Teamwork education improves trauma team performance in undergraduate health professional students

PURPOSE

Effective trauma resuscitation requires efficient and coordinated care from a team of providers; however, providers are rarely instructed on how to be effective members of trauma teams. Team-based learning using Team Strategies and Tools to Enhance Performance and Patient Safety (TeamSTEPPS) has been shown to improve team dynamics among practicing professionals, including physicians and nurses. The impact of TeamSTEPPS on students being trained in trauma management in an undergraduate health professional program is currently unknown. We sought to determine the impact of TeamSTEPPS on team dynamics among undergraduate students being trained in trauma resuscitation.

METHODS

We enrolled teams of undergraduate health professional students from four programs: nursing, physician assistant, radiologic science, and respiratory care. After completing an online training on trauma resuscitation principles, the participants completed a trauma resuscitation scenario. The participants then received teamwork training using TeamSTEPPS and completed a second trauma resuscitation scenario identical to the first. All resuscitations were recorded and scored offline by two blinded research assistants using both the Team Emergency Assessment Measure (TEAM) and Trauma Team Performance Observation Tool (TPOT) scoring systems. Pre-test and post-test TEAM and TPOT scores were compared.

RESULTS

We enrolled a total of 48 students in 12 teams. Team leadership, situational monitoring, and overall communication improved with TeamSTEPPS training (P=0.04, P=0.02, and P=0.03, respectively), as assessed by the TPOT scoring system. TeamSTEPPS also improved the team's ability to prioritize tasks and work together to complete tasks in a rapid manner (P<0.01 and P=0.02, respectively) as measured by TEAM.

CONCLUSIONS

Incorporating TeamSTEPPS into trauma team education leads to improved TEAM and TPOT scores among undergraduate health professionals.

Evaluation of Viewpoints of Health Care Professionals on the Role of Ethics Committees and Hospitals in the Resolution of Clinical Ethical Dilemmas Based on Practice Environment

We sought to evaluate whether health care professionals' viewpoints differed on the role of ethics committees and hospitals in the resolution of clinical ethical dilemmas based on practice location. We conducted a survey study from December 21, 2013 to March 15, 2014 of health care professionals at six hospitals (one tertiary care academic medical center, three large community hospitals and two small community hospitals). The survey consisted of eight clinical ethics cases followed by statements on whether there was a role for the ethics committee or hospital in their resolution, what that role might be and case specific queries. Respondents used a 5-point Likert scale to express their degree of agreement with the premises posed. We used the ANOVA test to evaluate whether respondent views significantly varied based on practice location. 240 health care professionals (108-tertiary care center, 92-large community hospitals, 40-small community hospitals) completed the survey (response rate: 63.6 %). Only three individual queries of 32 showed any significant response variations across practice locations. Overall, viewpoints did not vary across practice locations within question categories on whether the ethics committee or hospital had a role in case resolution, what that role might be and case specific queries. In this multicenter survey study, the viewpoints of health care professionals on the role of ethics committees or hospitals in the resolution of clinical ethics cases varied little based on practice location.

Osteopathic emergency medicine programs infrequently publish in high-impact emergency medicine journals

Introduction

Both the Accreditation Council for Graduate Medical Education (ACGME) and the American Osteopathic Association (AOA) require core faculty to engage in scholarly work, including publication in peer-reviewed journals. With the ACGME/AOA merger, we sought to evaluate the frequency of publication in high-impact peer-reviewed EM journals from authors affiliated with osteopathic emergency medicine (EM) programs.

Methods

We performed a retrospective literature review using the Journal Citation Report database and identified the top five journals in the category of ‘Emergency Medicine’ by their 2011 Impact Factor. We examined all publications from each journal for 2011. For each article we recorded article type, authors’ names, position of authorship (first, senior or other), the author’s degree and affiliated institution. We present the data in raw numbers and percentages.

Results

The 2011 EM journals with the highest impact factor were the following: Annals of Emergency Medicine, Resuscitation, Journal of Trauma, Injury, and Academic Emergency Medicine. Of the 9,298 authors published in these journals in 2011; 1,309 (15%) claimed affiliation with U.S.-based EM programs, of which 16 (1%) listed their affiliations with eight different osteopathic EM programs. The 16 authors claimed affiliation with 8 of 46 osteopathic EM programs (17%), while 1,301 authors claimed affiliation with 104 of 148 (70%) U.S.-based allopathic programs.

Conclusion

Authors from osteopathic EM programs are under-represented in the top EM journals. With the pending ACGME/AOA merger, there is a significant opportunity for improvement in the rate of publication of osteopathic EM programs in top tier EM journals.

Chest compressions do not disrupt the seal created by the laryngeal mask airway during positive pressure ventilation: a preliminary porcine study

OBJECTIVE

Pulmonary aspiration of gastric contents occurs 20 to 30% of the time during cardiopulmonary resuscitation (CPR) of cardiac arrest due to loss of protective airway reflexes, pressure changes generated during CPR, and positive pressure ventilation (PPV). Although the American Heart Association has recommended the laryngeal mask airway (LMA) as an acceptable alternative airway for use by emergency medical service personnel, concerns over the capacity of the device to protect from pulmonary aspiration remain. We sought to determine the occurrence of aspiration after LMA placement, CPR, and PPV.

METHODS

We inserted a size 4 LMA, modified so that a vacuum catheter could be advanced past the LMA diaphragm, into the hypopharynx of 16 consecutive postexperimental mixed-breed domestic swine. Fifteen millilitres of heparinized blood was instilled into the oropharynx. Chest compressions were performed for 60 seconds with asynchronous ventilation via a mechanical ventilator. We then suctioned through the LMA for 1 minute. The catheter was removed and inspected for signs of blood. The LMA cuff was deflated, removed, and inspected for signs of blood.

RESULTS

None of 16 animals (95% CI 0-17%) had a positive test for the presence of blood in both the vacuum catheter and the intima of the LMA diaphragm.

CONCLUSIONS

In this swine model of regurgitation after LMA placement, there were no cases with evidence of blood beyond the seal created by the LMA cuff. Future studies are needed to determine the frequency of pulmonary aspiration after LMA placement during CPR and PPV in the clinical setting.

Impact of checklists on peri-intubation care in ED trauma patients

BACKGROUND

Checklists have successfully been used in intensive care units (ICUs) to improve metrics of critical care. Proper peri-intubation care including use of appropriate induction agents and postintubation sedation is crucial when performing endotracheal intubation (ETI) on critically ill patients, especially in the emergency department (ED). We sought to evaluate the impact of checklists on peri-intubation care in ED trauma patients.

