA). Monosynaptic GABAA displays slight outward rectification of its current-voltage relation, is 97% eliminated by 10 microM bicuculline and coincides temporally with the excitatory components of GC postsynaptic currents as has been described for GABAA currents in other brain regions. The second is a novel GABA response that is detectable in 10 microM bicuculline and is present on GCs only at the earliest stages of their maturation. Unlike monosynaptic GABAA, this transient GABA is eliminated by glutamate receptor blockade and hence is likely to be generated by interneurons activated via an intervening glutamatergic synapse (polysynaptically). It is predominantly chloride mediated, has a relative bicarbonate/chloride permeability ratio of 26%, and is unchanged by bath-applied saclofen and strychnine or by intracellular calcium chelation. It is 97% antagonized by 100 microM picrotoxin and 99% antagonized by 100 microM bicuculline. This current is thus a relatively bicuculline (BMI)-resistant GABAA current (BMIR-GABAA). Compared with monosynaptic GABAA, BMIR-GABAA has a later peak, slower time course of decay, and marked outward rectification. Its reversal potential is 7-8 mV depolarized to that of monosynaptic GABAA whether recorded in whole cell or with gramicidin perforated patch to preserve native internal chloride concentration. Together these data may suggest that BMIR-GABAA is evoked by an anatomically segregated population of interneurons activating a unique, developmentally regulated GABAA receptor. Further, the transient nature of this current coupled with its temporal characteristics that preclude overlap with the excitatory components of the synaptic response are consistent with a role that is trophic or signaling rather than primarily inhibitory.

The syndrome of acute near-total intrauterine asphyxia in the term infant.

Eleven term infants sustained an acute, near-total intrauterine asphyxia at the end of labor. Imaging studies documented a consistent pattern of injury in subcortical brain nuclei, including thalamus, basal ganglia, and brainstem; in contrast the cerebral cortex and white matter were completely or relatively spared. This pattern of injury correlated with the acute and long-term neurologic syndromes in these patients. Four patients had a severe neonatal encephalopathy that included prominent signs of brainstem dysfunction. The other seven patients had a moderate neonatal encephalopathy. Three of these patients had dystonia consistent with basal ganglia injury; all seven remained normocephalic and had good cognitive outcomes consistent with sparing of cerebral cortex and white matter. Finally, in all 11 patients, injury to organs other than the brain was usually subtle. The distribution of injury in these patients reflects the hierarchy of metabolic needs that are unmet after a severe, sudden disruption of substrate supply as occurs in an acute, severe asphyxia. Thus, the higher metabolic rate of the brain compared with other organs explains the significant neonatal encephalopathy with relative sparing of nonbrain organs. Similarly, the higher metabolic rate of subcortical nuclei compared with cerebral hemispheres explains the preponderance of subcortical damage. This clinical and imaging syndrome is in contrast with that seen in more prolonged but less severe intrauterine asphyxia, in which shunting of blood flow from nonbrain organs to the brain and from cerebral hemispheres to the thalamus and brainstem renders nonbrain organs and cerebral hemispheres most vulnerable.

Metabotropic glutamate receptor mediated long-term depression in developing hippocampus.

The effects of bath application of the metabotropic glutamate receptor (mGluR) agonist 1S,3R-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD, 10 microM) were studied at the Schaffer collateral-CA1 synapse in hippocampal slices from rats of 8-33 days postnatal age. In immature animals (8-12 days) ACPD induced a biphasic response characterized by an acute decrease in field EPSP slope (approximately 50-60% of baseline) in the presence of the agonist, followed by long-term depression (LTD, approximately 75-80% of baseline) after washout. In animals older than 20 days, ACPD induced a slow onset potentiation or minimal change. Both the acute depression and LTD were blocked by the mGluR antagonist alpha-methyl-4-carboxyphenyl glycine (MCPG). ACPD-induced LTD was blocked by the N-methyl-D-aspartate receptor (NMDAR) antagonists D(-)-2-amino-5 phosphopentanoic acid (AP5) and dizocilpine maleate (MK-801), and by ethanol. Glutamic pyruvic transaminase, an enzyme that selectively metabolizes endogenous extracellular glutamate, also blocked LTD suggesting that the requisite NMDA currents were tonically activated by extracellular rather than synaptically released glutamate. ACPD-induced LTD was blocked by staurosporine, indicating a requirement for serinethreonine kinase activation, and was unaffected by the L-type voltage sensitive calcium channel blocker nitrendipine and the A1 adenosine receptor antagonist 8-cyclopentyl-1,3-dimethylxanthine (CPT). Because mGluR-mediated LTD was observed only in immature CA1, mGluRs may play a role in hippocampal development, perhaps by contributing to synapse pruning in a temporally restricted fashion.

