June L. Dahl

The purification and properties of rat brain glutamate dehydrogenase.

—A method is described for the preparation of glutamate dehydrogenase in a highly purified form from rat brain. Only one protein band was detected when the enzyme was subjected to electrophoresis on SDS polyacrylamide gels. The rat brain enzyme was essentially identical to the rat liver enzyme with respect to electrophoresis on SDS polyacrylamide gels, immunochemical properties and most kinetic parameters. However, the brain enzyme was much less reactive with glutamate, was more sensitive to inhibition by haloperidol, and was considerably more stable than the liver enzyme.

Institutionalizing pain management: the post-operative pain management quality improvement project

Clinical practice and quality improvement (QI) guidelines for acute postoperative pain management have been developed to address the well-documented problem of undertreatment of postoperative pain. The Post-Operative Pain Management Quality Improvement Project (the POP Project) was initiated to determine whether an intervention designed to support hospitals in the development of QI efforts would lead to improvements in structures, processes, and outcomes consistent with recommended guidelines. A nationwide sample of 233 hospitals joined the project. The intervention consisted of written resource materials accompanied by support services that included an e-mail list server, a resource Web page, and assistance from POP Project staff via telephone. Data regarding critical structures, processes (practice patterns), and patient outcomes were collected at baseline before the intervention began and at follow-up 12 to 18 months later. Results showed a statistically significant increase from baseline (45%) to follow-up (72%) in the presence of structural elements that are critical to improving pain management. There were statistically significant improvements in practices including documented use of pain rating scales, decreased use of intramuscular opioids, and increased use of nonpharmacologic strategies. Patient survey data showed no change in pain outcomes. Evaluation data showed that 70% of hospitals were very or extremely satisfied with their participation in the POP Project and 90% of them planned to continue efforts to improve pain management after the POP Project ended. Further research is needed to determine how to translate the excellent results obtained for structure and process into meaningful outcomes for patients.

Pain Management and Prescription Monitoring

Preventing diversion and abuse of prescription controlled substances while ensuring their availability for legitimate medical use is an important public health goal in the United States. In one approach to preventing and identifying drug diversion, 17 states have implemented prescription monitoring programs (PMPs) to monitor the prescribing of certain controlled substances. While PMPs are not intended to interfere with legitimate prescribing, some in the pain management community feel that they negatively affect prescribing for pain management. This article describes a collaborative project initiated by the Pain & Policy Studies Group that brought together regulatory and pain management representatives twice in 1998 to share perspectives and reconcile differing views on the effects of PMPs. The ultimate goals of this project are to provide accurate information to healthcare clinicians about PMPs, better define the balance between preventing drug diversion and providing pain management, and promote continued dialog and cooperation among the groups.

Changes in tubulin heterogeneity during postnatal development of rat brain.

Abstract Tubulin isolated from rat brain at various stages of postnatal development was subjected to isoelectric focusing on polyacrylamide gels. Multiple bands, indicative of the heterogeneity of the protein, were apparent at all developmental ages. When isoelectric focusing patterns of tubulin from brains of increasing developmental age were compared, changes in the distribution and relative intensities of the bands were observed. These changes were most pronounced between 8–12 days of age and were seen whether the tubulin was isolated by DEAE-cellulose chromatography or by successive cycles of assembly-disassembly. The isoelectric focusing pattern of tubulin isolated from the 22-day-old animal was indistinguishable from that of the protein obtained from 30-day-old rat brain. These developmental changes in tubulin heterogeneity may relate to changes in the assembly properties of the microtubule protein or may reflect age-dependent changes in the relative contributions of mitotic spindles, axons, dendrites, and glia to the total pool of tubulin in brain.

Quality improvement challenges in pain management

A great deal of attention has been paid to the quality of pain management in the last decade, with growing recognition that the under treatment of pain is a major, yet avoidable, public health problem. Studies have consistently shown poor pain control for postoperative and trauma pain, cancer pain and for many chronic pain problems not related to cancer. Major barriers to effective pain management have been identified including the inadequate knowledge of health care professionals, patients and the public; lack of institutional commitment; regulatory concerns; and limited access to and reimbursement for interdisciplinary care. Despite efforts to address these barriers and continued advances in our understanding of pain, the quality of pain management remains inconsistent at best. The need to measure and improve the quality of care is increasingly recognized by consumers, payors and health care professionals alike. Serious and widespread quality problems exist throughout American medicine. The Institute of Medicine’s (IOM) report, A New Health System for the 21st Century, highlighted the disturbing absence of real progress toward restructuring health care systems to address both quality and cost concerns or toward applying advances in information technology to improve administrative and clinical processes (Richardson et al., 2001). The report also cited the lack of careful analysis and alignment of payment incentives with quality improvement. Some have expressed concern that market forces, not good science, are driving current pain management practices (Harden, 2002). The pain community must become engaged in quality improvement efforts and act upon its responsibility to define, measure, and improve the quality of pain management.

Conditioned morphine tolerance in the rat: absence of a compensatory response and cross-tolerance with stress.

In four separate experiments with rats as subjects, strong evidence was obtained that tolerance development to morphine analgesia occurs most rapidly when morphine delivery is paired with salient contextual cues. However, contextual cues previously paired with morphine did not elicit conditioned drug-compensatory responses when presented to nondrugged animals. These results were obtained by different analgesia assessments, with different drug-administration--analgesia-test latencies, and in environments differing with respect to stress level. Stress level did influence nociceptive response, as it was found that the combination of bright illumination, white noise, and a strong odor resulted in antinociception in the absence of drug. Moreover, rats that had a history of receiving morphine in this stressful context were tolerant to this stress-induced antinociception, but only when morphine was present in their systems. In the final two studies, this antinociception, which was cross-tolerant with morphine, was characterized with respect to naloxone reversibility and brain levels of met- and leu-enkephalin as determined by radioimmunoassay.

