Quantitative EEG in babies at risk for hypoxic ischemic encephalopathy after perinatal asphyxia.

OBJECTIVE: To evaluate an electroencephalography (EEG)-based index, the Cerebral Health Index in babies (CHI/b), for identification of neonates with high Sarnat scores and abnormal EEG as markers of hypoxic ischemic encephalopathy (HIE) after perinatal asphyxia. STUDY DESIGN: This is a retrospective study using 30 min of EEG data collected from 20 term neonates with HIE and 20 neurologically normal neonates. The HIE diagnosis was made on clinical grounds based on history and examination findings. The maximum-modified clinical Sarnat score was used to grade HIE severity within 72 h of life. All neonates underwent 2-channel bedside EEG monitoring. A trained electroencephalographer blinded to clinical data visually classified each EEG as normal, mild or severely abnormal. The CHI/b was trained using data from Channel 1 and tested on Channel 2. RESULT: The CHI/b distinguished among HIE and controls (P<0.02) and among the three visually interpreted EEG categories (P<0.0002). It showed a sensitivity of 82.4% and specificity of 100% in detecting high grades of neonatal encephalopathy (Sarnat 2 and 3), with an area under the receiver operator characteristic (ROC) curve of 0.912. CHI/b also identified differences between normal vs mildly abnormal (P<0.005), mild vs severely abnormal (P<0.01) and normal vs severe (P<0.002) EEG groups. An ROC curve analysis showed that the optimal ability of CHI/b to discriminate poor outcome was 89.7% (sensitivity: 87.5%; specificity: 82.4%). CONCLUSION: The CHI/b identified neonates with high Sarnat scores and abnormal EEG. These results support its potential as an objective indicator of neurological injury in infants with HIE.

Chronic epilepsy in developing hippocampal neurons: electrophysiologic and morphologic features.

Despite the susceptibility of immature neurons to seizures, there are few models of epilepsy in the developing brain. By taking advantage of activity-dependent developmental changes in young neurons, we have developed a novel model of chronic epilepsy in cultured hippocampal slices. Incubating slices in tetrodotoxin (TTX) for at least 1 week produced significant changes in the electrical activity and appearance of CA1 pyramidal neurons. Extracellular recordings revealed multiple population spikes, and, in whole-cell recordings, evoked synaptic potentials lasting hundreds of milliseconds with many superimposed action potentials were present. Spontaneous firing with burst-like discharges was also evident. These changes were secondary to increased AMPA-receptor-mediated responses and decreased GABA(A) receptor events. Altered membrane properties involved increased expression of T-type Ca(2+) channels which are normally down-regulated in these neurons. TTX-treated neurons also showed abnormal dendritic branching. This model of chronic epilepsy in developing hippocampal neurons demonstrated many changes at the membrane, cellular and synaptic level that may provide new insights into the nature of epileptogenesis in the young brain.

N-type Ca2+ channels are located on somata, dendrites, and a subpopulation of dendritic spines on live hippocampal pyramidal neurons.

In the nervous system the influx of Ca2+ orchestrates multiple biochemical and electrical events essential for development and function. A major route for Ca2+ entry is through voltage-dependent calcium channels (VDCCs). It is becoming increasingly clear that the precise contribution VDCCs make to neuronal function depends not only upon their specific electrophysiological properties but also on their distribution over the nerve cell surface. One location where the presence of VDCCs may be critical is the dendritic spine, a structure known to be the major site of excitatory synaptic input. On spines, VDCCs are hypothesized to play an essential role in signal processing, learning, and memory. However, direct evidence for the presence of VDCCs on spines is lacking. Attempts to examine the distribution of VDCCs, or indeed any other components, on spines have been hampered since the size of many spines is close to the limits of resolution of conventional light microscopy. Using a new, biologically active, fluorescein conjugate of omega-conotoxin (Fl-omega-CgTx), a selective blocker of N-type VDCCs, and confocal microscopy, we have mapped the distributions of N-type VDCCs on live CA1 neurons in rat hippocampal slices. VDCCs were found on somata, throughout the dendritic arbor, and on dendritic spines in all hippocampal subfields. A comparison of three-dimensional reconstructions of structures labeled by Fl-omega-CgTx with those outlined by 1,1-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine (Dil) or Lucifer yellow confirmed the presence of N-type VDCCs on dendritic spines. However, spine frequency on dendrites labeled with Fl-omega-CgTx was much lower than the spine frequency on dendrites labeled with Lucifer yellow or Dil, suggesting that some spines lack N-type VDCCs. These results offer the first direct evidence for the localization of any voltage-dependent channel on dendritic spines. The presence of N-type VDCCs on dendrites and their spines argues that these channels may participate in the generation of active Ca2+ conductances in distal dendrites, and is consistent with a role for spines as specialized compartments for concentrating Ca2+.

