Expression of the APC tumor suppressor protein in oligodendroglia.

Mutations of the adenomatous polyposis coli (APC) tumor suppressor gene have been linked to familial polyposis, an inherited predisposition to colon cancer, and a high percentage of sporadic colon adenomas. Although this gene is best known for its role in development of bowel neoplasms, in recent studies we have found that APC mRNA levels are greatly enriched in brain compared with peripheral tissues. To help define its role in the nervous system, in this study we have determined its cellular localization immunohistochemically in adult rat brain sections and have detected intense APC immunoreactivity in oligodendrocytes. Since prominent APC immunostaining is detected in cell bodies of mature oligodendrocytes, these antibodies may provide a useful addition to available oligodendrocyte markers. Although the cellular function of APC remains undefined, previous biochemical studies have demonstrated that APC is associated with catenins, cytoplasmic proteins involved in regulating cell-cell adhesion. We propose that, in addition to its critical role in ensuring normal maturation of colonic epithelial cells, the APC tumor suppressor protein also regulates the adhesive properties of oligodendrocytes.

Immunocytochemical evidence for methamphetamine-induced serotonergic axon loss in the rat brain.

Central serotonin (5-HT) axons were visualized by immunocytochemistry to assess both acute and long-lasting changes in innervation density following methamphetamine administration to rats. Two morphologically distinct subtypes of 5-HT axons (fine and beaded) were differentially affected by d-methamphetamine (d-MA); the density of fine serotonergic axons was selectively decreased both 4 hours and 2 weeks after administration of d-MA. Acute depletion of 5-HT from fine axons, but not from beaded axons, was observed in the brains of all rats treated 4 hours previously with either a 100 mg/kg or 15 mg/kg dose of d-MA. Persistent loss of 5-HT axons was observed in 30% of rats treated 1 or 2 weeks previously with doses of d-MA which produce long-term deficits in biochemical markers for 5-HT. In the fraction of animals that exhibited denervation, fine serotonergic fibers were selectively ablated by d-MA, but beaded serotonergic fibers were spared. Thus, d-MA is similar to other amphetamine derivatives (e.g., p-chloroamphetamine, 3,4-methylenedioxyamphetamine) in that it acts selectively upon a morphologically distinct class of 5-HT axons but differs in that it produces long-lasting axon loss in only a fraction of animals. These data provide morphologic evidence of 5-HT axon loss following methamphetamine administration and further confirm the differential vulnerability of a particular morphological subtype of serotonergic axons to the neurotoxic effects of substituted amphetamines.

alpha-Methyl-p-tyrosine pretreatment partially prevents methamphetamine-induced endogenous neurotoxin formation.

Depletion of brain dopamine (DA) by pretreatment with the tyrosine hydroxylase inhibitor alpha-methyl-p-tyrosine (AMT) has been shown to prevent the long-term neurotoxic effects of methamphetamine (MA). In addition, it has recently been reported that the neurotoxins 6-hydroxydopamine (6-OHDA) and 5,6-dihydroxytryptamine (5,6-DHT) are formed endogenously in neostriatum and hippocampus, respectively, following a single neurotoxic dose of MA. We, therefore, have examined the ability of AMT pretreatment to prevent the MA-induced formation of 6-OHDA and 5,6-DHT. We report that AMT pretreatment significantly decreases the frequency with which 6-OHDA and 5,6-DHT are detected following MA administration. Neurotoxin formation is compared with brain levels of DA and 5-hydroxytryptamine (5-HT) 2 weeks after MA administration. It is concluded that the ability of AMT to attenuate both 6-OHDA formation and long-term depletions of DA is due to a decrease in the MA-releasable pool of DA. The effect of AMT on MA-induced depletions of 5-HT is less clear and may involve additional factors.

alpha-Methyl-p-tyrosine partially attenuates p-chloroamphetamine-induced 5-hydroxytryptamine depletions in the rat brain.

alpha-Methyl-p-tyrosine (AMT) partially attenuates the long-term p-chloroamphetamine (pCA)-induced 5-hydroxytryptamine (5-HT) depletions. Pretreatment of rats with the tyrosine hydroxylase inhibitor AMT before treatment with the serotonin neurotoxin pCA decreased the extent of 5-HT depletion in the two brain regions examined. In these experiments, rats were administered AMT (150 mg/kg) 1 and 5 hours prior to an injection of pCA (5, 10, or 15 mg/kg). AMT reduced the pCA-induced 5-HT depletions in the striatum and to a lesser extent in the hippocampus. Furthermore, the attenuation of neurotoxicity was dependent on dose of pCA, with greater AMT effects at higher doses of pCA. AMT-pretreated rats were still significantly depleted of brain 5-HT following all doses of pCA. However, at the higher doses of pCA, the AMT-pretreated rats were significantly less depleted than saline-pretreated, pCA-treated rats. These results suggest that the neurotoxic effects of high doses of pCA on 5-HT-containing nerve terminals may be in part dependent on the availability of newly synthesized dopamine (DA).

