Vascular compromise and amputation after intramedullary nailing of a tibia fracture

A case is presented of a fifty-three-year-old man with a displaced tibia-fibula fracture that was treated with an intramedullary nail. The morning after surgery pulses were absent and did not improve after fasciotomies. The patient was transferred to our institution, where an arteriogram showed tapering of the anterior tibial and peroneal vessels in the mid-calf and occlusion of the posterior tibial artery at the level of the ankle. Vascular status did not improve after heparinization and arteriogram thrombolysis. The patient ultimately underwent below-the-knee amputation and subsequent revision to above-the-knee amputation.

Characteristics of patients with shingles admitted to a district general hospital

Little is known about why some patients with shingles are admitted to hospital. We reviewed 72 case notes from a list of 80 patients admitted to hospital with shingles over a six-year period. Pain was the main complaint of the patients admitted, most of whom were elderly and lived alone. The commonest site of involvement in hospital admissions was the eye (herpes zoster ophthalmicus). Diagnosis of shingles was made after admission in 12 patients, eight of whom had originally been diagnosed as having an acute medical or surgical condition. We conclude that the prodromal phase of shingles may lead to misdiagnosis.

Quetiapine: results of four phase II and III clinical trials

The data on efficacy and tolerance from four (phase II and III) trials of quetiapine (Seroquel(R) or ICI 204,636) in a total of 1,461 patients with acute exacerbations of chronic or sub-chronic schizophrenia are briefly reviewed. Together, the results of these trials have demonstrated antipsychotic efficacy in comparison with placebo and equivalent efficacy to haloperidol. In spite of its short plasma elimination half-life, quetiapine is equally effective when given in twice-daily and three-time daily doses. The optimum dose is between 300 mg and 400 mg per day, and the main and most consistent adverse effect is sedation. It has a low extrapyramidal side effect liability and does not produce sustained elevations in plasma prolactin levels.

Gender affects renal vasoconstrictor response to Ang I and Ang II

This study tested the hypothesis that gender affects the pressor and renal vasoconstrictor responses to angiotensin (Ang) I and Ang II in salt-replete normotensive subjects. Ang I and Ang II were infused in graded doses into 9 men and 8 women in a randomized, single-blind, crossover study. There were no differences between genders in baseline blood pressure, heart rate, sodium excretion, renal plasma flow, angiotensin-converting enzyme (ACE) genotype, ACE activity, plasma renin activity, aldosterone, or Ang II levels. Although pressor responses to Ang I and Ang II were similar in men and women, there was a negative relationship between the change in mean arterial pressure and the change in heart rate during Ang I and II infusion in women only. The half-time of the pressor response after discontinuation of Ang I but not Ang II infusion was greater in men than in women (9.5+/-2.2 versus 4.3+/-2.1 minutes, P<.05). This difference in duration did not result from gender differences in the metabolism of Ang I because Ang II levels measured during Ang I infusion were identical in men and women. In contrast, the renal vasoconstrictor response to Ang I and Ang II was significantly increased in women compared with that in men (Ang I, -243+/-31 versus -138+/-13 U/1.73 m2; Ang II, -233+/-25 versus -175+/-18 U/1.73 m2; P<.03). These data suggest an effect of gender on baroreflex reactivity during angiotensin infusion. Moreover, in the setting of similar Ang II concentrations, the dramatic difference in the renal vasoconstrictor responses to Ang I and Ang II between salt-replete men and salt-replete women suggests gender differences at a pharmacodynamic level.