Poliomyelitis-like paralysis during recovery from acute bronchial asthma: possible etiology and risk factors.

A poliomyelitis-like paralytic disease during recovery from an attack of bronchial asthma is described in two young children. They presented at the age of 13 and 22 months, respectively, with acute flaccid paralysis of one or both lower limbs and preserved sensation. Cerebrospinal fluid examinations revealed mild protein elevation in both and pleocytosis in the second infant. Enteroviruses were isolated in a nasal swab and stools of the second patient. Acute onset of flaccid paralysis with absent motor action potential and normal sensory responses, detected by electrophysiologic studies, are highly suggestive of motor anterior horn cell disease in these infants. A multifactorial setup of immune suppression, stress, and neurotoxic drugs during an acute bronchial asthma attack triggered by a viral disease may render the patient vulnerable to viral invasion of the anterior horn cell with enteroviruses other than poliovirus. The overall experience of 22 patients with this serious complication is reviewed.

Postsynaptic and presynaptic effects of the calcium chelator BAPTA on synaptic transmission in rat hippocampal dentate granule neurons.

When applied to rat hippocampal slices, the permeable calcium chelator, BAPTA-AM, caused a reduction of both post-spike train slow afterhyperpolarizations (AHPs) and spike-frequency adaptation in dentate granule cells. This indicated that BAPTA-AM can, like microinjected EGTA, block calcium-activated potassium channels. At perforant pathway synapses, BAPTA-AM caused a reduction of inhibitory postsynaptic potentials (IPSPs) and an initial increase and later decrease of excitatory postsynaptic potentials (EPSPs). The initial increase in EPSPs may be caused by presynaptic spike-broadening owing to inhibition of calcium-activated potassium channels which normally regulate the duration of the presynaptic action potential. These channels may be affected at lower doses of chelator than synaptic transmitter release. BAPTA salt injected into individual dentate granule cells caused, as expected, decreased AHPs and spike-frequency adaptation. Also, paradoxically, both excitatory and inhibitory synaptic potentials were increased although input resistance was not.

Amphetamine actions on pre- and postpubertal rat hippocampal dentate granule neurons.

Clinical evidence suggests different actions of amphetamine (AMPH) in children and adults. Using intracellular recording techniques, the actions of AMPH at 10 and 40 microM were investigated in granule neurons of hippocampal slices from pre- and postpubertal rats. AMPH (10-40 microM) caused depolarization of most postpubertal neurons, often with increased spontaneous activity, whereas most prepubertal neurons were hyperpolarized. In both age groups, AMPH caused increased neuronal excitability by reducing spike threshold, attenuating the postspike train afterhyperpolarization, reducing spike frequency adaptation, and potentiating excitatory postsynaptic potentials. Changes in cell input resistance were variable and Ca2+ currents were unaffected. AMPH actions took 10-15 min to appear and became maximal 30-55 min after application. The effects were reversible at 10 microM, but at 40 microM, prolonged washout for up to 2 h did not completely reverse these actions. The beta-adrenergic blocker, propranolol, partially blocked AMPH actions. The dopamine (D2) blocker, haloperidol, did not block AMPH actions. Mature neurons were also tested with 2.5 microM AMPH showing similar but more reversible effects as the higher concentrations. Depleting catecholamines by reserpine partly attenuated the effects of 40 microM AMPH in mature neurons. Perfusion of neurons with 10 and 20 microM cocaine did not produce effects similar to those of AMPH. It is suggested that AMPH produces its effects on granule neurons only in part through the release of norepinephrine. The involvement of other neurotransmitters and/or neuromodulators released by AMPH, or direct postsynaptic actions of AMPH are also possible.

Pharmacological and anatomical separation of calcium currents in rat dentate granule neurones in vitro.

