Ionic channel currents in cultured neurons from human cortex.

Ionic channels in human cortical neurons have not been studied extensively. HCN-1 and HCN-1A cells, which recently were established as continuous cultures from human cortical tissue, have been shown by histochemical and immunochemical methods to exhibit a neuronal phenotype, but expression of functional ionic channels was not demonstrated. For the present study, HCN-1 and HCN-1A cells were cultured in Dulbecco's modified Eagle's medium with 15% fetal calf serum, in some cases supplemented with 10 ng/ml nerve growth factor, 10 microM forskolin, and 1 mM dibutyryl cyclic adenosine monophosphate to promote differentiation. Cells or membrane patches were voltage clamped using conventional patch clamp techniques. In HCN-1A cells, we identified a tetrodotoxin-sensitive Na+ current, two types of Ca2+ channel current, including L-type current and a second type that in some respects resembled N-type current, and four types of K+ current, including a delayed outward rectifier that showed voltage-dependent inactivation, two types of noninactivating Ca(2+)-activated K+ channels with slope conductances of 146 and 23 pS (K+i/K+o 145 mM/5 mM), and less frequently, a noninactivating, intermediate conductance channel that was not sensitive to internal Ca2+. When HCN-1A cells were examined after 3 days of exposure to differentiating agents, pronounced morphological changes were evident but no differences in ionic currents were apparent. HCN-1 cells also exhibited K+ and Ca2+ channel currents, but Na+ currents were not detected in these cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuromagnetic evidence of a dynamic excitation pattern generating the N100 auditory response.

Evoked magnetic field recordings were used to localize multiple sources of the negative component of cortical responses to auditory stimuli. The negative cortical component of the auditory evoked response, often called the N100, has traditionally been of interest due to its sensitivity to both stimulation parameters and cognitive variables. Results indicate that this component appears to reflect spreading activation of adjacent cortical columns within the primary projection area of the temporal lobe, extending anteriorly for about 1 cm following the downward slope of the superior surface of the lobe.

Desmopressin, but not vasopressin, decreases activity of the hypothalamo-neurohypophysial system in Brattleboro rats.

The pituitary neural lobe of homozygous Brattleboro rats has high rates of glucose utilization not affected by chronic treatment with exogenous vasopressin, despite attenuation of polydipsia and polyuria. We evaluated whether this effect may result from the inability of vasopressin to affect the hypothalamo-neurohypophysial metabolism or from the development of resistance to chronic vasopressin treatment. We used the [14C]deoxyglucose method to compare 28-h effects of vasopressin treatment (5 U/kg, i.m., twice a day) with that of desmopressin (100 micrograms/kg, i.p., once a day), a long-lasting antidiuretic hormone, on glucose utilization of the hypothalamo-neurohypophysial system and related structures in conscious homozygous Brattleboro rats. Vasopressin and desmopressin reduced water intake, plasma osmolality and plasma Na+ concentration similarly. Vasopressin decreased glucose utilization in the supraoptic nucleus, subfornical organ and median preoptic nucleus, but did not alter activity in the paraventricular nucleus and neural lobe. Desmopressin decreased glucose utilization in all these structures. The results indicate that desmopressin has a more potent inhibitory action on the hypothalamo-neurohypophysial system than vasopressin over this short duration of treatment. The lack of response in the neural lobe from chronic treatment with vasopressin seems to be due to its inability to affect the paraventricular nucleus metabolism. The maintenance of metabolic activity in the paraventricular nucleus of vasopressin-treated Brattleboro rats suggests that this structure contributes importantly to the metabolism of neural lobe.

Localization of auditory response sources using magnetoencephalography and magnetic resonance imaging.

