Hallux ulceration in diabetic patients.

We undertook a prospective cohort study to assess risk factors associated with hallux ulceration, and to determine the incidence of healing or amputation, in consecutive patients with diabetes mellitus who were treated over the observation period extending from September 2004 to March 2005, at the Jabir Abu Eliz Diabetic Centre, Khartoum City, Sudan. There were 122 diabetic patients in the cohort (92 males and 30 females) with an overall mean age of 58 +/- 9 years. Fifty-three percent of patients had complete healing within 8 weeks and 43% healed within 20 weeks. The overall mean time to healing was 16 +/- 8 weeks. In 32 (26.2%) patients, osteomyelitic bone was removed, leaving a healed and boneless hallux. The hallux was amputated in 17 (13.9%) patients; in 2 (1.6%) patients it was followed by forefoot amputation and in 7 (5.7%) patients by below-the-knee amputation. In 90 (73.8%) patients the initial lesion was a blister. In conclusion, hallux ulceration is common in patients with diabetes mellitus and is usually preceded by a blister. Neuropathy, foot deformity, and wearing new shoes are common causative factors; and ischemia, osteomyelitis, any form of wound infection, and the size of the ulcer are main outcome determinants. Complete healing occurred in 103 (85%) of diabetic patients with a hallux ulcer. Vascular intervention is important relative to limb salvage when ischemia is the main cause of the ulcer.

Aggressive behavior and altered amounts of brain serotonin and norepinephrine in mice lacking MAOA.

Deficiency in monoamine oxidase A (MAOA), an enzyme that degrades serotonin and norepinephrine, has recently been shown to be associated with aggressive behavior in men of a Dutch family. A line of transgenic mice was isolated in which transgene integration caused a deletion in the gene encoding MAOA, providing an animal model of MAOA deficiency. In pup brains, serotonin concentrations were increased up to ninefold, and serotonin-like immunoreactivity was present in catecholaminergic neurons. In pup and adult brains, norepinephrine concentrations were increased up to twofold, and cytoarchitectural changes were observed in the somatosensory cortex. Pup behavioral alterations, including trembling, difficulty in righting, and fearfulness were reversed by the serotonin synthesis inhibitor parachlorophenylalanine. Adults manifested a distinct behavioral syndrome, including enhanced aggression in males.

Lack of barrels in the somatosensory cortex of monoamine oxidase A-deficient mice: role of a serotonin excess during the critical period.

In a transgenic mouse line (Tg8) deficient for the gene encoding monoamine oxidase A (MAOA), we show that the primary somatosensory cortex (S1) lacks the characteristic barrel-like clustering of layer IV neurons, whereas normal pattern formation exists in the thalamus and the trigeminal nuclei. No barrel-like patterns were visible with tenascin or serotonin immunostaining or with labeling of thalamocortical axons. An excess of brain serotonin during the critical period of barrel formation appears to have a causal role in these cortical abnormalities, since early administration of parachlorophenylalanine, an inhibitor of serotonin synthesis, in Tg8 pups restored the formation of barrels in S1, whereas inhibition of catecholamine synthesis did not. Transient inactivation of MAOA in normal newborns reproduced a barrelless phenotype in parts of S1.

Transient uptake and storage of serotonin in developing thalamic neurons.

Serotonin (5-HT) has been shown to affect the development and patterning of the mouse barrelfield. We show that the dense transient 5-HT innervation of the somatosensory, visual, and auditory cortices originates in the thalamus rather than in the raphe: 5-HT is detected in thalamocortical fibers and most 5-HT cortical labeling disappears after thalamic lesions. Thalamic neurons do not synthesize 5-HT but take up exogenous 5-HT through 5-HT high affinity uptake sites located on thalamocortical axons and terminals. 3H-5-HT injected into the cortex is retrogradely transported to thalamic neurons. In situ hybridization shows a transient expression of the genes encoding the serotonin transporter and the vesicular monoamine transporter in thalamic sensory neurons. In these glutamatergic neurons, internalized 5-HT might thus be stored and used as a "borrowed transmitter" for extraneuronal signaling or could exert an intraneuronal control on thalamic maturation.

Deficiency of the 5-hydroxytryptamine transporter gene leads to cardiac fibrosis and valvulopathy in mice.