Topographic distribution of seizure onset and hippocampal atrophy: relationship between MRI and depth EEG

Medial temporal lobe epilepsy (MTLE) is associated with hippocampal cell loss and organization of the dentate gyrus. Some studies suggest a correlation between the topographic distribution of cell loss and site of epileptogenesis. We studied the relationship between the site of ictal onset with the presence of segmental atrophy in patients with non-lesional MTLE using magnetic resonance imaging (MRI) and depth EEG. Ictal recordings were obtained from 27 patients with longitudinal hippocampal depth electrodes and variable combinations of subdural strips sampling medial temporal structures. The location of the depth electrode contacts was correlated with anatomical landmarks. Seizures were analyzed for the distribution of onset along the long axis of the hippocampus. MRI analysis were performed to detect segmental atrophy. Outcome was assessed 1 year or more following anterior temporal lobectomy. Twenty-five patients had unilateral, and two had bilateral, hippocampal atrophy. One hundred and forty-seven seizures were reviewed: 21 showed focal onset and 126 showed regional onset. Ictal onset involved the amygdala and anterior half of the hippocampus in 80% of the seizures while only 40% of patients had atrophy of these segments. Most patients had excellent outcome. In patients with MTLE the primary area of epileptogenesis does not parallel the hippocampal segments with the greatest degree of volume loss.

Apparent and true metabolizable energy values of feedstuffs for ducks

Two experiments were conducted, each with 24 White Pekin ducks, to determine the AME and TME content of five feedstuffs for ducks. In each experiment, fasting losses were obtained from six ducks and six ducks were used for each feedstuff. Each experiment lasted 102 h with an initial 48-h period and a 54-h excreta collection period. During the first 48-h period, all birds were tube-fed dextrose (30 g/100 mL of water) at 8 and 32 h after feed was withdrawn. Thirty grams of each feedstuff were tube-fed (30 g/100 mL of water) at 48 and 54 h after feed was withdrawn. The birds from which fasting losses were obtained were intubated with 30 g dextrose (30 g/100 mL of water) at 48 and 54 h after feed was withdrawn. Excreta were collected during the last 54 h into bags screwed onto lids sutured around the vent of each bird. In the first experiment, the feedstuffs evaluated were corn, dehulled oats, and wheat. The fasting energy and nitrogen losses per bird in the 54-h collection period were 12.1 kcal and 0.29 g, respectively. The AMEn values for the birds fed corn, dehulled oats, and wheat were 3.10, 3.48, and 3.14 kcal/g, respectively. The TMEn values for the respective feedstuffs were 3.27, 3.64, and 3.30 kcal/g. In the second experiment, the feedstuffs evaluated were corn, parboiled rice, and rye. The fasting energy and nitrogen losses per bird in the 54-h collection period were 18.9 kcal and 1.09 g, respectively. The AMEn values for the birds fed corn, parboiled rice, and rye were 3.24, 3.45, and 2.69 kcal/g, respectively. The TMEn values for the respective feedstuffs were 3.40, 3.61, and 2.85 kcal/g. The data provide new information on AMEn and TMEn values of corn, wheat, parboiled rice, dehulled oats, and rye for ducks.

Loss of dopamine terminals in the medial prefrontal cortex increased the ratio of DOPAC to DA in tissue of the nucleus accumbens shell: role of stress

We examined whether dopamine depletion in the medial prefrontal cortex of the rat differentially affects basal and evoked dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) content in the subareas of the neostriatum and nucleus accumbens. Loss of approximately 80% of tissue dopamine content in the medial prefrontal cortex did not significantly alter basal tissue concentrations of dopamine or DOPAC or the DOPAC:dopamine ratio in either the nucleus accumbens core or shell or the medial or lateral neostriatum. However, tail pressure stress significantly increased the DOPAC:dopamine ratio in the nucleus accumbens shell of lesioned rats. Because dorsal and ventral areas of the medial prefrontal cortex preferentially innervate the core and shell, respectively, we sought to determine whether the selective effect of lesions on dopamine terminals in the shell of the nucleus accumbens are paralleled by greater dopamine loss in the ventral medial prefrontal cortex. 6-Hydroxydopamine decreased tissue concentrations of dopamine in both the dorsal (-74%) and ventral medial prefrontal cortex (-68%). In lesioned rats, few tyrosine hydroxylase-immunoreactive fibers remained in the dorsal medial prefrontal cortex whereas a dense innervation remained in the ventralmost area. The present data suggest that the influence of mesocortical dopamine neurons on the dopamine projection to the nucleus accumbens shell is expressed only under conditions of stress. Furthermore, lesion-induced alterations in dopamine neurons projecting to the nucleus accumbens shell are not due to a more extensive loss of dopamine terminals in the ventral than in the dorsal medial prefrontal cortex.