METHODS

We performed a retrospective review of all trauma patients intubated in the ED of an urban, level 1 academic center from November 2010 to October 2012. As part of a quality improvement project, a peri-intubation checklist was instituted on November 1, 2011 to guide peri-intubation care. Using a predesign and postdesign, we compared peri-intubation parameters using parametric and nonparametric statistics when appropriate to evaluate the impact of a checklist on peri-intubation care. We also evaluated outcome measures including mortality and lengths of stay.

RESULTS

During the 2-year study period, 187 trauma patients underwent ETI in the ED, 90 prechecklist and 97 postchecklist. Rapid sequence intubation (RSI) use was greater with the checklist than without (90.7% vs 75.6%, P=.005). No difference was found between the number of ETI attempts per patient, hemodynamic parameters (heart rate, blood pressure, and oxygen saturation), postintubation anxiolysis, median number of ventilator days, length of ED stay, length of ICU stay, or mortality.

CONCLUSION

Peri-intubation checklists result in higher rates of RSI in ED trauma patients but do not alter other measured metrics of peri-intubation care.

Comparison of video laryngoscopy and direct laryngoscopy in a critical care transport service

OBJECTIVE

We evaluated video laryngoscopy (VL) (C-MAC, Karl Storz, Tuttlingen, Germany) for use in a critical care transport system. We hypothesized that the total number of airway attempts would decrease when using a video laryngoscope versus use of direct laryngoscopy (DL).

METHODS

We performed a nonrandomized group-controlled trial where six aircraft were outfitted with VL and the remainder utilized DL responding to a mix of scene runs and interfacility transports. Our primary outcome measure was the number of intubation attempts. We also compared the first-pass success (FPS) rates, laryngoscopic grades, and frequencies of rescue device use (including utilization of surgical airways) between VL and DL.

RESULTS

Crews intubated 348 patients with VL and 510 with DL. Successful endotracheal intubation within three attempts occurred 97.6% (confidence interval [CI] 96.5-98.6) of the time. The FPS rate was 85.8% (CI 83.4-88.1). In this cohort of patients, VL did not differ from DL with respect to total number of airway attempts (1.17 [CI 1.11-1.22] vs. 1.16 [CI 1.12-1.20]), FPS rate (85.6% [CI 82-89%] vs. 86.1% [CI 83-89]), or use of rescue airways (2.6% vs. 2.2%). The laryngoscopic view was superior in the VL group relative to the DL group (median Cormack-Lehane grade 1 [interquartile range (IQR) 1, 2] vs. 2 [IQR 1, 2]).

CONCLUSION

VL using the C-MAC video laryngoscope did not reduce the total number of airway attempts or improve intubation compared with DL in a system of highly trained providers.

Estimates of sedation in patients undergoing endotracheal intubation in US EDs

BACKGROUND

Sedations after endotracheal intubation (ETI) reduce the risk of self-extubation, uncontrolled pain, and myocardial infarction. Although several small single-center studies demonstrate low rates of sedative drug administration after ETI in the emergency department (ED), little is known regarding post-ETI sedative drug practices nationally.

METHODS

We performed a retrospective cohort analysis of the ED portion of the National Hospital Ambulatory Medical Care Survey from 2006 to 2009. We identified all ED patient visits with ETI. Using the multiple probability sampling design of the National Hospital Ambulatory Medical Care Survey, we estimated the proportion of ETI patients receiving pharmacologic sedation, defined as benzodiazepines, opiates, or other sedative agents (propofol, ketamine, etc). We compared patients receiving sedative drugs with those who did not using descriptive statistics and univariable logistic regression.

RESULTS

During the 4-year study period, 1071000 patients (95% confidence interval [CI], 839000-1303000) underwent ETI in the ED. Of intubated patients, 46.4% (95% CI, 40.2%-52.7%) received sedative drugs, most commonly benzodiazepines (67.9%). Of patients who survived to hospital admission, 57.4% (95% CI, 48.7%-65.7%) received sedative drugs. Patients were less likely to receive sedation if they were diagnosed with circulatory or cardiac disease (odds ratio, 0.51; P = .026). Use of sedative drugs was not associated with patient age, sex, race, geographic location, or extended ED length of stay (>2 hours).

CONCLUSION

Less than one-half of patients undergoing ETI in the ED receive sedative drugs while in the ED. These findings are congruent with prior smaller studies from single academic centers.

Endotracheal intubation versus supraglottic airway insertion in out-of-hospital cardiac arrest

OBJECTIVE

To simplify airway management and minimize cardiopulmonary resuscitation (CPR) chest compression interruptions, some emergency medical services (EMS) practitioners utilize supraglottic airway (SGA) devices instead of endotracheal intubation (ETI) as the primary airway adjunct in out-of-hospital cardiac arrest (OHCA). We compared the outcomes of patients receiving ETI with those receiving SGA following OHCA.

METHODS

We performed a secondary analysis of data from the multicenter Resuscitation Outcomes Consortium (ROC) PRIMED trial. We studied adult non-traumatic OHCA receiving successful SGA insertion (King Laryngeal Tube, Combitube, and Laryngeal Mask Airway) or successful ETI. The primary outcome was survival to hospital discharge with satisfactory functional status (Modified Rankin Scale ≤3). Secondary outcomes included return of spontaneous circulation (ROSC), 24-h survival, major airway or pulmonary complications (pulmonary edema, internal thoracic or abdominal injuries, acute lung injury, sepsis, and pneumonia). Using multivariable logistic regression, we studied the association between out-of-hospital airway management method (ETI vs. SGA) and OHCA outcomes, adjusting for confounders.

RESULTS

Of 10,455 adult OHCA, 8487 (81.2%) received ETI and 1968 (18.8%) received SGA. Survival to hospital discharge with satisfactory functional status was: ETI 4.7%, SGA 3.9%. Compared with successful SGA, successful ETI was associated with increased survival to hospital discharge (adjusted OR 1.40; 95% CI: 1.04, 1.89), ROSC (adjusted OR 1.78; 95% CI: 1.54, 2.04) and 24-h survival (adjusted OR 1.74; 95% CI: 1.49, 2.04). ETI was not associated with secondary airway or pulmonary complications (adjusted OR 0.84; 95% CI: 0.61, 1.16).

CONCLUSIONS

In this secondary analysis of data from the multicenter ROC PRIMED trial, ETI was associated with improved outcomes over SGA insertion after OHCA.