BACKGROUND: Serotonin (5-hydroxytryptamine; 5-HT) overproduction is responsible for cardiac valvular disease in patients with carcinoid tumors. Reduced 5-HT inactivation is one proposed mechanism of the valvulopathy observed in individuals treated with the appetite suppressants fenfluramine and phentermine. One key protein limiting systemic availability of 5-HT is the 5-HT transporter (5-HTT) expressed by platelets and pulmonary vascular cells; 5-HTT is responsible for 5-HT uptake and subsequent inactivation of the amine passing through the lung. Here we investigated whether 5-HTT-deficient (5-HTT-KO) mice developed structural and/or functional cardiac abnormalities and valvulopathy. METHODS AND RESULTS: Cardiac endothelial cells expressed large amounts of 5-HTT in wild-type mice. 5-HTT deficiency appeared to be associated with marked interstitial, perivascular, and valvular fibrosis as evidenced by staining of cardiac collagen in 5-HTT-KO mice. Histological analysis provided evidence for valvulopathy characterized by valvular hyperplasia and prominent fibrosis at the attachment site and base of the leaflets. Echocardiography revealed an increase in left ventricular lumen diameter and a decrease in left ventricular diameter fractional shortening. Although 5-HT1B receptors mediated the 5-HT-induced collagen secretion by human cardiac myofibroblasts, the contribution of this receptor type to valvulopathy was ruled out because double-KO mice deficient in both 5-HTT and 5-HT1B receptors showed the same cardiac alterations as 5-HTT-KO mice. CONCLUSIONS: The present results establish a link between 5-HTT and the development of cardiac fibrosis and valvulopathy in vivo. 5-HTT-KO mice represent an especially relevant model for studying the mechanisms by which 5-HT induces valvulopathy.

Rat cells transformed by simian virus 40 give rise to tumor cells which contain no viral proteins and often no viral DNA.

Rat 3T3 cells transformed by simian virus 40 were injected into rats to examine their capacity to develop into tumors. Both large T-dependent (N) transformants and large T-independent (A) transformants were used. All the transformed cell lines contained large T and small t and could multiply efficiently in agar. Only some transformants could develop into tumors. All tumor cells examined had lost both large T and small t. Tumor cells in which the viral genome could still be detected were found together with tumor cells in which the simian virus 40 DNA could no longer be detected. N transformants which displayed the transformed phenotype in a temperature-sensitive manner became temperature insensitive during tumor formation.

Acquisition and extinction of a conditioned passive avoidance reflex in mice with genetic knockout of monoamine oxidase A.

We report here the results obtained from comparative analysis of learning and the dynamics of extinction of a conditioned passive avoidance response in mice with genetic knockout of monoamine oxidase A (MAO A) and the progenitor line C3H. Mice of both lines acquired the conditioned passive avoidance reaction efficiently. Mice with genetic knockout of MAO A were characterized by prolonged retention of reproduction of the memory trace, as compared with rapid extinction in C3H mice. Smaller numbers of transfers, and vertical rearings on days 7-13 and the numbers of glances into and rom the dark sector on days 11-13 of extinction in MAO A-knockout mice appear to reflect their more marked fear reactions when confronted with the "dangerous" sector, along with increased anxiety, these facilitating longer-lasting retention of the memory trace.

Excess of serotonin (5-HT) alters the segregation of ispilateral and contralateral retinal projections in monoamine oxidase A knock-out mice: possible role of 5-HT uptake in retinal ganglion cells during development.

Retinal ganglion cell (RGCs) project to the ipsilateral and contralateral sides of the brain in the dorsal lateral geniculate nucleus (dLGN) and the superior colliculus (SC). Projections from both eyes are initially intermingled until postnatal day 3 (P3) but segregate into eye-specific layers by P8. We report that this segregation does not occur in monoamine oxidase A knock-out mice (MAOA-KO) that have elevated brain levels of serotonin (5-HT) and noradrenaline. The abnormal development of retinal projections can be reversed by inhibiting 5-HT synthesis from P0 to P15. We found that in MAOA-KO mice, 5-HT accumulates in a subpopulation of RGCs and axons during embryonic and early postnatal development. The RGCs do not synthesize 5-HT but reuptake the amine from the extracellular space. In both MAOA-KO and normal mice, high-affinity uptake of 5-HT and serotonin transporter (SERT) immunoreactivity are observed in retinal axons from the optic cup to retinal terminal fields in the SC and dLGN. In the dLGN, transient SERT labeling corresponds predominantly to the ipsilateral retinal projection fields. We show that, in addition to SERT, developing RGCs also transiently express the vesicular monoamine transporter gene VMAT2: thus, retinal axons could store 5-HT in synaptic vesicles and possibly use it as a borrowed neurotransmitter. Finally we show that the 5-HT-1B receptor gene is expressed by RGCs throughout the retina from E15 until adult life. Activation of this receptor is known, from previous studies, to reduce retinotectal activity; thus 5-HT in excess could inhibit activity-dependent segregation mechanisms. A hypothesis is proposed whereby, during normal development, localized SERT expression could confer specific neurotransmission properties on a subset of RGCs and could be important in the fine-tuning of retinal projections.