Doctors' knowledge of post-splenectomy prophylaxis

A questionnaire was sent to 160 hospital doctors and 200 general practitioners about post-splenectomy prophylaxis during the month of September 1995. A total of 118 questionnaires were returned (43% hospital doctors and 25% GPs). Most doctors (99%) knew that splenectomised patients were at risk of pneumococcal infection; 72% of hospital doctors and 50% of GPs knew of the risk of Haemophilus influenza infection but only 50% of hospital doctors and 33% of GPs knew of the same risks involving meningococcal infection and malaria. Half of the GPs were not aware of H. influenzae type B (Hib) vaccine for prophylaxis and 85% of these and 50% of hospital doctors did not know prophylaxis should be lifelong. There was no significant difference in the knowledge between hospital doctors and GPs.

Determination of metabolizable energy contents of feed ingredients for ducks

The objective of the present experiments was to determine the AMEn and TMEn of various feed ingredients used in duck diets. In each of two experiments, 48 mature, male, White Pekin ducks were assigned in pairs to 24 cages based on initial weight. In each experiment, 12 ducks were assigned to each of three test ingredients and 12 ducks received dextrose for determination of endogenous losses of nitrogen and energy. The test ingredients were tube-fed in wet form and consisted of corn, barley, and pearl millet in Experiment 1, and corn, sorghum, and triticale in Experiment 2. Feed was withdrawn 48 h prior to feeding the test ingredients and ducks were tube-fed 30 g of dextrose in 100 mL of water at 8 and 32 h after feed withdrawal. Ducks were tube-fed 30 g of their assigned test ingredient in 100 mL of water at 48 and 54 h after feed withdrawal. Ducks used in estimating endogenous nitrogen and energy losses were tube-fed 30 g of dextrose in 100 mL of water at 48 and 54 h after feed withdrawal. The method of excreta collection utilized was surgical fixation of a collection apparatus to the vent area of ducks to facilitate total collection of excreta. Collection of excreta was initiated at the first feeding of test ingredients and was continued for a total of 54 h. In Experiment 1, the AMEn and TMEn of corn, barley, and pearl millet on an as-fed basis were determined to be 3.208 and 3.339, 2.730 and 2.863, and 3.350 and 3.484 kcal/g, respectively. In Experiment 2, the AMEn and TMEn of corn, sorghum, and triticale on an as-fed basis were determined to be 3.151 and 3.459, 3.260 and 3.567, and 2.757 and 3.065 kcal/g, respectively. In conclusion, the use of the modified TME assay, in addition to total collection of excreta from individual ducks, provides a means of accurately estimating the ME content of feed ingredients used to formulate diets for ducks.

Qualitative MR imaging of refractory temporal lobe epilepsy requiring surgery: correlation with pathology and seizure outcome after surgery

OBJECTIVE

The purpose of this study was to compare MR imaging findings with histologic findings of either hippocampal sclerosis or gliosis in patients with intractable temporal lobe epilepsy requiring surgery and to correlate MR imaging findings with seizure outcome after surgery and with clinical parameters such as febrile seizure history.

MATERIALS AND METHODS

A retrospective study of MR scans of 66 patients with medically refractory temporal lobe epilepsy requiring surgery was performed. Qualitative diagnosis was done by visual inspection of MR images. MR imaging findings of hippocampal atrophy, signal intensity changes, and segmental findings were correlated with histopathology and with neuronal density. The final MR imaging diagnosis was also correlated with seizure outcome after surgery and with febrile seizure history.