Long-term depression at the medial perforant path-granule cell synapse in developing rat dentate gyrus.

Long-term depression (LTD) is a decrease in synaptic efficacy that may model the elimination of inappropriate synapses during brain development. LTD might therefore be expected to be prominent in the juvenile hippocampal dentate gyrus (DG), where the majority of neuronogenesis and excitatory synapse production and pruning occur in the first postnatal month. Thus far, however, LTD in immature DG remains unexplored. Low-frequency stimulus induced homosynaptic LTD was studied at the medial perforant path-granule cell synapse in rats 8-30 days of age. LTD was most consistent and was of greatest magnitude in the youngest animals, and was more robust in response to stimulation at 1 Hz than at 3 or 5 Hz. LTD was saturable by repetitive delivery of low-frequency stimulation, and reversible by tetanic stimulation that induced long-term potentiation (LTP). LTD of the field EPSP was not prevented by bath application of the NMDA receptor antagonist AP5, the mGluR antagonist MCPG, or the L-type voltage sensitive calcium channel antagonist nitrendipine. In whole cell recordings LTD induction was blocked by hyperpolarization of the postsynaptic neuron but not by calcium chelation with BAPTA. Calcium chelation blocked LTP and simultaneously unmasked tetanus induced LTD. These data demonstrate that LTD is prominent in immature DG, that LTP and LTD are complementary processes, and that LTD is likely to be induced postsynaptically because it is voltage dependent, although the mechanism of voltage dependence remains to be elucidated.

Developmental changes in membrane properties and postsynaptic currents of granule cells in rat dentate gyrus.

1. Whole cell patch-clamp recordings were used to study dentate gyrus granule cells in hippocampal slices from juvenile rats (postnatal days 8-32). Membrane properties were measured with the use of current-clamp recordings and were correlated with the morphology of a subgroup of neurons filled with biocytin. The components of the postsynaptic currents (PSCs) induced by medial perforant path stimulation were characterized with the use of specific receptor antagonists in voltage-clamp recordings. 2. Granule cells located in the middle third of the superior blade of stratum granulosum from the rostral third of hippocampus were divided into three groups according to their input resistance (IR). Neurons with low IR (206 +/- 182 M omega, mean +/- SD) had hyperpolarized resting membrane potentials (-82 +/- 7 mV) and high-amplitude action potentials (108 +/- 23 mV). Neurons were high IR (1,259 +/- 204 M omega) had more depolarized resting membrane potentials (-54 +/- 6 mV) and lower-amplitude action potentials (71 +/- 10 mV). Neurons with intermediate IR (619 +/- 166 M omega) also had intermediate resting membrane potentials (-63 +/- 7 mV) and action potential amplitudes (86 +/- 14 mV). Low-IR neurons became increasingly prevalent with advancing postnatal age, but neurons from each group could be found throughout the entire period under study. 3. Morphological studies of low-IR neurons revealed an extensive dendritic arborization that traversed the entire molecular layer and was characteristic of mature granule cells. High-IR cells had smaller somata and short, simple dendritic arborization that incompletely penetrated the molecular layer and were classified as immature. Intermediate-IR cells had morphological features of intermediate maturity. 4. The initial phase of the PSC evoked at -80 mV was a fast inward current that was comparable with respect to latency to peak, latency to onset, and 10-90% rise time in neurons of all maturities held at -80 mV. This current was 6-cyano-7-nitroquinoxaline-2,3-dione sensitive. 5. The decay phases of PSCs at -80 mV varied with neuronal maturity. Mature neurons had monoexponential decays (tau = 8.9 +/- 3.6). Intermediate and immature neurons had prominent later inward currents that resulted in slower decays. In the case of the immature neurons, the inward current during the decay phase could be separated from the initial fast inward peak. The later inward currents in intermediate and immature neurons were bicuculline sensitive. 6. With the use of uniform ionic conditions of the extracellular and patch solutions, current-voltage relations and reversal potentials for pharmacologically isolated alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), N-methyl-D-aspartate (NMDA), and gamma-aminobutyric acid-A (GABAA) currents were comparable across all cell maturities. Calculated ratios for peak GABAA/NMDA/AMPA currents decreased significantly with maturation as follows: 9.4 +/- 2.9/1.4 +/- 0.5/1.0 for immature cells, 7.2 +/- 2.5/1.5 +/- 0.7O/1.0 for intermediate cells, and 2.0 +/- 1.2/0.9 +/- 0.4/1.0 for mature cells. 7. GABA current was mediated both by polysynaptic activation of interneurons and by direct activation of interneurons with monosynaptic input onto granule cells. The proportional contributions of mono- and polysynaptic GABA to total GABA were comparable across all cell maturities; latency to peak GABA current decreased with increasing cell maturity for both mono- and polysynaptic components. 8. We conclude that PSCs evoked in granule cells by medial perforant path activation in neurons of all maturities consist of both glutamatergic and GABAergic components. PSCS are dominated by GABAergic neurotransmission in immature granule cells, and the contribution of glutamatergic neurotransmission increases with neuronal maturation. The greater ratio of peak GABAA to glutamate currents and the longer time interval between their respective peaks combine to produce a distinctive PSC shape

AP5 blocks LTP in developing rat dentate gyrus and unmasks LTD.