1. Rat dentate granule neurones in hippocampal slices were voltage-clamped at 21-23 degrees C using CsCl-filled microelectrodes. The perfusate contained TTX and K+ channel blockers to isolate pharmacologically inward Ca2+ currents. 2. From hyperpolarized holding potentials of -65 to -85 mV, depolarizing test potentials to between -50 and -40 mV elicited a transient (100-200 ms) low-threshold (TLT) current which was also elicited from more depolarized holding potentials following hyperpolarizing voltage steps of -40 mV or greater. 3. Larger depolarizing steps from a hyperpolarized holding potential triggered a large (2-6 nA), transient high-threshold (THT) inward current, rapidly peaking and decaying over 500 ms, followed by a sustained inward current component. 4. At depolarized holding potentials (-50 to -20 mV), the THT current was apparently inactivated and a sustained high-threshold (SHT) inward current was evident during depolarizing voltage steps of 10 mV or more. 5. From hyperpolarized holding potentials with depolarizing voltage steps of 10-30 mV, most neurones demonstrated a small-amplitude, sustained low-threshold (SLT) inward current with similar characteristics to the SHT current. 6. Zero-Ca2+ perfusate or high concentrations of Ca2+ channel blockers (Cd2+, Mn2+ or Ni2+) diminished or abolished all inward currents. 7. Repetitive voltage step activation of each current at 0.5 Hz reduced the large THT current to less than 25% of an unconditioned control current, reduced the SHT current by 50%, but had little effect on the TLT current. 8. A low concentration of Cd2+ (50 microM) blocked the THT and SHT currents with little effect on the TLT current. Nimodipine (1 microM) attenuated the SHT current. Ni2+ (100 microM) selectively attenuated the TLT current. 9. In low-Ca2+ perfusate, high concentrations of Ca2+ (10-15 mM), focally applied to different parts of the neurone, increased the THT current when applied to the dendrites, the SHT current when applied to the soma and the TLT current at all locations. Conversely, in regular perfusate, Cd2+ (1-5 mM), focally applied to the dendrites decreased the THT current and somatic applications decreased the SHT current. The TLT current was diminished regardless of the site of Cd2+ application. 10. These results suggest the existence of three different Ca2+ currents in dentate granule cells separable by their activation and inactivation characteristics, pharmacology and site of initiation.

Modulatory actions of serotonin on ionic conductances of hippocampal dentate granule cells.

Pressure ejection of serotonin (2 x 10(-4) M) onto dentate granule neurons in vitro produced a short-lasting membrane hyperpolarization associated with a 10-30% decrease in the input resistance. The hyperpolarization magnitude depended on the extracellular K+ concentration but not on the extra or intracellular Ca2+ concentration. It was followed by a depolarization, especially when serotonin was applied onto the perisomatic area of the neuron. The post-spike-train afterhyperpolarization, which represents a Ca2+-dependent K+ conductance, was decreased by serotonin by 10-100% and remained reduced for 2-10 min following the serotonin-induced hyperpolarization. Decreased adaptation of cell firing was also observed following serotonin application. Ca2+ action potentials evoked by intracellular depolarizing current pulses in the presence of the Na+ channel blocker tetrodotoxin and the K+ channel blocker tetraethylammonium were followed by a large afterhyperpolarization, which was markedly reduced for several minutes following serotonin application. The preceding Ca2+ action potential was either unaffected or prolonged. The hyperpolarization occurring in response to localized application of serotonin, and the reduction of the afterhyperpolarization, may represent two different mechanisms of serotonin action, probably mediated by different mechanisms. The slow time course of the late depolarization and the afterhyperpolarization depression represent modulatory effects of serotonin on dentate granule neurons.

Reversed ethanol effects on potassium conductances in aged hippocampal dentate granule neurons.

The effect of low dose (20 mM) ethanol superfusion on the membrane and synaptic properties of dentate granule neurons was studied in hippocampal slices from young-mature (6-8 months) and old (25-29 months) Fischer-344 rats. In young neurons, ethanol hyperpolarized the resting membrane potential (RMP) and prolonged the post-spike train afterhyperpolarization (AHP). By contrast, ethanol depolarized old neurons and decreased their AHPs, in addition to reducing IPSP amplitudes and spike frequency adaptation. These effects can be explained by ethanol-enhancing potassium conductance (gK) in young neurons and diminishing gK in old neurons.

Altered modulatory actions of serotonin on dentate granule cells of aged rats.

The effects of serotonin (5-HT) on dentate granule (DG) neurons in hippocampal slices taken from young mature (6-8 months) and old (25-29 months) rats were compared. Intracellular measurements of membrane potential, cell input resistance and slow postspike afterhyperpolarization did not differ significantly between young and old neurons. Neurons recorded in slices taken from old animals responded with less hyperpolarization to increasing doses of the drug, and their responses were significantly reduced after repeated applications of 5-HT. Serotonin-mediated reduction of the slow afterhyperpolarization in young DG neurons was less prominent or totally absent in the old cells. It is concluded that serotonergic postsynaptic actions are impaired in old age.