RESULTS

Histologic findings consisted of hippocampal sclerosis in 55 patients and nonspecific gliosis in 11 patients. Two variables, MR imaging findings of hippocampal sclerosis (hippocampal atrophy or signal intensity change) and a febrile seizure history, were significantly associated with hippocampal sclerosis. MR images of nonspecific gliosis usually showed normal findings, although some cases showed mild hippocampal atrophy. When comparing MR imaging findings with histology, our observers achieved sensitivities of 87-98% and specificities of 45-100%. In patients with successful outcomes after surgery, sensitivity ranged from 85% to 98% for MR imaging findings suggesting hippocampal sclerosis, specificity ranged from 17% to 85%, and positive predictive values ranged from 82% to 90%.

CONCLUSION

Qualitative visual analysis of MR images correlates well with histologic findings, febrile seizure history, and seizure outcome after surgery. MR imaging findings and febrile seizure history help differentiate between hippocampal sclerosis and nonspecific gliosis, two similar clinical conditions associated with temporal lobe epilepsy that often have different outcomes after surgery.

Short-chain fatty acids in the treatment of radiation proctitis: a randomized, double-blind, placebo-controlled, cross-over pilot trial

PURPOSE

Treatment of chronic radiation proctitis remains unsatisfactory. Short-chain fatty acids are the preferred energy source for the colonic epithelium. We aimed to determine for the first time whether topical butyric acid enemas relieve symptoms and improve the macroscopic and microscopic findings in chronic radiation proctitis.

METHODS

A randomized, double-blind, placebo-controlled, cross-over pilot trial compared patients given two weeks of butyric acid enemas (40 mmol) twice per day with those given placebo, with a one-week washout period; 15 patients were randomized and 12 completed both arms of the trial. A total symptom score combined six symptom items per week (rectal pain, episodes of rectal bleeding, amount of blood passed, days with diarrhea, number of stools, and urgency). Symptom, endoscopic, and histologic scores were obtained at the beginning of the study and again at the last week of each treatment arm.

RESULTS

Total symptom score at baseline (median, 5.5) improved for those patients receiving active treatment (median, 3.5), but compared with placebo (median, 4.5), the change was not significant. Endoscopic appearances were largely unaltered by active treatment. Histology was abnormal in 82 percent of patients receiving placebo compared with 55 percent of those given butyric acid enemas (P = not significant).

CONCLUSION

Butyric acid enemas do not appear to be superior to placebo in the treatment of chronic radiation proctitis.

Olestra dose response on fat-soluble and water-soluble nutrients in the pig

Groups of weanling pigs were fed a purified diet containing graded concentrations of olestra ranging from 1.1 to 7.7% (wt/wt) and the NRC's requirements for micronutrients for 12 wk. Each group consisted of 12 pigs, with the exception of the control group, which had 20, with equal numbers of females and castrated males. The purpose of the study was to determine the dose-response effects of olestra on fat-soluble vitamins and selected water-soluble micronutrients. At wk 0, 4, 8 and 12, hematology, clinical chemistry and blood concentrations of vitamins A, E, K and B12, and 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, folate, calcium, iron, zinc and adipose concentration of vitamin E were measured. Cumulative weight gain and feed efficiency were determined weekly. Prothrombin time was measured weekly for the control group and the groups fed 5.5 or 7.7% olestra, and monthly for other groups. Liver concentrations of vitamins A, E, and B12 and iron and bone concentrations of calcium, phosphorus, zinc and ash were measured for 12 pigs killed at wk 0 and for all animals at wk 12. By wk 12, the pigs were eating from 20 to 155 g/d of olestra. Olestra did not affect the pigs' growth or feed efficiency, indicating that the digestion and absorption of macronutrients were unaffected. Olestra reduced tissue concentrations of vitamin A, vitamin E and 25-hydroxyergocalciferol in a dose-responsive manner but did not affect prothrombin time. Olestra had no effect on the status of folate, vitamin B12, zinc or iron. Statistically reduced liver concentrations of vitamin B12 and iron in groups fed 5.5 or 7.7% olestra and a significant trend in bone ash content with olestra intake were possibly due to the poor vitamin A and/or vitamin E status of the pigs.

Central venous catheter replacement strategies: a systematic review of the literature

OBJECTIVE

To evaluate the effect of guidewire exchange and new-site replacement strategies on the frequency of catheter colonization and infection, catheter-related bacteremia, and mechanical complications in critically ill patients.