Excessive activation of serotonin (5-HT) 1B receptors disrupts the formation of sensory maps in monoamine oxidase a and 5-ht transporter knock-out mice.

Deficiency in the monoamine degradation enzyme monoamine oxidase A (MAOA) or prenatal exposure to the monoamine uptake inhibitor cocaine alters behavior in humans and rodents, but the mechanisms are unclear. In MAOA knock-out mice, inhibiting serotonin synthesis during development can prevent abnormal segregation of axons in the retinogeniculate and somatosensory thalamocortical systems. To investigate this effect, we crossed MAOA knock-outs with mice lacking the serotonin transporter 5-HTT or the 5-HT1B receptor, two molecules present in developing sensory projections. Segregation was abnormal in 5-HTT knock-outs and MAOA/5-HTT double knock-outs but was normalized in MAOA/5-HT1B double knock-outs and MAOA/5-HTT/5-HT1B triple knock-outs. This demonstrates that the 5-HT1B receptor is a key factor in abnormal segregation of sensory projections and suggests that serotonergic drugs represent a risk for the development of these projections. We also found that the 5-HT1B receptor has an adverse developmental impact on beam-walking behavior in MAOA knock-outs. Finally, because the 5-HT1B receptor inhibits glutamate release, our results suggest that visual and somatosensory projections must release glutamate for proper segregation.

A large giant cell tumor of the sacrum. Advantage of an abdomino-sacral approach.

We report a case of giant cell tumor of the sacrum, presenting with sacral pain, swelling, and change of bowel habits. Rectal examination revealed a huge retrorectal mass fixed to the sacrum but not to the wall of the rectum. Abdominal ultrasonography, computed tomography CT scan, and magnetic resonance imaging MRI showed a huge pelvic mass invading the sacrum. Exploration via posterior sacral approach was not successful due to both, extensive bleeding and difficult accessibility. Re-exploration was carried out 2 days later with the patient in lithotomy position. Using abdomino-sacral approach the mass together with part of the sacrum and the whole coccyx were excised. Histopathology reported giant cell tumor of the sacrum with no evidence of mitosis. The patient was symptomless 12 months after surgery and on follow up.

[Training and extinction of passive avoidance in mice lacking monoamine oxidase A].

The passive avoidance learning and memory trace retention in mice lacking monoamine oxidase A (MAO A) and control C3H strain were analyzed. It is shown that mice of both strains were well the passive avoidance learners. A delay of the memory trace extinction was found in lacking MAO A mice as compared with control C3H strain. Mice with a genetic MAO A knockout showed decreased amounts of transitions, rearings, looking to a dark compartment and appearing from it. These findings seem to reflect more expressed fear reaction to a dangerous compartment and increased anxiety promoting longer retention of memory trace on a high level of retrieval.

Structure and expression of a new murine interferon-alpha gene: MuIFN-alpha I9.

A new murine alpha interferon gene, MuIFN-alpha I9, isolated from a BALB/c genomic clone, was characterized. It encodes a mature polypeptide of 167 amino acids (aa), presenting from 77 to 86% homology with the seven other MuIFN-alpha I aa sequences previously described. When compared to the latter, pre-IFN-alpha I9 has 13 distinctive aa, and, remarkably, ten of these occur in pairs. The coding region, fused to the SV40 early promoter and introduced into COS monkey cells, directed the transient secretion of an acid-stable functional IFN of 18-21 kDa. The production in this system reached levels of 300 000 units per 0.15 ml. A comparison of the aa sequence of different murine, rat, bovine, and human alpha and beta IFNs revealed certain common features allowing us to propose a putative secondary structure of the IFN proteins. A detailed analysis of results previously published by us and by others showed that the MuIFN-alpha I9 gene is, together with a least twelve other MuIFN-alpha I genes, located on chromosome 4.