The hippocampal dentate gyrus undergoes active neuronogenesis as well as growth and regression of neuronal elements and connections during the early postnatal period. In some brain regions, most notably in the visual system, both activity-dependent synaptic plasticity and NMDA receptor activation are candidate mechanisms by which neuronal architecture may be refined during brain maturation. To investigate whether similar mechanisms might obtain in developing dentate, we studied the effects of tetanic stimulation before and after NMDA receptor blockade in hippocampal slices from rats at 7-33 days. Field potentials were recorded in the suprapyramidal granule cell layer in response to stimulation of the medial perforant path. Robust long-term potentiation (LTP) of population spike amplitude (approximately 200% of baseline) was produced by a single tetanus (100 Hz, 2 s, 200 microseconds) at all ages studied. Application of 10 microM AP5 depressed population spike amplitude only in the younger slices (approximately 81% of baseline at 8-15 days; approximately 86% of baseline at 16-24 days), suggesting that the NMDA receptor-mediated component of normal synaptic transmission is higher in early development and decreases with maturation. AP5 prevented or significantly diminished LTP at all ages, establishing the NMDA dependence of LTP induction in the medial perforant path throughout development. AP5 also unmasked tetanus-induced homosynaptic long-term depression (62-75% of baseline) in the younger slices (8-24 days). Thus, prominent NMDA receptor-mediated activity and the capacity for bidirectional synaptic plasticity are characteristic of immature dentate. These processes may influence dentate morphogenesis by contributing to the growth, regression, and stabilization of neuronal elements.

Perforant path kindling alters dentate gyrus field potentials and paired pulse depression in an age-dependent manner.

The effects of rapid perforant path kindling on field potentials and paired pulse depression were studied in the dentate gyrus of rats at four developmental stages: 14-16 days, 20-22 days, 27-29 days and 40-60 days (adult). In rats 14-29 days kindling was associated with sustained potentiation of population spike amplitude and population EPSP slope; in adults a progressive decline was seen in both measures. Inhibitory circuitry as assessed by paired pulse depression was intact at all ages studied. Kindling produced no lasting changes in this measure at 14-22 days; in the older age groups a significant increase in paired pulse depression was seen. Thus immature animals differed from adults in that they manifested persistent facilitation of excitatory transmission as a result of kindling and failed to mount a compensatory inhibitory response. These results suggest that the balance between excitation and inhibition is more readily shifted toward excitation in immature animals in a manner that may contribute to their unique vulnerability to epileptogenesis.

Hypoxic-ischemic brain damage in the term infant. Lessons from the laboratory.

Term infants who have sustained brain damage from intrauterine asphyxia can often be classified into one of two distinct clinical and radiologic syndromes. The first consists of damage to the cerebral hemispheres. The second consists of damage predominantly involving the basal ganglia and thalamus. Results of studies of asphyxia in experimental animals are presented.

Fetal stroke associated with elevated maternal anticardiolipin antibodies.

Middle cerebral artery infarction explains some cases of congenital hemiparesis with or without neonatal stroke. The etiology of the stroke is often obscure. We describe two infants with imaging evidence of middle cerebral artery infarction whose mothers had elevated anticardiolipin antibody levels after delivery. We speculate that these antibodies may have been responsible for intrauterine thromboembolic stroke.

Neonatal asphyxia: vulnerability of basal ganglia, thalamus, and brainstem.

Two infants who suffered acute intrapartum asphyxia resulting in severe neonatal encephalopathy are described. Although computed tomography revealed no abnormalities, magnetic resonance imaging documented unequivocal lesions in the thalamus, basal ganglia, parasagittal cortex, brainstem tectum, and midline cerebellum in one patient and in the basal ganglia and parasagittal cortex in the other. Thus, magnetic resonance imaging was more sensitive than computed tomography in detecting acute brain damage after neonatal asphyxia and may become an important tool in improving our understanding of the relationship between adverse perinatal events, neonatal encephalopathy, and neurologic morbidity.

NMDA receptor antagonists inhibit kindling epileptogenesis and seizure expression in developing rats.