Variables associated with successful intubation attempts using video laryngoscopy: a preliminary report in a helicopter emergency medical service

BACKGROUND

Multiple studies have demonstrated varying rates of successful endotracheal intubation (ETI). Until the application of video laryngoscopy, little information regarding prehospital intubation could be analyzed objectively by individuals other than the provider performing the ETI.

OBJECTIVE

To evaluate the association of variables recorded during video laryngoscopy and successful ETI attempts, defined as placing the endotracheal tube in the trachea.

METHODS

We retrospectively reviewed intubations performed by a single helicopter emergency medical service (HEMS) using a video larygoscope from March 1, 2010, to October 1, 2010. All videos were de-identified and analyzed by a single researcher. Time intervals (e.g., attempt time) and intubation process variables (e.g., Cormack-Lehane [C-L] view) were abstracted from all videos. Time intervals were begun when the laryngoscope blade passed the lips and entered the oral cavity (entry). We describe variables using means and standard deviations (continuous), medians with interquartile ranges (ordinal), and percentages with 95% confidence intervals (categorical). We then looked at univariate associations between these variables and ETI success using logistic regression.

RESULTS

We recorded 116 intubations during the study period. Twenty-nine recordings were either incomplete (n = 26) or of insufficient quality for analysis (n = 3). The remaining 87 videos represented 87 different patients with a total of 102 attempts at laryngoscopy. Thirty-six providers performed 64 cases, with the majority of providers (n = 21) performing only one intubation. The first-pass success rate in this series was 76% (n = 66), with 98% success within three attempts. Successful ETI attempts had lower entry-to-percentage of glottic opening (POGO) times (16.6 sec vs. 32.1 sec, p = 0.013), entry-to-first view of the endotracheal tube or entry-to-tube times (17.6 sec vs. 27.4 sec, p = 0.04), higher POGO scores (76 vs. 39, p < 0.001), and a lower C-L view (one vs. three, p < 0.001). Recognized esophageal intubation was more likely to occur during unsuccessful ETI attempts (43% vs. 8%, p < 0.001).

CONCLUSION

Video laryngoscopy can measure multiple components of ETI performance. Successful ETI attempts have significantly shorter entry-to-POGO times and entry-to-tube times, obtain better views of the glottic opening (POGO and C-L view), and have a lower incidence of recognized esophageal intubation.

Sedative and anxiolytic effects of zopiclone's enantiomers and metabolite

We evaluated racemic zopiclone, its (S)- and (R)-enantiomers and a metabolite, (S)-desmethylzopiclone, for their actions on locomotor activity, rotarod performance, the elevated plus maze and the Vogel conflict test of anxiety, and electroconvulsive shock-induced seizures duration. Zopiclone and its (R)- and (S)-enantiomers reduced locomotor activity, and zopiclone and its (S)-enantiomer disrupted rotarod performance at 10 mg/kg. (S)-desmethylzopiclone did not alter these measures at doses of less than 200 mg/kg. (S)-desmethylzopiclone altered plus maze performance at the lowest dose of all the zopiclone derivatives tested, caused a dose-related effect on the Vogel conflict test and caused a dose-related reduction of electroconvulsive shock-induced seizure durations. The data indicate that (S)-desmethylzopiclone can bring about an anxiolytic effect without a substantial degree of central nervous system depression, and suggest that the agent may be particularly useful clinically in the treatment of anxiety.

Enantioselective behavioral effects of sibutramine metabolites

The anti-obesity agent, racemic (RS)-sibutramine, has two active metabolites, desmethylsibutramine and didesmethylsibutramine. To the extent that sibutramine itself mediates some of its side effects, desmethylsibutramine and/or didesmethylsibutramine might be safer and just as therapeutically effective. Because both desmethylsibutramine and didesmethylsibutramine are also optically active, the present study assessed the anorexic effects (2.5-10 mg/kg, i.p., for all drugs), in rats, of the R(+)-and S(-)-enantiomers of both metabolites and compared them to the effects of racemic sibutramine. Locomotor activity (2.5-10 mg/kg, i. p., for all drugs), a dopamine dependent behavior, was also measured in view of some uncertainty regarding dopaminergic effects of sibutramine. In view of sibutramine's antidepressant profile in animal models, the same drugs were also tested in the Porsolt swim test (0.1-2.5 mg/kg, i.p., for all drugs). Lastly, the IC(50)s of all drugs to inhibit uptake in vitro of norepinephrine, serotonin and dopamine were determined. Both (R)-enantiomers had significantly greater anorexic effects than those of their respective (S)-enantiomers as well as of sibutramine. All of the agents increased locomotor activity and reduced immobilized time ("behavioral despair") in the swim test; again, the (R)-enantiomers were more potent than the (S)-enantiomers and sibutramine. However, the anorexic and locomotor effects could be dissociated from each other as well as from effects in the swim test. Both (R)-desmethylsibutramine and (R)-didesmethylsibutramine as well as sibutramine decreased food intake at a time (24-42 h post-treatment) when locomotor activity was unaffected. All of the drugs appeared to be more potent in the swim test than in the other tests and all of the drugs were more potent at inhibiting uptake of norepinephrine and dopamine than of serotonin. The results suggest that these enantioselective metabolites of sibutramine could be safe and effective treatments for obesity as well as possibly for depression.

Left and right 6-hydroxydopamine lesions of the medial prefrontal cortex differentially affect voluntary ethanol consumption

Dopaminergic projections to the medial prefrontal cortex (mPFC) were unilaterally lesioned with 6-hydroxydopamine (6-OHDA) to examine how dopamine (DA) asymmetry in the mPFC influences voluntary ethanol consumption. Differences in nucleus accumbens (NAS) DA neurotransmission have been related to individual differences in locomotor activity and in the rewarding efficacy of ethanol. Therefore, differences in locomotor activity were used to further characterize the effects of unilateral mPFC 6-OHDA lesions on ethanol consumption. Male Long Evans rats were assessed for high versus low levels of spontaneous locomotor activity. DA terminals in the left or right mPFC were unilaterally lesioned with 6-OHDA, resulting in an average DA depletion of 54% and 50%, respectively. After a minimum seven-day recovery period, preference for a 10% ethanol solution vs. water was determined in a 24-h 2-bottle home-cage free-choice paradigm. Left mPFC 6-OHDA lesions increased and right lesions decreased ethanol consumption. These differential effects of left and right lesions were primarily attributable to rats exhibiting low locomotor activity prior to surgery. The present data suggest that right greater than left cortical DA asymmetry in combination with low endogenous NAS DA (predicted by low locomotor activity levels) may increase the vulnerability to abuse ethanol.