Ginkgo biloba abolishes aggression in mice lacking MAO A.

Mice deficient in monoamine oxidase A (MAO A) have increased brain levels of serotonin (5-HT) and norepinephrine and show enhanced aggression. We used MAO A knock-out (KO) mice as a model to study the effect of ginkgo biloba (EGb) on aggression. When EGb was administered to MAO A KO mice, their aggressive behavior in resident-intruder confrontations was reduced to levels seen in wild types. EGb did not affect the locomotive behavior of MAO A KO mice, which suggests that its effects on aggression were not due to sedation. EGb caused a significant 16.9% decrease in [3H]ketanserin binding to 5-HT2A receptors in the frontal cortex of MAO A KO mice but did not change the receptor affinity for [3H]ketanserin. This suggests that the antiaggressive effect of EGb may be mediated by 5-HT2A receptors and that EGb may be developed as a novel antiaggressive agent.

Effects of monoamine oxidase A inhibition on barrel formation in the mouse somatosensory cortex: determination of a sensitive developmental period.

Genetic inactivation of monoamine oxidase A (MAOA) in C3H/HeJ mice causes a complete absence of barrels in the somatosensory cortex, and similar alterations are caused by pharmacological inhibition of MAOA in wild type mice. To determine when and how MAOA inhibition affects the development of the barrel field, the MAOA inhibitor clorgyline was administered to mice of the outbred strain OF1 for various time periods between embryonic day 15 (E15) and postnatal day 7 (P7), and the barrel fields were analyzed with cytochrome oxidase and Nissl stains in P10 and adult mice. High-pressure liquid chromatography measures of brain serotonin (5-HT) showed three- to eightfold increases during the periods of clorgyline administration. Perinatal mortality was increased and weight gain was slowed between P3 and P6. Clorgyline treatments from E15 to P7 or from P0 to P7 disrupted the formation of barrels in the anterior snout representation and in parts of the posteromedial barrel subfield (PMBSF). Treatments from P0 to P4 caused similar although less severe barrel field alterations. Clorgyline treatments only during embryonic life or starting on P4 caused no detectable abnormalities. In cases with barrel field alterations, a rostral-to-caudal gradient of changes was noted: Rostral barrels of the PMBSF were most frequently fused and displayed an increased size tangentially. Thus, MAOA inhibition resulting in increased brain levels of 5-HT affects barrel development during the entire first postnatal week, with a sensitive period between P0 and P4. The rostral-to-caudal gradient of changes in the barrel field parallels known developmental gradients in the sensory periphery and in the maturation thalamocortical afferents. The observed barrel fusions could correspond to a default in the initial segregation of thalamic fibers or to a continued, exuberant growth of these fibers that overrides the tangential domain that is normally devoted to individual whiskers.

Regional cerebral cortical activation in monoamine oxidase A-deficient mice: differential effects of chronic versus acute elevations in serotonin and norepinephrine.

Mice deficient in monoamine oxidase A have previously been shown to demonstrate a chronic elevation of serotonin and norepinephrine in the brain. Using the autoradiographic [14C]iodo-antipyrine method, we examined cerebral cortical blood flow in conscious, restrained four- to five-month-old knock-out and wild-type animals following the intraperitoneal administration of either saline or D-fenfluramine. Knock-out animals administered saline, compared to their wild-type counterparts, demonstrated a significantly higher regional cortical blood flow in somatosensory and barrel field neocortex, an area which previous histological studies have shown to be characterized by abnormal serotonergic projection fibers and absent barrel formation. Regional cortical blood flow was significantly lower in knock-out than in wild-type mice in the entorhinal and midline motor cortex, with non-significant decreases noted in the olfactory, piriform and retrosplenial cortices and the amygdala. We compared the above findings to those obtained in response to D-fenfluramine which, in conjunction with its metabolite D-norfenfluramine, results in acute elevations of brain levels of serotonin and norepinephrine. Administration of D-fenfluramine (21. 2mg/kg) resulted in changes in regional cortical perfusion in most brain regions of both knock-out and wild-type mice that were opposite to the genotypic differences seen in perfusion in response to saline. Fenfluramine significantly increased regional cortical blood flow in the allocortex (olfactory, piriform, entorhinal) and the amygdala, and significantly decreased regional cortical blood flow in the somatosensory, barrel field, midline motor and retrosplenial cortices. Changes in regional perfusion in response to fenfluramine were topographically equivalent in knock-out and wild-type mice, although in knock-out mice such changes were of greater magnitude. Our study suggests that the effects on regional cortical blood flow of a lifelong absence of monoamine oxidase A, and the consequent chronic increase in serotonin and norepinephrine, differ from those attributable to acute increases in these neurotransmitters following fenfluramine administration. Such a differential response may reflect neurodevelopmental abnormalities and/or effects of a chronic physiological adaptation on the regulation of cortical activation.

