Central neuronal mechanisms in cancer-induced bone pain.

PURPOSE OF REVIEW: To consider distinct neuropharmacological substrates that underlie transmission of impulses from the periphery to the central nervous system in cancer pain. RECENT FINDINGS: Advances reveal that plasticity, the ability of the nervous system to alter in response to external events, leads to changes throughout the pathways involved in the perception of pain. Exploitation of pharmacological, functional, molecular and genomic techniques is a basis for new insights into the molecular and cellular mechanisms that contribute to the pain that follows pathophysiology. Characteristic changes experienced with chronic or persistent pain from various causes include expanded receptive fields, allodynia and spontaneous pain in the absence of external stimuli. In addition there are the affective and emotional responses that have to be considered along with these sensory aspects of pain. SUMMARY: It is clear that although the sensory and psychological aspects of pain are separable, the neural pathways that contribute to these aspects of pain are interlinked. Furthermore, at both peripheral and central sites, there are mechanisms that amplify and prolong the painful stimulus--this can result in severe pain in the presence of relatively minor peripheral pathology. This review considers these signalling systems and changes therein in the context of pain in cancer.

Stabilization, injection and control of quantum cascade lasers, and their application to chemical sensing in the infrared.

Quantum cascade lasers (QCLs) are a relatively new type of semiconductor laser operating in the mid- to long-wave infrared. These monopolar multilayered quantum well structures can be fabricated to operate anywhere between 3.5 and 20 microm, which includes the molecular fingerprint region of the infrared. This makes them an ideal choice for infrared chemical sensing, a topic of great interest at present. Frequency stabilization and injection locking increase the utility of QCLs. We present results of locking QCLs to optical cavities, achieving relative linewidths down to 5.6 Hz. We report injection locking of one distributed feedback grating QCL with light from a similar QCL, demonstrating capture ranges of up to +/-500 MHz, and suppression of amplitude modulation by up to 49 dB. We also present various cavity-enhanced chemical sensors employing the frequency stabilization techniques developed, including the resonant sideband technique known as NICE-OHMS. Sensitivities of 9.7 x 10(-11) cm(-1) Hz(-1/2) have been achieved in pure nitrous oxide.

Frequency stabilization of quantum-cascade lasers by use of optical cavities.

We report a heterodyne beat with a linewidth of 5.6+/-0.6 Hz between two cavity-stabilized quantum-cascade lasers operating at 8.5 microm . We also present a technique for measuring this beat that avoids the need for extreme isolation of the optical cavities from the environment, that of employing a third servo loop with low bandwidth to force one cavity to track the slow drifts and low-frequency fluctuations of the other. Although it is not fully independent, this technique greatly facilitates heterodyne beat measurements for evaluating the performance of cavity-locked lasers above the bandwidth of the third loop.