Neuronal activity evoked by chronically implanted intracortical microelectrodes

The averaged evoked compound action potentials (AECAPs) were recorded from the ipsilateral pyramidal tract of awake, unrestrained cats before, during, and after continuous electrical stimulation of the cerebral cortex via chronically implanted activated iridium or platinum-30% iridium (Pt30%Ir) microelectrodes. After stimulating 24 h at 20 pulses per second (pps), using charge-balanced, 200-microseconds pulse pairs of 40 to 80 microA (400 to 800 microC/cm2, 8 to 16 nC/phase (ph), 2 to 4 A/cm2), there was a transient elevation of the threshold of the early (direct) and of the alte (transynaptic) components of the AECAP. After cessation of continuous stimulation at 80 microA, the threshold of the early component of the AECAP remained elevated for as long as 24 h and the late component as long as 4 days, indicating significant but reversible depression of the electrical excitability of cortical neurons close to the microelectrodes. In three cats stimulated 23 h/day for 1 week, the AECAP also recovered to their prestimulus threshold. In contrast, pulsing for 24 h at 320 microA (3200 microC/cm2, 64 nC/ph, 16 A/cm2) produced marked elevation of the threshold of the AECAPs which was not reversed by 7 to 12 days after termination of intracortical stimulation. The electrical excitability of neurons adjacent to (unpulsed) microelectrodes 2 mm from the pulsed electrode was not affected. The observations reported here, in conjunction with the histologic results reported in the companion paper, indicate that both the Pt30%Ir and the iridium microelectrodes can be operated safely at currents to at least 80 microA, charge/ph of 16 A/cm2, and a charge density of 800 microC/cm2 X ph. However, on the basis of the electrophysiologic criteria, both types appear to be unsafe when pulsed at 320 microA (64 nC/ph, 3200 microC/cm2 X ph, 16 A/cm2).     

Anterior interosseous nerve syndrome. Electromyographic characteristics (2 cases) and review of the literature (62 cases)

The anterior interosseous nerve syndrome is a rare entrapment neuropathy of the median nerve. It is a pure motor deficit characterized by pinch loss. Anterior interosseous nerve lesions are easily assessed by EMG. The data from literature being incomplete in a majority of cases (85%), we propose EMG criteria to assert the presence of an anterior interosseous nerve syndrome and to exclude other diagnoses. The study of the anterior interosseous nerve in 20 healthy patients shows that the difference in motor potential latency between the healthy and the non-healthy side is the most predictive stimulo-detection sign. Detection, however, remains the most important element for diagnosis.     

Vitamin D3 derivatives inhibit the differentiation of Friend erythroleukemia cells

A number of vitamin D3 metabolites inhibit benzodiazepine- and dimethyl sulfoxide-induced differentiation of Friend erythroleukemia cells. The inhibition is dose dependent and occurs at nM concentrations. The order of potency of these compounds is 1,25-dihydroxycholecalciferol greater than 1,25,26-trihydroxycholecalciferol greater than 1,24R,25-trihydroxycholecalciferol greater than 1 alpha-hydroxycholecalciferol greater than 24R,25-dihydroxycholecalciferol greater than 25S,26-dihydroxycholecalciferol. The inhibition is maximal when the vitamin D3 analogs are added together with the inducer, and becomes progressively decreased with delayed addition. These results suggest that the vitamin D3 metabolites may play a regulatory role in erythropoiesis.     

Pharmacokinetics of intravenous bepridil in patients with coronary disease

The pharmacokinetics of intravenous bepridil (1-[2-(N-benzylanilino)-1-(isobutoxymethyl)ethyl]pyrrolidine ) were studied in 16 patients undergoing cardiac catheterization for evaluation of coronary disease, all with normal base-line hemodynamic and renal functions. Ten patients received 3 mg/kg and six patients received 4 mg/kg of bepridil infused over a period of 30 min. Plasma bepridil concentrations were measured by HPLC and analyzed by model-dependent and model-independent methods. The mean (+/- SD) maximum plasma bepridil concentrations at the end of the infusion were 2047 +/- 820 ng/mL (3 mg/kg) and 2478 +/- 1426 ng/mL (4 mg/kg). Postinfusion bepridil concentrations were best described by a two-compartment open model. The model-dependent harmonic mean distribution and elimination half-lives were 1.7 h (range: 1.1-2.2 h) and 19.7 h (range: 8.0-61.9 h), respectively. The harmonic mean elimination half-life from model-independent analysis was 14.9 h (range: 7.4-64.0 h). The arithmetic means of other model-independent kinetic parameters were systemic clearance, 0.524 +/- 0.215 L X kg-1 X h-1; Vd, 15.3 +/- 10.9 L/kg; and Vdss, 10.1 +/- 6.0 L/kg. Model-dependent and model-independent estimates of half-life and clearance agreed reasonably well. Bepridil was well tolerated, effecting little or no change in central hemodynamics or EKG intervals. The extensive distribution and relatively slow clearance of bepridil account for its long elimination half-life. Intravenous bepridil appears to be a safe calcium (II) antagonist that is suitable for once-a-day dosing.     

Comparison of onset and steady-state responses of hearing aids: implications for use of the auditory brainstem response in the selection of hearing aids

Input-output (I/O) functions of hearing aids were measured in response to a 2000-Hz tone burst, having 0.5 ms rise/fall time and 10 ms duration. I/O functions, measured with a hearing-aid analyzer, served as reference conditions. Hearing-aid outputs at onset and during the steady-state portion of the waveform differed; these differences often depended upon stimulus rate. The relation between onset and steady-state estimates of output were not always predictable from hearing-aid attack and release times. These findings indicate that the steady-state output limitation characteristics of hearing aids cannot be estimated from their onset responses. In turn, this suggests that ABR measurements may not provide accurate estimates of the compressive characteristics of hearing aids.     

The incidence of AIDS among blacks and Hispanics

Compared with whites, the acquired immune deficiency syndrome (AIDS) has affected blacks and Hispanics disproportionately. The cumulative incidence (CI) for black men was 2.6, and for Hispanic men 2.5, times the rate for white men. Intravenous (IV) needle use alone does not account for this difference. Not counting IV needle-using cases, the CIs for black and Hispanic men were 1.7 times the CI for white men. Although there were fewer cases in women than men, the white-to-minority disparity was greater for women. The CIs for black and Hispanic women were 12.2 and 8.5 times, respectively, the CI for white women. Prevention programs are urgently needed and should focus on risky behavior (IV needle sharing and receptive anal intercourse), not just risk groups.