Lack of 5-HT(1B) receptor and of serotonin transporter have different effects on the segregation of retinal axons in the lateral geniculate nucleus compared to the superior colliculus.

We have shown previously that raised levels of serotonin (5-hydroxytryptamine or 5-HT) during development prevent retinal ganglion cell axons from segregating into eye-specific regions in their principal targets: the superior colliculus and the dorsal lateral geniculate nucleus. Possible mediators of 5-HT in this system include its plasma membrane transporter, which is transiently expressed by a sub-population of retinal ganglion cells, and the presynaptic 5-HT(1B) receptor carried on retinal ganglion cell axons. We analysed the retinal projections of 5-HT(1B) knockout (n=15), serotonin transporter knockout (n=14), serotonin transporter/5-HT(1B) double knockout (n=4) and monoamine oxidase A/5-HT(1B) double knockout (n=3) mice. In all four different knockout mice, the ipsilateral retinal projection to the superior colliculus was more diffuse and lost its characteristic patchy distribution. The alterations were most severe in the serotonin transporter knockout mice, where the ipsilateral retinal fibres covered the entire rostrocaudal and mediolateral extent of the superior colliculus, whereas in the 5-HT(1B) and double knockout mice, fibres retracted from the caudal and lateral superior colliculus. Abnormalities in the 5-HT(1B) knockout mice appeared only after postnatal day (P) 4. Treatment with parachlorophenylalanine (at P1-P12) to decrease serotonin levels caused an exuberance of the ipsilateral retinal fibres throughout the superior colliculus (n=9). In the dorsal lateral geniculate nucleus in contrast, the distribution and size of the ipsilateral retinal projection was normal in all four knockout mice. In the serotonin transporter knockout mice however, the contralateral retinal fibres failed to retract from the mediodorsal dorsal lateral geniculate nucleus, an abnormality that was reversed by early treatment with parachlorophenylalanine and in the serotonin transporter/5-HT(1B) double knockout. OUR OBSERVATIONS INDICATE: (1) that the lack of 5-HT transporter and the associated changes in 5-HT levels impair the segregation of retinal axons in both the superior colliculus and the dorsal lateral geniculate nucleus; (2) that 5-HT and 5-HT(1B) receptors are necessary for the normal refinement of the ipsilateral retinal fibres in the superior colliculus, but are not essential for the establishment of eye-specific segregation in the thalamus. Thus, both an excess and a lack of 5-HT affect the refinement of the superior colliculus retinal projection, while the establishment of eye-specific patterns in the dorsal lateral geniculate nucleus appears not to be sensitive to the lack of 5-HT or 5-HT(1B) receptors.

Effects of genetic depletion of monoamines on somatosensory cortical development.

Raised levels of serotonin cause alterations in the development of the barrelfield of the primary somatosensory cortex (S1) in rodents. We examined the development of S1 in genetic mouse models in which the levels of serotonin and/or dopamine and noradrenaline are drastically reduced. Mice lacking the vesicular monoamine transporter type 2 (VMAT2 KO) are hypomorphic with rare pups surviving until postnatal day (P) 6. Serotonin, dopamine and noradrenaline are almost undetectable in the brain. In S1 we find that the segregation of thalamocortical axons into whisker patterns is delayed by 1 day and that layer IV granular neurons fail to form normal barrels. Moreover, the growth of cortical layers II-IV is reduced. Despite severe malnutrition, we show that these alterations are not caused by increased cell death in the thalamus or S1. Moreover, the maturation of cortical neurons is not altered as reflected by calcium-binding protein immunolabeling. Mice lacking both VMAT2 and monoamine oxidase type A (MAOA) were generated. VMAT2-MAOA DKO mice are hypomorphic but survive until P13. Increased levels of serotonin but profoundly reduced dopamine and noradrenaline levels are found in the brains. In S1, alterations are similar to those observed in MAOA KO mice: thalamocortical axons and granular neurons failed to form barrels. In addition there is a severe reduction in the thickness of the upper cortical layers as in the VMAT2 KO mice. These results show that monoamines have no instructive effect per se on the formation of thalamocortical patterning in S1. However, monoamines appear to be essential for the normal cytoarchitectonic maturation of the granular (IV) and supragranular cortical layers (II-III). Since developmental cell death and chemoarchitectonic differentiation of these neurons are not modified, it is possible that these alterations result from migration defects and/or from altered synaptic maturation.