Rotation, locomotor activity and individual differences in voluntary ethanol consumption

Spontaneous turning behavior and locomotor activity were evaluated for their ability to predict differences in the voluntary consumption of ethanol in male Long-Evans rats. Animals were assessed for their preferred direction of turning behavior and for high vs. low levels of spontaneous locomotor activity, as determined during nocturnal testing in a rotometer. Subsequently, preference for a 10% ethanol solution vs. water was determined in a 24-h two-bottle home-cage free-choice paradigm. Rats exhibiting a right-turning preference consumed more ethanol than rats showing a left-turning preference. While locomotor activity alone did not predict differences in drinking, turning and locomotor activity together predicted differences in ethanol consumption. Low-activity right-turning rats consumed more ethanol than all the other groups of rats. Previous studies from this laboratory have shown that individual differences in turning behavior are accompanied by different asymmetries in dopamine (DA) function in the medial prefrontal cortex (mPFC). Individual differences in locomotor activity are associated with differences in nucleus accumbens (NAS) DA function. The present data suggest that variations in mPFC DA asymmetry and NAS DA function may underlie differences in the voluntary consumption of ethanol.

Ethanol induced differences in medial prefrontal cortex dopamine asymmetry and in nucleus accumbens dopamine metabolism in left- and right-turning rats

Ethanol (0.5 g/kg i.p.) 15 min prior to sacrifice increased homovanillic acid (HVA) levels in the left medial prefrontal cortex (mPFC) of left-turning rats and in the right mPFC of right-turning rats. In the nucleus accumbens (NAS), ethanol decreased dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), and HVA levels in rats that exhibited low levels of locomotor activity but not in rats that exhibited high levels of locomotor activity. This laboratory has previously shown that rats exhibiting differences in turning and locomotor activity behavior display different preferences for ethanol. The present results suggest that ethanol-induced differences in mPFC and NAS DA activity may be related to individual differences in the susceptibility to abuse ethanol.

Differential immune responses in mice with left- and right-turning preference

Humoral and cell-mediated immune responses of inbred BALB/c male mice were assayed for differential reactivities associated with behavioral sidedness, which was evaluated by spontaneous rotational behavior in a circular cage model system. Mice with left-turning preference had lower in vivo primary IgM and IgG anti-Keyhole Limpet Hemocyanin (KLH) antibody responses, delayed-type hypersensitivity (DTH) responses, and host-resistance against the intracellular bacteria, Listeria monocytogenes, than mice with right-turning preference. The only immune parameter not shown to be associated with turning preference was the secondary humoral immune response to KLH. The weak innate immune response of left-turners for clearance of Listeria showed close intercorrelation with elevated serum IL-6 levels. Serum corticosterone and splenic norepinephrine levels were differentially increased and decreased by infection, respectively. We suggest that the observed differential immune reactivities of individual animals with same age, gender, and genetic background are associated with functional asymmetries within the brain, that the hypothalamic-pituitary-adrenal (HPA) axis and sympathetic innervation are involved in the regulatory brain: immune interconnection after infection, and that the HPA axis and sympathetic nervous system are involved in the brain laterality effects on immune responses.

Paw preference, rotation, and dopamine function in Collins HI and LO mouse strains

Mice have paw preferences that are consistent upon repeated measurement. The Collins HI and LO strains are two populations of mice that have been selectively bred to differ markedly in the degree of paw preference. They represent a unique genetic model of functional cerebral lateralization. Rotation (or circling) behavior in normal unlesioned animals reflects an endogenous lateralization of the functioning brain dopamine (DA) systems. In the present study, rotational behavior and lateralized brain DA neurochemistry were assessed in the Collins HI and LO strain mice. Confirming Collins findings, HI strain mice exhibited stronger paw preferences than LO strain mice. HI strain mice also showed stronger percent directional preferences during nocturnal tests of spontaneous rotation. Neurochemical differences were also apparent between the strains. DA and its metabolites were measured in the medial prefrontal cortex (PFC), nucleus accumbens (NAS), and striatum. Degrees of rotational and paw preference in HI, but not LO, mice were correlated with PFC asymmetries in DA and the DA metabolite dihydroxyphenyl acetic acid (DOPAC), respectively. Hemisphere, paw preference, turning preference, and strain interacted in a complex way to determine measures of DA utilization in the NAS and striatum. Even though the directions of paw preference and rotation were not correlated, HI and LO mice of differing paw and rotational directional preferences showed differences in DA neurochemistry in the NAS and striatum.

Effects of prenatal cocaine exposure on the mesocorticolimbic dopamine system: an in vivo microdialysis study in the rat

Microdialysis studies were conducted on prenatally saline-treated and prenatally cocaine-treated rats, either as pups (10-30 days old) or young adults (40-190 days old), to study the effects of prenatal cocaine exposure on the mesolimbic dopamine (DA) system. In the n. accumbens of saline-treated rats, basal dialysate concentrations of DA were similar in pups and adults; however, the levels of DA metabolites, DOPAC, HVA, and the serotonin metabolite, 5-HIAA, were markedly lower in pups. In pups, prenatal cocaine exposure led to basal dialysate levels of DA in the n. accumbens that were twice control levels; however, there was no difference in response to a period of intermittent tail pinch or an acute injection of cocaine (20 mg/kg). In the adult, basal levels of DA, DOPAC, HVA and 5-HIAA in n. accumbens did not differ across prenatal treatments. However, in prenatally cocaine-treated adults a cocaine injection led to an enhanced rise in extracellular DA compared to controls. In frontal cortex of adult rats, basal levels of DA, DOPAC and HVA did not differ across prenatal treatments; however, basal levels of 5-HIAA in this region were significantly elevated in prenatal-cocaine rats. No group differences were observed in the frontal cortex in response to either tail pinch or cocaine. Thus prenatal cocaine exposure produces an increase in basal extracellular DA in the n. accumbens of pups which returns to normal with aging. While this initial difference normalizes, prenatal cocaine exposure induces other persistent changes in adulthood.