Dynorphin (1–13): Analgesia, hypothermia, cross-tolerance with morphine and β-endorphin

Intracerebroventricular administration of 20, 40 and 60 nmol of dynorphin (1-13) produced analgesia, as assessed by flinch/jump response to footshock, and hypothermia in the rat. Rats developed tolerance to both the analgesic and thermic effects of the 20 nmol dose of dynorphin. Dynorphin and beta-endorphin showed cross-tolerance with respect to their analgesic but not their thermic effects. Dynorphin and morphine also produced cross-tolerant analgesic effects. Naloxone (10 mg/kg, IP) completely blocked the barrel rolling produced by 20 nmol dynorphin but did not alter its analgesic or thermic effects.

THE MYENTERIC PLEXUS REGULATES CELL GROWTH IN RAT JEJUNUM

The roles of the myenteric and extrinsic nerves in the control of proliferation and cell growth in the rat jejunum were studied. The myenteric plexus and/or the extrinsic nerves in a segment of rat jejunum were ablated by serosal application of the surfactant benzyldimethyltetradecylammonium chloride or by crushing the nerves passing through the mesentery, respectively. Ablation of both myenteric and extrinsic nerves, but not the extrinsic nerves alone, resulted in a significant increase in the mitotic rate of the crypt-epithelial cells and in the size of VIP-immunoreactive neurons in the submucosal plexus. The increased mitotic rate was correlated with an increase in the weight of the mucosa per unit length of gut and in the villus length and crypt depth. Neither extrinsic denervation alone nor serosal application of saline had any effect on these parameters. Our results suggest that the myenteric plexus is able to influence the rate of cell proliferation and cell growth in the rat jejunum.

Neuroplasticity in the smooth muscle of the myenterically and extrinsically denervated rat jejunum

The objective of this study was to examine the effects of two different denervation procedures on the distribution of nerve fibers and neurotransmitter levels in the rat jejunum. Extrinsic nerves were eliminated by crushing the mesenteric pedicle to a segment of jejunum. The myenteric plexus and extrinsic nerves were eliminated by serosal application of the cationic surfactant benzyldimethyltetradecylammonium chloride (BAC). The effects of these two denervation procedures were evaluated at 15 and 45 days. The level of norepinephrine in whole segments of jejunum was initially reduced by more than 76% after both denervation procedures, but by 45 days the level of norepinephrine was the same as in control tissue. Tyrosine hydroxylase (nor-adrenergic nerve marker) immunostaining was absent at 15 days, but returned by 45 days. However, the pattern of noradrenergic innervating axons was altered in the segment deprived of myenteric neurons. Immunohistochemical studies showed protein gene product 9.5 (PGP 9.5)-immunoreactive fibers in whole-mount preparations of the circular smooth muscle in the absence of the myenteric plexus and extrinsic nerves. At 45 days, the number of nerve fibers in the circular smooth muscle increased. Vasoactive intestinal polypeptide (VIP)-immunoreactive fibers, a subset of the PGP 9.5 nerve fibers, were present in the circular smooth muscle at both time points examined. Choline acetyltransferase (CAT) activity and VIP and leucine enkephalin levels were measured in separated smooth muscle and submucosa-musosal layers of the denervated jejunum. VIP and leucine-enkephalin levels were no different from control in tissue that was extrinsically denervated alone. However, the levels of these peptides were elevated two-fold in the smooth muscle 15 and 45 days after myenteric and extrinsic denervation. In the submucosa-mucosa, VIP and leucine enkephalin levels also were elevated two-fold at 15 days, but comparable to control at 45 days. CAT activity was equal to control in the smooth muscle but elevated two-fold in the submucosa-mucosa at both times. These results provide evidence for innervation of the circular smooth muscle by the submucosal plexus. Moreover, these nerve fibers originating from the submucosal plexus proliferate in the absence of the myenteric plexus. Furthermore, the myenteric neurons appear to be essential for normal innervation of the smooth muscle by the sympathetic nerve fibers. It is speculated that the sprouting of the submucosal plexus induced by myenteric plexus ablation is mediated by increased production of trophic factors in the hyperplastic smooth muscle.

Effect of chemical ablation of myenteric neurons on neurotransmitter levels in the rat jejunum

We have quantified neurotransmitter changes in the rat jejunum in which the myenteric neurons were ablated by serosal application of benzalkonium chloride. Within 2 days after benzalkonium chloride treatment, there was a 40% reduction in the activity of choline acetyltransferase, a specific marker for cholinergic neurons, and a 25% reduction in the amount of vasoactive intestinal peptide per centimeter length of jejunum. By 15 days, levels were comparable to those in control segments, and by 45 days after myenteric neuronal ablation, levels in treated tissues were twice those in controls. In contrast, we observed no reduction in the amount of leucine-enkephalin per centimeter length of jejunum at early times after benzalkonium chloride treatment, although by 45 days, levels of this neurotransmitter in treated segments of jejunum were more than twice those in controls. Significant increases in muscle thickness and tissue weight were also observed at 15, 30, and 45 days after myenteric neuronal ablation. Thus we have observed that in response to chemical ablation of myenteric neurons in the rat jejunum, there is a thickening of the smooth muscle layers and a compensatory increase in the production of certain neurotransmitters by the surviving neuronal elements in the gut.