Magnetoencephalography offers the possibility of localizing accurately and noninvasively the source of intracranial currents associated with normal and abnormal brain activity. The purpose of this study was to assess the validity and across-subject reliability of localization of cortical sources responding to ipsilateral and contralateral auditory stimulation. Magnetic evoked fields to both stimulation conditions were measured in eight consecutive normal subjects, and the cortical sources of these fields were estimated on the basis of these measurements. Subsequent projection of the source location coordinates onto magnetic resonance images showed that in all subjects the sources were accurately estimated to fall in the vicinity of the auditory cortex and that two separate sources may account for the response to ipsilateral and contralateral stimulation.

Source localization of two evoked magnetic field components using two alternative procedures.

The purpose of this study was to compare the relative efficacy of two methods in assessing the location of the sources of the N100 and P200 components of evoked magnetic fields (EMFs) to transient tone stimuli. EMFs to left ear stimulation, containing both components, were recorded over the right hemisphere of six normal subjects. The magnetic scalp distributions calculated at several adjacent time points, covering the duration of each component's peak, were used to estimate the source parameters of each component. Good estimates of the source of both components were obtained from all magnetic field distributions. The averaged spatial parameters derived from all distributions of each component as well as the parameters derived from the distribution that gave the best source estimate for each component were projected onto magnetic resonance images of subject's head. It was found that the source of each component is located on the superior surface of the temporal lobe and that the source of the P200 component is anterior to the N100 source in all subjects using both procedures.

The effect of hyperbaric oxygen on glucose utilization in a freeze-traumatized rat brain.

Local cerebral glucose utilization was measured with the autoradiographic 2-deoxyglucose technique in rats injured by a focal parietal cortical freeze lesion then treated with hyperbaric oxygen (HBO). The cold lesion depressed glucose utilization in the contralateral as well as in the ipsilateral hemisphere. The largest decreases were observed in ipsilateral cortical areas. Treatment of lesioned animals with HBO at 2 atm for 90 minutes on each of 4 consecutive days tended to increase the overall cerebral glucose utilization measured 5 days after injury when compared to animals exposed to normobaric air. This improvement reached statistical significance in five of the 21 structures studied: the auditory cortex, medial geniculate body, superior olivary nucleus, and lateral geniculate body ipsilateral to the lesion, and the mammillary body. The data indicate that changes in lesioned rats exposed to HBO are not restricted to the period of time that the animals are in the hyperbaric chamber but are persistent.

Task-related EEG asymmetries: a comparison of alpha blocking and beta enhancement.

Alpha and beta content of spectrally analyzed EEG were used to assess differential hemispheric engagement during two linguistic tasks (semantic and phonetic) and one acoustic task involving detection of target items embedded within the same stimulus series. Beta content of the EEG increased reliably in the left hemisphere during the linguistic tasks, whereas the expected attenuation or blocking of alpha did not occur reliably. These data suggest that left hemisphere beta enhancement rather than alpha blocking is a more efficient index of differential hemispheric engagement during language processing.

Age-related differences in recovery cycle of auditory evoked potentials.

Age-related differences in cerebral responsiveness to stimuli as reflected by the recovery cycle of cortical auditory evoked potentials (EPs) were investigated in healthy young and elderly adults. Pairs of identical tones separated by a fixed 350 msec interval were presented at rates of 1.0/sec, 0.5/sec, and 0.2/sec (inter-pair-intervals of 650, 1650, or 4650 msec). No age difference in the P1-N1 or N1-P2 amplitudes to either tone of the pair was present with the two faster stimulation rates. However, age-specific amplitude effects emerged for the slowest rate. The P1-N1 and especially the N1-P2 amplitude of the EP to the first as compared to that of the second tone was greatly enhanced among the young, but not as much among the elderly adults. Similarly, group differences in baseline to N1 and P2 amplitude measures of EPs to the first tone of the pair were most pronounced at the fastest stimulation rate. These data indicate clear differences in the recovery cycle of EPs between normal young and elderly subjects and demonstrate the applicability of the two-tone stimulation procedure in the assessment of cerebral responsivity in normal and pathologic populations.