Left and right 6-hydroxydopamine lesions of the medial prefrontal cortex differentially alter subcortical dopamine utilization and the behavioral response to stress

The effects of left and right prefrontal cortical dopamine (DA) depletion on circling behavior, stress-escape behavior and subcortical DA function were examined in rats exhibiting left or right turning biases. 6-Hydroxydopamine lesions of the medial prefrontal cortex (PFC) caused significant DA depletions when assessed in separate studies at 3 days and 3-4 weeks. However, depletions were smaller at 3-4 weeks and there was a significant increase in DA concentration on the left side following right lesions. Significant increases in striatal DA content were observed following lesions of either side at 3-4 weeks, but not at 3 days. No changes in DA concentration were observed in the nucleus accumbens septi (NAS). Left circling rats significantly increased their circling behavior following right sided lesions and showed disrupted footshock-escape behavior following left sided lesions. Performance of the footshock-escape task exerted an effect on striatal and NAS DA utilization as indicated by the ratio of 3,4-dihydroxyphenylacetic acid (DOPAC) to DA. The effects of footshock on NAS DA utilization were greater following left PFC lesions as compared to the right lesion and sham conditions. These lesion effects were also greater in left- than in right-turning animals. The data indicate that an intrinsic asymmetry in brain DA systems interacts with left and right PFC lesions to differentially determine subcortical DA function and behaviors that it subserves.

Enhanced cocaine self-administration in adult rats prenatally exposed to cocaine

Rats that had been prenatally exposed to either cocaine or saline were examined as adults using continuous reinforcement (FR1) cocaine self-administration. Initially these rats were water-deprived and trained to bar-press for water; no differences across prenatal treatments were observed during this training phase. After complete rehydration and implantation of an intravenous cannula into the external jugular vein, animals were introduced to cocaine self-administration with a nocturnal and subsequent 3 h exposure. During daily test sessions rats were allowed to self-administer cocaine for 1 h/day. Prenatal cocaine exposure led to a marked and stable enhancement of the rates of self-administration for up to 13 days, the longest time point examined. These results suggest that prenatal cocaine exposure can alter cocaine reinforcement in adult animals.

Chronic antidepressant drug treatment reduces turning behavior and increases dopamine levels in the medial prefrontal cortex

The effects of chronic administration of the antidepressant drugs desipramine, nortryptiline and paroxetine (PAR) (10 mg/kg/day, 21 days) on changes in turning (circling) behavior and on norepinephrine (NE), dopamine (DA) and serotonin and their metabolites 3,4-dihydroxyphenylacetic acid and 5-hydroxyindole acetic acid (5-HIAA) in the medial prefrontal cortex (PFC), nucleus accumbens and striatum were evaluated in rats. All three drugs eliminated turning biases in right turning rats. All drugs increased DA concentrations in the PFC while PAR increased NE in the PFC and reduced 5-HIAA in all three structures. The results are discussed with reference to previous findings involving brain asymmetry in depression.

Effects of iboga alkaloids on morphine and cocaine self-administration in rats: relationship to tremorigenic effects and to effects on dopamine release in nucleus accumbens and striatum

Ibogaine, a naturally occurring alkaloid, has been claimed to be effective in treating addiction to opioid and stimulant drugs and has been reported to decrease morphine and cocaine self-administration in rats. The present study sought to determine if other iboga alkaloids, as well as the chemically related harmala alkaloid harmaline, would also reduce the intravenous self-administration of morphine and cocaine in rats. Because both ibogaine and harmaline induce tremors, an effect that may be causally related to neurotoxicity in the cerebellar vermis, the temorigenic activities of the other iboga alkaloids were assessed. Lastly, in view of the involvement of the dopaminergic mesolimbic system in the actions of drugs of abuse, the effects of some of the iboga alkaloids on extracellular levels of dopamine and its metabolites in the nucleus accumbens and striatum were determined. All of the tested alkaloids (i.e., ibogaine, tabernanthine, R- and S-coronaridine, R- and S-ibogamine, desethylcoronaridine, and harmaline) dose-dependently (2.5-80 mg/kg) decreased morphine and cocaine intake in the hour after treatment; decreases in morphine and cocaine intake intake were also apparent the day after administration of some but not all of these alkaloids (i.e., ibogaine, tabernanthine, desethylcoronaridine, and the R-isomers of coronaridine and ibogamine). In some rats, there were persistent decreases in morphine or cocaine intake for several days after a single injection or after two or three weekly injections of one or another of these alkaloids; R-ibogamine produced such effects more consistently than any of the other alkaloids.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurochemical predisposition to self-administer cocaine in rats: individual differences in dopamine and its metabolites

Using in vivo microdialysis, this study attempted to determine whether a neurochemical predisposition to self-administer cocaine could be identified. Estimated extracellular levels of dopamine and its metabolites were measured bilaterally in the mesocorticolimbic and nigrostriatal systems of naive rats that were subsequently trained to self-administer cocaine intravenously. There were several significant relationships between dopamine and dopamine metabolite (3,4-dihydroxyphenylacetic acid and homovanillic acid) levels and rates of cocaine self-administration during both acquisition and asymptotic phases of testing. Dopamine levels in the nucleus accumbens were non-monotonically related to rates of self-administration during both phases: low to moderate dopamine levels were positively correlated with self-administration rates whereas moderate to high dopamine levels were negative correlated with self-administration rates. Dopamine, DOPAC (3,4-dihydroxyphenylacetic acid) and HVA (homovanillic acid) levels in the striatum were inversely correlated with self-administration rates during the acquisition phase. DOPAC and HVA levels in the left and right sides of the medial prefrontal cortex were positively and negatively correlated, respectively, with self-administration rates during the asymptotic phase; left/right asymmetrics in cortical metabolite levels were also correlated with asymptotic rates. There were no significant relationships between any neurochemical indices and rates of bar-pressing for water. These results suggest that the normal variability in drug seeking behavior is at least in part attributable to individual differences in the activity of brain dopamine systems.(ABSTRACT TRUNCATED AT 250 WORDS)

Estimating extracellular concentrations of dopamine and 3,4-dihydroxyphenylacetic acid in nucleus accumbens and striatum using microdialysis: relationships between in vitro and in vivo recoveries