Influence of monoamines on differentiating gonadotropin-releasing hormone neurones in foetal mice.

This study evaluated the influence of monoamines, serotonin (5-hydroxytryptamine, 5-HT) and noradrenaline, on differentiating gonadotropin-releasing hormone (GnRH)-producing neurones in foetal mice. The differentiation and migration of GnRH neurones were compared in Tg8 mice (the knocked-out gene encoding monoamine oxidase A) with increased levels of 5-HT and noradrenaline and in C3H mice with normal metabolism of monoamines in C3H mice. To achieve this, immunocytochemistry for GnRH combined with quantitative and semiquantitative image analysis were employed. GnRH neurones in foetuses at the 18th embryonic day were detected in the forebrain along the trajectory of their migration from the olfactory bulbs to the hypothalamic retrochiasmatic region. The total number of GnRH neurones in the forebrain in knockout mice was significantly lower compared to C3H mice, suggesting an inhibiting influence of monoamines on the proliferation of precursor cells. The fraction of GnRH neurones in the caudal part of the trajectory of their migration in Tg8 mice exceeded significantly those in C3H foetuses, whereas there was a reverse in the rostral part of the trajectory. These data suggest that an excess of 5-HT and noradrenaline served to accelerate the GnRH neurone migration in Tg8 mice. Moreover, an excess of 5-HT and noradrenaline provided a minor effect on the area and optical density of GnRH neurones (i.e. on GnRH neurone differentiation). Thus, an excess of 5-HT and noradrenaline appears to inhibit the proliferation of the precursor cells of GnRH neurones and stimulates the GnRH neurone migration to the place of their final location in the septo-preoptic region.

Monoamine oxidase B (MAOB)-containing structures in MAOA-deficient transgenic mice.

Monoamine oxidase (MAO)-containing structures were studied for the first time in type A MAO (MAOA)-deficient transgenic mice (Tg8) derived from C3H strain, using MAO enzyme histochemistry. In this mutant line, MAOA activity was not detected in neurons of the locus coeruleus. In contrast, in their dorsal raphe neurons, we noted an intense activity of type B MAO (MAOB). Based on pharmacological MAOA suppression experiments employing a specific inhibitor (clorgyline), we confirmed that the localization of MAOB-positive structures are not different between Tg8 mutant and normal C3H line. Many of MAOB-positive structures which have not been described previously in the rat, cat and primates were described in this study. In the forebrain, MAOB-containing neurons were discriminated in the striatum, septal nuclei, major island of Calleja, diagonal band, medial forebrain bundle, ventral pallidum and amygdaloid nucleus. Stained neurons in the thalamus and hypothalamus were much more extensively distributed in the mouse than the rat. Pontine laterodorsal tegmental neurons showed MAOB activity. The present data suggest that serotonin, a preferential substrate for MAOA, can be oxidized by MAOB in MAOA-deficient Tg8 mice.

Electron-microscopic study of MAOB-containing structures in the nucleus accumbens shell: using MAOA-deficient transgenic mice.

MAOB-containing structures in the nucleus accumbens were ultrastructurally studied for the first time, using MAOA-deficient transgenic mice and MAO enzyme histochemistry. Among the striatal structures, the nucleus accumbens, and in particular its dorsal shell, showed the strongest MAOB activity. MAOB-active cell bodies were embedded in a dense MAOB-active fiber plexus. MAOB-positive terminals formed axo-dendritic synapses which were exclusively of the asymmetric type. It is suggested that dopamine in the nucleus accumbens shell is transported into MAOB-positive fibers where it is degraded by MAOB.