DATA SOURCES

We searched for published and unpublished research by means of MEDLINE and Science Citation Index, manual searching of Index Medicus, citation review of relevant primary and review articles, review of personal files, and contact with primary investigators.

STUDY SELECTION

From a pool of 151 randomized, controlled trials on central venous catheter management, we identified 12 relevant randomized trials of catheter replacement over a guidewire or at a new site.

DATA EXTRACTION

In duplicate and independently, we abstracted data on the population, intervention, outcome, and methodologic quality.

DATA SYNTHESIS

As compared with new-site replacement, guidewire exchange is associated with a trend toward a higher rate of catheter colonization (relative risk 1.26, 95% confidence interval 0.87 to 1.84), regardless of whether patients had a suspected infection. Guidewire exchange is also associated with trends toward a higher rate of catheter exit-site infection (relative risk 1.52, 95% confidence interval 0.34 to 6.73) and catheter-related bacteremia (relative risk 1.72, 95% confidence interval 0.89 to 3.33). However, guidewire exchange is associated with fewer mechanical complications (relative risk 0.48, 95% confidence interval 0.12 to 1.91) relative to new-site replacement. Exchanging catheters over guidewires or at new sites every 3 days is not beneficial in reducing infections, compared with catheter replacement on an as-needed basis.

CONCLUSIONS

Guidewire exchange of central venous catheters may be associated with a greater risk of catheter-related infection but fewer mechanical complications than new-site replacement. More studies on scheduled vs. as-needed replacement strategies using both techniques are warranted. If guidewire exchange is used, meticulous aseptic technique is necessary.

Olestra ingestion and dietary fat absorption in humans

The effect of olestra, a zero-calorie fat replacement, on the absorption of dietary fat was determined with a dual-isotope technique in 67 healthy male subjects. After a 30-d adaptation period in which they consumed potato chips which delivered either 10 g/d olestra or 10 g/d triglyceride under free-living conditions, the subjects were housed in a metabolic ward and given 0, 8, 20 or 32 g olestra in potato chips. The chips were eaten as part of a breakfast containing about 38 g of fat, about 0.16 mg of 14C-triolein, and a nonabsorbable marker, 51CrCl3. Feces were collected for 7 d, and aliquots of the two daily collections containing the highest levels of 51Cr were oxidized. The CO2 was collected, and 14C content was determined by liquid scintillation spectrometry. The fractional absorption of 14C-triolein was calculated from the average ratios of 14C/51Cr dosed and measured in the feces. Olestra had a slight but significant dose-response effect on triglyceride absorption: the highest olestra dose (32 g) reduced absorption by 1.2%. This effect is not nutritionally significant with respect to either availability of essential fatty acids or energy intake.

Olestra ingestion and retinyl palmitate absorption in humans

This study examined the effect of olestra, a zero-calorie fat replacement, on the absorption of retinyl palmitate in humans. After a 30-d adaptation period during which they consumed 10 g olestra/d in potato chips under free-living conditions, 68 healthy male subjects were housed in a metabolic ward and given a single dose of retinyl palmitate (0.33 RDA) containing a trace amount of 3H-retinyl palmitate with a breakfast that contained 0, 8, 20 or 32 g of olestra and about 38 g of triglyceride. Blood was collected at defined intervals for 48 h and plasma analyzed for 3H-retinyl esters by HPLC and liquid scintillation spectrometry. There was no significant effect on retinyl palmitate absorption as determined from the area under the plasma 3H-retinyl esters concentration-time curve. However, an area under the plasma concentration-time curve in the 32-g olestra group that was 81% (mean value) or 70% (median value) of the area under the curve for the placebo group suggested that olestra may have affected retinyl palmitate absorption. Inclusion or exclusion of 13 high responders did not change the results.

Surface and depth EEG findings in patients with hippocampal atrophy

OBJECTIVE

To establish if MRI evidence of hippocampal atrophy (HcA) is an independent surrogate of EEG criteria for the diagnosis of medial temporal lobe (MTL) epilepsy (MTLE).