N-Methyl-D-aspartate (NMDA) receptor antagonists inhibit both the kindling process and the expression of seizures in previously kindled adult rats. Experimental seizures are more readily produced in infant than adult rats, possibly related to a developmental predominance of NMDA receptor-mediated effects. If so, reduction of seizure susceptibility by NMDA receptor antagonists should be more dramatic in infant rats than in adults. We studied the effect of ketamine and MK-801 on kindling epileptogenesis and seizure expression in 15-day-old rats. Ketamine (5, 10, and 20 mg/kg) and MK-801 (0.033 and 0.1 mg/kg) both significantly increased the latency to stage 3 or 4 seizures in dose-dependent fashion. These results were similar to those found in adults but occurred at slightly lower doses. Ketamine 20 mg/kg and MK-801 0.33 mg/kg totally eliminated clinical seizure activity and nearly abolished afterdischarge in previously kindled infant rats, effects exceeding those reported in adults using doses up to 6 times as great. These results support the hypotheses that NMDA receptor-mediated neurotransmission plays an important role in seizure production and the increased seizure susceptibility in immature brain and raise the possibility that NMDA receptor antagonists could be useful antiepilepsy agents in young children.

Flunarizine does not delay the development of generalized seizures by amygdala kindling.

Adult rats underwent amygdala kindling after the administration of vehicle, flunarizine 20 mg/kg/day, or flunarizine 40 mg/kg/day. Stimuli were delivered thrice daily at current intensities twice after-discharge threshold (ADT). Flunarizine did not alter initial or post-kindling ADT and did not affect the latency (number of stimuli) to the first stage 5 seizure. Apart from a tendency to increase the latency between the first and the 4th stage 5 seizures, flunarizine had little if any effect on amygdala kindling in this protocol.

Proconvulsant effects of aminophylline during amygdala kindling in developing rats.

Aminophylline (A) is a proconvulsant in adult rats. We studied the effect of A on amygdala kindling in 15-day-old rat pups. Production of generalized seizures was significantly promoted by A at doses ranging from 10 to 100 mg/kg. Terminal status epilepticus (TSE) was produced in 33% of pups receiving 25 mg/kg A, 75% of pups receiving 50 mg/kg A, and 100% of pups receiving 100 mg/kg A. The number of stimuli needed to produce a stage 4-5 generalized seizure was significantly smaller in animals receiving 10 mg/kg A (5.7 +/- 3.4), 25 mg/kg A (3.4 +/- 2.4), 50 mg/kg A (1.9 +/- 1.4), or 100 mg/kg A (1.9 +/- 1.6) than in saline-treated controls (12.3 +/- 3.7) (P less than 0.001). In addition, 16% of pups receiving 50 mg/kg and 33% of pups receiving 100 mg/kg A and never stimulated developed TSE. These seizure-promoting effects of A in rat pups undergoing amygdala kindling are far more dramatic and occur at far lower doses than those previously reported in adults.

Revascularization for moyamoya disease: five-year follow-up.

We present a case of severe moyamoya disease in a 4-year-old child involving the anterior and posterior circulations. Encephaloduroarteriosynangiosis was performed and the child was followed for 5 years with serial angiography. Early clinical stabilization was attained and the child has normal or superior intellectual development despite her early fixed deficits. Follow-up angiography revealed the development of several large direct anastomotic channels.

Quantitative analysis of cerebral vessels in the newborn puppy: the structure of germinal matrix vessels may predispose to hemorrhage.

Intracerebral hemorrhage in premature infants commonly originates in the germinal matrix (GM). We performed a quantitative analysis of cerebral microvasculature from newborn puppies, a model for neonatal periventricular and intraventricular hemorrhage, at the light and electron microscopic level. GM vessels were compared with those of other brain regions in an effort to delineate pathogenetically significant structural features that might predispose to hemorrhage. Light microscopic examination revealed that GM vessel density (103.0 vessels/mm2) was similar to that in white matter (98.3 vessels/mm2), but lower than that of cortex (155.6 vessels/mm2) or caudate (259.9 vessels/mm2). Mean blood vessel diameter was slightly larger in GM (9.0 mu) than cortex (6.9 mu), caudate (7.9 mu), and white matter (8.9 mu). Ultrastructurally, GM vessels were thinner along greater portions of their circumferences than vessels from other brain regions, as shown by their smaller ratio of vessel wall area/vessel lumen area and their greater fraction of vessel wall with thickness less than 0.25 mu. In addition, a significantly larger fraction of GM capillary wall lacked direct contact with perivascular structures. We postulate that the larger size, thinner walls, and diminished support from surrounding neuropil, which characterize GM vessels, may render them more susceptible to both physical (e.g. hypertension) and metabolic (e.g. hypoxia) insults than vessels from other brain regions.

Parasagittal infarction in neonatal asphyxia.

A patient is described who suffered a bilateral hemorrhagic infarction in the parasagittal cerebrum following neonatal asphyxia. This case confirms experimental results that show the parasagittal cerebrum is especially vulnerable to ischemic damage in newborns.