It is common practice in microdialysis studies for probes to be "calibrated" in artificial CSF and in vitro recoveries determined for all substances to be measured in vivo. Dialysate concentrations of such substances are then "corrected" for in vitro recoveries to provide "estimates" of extracellular concentrations. At least for dopamine, in vitro and in vivo recoveries are significantly different and, therefore, an estimate of extracellular dopamine based on correction for in vitro recovery is likely to be erroneous. Generally, however, the relative relationships of such estimates among animals are of interest rather than the "true" extracellular values. Such relationships would be valid to the extent that estimated values are correlated with or predictive of true values. Using the "no net flux" procedure, the present study sought to determine, for both dopamine and its metabolite 3,4-dihydroxyphenylacetic acid (DOPAC), whether in vitro and in vivo recoveries would correlate with each other as well as whether respective estimated and true (no net flux) values of these substances would correlate with each other. Probes (3 mm; BAS/CMed MF-5393), previously calibrated, were lowered into both the nucleus accumbens and striatum of freely moving rats the day before sample collection was begun. In vitro and in vivo recoveries were not significantly correlated (r = 0.1-0.3), for either dopamine or DOPAC. For both dopamine and DOPAC, however, there were significant correlations (r = 0.7-0.8) between estimated and true values. Surprisingly, when using these commercial probes, absolute dialysate levels for both substances were even better correlated (r = 0.9-0.95) with true values.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of prenatal cocaine exposure on the nigrostriatal dopamine system: an in vivo microdialysis study in the rat

Pregnant rats were given injections of saline (0.5 ml/kg) or cocaine (10 mg/kg, 20 mg/ml, s.c.) twice daily between gestational days 7-21. Offspring were examined by microdialysis between postnatal days 10-125 to study the effects of prenatal cocaine exposure on the nigrostriatal dopamine (DA) system. Twenty-min dialysis samples were collected and assayed for DA, DOPAC and HVA. After four baseline samples, the rat was exposed to 20 min of intermittent tail pinch and monitored for four samples; then each rat received an acute injection of cocaine (20 mg/kg, i.p.) and six additional samples were collected. Basal dialysate concentrations of all DA markers, estimated from pre-implantation calibration of the probes, were markedly reduced in young rats ('pups', 10-30 days old) as compared with adult rats (40-125 days old). Compared to control pups, basal DA, as well as DOPAC and HVA, were elevated in the prenatal-cocaine pups. Tail pinch (a mild stressor) produced a significant increase in DA only in the pups prenatally exposed to cocaine. The increase in basal DA induced by an acute cocaine injection (20 mg/kg) was also greater and more prolonged in the prenatal-cocaine pups. In older rats (40-125 days) there were no group differences in any of the DA parameters. Thus prenatal exposure to cocaine produces an activation of the DA system which persists after birth but returns to normal in older rats.

Lateralized changes in prefrontal cortical dopamine activity induced by controllable and uncontrollable stress in the rat

Exposure to stressors that are not controlled results in a variety of changes in behavior and in brain chemistry. Among these is the activation of dopamine-containing neuronal systems projecting to the medial prefrontal cortex (PFC), to a lesser extent the nucleus accumbens (NAC) and, in a few studies, the striatum. Previous data have shown that stressor evoked PFC activation is asymmetrical. The present experiments were designed to assess the effects of controlled and uncontrolled stressors on these DA systems using the procedures of the learned helplessness (LH) model. In a first experiment, 80 trials of either a controllable (ESC) or identical uncontrollable footshock stressor (YOK) caused an activation, as indicated by increased metabolite concentrations of DA in the PFC, NAC and striatum. In the PFC, YOK caused a bilateral DA depletion, relative to ESC and control animals, and a right > left increase in DOPAC/DA which was not seen in ESC animals. These findings suggested a preferential effect of YOK in the right PFC. A second experiment used rats that had been grouped according to their turning behavior, YOK right-biased rats showed an increase in DOPAC on the right side of the PFC and YOK left-biased rats displayed a similar increase on the left side in response to a brief (5 min) controllable footshock stressor. Since right-turning rats had been shown to be more sensitive to a LH behavioral phenomenon, the data suggested that right PFC activation is responsible for the greater LH sensitivity. A final experiment evaluated the neurochemical and behavioral responses to a prolonged footshock stressor 24 h after uncontrolled footshock. Right-biased YOK animals displayed depressed footshock escape behavior and a right > left depletion in PFC DA and HVA. Across-groups footshock escape performance was correlated with DA and HVA concentrations on the right but not on the left side of the PFC. Thus a disturbance of right PFC DA utilization was again associated with compromised coping behavior. The data suggest that the inability to control a stressor causes a lateralized alteration of PFC DA and this results in a disruption of the ability to respond to a new stressor. These findings indicate that the two sides of the PFC are differentially specialized for responding to a stressor.

Effects of ibogaine on acute signs of morphine withdrawal in rats: independence from tremor

Because of the claim that ibogaine suppresses the symptoms of "narcotic withdrawal" in humans, the effect of ibogaine on naltrexone-precipitated withdrawal signs in morphine-dependent rats was assessed. Morphine was administered subcutaneously through implanted silicone reservoirs for 5 days. Ibogaine (20, 40 or 80 mg/kg, i.p.) or saline was administered 30 min prior to challenge with naltrexone (1 mg/kg, i.p.) and withdrawal signs were counted for the following 2 hr. Ibogaine (40 and 80 mg/kg) significantly reduced the occurrence of four signs (wet-dog shakes, grooming, teeth chattering and diarrhea) during naltrexone-precipitated withdrawal; three other signs (weight loss, burying and flinching) were unaffected. Ibogaine induces head and body tremors lasting for 2-3 hr and the tremors might have interfered with the expression of opioid withdrawal. To examine this issue, another experiment was conducted in which ibogaine (40 mg/kg) or saline was administered 4 hr prior to challenge with naltrexone. Although there was a complete absence of tremors, ibogaine still significantly reduced the occurrence of the same four signs of withdrawal.

Within-subject sensitization of striatal dopamine release after a single injection of cocaine: an in vivo microdialysis study

Repeated microdialysis measurements, conducted 1 week apart at the same tissue site, were used to investigate the changes in basal and cocaine-stimulated extracellular dopamine (DA) levels after a single prior exposure to either saline or cocaine. Dialysis probes were placed into rats previously implanted with guide cannulas and basal levels of dopamine (DA), and its metabolites (DOPAC and HVA) were estimated in 20-min fractions of the dialysate. Basal levels in the extracellular fluid (ECF), estimated from pre-implantation calibration of the probes, were 7.9 +/- 0.7 nM DA, 4.9 +/- 0.8 microM DOPAC, and 3.6 +/- 0.6 microM HVA. After a stable baseline was obtained saline (1 ml/kg, i.p.) or cocaine (20 mg/kg, i.p.) was injected. Saline produced no significant changes in any of the neurochemical markers. A cocaine injection produced a sixfold increase in DA, while DOPAC and HVA were unchanged. One week later the same procedure was repeated except this time both groups received cocaine. In rats that had received cocaine 1 week earlier, basal DA levels in the ECF were doubled, whereas they were unchanged in rats that received saline a week earlier. Furthermore, the dopamine release in response to acute cocaine during the second week was elevated in animals which had been previously exposed to cocaine. Rotation was also measured during both weeks and, while a tendency toward behavioral sensitization was observed, it did not reach significance.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurochemical predisposition to self-administer morphine in rats

