The University of Arizona

The Ossipov Laboratory


We are one of the laboratories that comprise the collaborative efforts of the Arizona Pain Research Group. This collaboration combines the many skills and expertise of a number of individuals with a strong interest in pain research. Our collective efforts are aimed towards discovering and understanding the mechanisms that drive chronic pain states as well as an understanding of how pain may become chronic, or as some have suggested, the "chronification" of pain.

We oftentimes have visitors that stay for as little as a week and up to a year or more. this is yet another exciting aspect of our work here, as we enjoy the interactions and making new friends from all over the globe.

Areas of Research Interest

A dominant part of our research has been on the changes that occur in the peripheral and central nervous system in response to nerve injury that results in the enhancement in the generation and transmission of pain. While experimental conditions and laboratory animals can be controlled for various factors, resulting in fairly consistent results, the general population is highly varied. Consequently, we find that the large majority, more than 90%, of us do not develop neuropathic pain after peripheral nerve injury. The reasons as to why some unfortunate individuals become afflicted with chronic pain conditions while the large majority of us escape it are largely unknown. One of our ongoing research projects is designed to address the question: What are the differences found in those animals that develop neuropathic pain when compared to those that do not?" Considerable evidence shows that neurons of the rostral ventromedial medulla (RVM) can influence the manifestation of pain. Cells in the RVM project to the dorsal horn of the spinal cord and either enhance (i.e., On cells) or inhibit (i.e., Off cells) nociceptive inputs. After experimental nerve injury, activation of the pain facilitatory system from the RVM maintains central sensitization and expression of neuropathic pain behaviors. On the other hand, an activation of the pain inhibitory system prevents the augmentation of pain expected from the nerve injury. This is exemplified by the observations that the most effective medications against neuropathic pain are those that either engage descending pain inhibitory circuits or that mimic the consequences of descending inhibition. Examples of these are the tricyclic antidepressants, serotonin-norepinephrine reuptake inhibitors (SNRI's), norepinephrine (NE) reuptake blockers, spinal clonidine and the gabapentinoids. One of the critical obstacles to our understanding of this problem is that the large majority of experimental animal work is performed with Sprague-Dawley outbred rats derived from a common stock, thus having a highly consistent genetic background. Consequently, approximately 90% of these rats respond to nerve injury with behavioral evidence of neuropathic pain. However, we recently found a closely related strain of rat, the Holtzman rat, that produced variable results in a model of nerve injury. Approximately one-half of these animals would develop behavioral signs of neuropathic pain whereas the remaining half would appear protected from the consequences of the nerve injury. Using these strains of animals, we were able to explore the differences in functioning of the descending pain modulatory systems that may confer protection from enhanced pain. We found that nerve injury resulted in two distinct populations of rats expressing varying levels of neuropathic pain. Those animals that showed signs of neuropathic pain were found to have activated descending pain facilitatory system, since blocking the activity of RVM neurons blocked pain. On the other hand, those not showing evidence of pain likely had increased pain inhibition, since blocking the inhibitory pathway by attenuating activity of the inhibitory neurons of the RVM or of the inhibitory transmitter in the spinal cord unmasked an underlying neuropathic pain. Our findings raise the interesting and unexpected concept that in many individuals, despite the presence of a mechanism capable of inducing pain, countervailing modulatory influences might prevent its behavioral manifestation. Failure to either engage descending inhibition or to remove a descending facilitation can result in chronic neuropathic pain. The "chronification" of pain may ultimately depend on descending modulation that regulates the spinal consequences of peripheral nerve injury. Our ongoing studies aim to examine the mechanisms that decide whether descending inhibition of facilitation dominates after injury.

Descending Pain Modulation Primary afferent nerves synapse onto second-order neurons in the spinal dorsal horn to transmit nociceptive inputs to the CNS. Ascending projection tracts from the dorsal horn target the thalamus, and collaterals project to the dorsal reticular nucleus (DRt), rostral ventromedial medulla (RVM) and periaqueductal grey (PAG). Projections from the thalamus target cortical structures and the amygdala. The lateral capsular (CeA) part of the “nociceptive amygdala” receives inputs from the brainstem and spinal cord, and bidirectional communications from thalamic and cortical sites pass through the lateral (LA) and basolateral (BLA) amygdala. Descending pain modulation is mediated through the PAG, which communicates with the RVM, which sends descending pain inhibitory and facilitatory projections to the spinal dorsal horn. The noradrenergic locus coeruleus (LC) receives inputs from the PAG, communicates with the RVM, and sends descending noradrenergic inhibitory projections to the spinal cord.

The J-FlashCalc Project


A project I have been working on for quite a while is the ever-evolving FlashCalc suite of computer programs for calculations relevant to pharmacology and related disciplines. FlashCalc was originally written in Visual Basic, and included algorithms for the calculation of dose-response curves, including the determination of A50 values and associated confidence intervals. FlashCalc could also provide analyses of relative potencies of dose-response curves compared to an initial reference standard, and tell you if any of the DRCs are significantly different from the reference. Tests for parallellism were also available. My Opus Magnum here was the writing a program for Isobolographic Analyses. based on DRCs for 2 drugs alone, and for a combination given in a fixed ratio, this analyses would determin if the combination was synergistic or simply additive. There were also routines for a number of common statistical analyses, tests for outliers, and concentration calculators, etc.

A big drawback to programming in Visual Basic 6 was the simple fact that the compiled program would only run on a computer running the Windows operating system. I was dealt a setback by the unveiling of Windows Vista, which is not too happy with older versions of Visual Basic (VB6), and by the intriduction of the Visual Studio 2005 by MS. This would be like learning a new language, and all my routines would have to be recoded and recomiled. So, instead, I decided that if I was to learn yet another programming language, then let it be JAVA! Now my programs can run anywhere, and can be run from browser, also - yet another advantage of JAVA. Earlier, I had to distribute FlashCalc on CD. I finally got some of the code reworked into JAVA, and am now able to introduce J-FlashCalc! It is still a work in progress, and additional functionalities will be added as soon as I can rewrite and test the applets. In the emantime, here is what is available:

  • A quick and dirty t-test routine. Just feed in the mean, N, and standard error or stndard deviation for each of 2 groups, and the program will tell you if they are significantly different or not. - Great for keeping your colleagues on thier toes.
  • J-FlashCalc to calculate and graph dose-response curves and A50 values
  • J-FlashCalc to perform isobolographic analyses and to graph the DRCs and the isobologram
  • An "up-down" calculator for determining the 50% withdrawal threshold for those using von Frey filaments applied incrementally (as per Chapman et al. 1994)
  • If you have degrees of freedom and the F-, t- or Chi-Squared value, this will give you the P value
  • and so very much more to come. Stay tuned...

So, go ahead and check out J-FlashCalc, or check back later on to see what upgrades have been implemented. Feel free to contact me if you have any difficulties with the program, or for suggestions and ideas.







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OSSIPOV

Michael H. Ossipov, Ph.D.
Research Professor
Dept of Pharmacology
College of Medicine
University of Arizona
1501 N. Campbell Ave.
PO Box 245050
Tucson AZ 85724-5050
Phone: 520-626-7495
Fax: 520-626-2204
michaelo@u.arizona.edu

A Majestic Saguaro