Cannabinoid receptor agonists inhibit depolarization-induced calcium influx in cerebellar granule neurons.

Neuronal cannabinoid receptors (CB(1)) are coupled to inhibition of voltage-sensitive Ca(2+) channels (VSCCs) in several cell types. The purpose of these studies was to characterize the interaction between endogenous CB(1) receptors and VSCCs in cerebellar granule neurons (CGN). Ca(2+) transients were evoked by KCl-induced depolarization and imaged using fura-2. The CB(1) receptor agonists CP55940, Win 55212-2 and N-arachidonylethanolamine (anandamide) produced concentration-related decreases in peak amplitude of the Ca(2+) response and total Ca(2+) influx. Pre-treatment of CGN with pertussis toxin abolished agonist-mediated inhibition. The inhibitory effect of Win 55212-2 on Ca(2+) influx was additive with inhibition produced by omega-agatoxin IVA and nifedipine but not with omega-conotoxin GVIA, indicating that N-type VSCCs are the primary effector. Paradoxically, the CB(1) receptor antagonist, SR141716, also inhibited KCl-induced Ca(2+) influx into CGN in a concentration-related manner. SR141716 inhibition was pertussis toxin-insensitive and was not additive with the inhibition produced by Win 55212-2. Confocal imaging of CGN in primary culture demonstrate a high density of CB(1) receptor expression on CGN plasma membranes, including the neuritic processes. These data demonstrate that the CB(1) receptor is highly expressed by CGN and agonists serve as potent and efficacious inhibitory modulators of Ca(2+) influx through N-type VSCC.

A one-solar-constant irradiance standard.

A new high-intensity standard of total and spectral irradiance has been developed recently at the National Bureau of Standards. The standard consists of a 1000-W tungsten-halogen lamp mounted in a ceramic reflector, the reflecting surface of which is coated with flame-sprayed Al(2)O(3). The lamp-reflector combination results in a source having a relatively small (3 cm x 5 cm) radiating area yielding a total irradiance, at a distance of 40 cm, of about 136 mW cm(-2). The total irradiance calibrations are based on the radiance of a 1400-K blackbody and have an estimated maximum systematic error of 0.9% and a maximum estimated standard error of 0.19%. The spectral measurements were made over the wavelength range of 0.3 microm to 2.5 microm relative to the NBS 1000-W tungsten-halogen irradiance standards. The estimated uncertainty in these measurements ranges from 4% in the visible and near ir to 8% in the uv.

Procedures for determining the spectral responsivity of an infrared radiometer.

With the increasing number of commercial radiometers employing rather varied and sophisticated optical designs, the determination of the spectral responsivity of these radiometers has accordingly become more involved. A joint National Bureau of Standards-U. S. Army (Missile Electronics Warfare Technical Area, White Sands Missile Range, New Mexico) calibration of an ir radiometer was conducted at the White Sands Missile Range facility. The radiometer chosen for the measurements employed an uncooled PbS detector with a 10-cm Cassegrainian optical system. The selection of this particular type of instrument permitted two methods of measurement (each employing different standards and techniques) to be investigated. In order to simulate infinitely distant point sources, a 30-cm off-axis collimator was used in both methods of calibration. The methods of calibration and the uncertainties associated with each method are described and the application of the responsivity values to field measurements is discussed. The agreement of the spectral responsivity values as determined by each method is within the estimated uncertainty computed for each procedure.

The new tungsten-filament lamp standards of total irradiance.

The National Bureau of Standards standard of total irradiance as presently issued in the form of a 50-W carbon filament lamp was originally calibrated more than fifty years ago. Recently, needs for higher accuracy and wider ranges of total irradiance have necessitated the setting up of three sizes (100 W, 500 W, and 1000 W) of tungsten-filament lamp standards of total irradiance. These standards operate at a higher temperature than was possible with the carbon-filament lamps, and are shielded, except for a narrow area of the bulb in front of the filament, so the reception of long wavelength flux from the lamps is reduced to a minimum. The new lamps were calibrated by the use of a blackbody at a known temperature together with a quartz plate whose spectral transmittance was accurately determined. The quartz plate limits the flux received from the blackbody to the spectral region below about 4.5 micro and thus reduces errors resulting from water vapor absorption at 6 micro and longer wavelengths. Comparisons sow the new standards to be in close agreement with the carbon-filament lamp standard.

Spectral rradiances as determined through the use of prism and filter spectroradiometric techniques.

Two spectroradiometers, one based on a conventional prism monochromator and the other on a system employing narrow band pass interference filters, have been set up and independently used in the determination of the spectral irradiances of a number of sources over the wavelength range from 0.25 micro to 2.5 micro. Basically, the method of calibration for each system consists of comparing the spectral irradiance of the source under investigation with that of an NBS standard of spectral irradiance. The results obtained wit h each system on a number of continuous sources agree to about 1% whereas the differences in the spectral irradiances obtained with the two setups on a number of line sources range up to several percent.