Using in vivo microdialysis, this study attempted to determine whether a neurochemical predisposition to self-administer morphine could be identified. Extracellular levels of dopamine and its metabolites were measured bilaterally in the mesocorticolimbic and nigrostriatal systems of naive rats that were subsequently trained to self-administer morphine intravenously. There were several significant relationships between dopamine metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) levels and rates of morphine self-administration during both acquisition and asymptotic phases of testing. DOPAC and HVA levels in the striatum were inversely correlated with self-administration rates during the asymptotic phase whereas hemispheric asymmetries in striatal metabolite levels were inversely correlated with self-administration during the acquisition phase. DOPAC and HVA levels in in the right but not in the left side of the medial prefrontal cortex were positively correlated with self-administration rates during the acquisition phase; right/left asymmetries in cortical metabolite levels were also correlated with acquisition rates. There were no significant relationships between neurochemical indices and rates of bar-pressing for water. These results suggest that the normal variability in drug seeking behavior is at least in part attributable to individual differences in the organization and activity of brain dopamine systems. Furthermore, different mechanisms appear to be responsible for the initiation and maintenance of morphine intake: DA release in the nucleus accumbens appears to be a critical component of both mechanisms; DA release in the striatum appears to modulate maintenance and, in relationship to striatal lateralization, modulate initiation; DA release in the right but not in the left medial prefrontal cortex appears to be an important predictor of initiation.

The effects of acute administration of gepirone in rats trained on conflict schedules having different degrees of predictability

The anticonflict activity of gepirone, a putative anxiolytic and antidepressant, was examined on three schedules which conditioned the suppression of licking. The novel schedules differed in the degree to which they predicted (signalled) the presentation of a conflict-inducing electric shock. Three doses of gepirone (1.25, 2.5, and 5 mg/kg SC) were evaluated on a predictable, a moderately predictable, and an unpredictable schedule of shock presentation. Gepirone induced a nondose-dependent increase from baseline in punished licking on the predictable schedule on the last two days of a five-day test period. The lowest dose (1.25 mg/kg) of gepirone induced a significant increase in punished licking on the moderately predictable schedule on the last two days of testing. The highest dose (5 mg/kg) induced initial decreases in overall responding on this schedule. However, responding returned to baseline over the course of the four days of testing. When administered to rats trained on an unpredictable schedule of shock presentation, all doses of gepirone induced an initial decrease from baseline. The lowest dose group returned to baseline control response levels over the next four days, whereas the suppressive effects of the higher doses persisted. The initial decrease in responding observed on all schedules may be due to the effects of gepirone on motor functioning. However, the 2.5-mg/kg dose induced a proconflict or anxiogenic effect on the last test day (decreased punished responding alone) on the unpredictable schedule, while inducing an anticonflict effect on the predictable one. The unpredictable schedule is sensitive to detecting decreases as well as increases in punished responding and as such may be a unique conflict model for evaluating novel anxiolytics.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute administration of diazepam and buspirone in rats trained on conflict schedules having different degrees of predictability

The anti-conflict activities of diazepam and buspirone were examined on three schedules designed to condition the suppression of licking. The schedules differed in the degree to which they predicted (signalled) the presentation of a conflict inducing electric shock. The first study investigated the effects of three doses of diazepam (0.5, 2, and 5 mg/kg IP) on a predictable, a moderately predictable, and an unpredictable schedule of shock presentation. Diazepam induced a significant increase from baseline in licking during the shock component on all three schedules. These anticonflict effects were the most consistent on the predictable schedule, and least consistent on the unpredictable schedule. A second experiment investigated the anticonflict activity of three doses of buspirone (0.125, 0.25, and 0.625 mg/kg SC) on each of these three schedules. The predictable and moderately predictable schedules failed to detect anticonflict activity at any dose of buspirone. However, the lowest dose (0.125 mg/kg) of buspirone increased shocked licking and the highest dose (0.625 mg/kg) decreased shock component licking on the unpredictable schedule. Thus the unpredictable schedule was sensitive to both anticonflict (anxiolytic) and proconflict (anxiogenic) effects of buspirone.

Side and region dependent changes in dopamine activation with various durations of restraint stress

Exposure to various mild stressors has been shown to result in the activation of dopamine containing neuronal systems projecting to the medial prefrontal cortex (PFC), to a lesser extent the nucleus accumbens septi/olfactory tubercle (NAS) and, in a few studies, the striatum. It has also been shown that dopamine (DA) systems on different sides of the PFC are successively activated as stressors are prolonged. We have therefore examined the effects of variation in the duration of a restraint stressor (15, 30 and 60 min) on region and side dependent alterations in DA utilization in the PFC, NAS and striatum. Increases in the concentrations of the DA metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and/or homovanillic acid (HVA) or in their ratios with DA were seen in all regions examined with the largest effects occurring in the PFC and lesser effects in the NAS and striatum. In each region, the magnitude of these effects varied with time of restraint exposure. In the PFC, lateralized alterations in HVA and DA were seen over time with effects progressing from a left greater than right involvement at 15 min to a right greater than left involvement at 60 min. These results are discussed with reference to side and region dependent effects on brain DA systems as stressors are prolonged and the implications they may have for lateralized regional brain activity associated with stressor precipitated psychiatric disease.

Brain laterality as a determinant of susceptibility to depression in an animal model

Rats exposed to stressors that cannot be controlled may develop a deficit in their ability to subsequently learn to control a new stressor. This phenomenon is known as 'learned helplessness' and is a well-accepted animal model of depression. Evidence is presented showing that rats having different directional biases of brain laterality, as indicated in tests of rotational behavior, differ greatly in their response to stressors and to the lack of stressor control. Differences in brain laterality appear to be an important source of variability within the animal model of depression. As with humans, only some rats are vulnerable to depression-like symptoms. These findings are relevant to biological theories of depression that are based upon lateralized specialization of the human brain for affect.