Variability among brain regions in the specificity of 6-hydroxydopamine (6-OHDA)-induced lesions.

6-Hydroxydopamine (6-OHDA; 200 micrograms, 150 micrograms or 110 micrograms) or vehicle was infused stereotaxically into the lateral ventricles of rats, usually following pretreatment with desmethylimipramine (DMI). Various brain regions were then assayed for dopamine (DA), serotonin (5-HT) and norepinephrine (NE). As expected, 6-OHDA depleted DA in all brain regions examined. Unexpectedly, however, the two highest doses of 6-OHDA significantly decreased 5-HT levels in the hippocampus and increased 5-HT levels in the striatum. In addition, despite pretreatment with doses of DMI commonly considered adequate to block 6-OHDA-induced depletion of NE, all doses of 6-OHDA tested significantly reduced NE levels in the hippocampus, hypothalamus and septum. We interpret our data as suggesting that some brain regions are susceptible to nonspecific toxic effects of 6-OHDA at doses commonly employed. Furthermore, these nonspecific effects may or may not occur, depending on seemingly minor variations in experimental technique.

Endogenously produced 5,6-dihydroxytryptamine may mediate the neurotoxic effects of para-chloroamphetamine.

Para-chloroamphetamine (PCA) has been used to deplete brain serotonin (5-HT) in numerous studies of serotonergic involvement in various behaviors and physiological functions. PCA is believed to cause long-lasting depletions of 5-HT by causing the selective degeneration of serotonergic nerve terminals, but the mechanism by which it exerts this neurotoxic effect is not understood. In this experiment, 5,6-dihydroxytryptamine (5,6-DHT), a serotonergic neurotoxin, was detected by high performance liquid chromatography in the rat hippocampus 0.5-4 h after a single 15 mg/kg i.p. injection of PCA. 5,6-DHT was also detected in the somatosensory cortex following PCA administration, but much less frequently than in the hippocampus. Degenerating nerve terminals were observed in the striatum and somatosensory cortex in silver-stained brain sections from rats injected with PCA 1 or 2 days prior to sacrifice. Laminae III and IV of the somatosensory cortex also contained degenerating neuronal perikarya. The neurochemical and histological effects of PCA are very similar to those produced by a large dose of methylamphetamine (MA) in that both drugs are toxic to serotonergic nerve terminals and neuronal perikarya in the somatosensory cortex. We hypothesize that the formation of 5,6-DHT, perhaps from endogenous 5-HT, may mediate the toxic effects of PCA, MA and other amphetamine-related drugs on serotonergic neurons and on a subpopulation of cortical neurons.

5,6-Dihydroxytryptamine, a serotonergic neurotoxin, is formed endogenously in the rat brain.

Methamphetamine (MA) in high doses produces long-term toxic effects on the serotonergic system in the rat brain, including depletions of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid and reductions in 5-HT reuptake and tryptophan hydroxylase activity. In this study, the formation of 5,6-dihydroxytryptamine (5,6-DHT), a serotonergic neurotoxin, was observed in the rat hippocampus after a single 100 mg/kg injection of MA. The 5,6-DHT was detected by reverse-phase high-performance liquid chromatography with electrochemical detection in tissue samples taken 0.5-4 h after MA administration; the highest levels of 5,6-DHT (0.032 ng/mg wet tissue) were detected at 1 h. Following administration of MA, 5-HT was also depleted in the neocortex, but 5,6-DHT was not detected as frequently in this brain region as in the hippocampus. Comparisons were made between the long-term hippocampal 5-HT depletions seen either after an injection of MA or after intraventricular 5,6-DHT infusions and the levels of 5,6-DHT measured in the hippocampus shortly after each treatment. The amount of 5,6-DHT produced after MA administration appears to be adequate to cause the observed long-term 5-HT depletions. We suggest that 5,6-DHT formed from 5-HT may mediate the neurotoxic effects of MA on serotonergic nerve terminals.