BACKGROUND

MRI evidence of HcA has been shown to correlate with mesial temporal sclerosis (MTS), intracranial evidence of MTL seizure onset, and outcome after temporal lobectomy. The reported rate of discordance between scalp ictal EEG recordings and MRI evidence of unilateral HcA ranges from rare to moderate. We examined the surface and depth ictal EEG findings of patients with HcA, as detected by volumetric MRI, to clarify their significance in detecting areas of epileptogenicity in this group of patients.

METHODS

From a group of patients with refractory epilepsy, we identified 119 patients with HcA (97 with unilateral and 13 with bilateral HcA, 9 with HcA and mass lesion). MRI volumetric studies were used to obtain Hc ratios. Absolute volumes were used to detect bilateral atrophy. Surface and depth EEG recordings were analyzed for localization of ictal abnormalities, and their distribution was compared for concordance with the location of HcA. Surgical outcome was reviewed.

RESULTS

Of the 110 patients with isolated HcA, 63 had surgery; 82% of ictal depth EEG onsets were concordant with the atrophic Hc, and 72% ictal surface EEG onsets were concordant. Four patients with concordant EEG and HcA failed to achieve seizure control with resection of the atrophic Hc. Furthermore, 3 patients with discordant EEG and HcA had resection of the non-atrophic Hc with excellent results. Among the 47 non-operated patients, 54% had discordant or unlocalized ictal depth EEG results and 52% had discordant ictal surface EEG. Four of the 9 lesional patients with HcA had excellent outcome after lesionectomy without hippocampectomy.

CONCLUSION

The presence of HcA is not an independent predictor of the site of epileptogenesis.

Feeding and excreta collection techniques in metabolizable energy assays for ducks

Feeding and excreta collection techniques, lasting 102 h, for the determination of ME in feed ingredients for ducks are described. Eight and 32 h after feed withdrawal, all ducks received 30 g of dextrose in 100 g of water by orogastric administration. By orogastric administration, ducks received 30 g of test ingredients or dextrose (for ducks used in estimation of endogenous losses of energy and nitrogen) in 100 g of water at 48 and 54 h after feed withdrawal. The collection of excreta involved suturing a threaded plastic retainer ring to the vent and screwing a Whirl-Pak plastic bag, mounted on the top portion of a Playtex baby nurser set plastic bottle cut off 3 cm below the threads, to the retainer ring. Excreta were collected by replacing the Whirl-Pak bags at 54, 60, 72, 84, 96, and 102 h after feed withdrawal. In each of two experiments, ducks with an average weight of 3.7 kg were assigned to treatments. In Experiment 1, four ducks were assigned to each of three test ingredients (corn, dehulled oats, and wheat) and four ducks were assigned to be deprived of feed for estimation of endogenous losses of nitrogen and energy. In Experiment 2, six ducks were assigned to each of two test ingredients (corn and sorghum) and six ducks were assigned to be deprived of feed. Ducks lost an average of 537 g (Experiment 1) and 462 g (Experiment 2) during the 102-h experimental period and all the lost weight was regained within 7 d of return to full feed. Losses of nitrogen (milligrams per duck per 54 h) were 292 (Experiment 1) and 461 (Experiment 2) and energy (kilocalories per duck per 54 h) were 12.12 and 22.26 in feed-deprived group. The determined AMEn and TMEn for corn were 3.245 and 3.407, and 3.210 and 3.517 kcal/g for Experiments 1 and 2, respectively. For dehulled oats, wheat, and sorghum, the determined AMEn and TMEn were 3.464 and 3.625, 3.150 and 3.312, and 3.363 and 3.670 kcal/g, respectively.