Effects and aftereffects of ibogaine on morphine self-administration in rats

Ibogaine, a naturally occurring alkaloid, has been claimed to be effective in treating addition to opiate and stimulant drugs. As a preclinical test of this claim, the present study sought to determine if ibogaine would reduce the intravenous self-administration of morphine in rats. Ibogaine dose dependently (2.5-80 mg/kg) decreased morphine intake in the hour after ibogaine treatment (acute effect) and, to a lesser extent, a day later (aftereffect); while the acute effect could be attributed to abnormal motor behavior (whole body tremors), the aftereffect occurred at a time when ibogaine should have been entirely eliminated from the body and when there was no obvious indication of ibogaine exposure. In some rats, there was a persistent decrease in morphine intake for several days or weeks after a single injection of ibogaine; other rats began to show such persistent changes only after two or three weekly injections whereas a few rats were apparently resistant to prolonged aftereffects. Aftereffects could not be attributed to a conditioned aversion. Although ibogaine also depressed responding acutely in rats trained to bar-press for water, there was no evidence of any aftereffect a day or more later; the interaction between ibogaine and morphine reinforcement was therefore somewhat specific. Further studies are needed to characterize the nature of the ibogaine-morphine interaction as well as to determine if ibogaine also affects the self-administration of other drugs.

Right-sided population bias in male rats: role of stress

Recent studies have shown that rats develop a pronounced right-sided population bias when tested repeatedly over several days in a shock-escape T-maze paradigm. In the present study we sought to determine if this bias was the result of learning or of the repeated exposure to a stressor (footshock). Rats were tested in the T-maze for 5 trials on each of 6 consecutive days. One group of rats (HS-C) was allowed a free left or right choice on each trial whereas another group of rats (HS-A) was forced to alternate left and right turns on each trial for the first 5 days of testing and then allowed a free choice on Day 6. The population and individual laterality of the HS-A group did not differ from that of the HS-C group, indicating that learning does not account for the biases. A third group of rats (LS-C) was tested using a lower shock level; this decrease in stressor intensity delayed the development of a right-sided population bias without affecting the development of individual laterality. These results indicate that repeated exposure to a stressor, rather than learning, is primarily responsible for the marked right-sided population bias observed in the T-maze.

Regional changes in brain dopamine and serotonin metabolism induced by conditioned circling in rats: effects of water deprivation, learning and individual differences in asymmetry

Rats were trained, using water reinforcement, to turn in circles (rotation) during 1 h daily test sessions. After achieving criterion performance (100 full turns per hour) for at least 10 consecutive sessions, rats were sacrificed 20 min after starting a session and levels of dopamine, DOPAC (3,4-dihydroxyphenylacetic acid), serotonin, and 5-HIAA (5-hydroxyindoleacetic acid) were assayed in nigrostriatal (corpus striatum), mesolimbic (nucleus accumbens) and mesocortical (medial prefrontal cortex) brain regions. Other control groups of rats were comparably water deprived or satiated at the time of sacrifice. Although, as previously reported, evidence of 'two populations' of rats was again apparent with respect to the relationship between direction of spontaneous turning and asymmetry in striatal dopamine levels, there were no lateralized effects of operant rotational training on striatal dopamine and DOPAC levels nor on the DOPAC/dopamine ratio. There were, however, bilateral neurochemical effects of both rotational training and water deprivation in striatum: an increase in the 5-HIAA/serotonin ratio in both sexes was attributable to learning whereas an increase in the DOPAC/dopamine ratio in males was attributed to water deprivation. A bilateral decrease in the DOPAC/dopamine ratio in the mesolimbic and mesocortical regions of both sexes was also induced by water deprivation. The only lateralized neurochemical changes associated with learning to rotate in the operant task occurred in the medial prefrontal cortex: in both sexes, dopamine levels were higher in the ipsilateral than in the contralateral cortex and the DOPAC/dopamine ratio was greater in the contralateral than in the ipsilateral cortex.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral lateralization as a source of interindividual differences in behavior

Cerebral laterality can no longer be considered an exclusively human trait, as over the last 15 years there has been an emergence of data to suggest that animal brains are also lateralized. Morphologic, chemical and behavioral indices of brain asymmetry in the rodent have been reported, and it is suggested that variations in the magnitude and direction of these indices are determined by a complex interaction of genetic, hormonal and experiential factors. Interindividual differences in cerebral laterality have been shown to covary with, or predict, individual differences in spatial behavior and stress reactivity, as well as susceptibility to stress pathology and drug sensitivity. Such findings suggest that it is possible to study individual differences in lateralized brain function through the use of animal models.

Dose-dependent and baseline-dependent conditioning with d-amphetamine in the place conditioning paradigm

The place conditioning paradigm was used to evaluate the positively reinforcing effects of d-amphetamine. During conditioning, female rats were injected (IP) with saline or one of five doses (0.625-5 mg/kg) of d-amphetamine (d-A) and confined to the initially non-preferred side of the testing apparatus. The highest dose of d-A failed to produce a significant preference. The four middle doses of the drug induced a similar preference. A significant increase from baseline was observed on the 4th post-conditioning test day in the five drug groups and controls when given an injection of 1.5 mg/kg d-A 15 min prior to placement in the chamber. Control and drug groups were separated into high and low initial preference sub-groups. Place preferences were more readily induced by d-A in the subgroups with initially high baseline preferences. These findings as well as those of others led us to conclude that the place conditioning paradigm is a somewhat problematic way of measuring drug reinforcement and that the effects observed may not solely be the result of the conditioning of the drug's reinforcing properties to a particular environment.

Basal and amphetamine-induced asymmetries in striatal dopamine release and metabolism: bilateral in vivo microdialysis in normal rats

In vivo microdialysis was used to monitor bilaterally the release of dopamine and its metabolites 3,4-dihydroxyphenyl acetic acid (DOPAC) and homovanillic acid (HVA) in the striata of both anesthetized and awake, freely moving female rats. Under baseline conditions, an asymmetry in dopamine release was reciprocally related to an asymmetry in DOPAC. Baseline dopamine and DOPAC asymmetries were predictive of the preferred direction of amphetamine-induced rotation: the striatum having higher dopamine and lower DOPAC was contralateral to the preferred direction of rotation. Amphetamine (D-amphetamine sulfate, 1.25 mg/kg) enhanced dopamine release and decreased DOPAC and HVA; the increase in dopamine was greater in the ipsilateral striatum. Effects in anesthetized and awake rats were similar. Variations in rotation and in the dopamine asymmetry after amphetamine were correlated across time within individual awake rats.