Reward shifts and motor responses following microinjections of opiate-specific agonists into either the core or shell of the nucleus accumbens.

Differences in pharmacology, anatomical connections, and receptor densities between the "core" and "shell" of the nucleus accumbens suggest that behavioral activity normally modulated by the accumbens, such as reward and motor functions, may be differentially regulated across the mediolateral axis. This study investigated the effects of opiate receptor-specific agonists on reward and motor functions in either the accumbens core or shell, using the intracranial self-stimulation (ICSS) rate-frequency curve-shift method. Microinjections of the mu opiate receptor-specific agonist, DAMGO (vehicle, 0.03 nmol, and 0.3 nmol), or the delta opiate receptor-specific agonist DPDPE (vehicle, 0.3 nmol, 3.0 nmol), were administered bilaterally in a random dose order with a minimum of 3 days between injections. Rats were tested over three consecutive 20-min rate-frequency curves immediately following a microinjection to investigate the time course of drug effects. Both opiate agonists decreased the ICSS frequency necessary to maintain half-maximal response rates when injected into the medial and ventral shell region of the accumbens. However, DAMGO microinjections into the lateral accumbens core or the control site of the caudate increased the frequency necessary to elicit half-maximal response rates, while DPDPE microinjections into these regions had no effect. Evaluation of motor effects show that administration of DAMGO resulted in a suppression of activity in all locations. In contrast, DPDPE microinjections resulted in little or no effect on lever pressing activity at any location.

Does privatization serve the public interest?

"Does Privatization Serve the Public Interest?" ask John B. Goodman and Gary W. Loveman. Supporters of privatization claim that it will bring more efficiency and better quality. Critics, however, argue that other values--the broader public interest--must be accounted for. The authors draw a valuable lesson from the debate over corporate takeovers: the form of ownership is less important than the establishment of managerial accountability.

Stresses created by occlusal prematurities in a new photoelastic model system.

A new photoelastic model system incorporating a simulated periodontal ligament sleeve around an experimental first molar has been developed. The system was used to visualize internal compressive stresses created by various premature occlusal incline relationships in both buccolingual and mesiodistal dimensions. When prematurities were applied singly and observed buccolingually, both class 1 and and class 2 prematurities produced stresses along the lingual aspect of the root, whereas the class 3 prematurity produced stresses along the buccal aspect of the root. When viewed buccolingually, combinations of class 1 and class 2 prematurities resulted in stresses along the lingual aspect of the root. The stress pattern was similar to those created by the single class 1 or class 2 prematurities. A combination of class 2 and class 3 prematurities did not produce a well-defined indication of stress distribution. There was slightly more stress along the buccal aspect of the root. Comparison of this combination with individual class 2 and class 3 prematurities indicates that such a combination tended to diminish tipping of the tooth in any one direction. A combination of class 1 and class 3 prematurities showed slightly greater stress along the buccal aspect of the root surface. Again, the combination produced less tipping of the tooth in any one direction when compared with tipping caused by the individual prematurities. When all three prematurities were tested at the same time, the stress pattern was almost coincident with that achieved in the absence of prematurities. When prematurities were observed mesiodistally, the location of stresses was dependent on the mesial or distal placement of the prematurity, irrespective of its position buccolingually.