Tyrosine hydroxylase immunoreactivity and [3H]WIN 35,428 binding to the dopamine transporter in a hamster model of idiopathic paroxysmal dystonia.

Recent pharmacological studies and receptor analyses have suggested that dopamine neurotransmission is enhanced in mutant dystonic hamsters (dt(sz)), a model of idiopathic paroxysmal dystonia which displays attacks of generalized dystonia in response to mild stress. In order to further characterize the nature of dopamine alterations, the present study investigated possible changes in the number of dopaminergic neurons, as defined by tyrosine hydroxylase immunohistochemistry, as well as binding to the dopamine transporter labelled with [3H]WIN 35,428 in dystonic hamsters. No differences in the number of tyrosine hydroxylase-immunoreactive neurons were found within the substantia nigra and ventral tegmental area of mutant hamsters compared to non-dystonic control hamsters. Similarly, under basal conditions, i.e. in the absence of a dystonic episode, no significant changes in [3H]WIN 35,428 binding were detected in dystonic brains. However, in animals killed during the expression of severe dystonia, significant decreases in dopamine transporter binding became evident in the nucleus accumbens and ventral tegmental area in comparison to controls exposed to the same external stimulation. Since stimulation tended to increase [3H]WIN 35,428 binding in control brains, the observed decrease in the ventral tegmental area appeared to be due primarily to the fact that binding was increased less in dystonic brains than in similarly stimulated control animals. This finding could reflect a diminished ability of the dopamine transporter to undergo adaptive changes in response to external stressful stimulation in mutant hamsters. The selective dopamine uptake inhibitor GBR 12909 (20 mg/kg) aggravated dystonia in mutant hamsters, further suggesting that acute alterations in dopamine transporter function during stimulation may be an important component of dystonia in this model.

Regional changes in beta1 thyroid hormone receptor immunoreactivity in rat brain after thyroidectomy.

Quantitative [125I]protein G-based immunohistochemistry was used to map the distribution of beta1 thyroid hormone receptor (TRbeta1) in normal and thyroidectomized adult rat brain, using a previously characterized polyclonal antibody. The distribution of TRbeta1-like immunoreactivity in normal brain was largely but not perfectly concordant with previous accounts of TRbeta1 mRNA distribution in rat brain. Thyroidectomy resulted in increased immunolabeling in most brain regions (mean increase: 14%, range: -4% to +25%), with statistically significant effects being observed in 9 of the 36 brain regions examined. Brain regions showing the most pronounced effects included the habenular nucleus (+22%), the oriens layer of the hippocampal CA3 region (+24%), and the lateral geniculate nucleus of the thalamus (+23%). These results demonstrate that the TRbeta1 protein in brain is capable of plastic changes in response to adult-onset alterations in TH levels. The observed pattern of brain regional receptor changes following thyroidectomy may provide clues for functional effects of thyroid function alterations in adults.

Changes in serotonin and norepinephrine uptake sites after chronic cocaine: pre- vs. post-withdrawal effects.

Although acute cocaine is a strong reuptake inhibitor at dopamine (DA), norepinephrine (NE) and serotonin (5-HT) synapses, the effects of chronic cocaine on 5-HT and NE transporters have received less attention than its effects on DA transporters. In the present study, quantitative autoradiography was used to map effects of chronic cocaine exposure on the binding of [3H]nisoxetine and [3H]cyanoimipramine to NE and 5-HT transporters, respectively. Female Wistar rats were given increasing concentrations of cocaine in the drinking water for 4 weeks (mean dose during the final two weeks: approximately 25 mg/kg body weight) and sacrificed either on the 30th day of cocaine administration or at one of two time points after withdrawal (4 days or 30 days). In animals sacrificed while on cocaine. [3H]cyanoimipramine binding was significantly elevated in the infralimbic cortex (+13%, P < 0.05), n. accumbens (+16%, P < 0.05, P < 0.05), lateral septal n. (+21%, P < 0.05), pedunculopontine n. (+16%, P < 0.05), and vestibular n. (+19%, P < 0.05). These changes were no longer observed when brains were examined either 4 days or 30 days after cessation of cocaine. In animals sacrificed while on cocaine, [3H]nisoxetine binding was decreased in the bed n. of the stria terminalis (-18%, P < 0.05), the lateral parabrachial area (-35%, P < 0.05) and the inferior olive (-26%, P < 0.05). In animals sacrificed 4 days after cessation of cocaine, these effects were no longer apparent, except for a 16% reduction in the inferior olive (P < 0.05). In this 4-day withdrawal group, a significant increase in [3H]nisoxetine binding was seen in the paraventricular n. of the hypothalamus (PVN, +33%, P < 0.05). This PVN change was still seen in the group sacrificed 30 days after cessation of cocaine (+44%, P < 0.02). Binding of [3H]WIN 35,428 to dopamine transporters was unaltered in this group. Taken together, these observations indicate that chronic cocaine has different effects on brain 5-HT and NE transporters, both while the animals are on cocaine and after withdrawal. They support the notion that increased 5-HT uptake in limbic forebrain may play a role in behavioral/psychiatric effects of chronic cocaine. They are also consistent with previous indications that chronic cocaine does not induce degeneration of nerve terminals in noradrenergic or serotonergic neurons. The persistent increase in [3H]nisoxetine binding in the paraventricular hypothalamus suggests the possibility of neuroendocrine changes after withdrawal from chronic cocaine use.

Cytotoxic mechanisms of anti-tumour quinones in parental and resistant lymphoblasts.

The group I aziridinylquinone anti-cancer agents mitomycin C, diaziquone or trenimon were much more cytotoxic to DT-diaphorase-enriched L5178Y/HBM10 lymphoblasts than parental L5178Y cells and caused little oxygen activation. Furthermore, inactivation of cellular DT-diaphorase prevented cytotoxicity whereas catalase did not affect cytotoxicity. This suggests that DT-diaphorase activated these agents and the hydroquinone formed mediated DNA alkylation, crosslinking and cytotoxicity. The group II quinone agents phenanthrenequinone, 2-amino-1, 4-naphthoquinoneimine or naphthazarin were also more cytotoxic to L5178Y/HBM10 cells than parental cells and caused considerable oxygen activation. Inactivation of DT-diaphorase, however, prevented both oxygen activation and cytotoxicity. Furthermore added catalase decreased cytotoxicity, whereas catalase inactivation enhanced cytotoxicity. This suggests that DT-diaphorase activated these agents and the hydroquinone formed caused extensive oxygen activation sufficient to cause DNA oxidative damage and cytotoxicity. The group III quinone agents menadione, 2,3-dimethoxy-1,4-naphthoquinone and 2,6-dimethoxy-benzoquinone, on the other hand, were more cytotoxic to the parental cells than L5178Y/HBM10 cells and caused less oxygen activation than group II agents. Furthermore, inactivation of DT-diaphorase enhanced cytotoxicity and prevented oxygen activation than group II agents. Oxygen activation was therefore also attributed to hydroquinone autoxidation. However catalase did not affect cytotoxicity towards parental cells. This suggests that DT-diaphorase detoxified group III quinones and that cytotoxicity may involve DNA oxidative damage by the semiquinone radicals.