Development of a health-related quality of life instrument for use in children with spina bifida

The objective of this study was to develop a spina bifida health-related quality of life (HRQOL) instrument. Items were generated through semistructured interviews, and reduced by frequency-importance product ranking. Validity was assessed by correlating the HRQOL score with a global question concerning the child's well-being using the Spearman's rank coefficient, and the Piers-Harris Children's Self-Concept Scale (P-H) using the Pearson correlation coefficient. Reproducibility was assessed at 2-week intervals using the intra-class correlation coefficient (ICC). Field testing was undertaken in a larger sample to evaluate item-total correlation, internal consistency and construct validity. Patients taking part in the study were 329 children and adolescents with spina bifida attending two treatment centres. Over 600 items were generated. These were reduced to 47 questions and 50 questions, for children and adolescents respectively. The correlation between the HRQOL score and the global question was r = 0.57, and with the P-H was 0.26 (children). These values for adolescents were 0.63, and 0.89, respectively. Reproducibility was ICC = 0.78 (children) and 0.96 (adolescents). Following field testing, the questionnaire was further reduced to 44 questions (children) and 47 questions (adolescents) by eliminating questions with an item- total correlation less than 0.20. Cronbach's alphas for the final instrument were 0.93 (children) and 0.94 (adolescents), and construct validity correlations were 0.63 (children) and 0.37 (adolescents). The spina bifida HRQOL instrument has good measurement properties and may be used as a discriminative instrument. Assessment of responsiveness is necessary before using it to evaluate therapy in clinical trials.

Effects of dopamine depletion in the medial prefrontal cortex on the stress-induced increase in extracellular dopamine in the nucleus accumbens core and shell

In the present study we examined whether depletion of dopamine in the medial prefrontal cortex alters the neurochemical activity of mesoaccumbens dopamine neurons and/or their behavioral correlate, motor behavior. Infusion of 6-hydroxydopamine (1 microgram) into the medial prefrontal cortex of rats pretreated with a norepinephrine uptake blocker produced a 70% loss of tissue dopamine, with relative sparing of the norepinephrine content (-23%) in that region. Using in vivo microdialysis, we monitored basal and evoked extracellular dopamine in the nucleus accumbens core and shell of control and lesioned rats. The concentration of basal extracellular dopamine in the nucleus accumbens core was similar in control and lesioned rats; however, basal dopamine efflux in the nucleus accumbens shell was approximately 30% higher in lesioned rats than in controls. Lesions did not alter the ability of systemic D-amphetamine (1.5 mg/kg, i.p.) to increase extracellular dopamine in the nucleus accumbens shell, in contrast, the dopamine depletion in the medial prefrontal cortex attenuated the amphetamine-induced increase in extracellular dopamine in the nucleus accumbens core, as well as the amphetamine-induced increase in locomotor activity. Lesions did not significantly alter the effects of tail pressure (30 min) on extracellular dopamine in the nucleus accumbens core. However, the depletion of dopamine in the medial prefrontal cortex potentiated the stress-induced increase in extracellular dopamine in the nucleus accumbens shell. These data demonstrate that mesocortical dopamine neurons influence (i) amphetamine-induced dopamine efflux in the nucleus accumbens core and (ii) stress-evoked dopamine efflux in the nucleus accumbens shell. It has been proposed that a disruption in the interaction between cortical and subcortical dopamine neurons is involved in the pathophysiology of schizophrenia. The present data raise the possibility that a disruption in the interaction between mesocortical dopamine neurons and dopamine neurons projecting to the nucleus accumbens shell is involved in those symptoms of schizophrenia that are influenced by stress.

Simple sequence repeats as a source of quantitative genetic variation

Most traits in biological populations appear to be under stabilizing selection, which acts to eliminate quantitative genetic variation. Yet, virtually all measured traits in biological populations continue to show significant quantitative genetic variation. The paradox can be resolved by postulating the existence of an abundant, though unspecified, source of mutations that has quantitative effects on phenotype, but does not reduce fitness. Does such a source actually exist? We propose that it does, in the form of repeat-number variation in SSRs (simple sequence repeats, of which the triplet repeats of human neurodegenerative diseases are a special case). Viewing SSRs as a major source of quantitative mutation has broad implications for understanding molecular processes of evolutionary adaptation, including the evolutionary control of the mutation process itself.