Microdialysis was used to assess extracellular dopamine in striatum, nucleus accumbens, and medial frontal cortex of unanesthetized rats both under resting conditions and in response to intermittent tail-shock stress. The dopamine metabolites 3,4-dihydroxyphenylacetic acid and homovanillic acid also were measured. The resting extracellular concentration of dopamine was estimated to be approximately 10 nM in striatum, 11 nM in nucleus accumbens, and 3 nM in medial frontal cortex. In contrast, the resting extracellular levels of 3,4-dihydroxyphenylacetic acid and homovanillic acid were in the low micromolar range. Intermittent tail-shock stress increased extracellular dopamine relative to baseline by 25% in striatum, 39% in nucleus accumbens, and 95% in medial frontal cortex. 3,4-Dihydroxyphenylacetic acid and homovanillic acid also were generally increased by stress, although there was a great deal of variability in these responses. These data provide direct in vivo evidence for the global activation of dopaminergic systems by stress and support the concept that there exist regional variations in the regulation of dopamine release.

D1- and D2-dopamine receptor-mediated regulation of immediate early gene levels in identified populations of neurons in the striatum was examined with quantitative in situ hybridization histochemical techniques. Levels of messenger RNA (mRNA) encoding the immediate early genes zif268 and c-fos were examined in two experiments in rats with unilateral lesions of the nigrostriatal dopamine pathway. In a dose- response study, animals were treated with doses of 0.5, 1.0, and 1.5 mg/kg of the D1 agonist SKF-38393 either alone or in combination with the D2 agonist quinpirole (1 mg/kg). Levels of immediate early gene mRNAs 60 min following drug treatments showed a dose-related increase to the D1 agonist alone and a potentiation to combined D1 and D2 against treatment. In a second experiment, in animals receiving 1 mg/kg SKF-38393 either alone or in combination with 1 mg/kg quinpirole, the level of zif268 mRNA was measured with a double-labeling method in striatal neurons containing enkephalin mRNA, a marker of D2-containing neurons, and in neurons not containing enkephalin, putative D1- containing neurons. In the dopamine-depleted striatum, D1 agonist treatment alone did not affect enkephalin-positive neurons but significantly elevated zif268 mRNA levels in nearly all enkephalin- negative neurons. Combined D1 and D2 agonist treatment further increased zif268 mRNA levels in this population of enkephalin-negative neurons and decreased zif-268 mRNA levels in enkephalin-positive neurons. These data indicate that the synergistic response to combined D1- and D2-receptor stimulation is mediated by interneuronal interactions involving the activation of D1 and D2 receptors on separate populations of striatal neurons.

No abstract

The dorsal striatum is involved in motor-response learning, but the extent to which distinct populations of striatal efferent neurons are differentially involved in such learning is unknown. Activity-regulated, cytoskeleton-associated (Arc) protein is an effector immediate-early gene implicated in synaptic plasticity. We examined arc mRNA expression in striatopallidal vs. striatonigral efferent neurons in dorsomedial and dorsolateral striatum of rats engaged in reversal learning on a T-maze motor-response task. Male Sprague-Dawley rats learned to turn right or left for 3 days. Half of the rats then underwent reversal training. The remaining rats were yoked to rats undergoing reversal training, such that they ran the same number of trials but ran them as continued-acquisition trials. Brains were removed and processed using double-label fluorescent in situ hybridization for arc and preproenkephalin (PPE) mRNA. In the reversal, but not the continued-acquisition, group there was a significant relation between the overall arc mRNA signal in dorsomedial striatum and the number of trials run, with rats reaching criterion in fewer trials having higher levels of arc mRNA expression. A similar relation was seen between the numbers of PPE(+) and PPE(-) neurons in dorsomedial striatum with cytoplasmic arc mRNA expression. Interestingly, in behaviourally activated animals significantly more PPE(-) neurons had cytoplasmic arc mRNA expression. These data suggest that Arc in both striatonigral and striatopallidal efferent neurons is involved in striatal synaptic plasticity mediating motor-response learning in the T-maze and that there is differential processing of arc mRNA in distinct subpopulations of striatal efferent neurons.

Methamphetamine abuse results in lasting, partial depletions of striatal dopamine and cognitive dysfunction. However, the effect of partial dopamine depletions on the expression of an effector immediate early gene, Arc (activity regulated, cytoskeletal-associated protein), known to be involved in synaptic modifications underlying learning and memory has heretofore not been examined. Male Sprague-Dawley rats were pretreated with a neurotoxic regimen of methamphetamine or saline. Seven weeks later, rats were trained in a motor-response task on a T-maze for five days, and then underwent reversal training on day five. Rats were sacrificed 5 min after reaching criterion on the reversal task, and the brains removed and processed using double-label fluorescent in situ hybridization for Arc and preproenkephalin (PPE) mRNA expression in the dorsomedial striatum. Rats pretreated with methamphetamine had an average (±SEM) 54.4±7.9% loss of dopamine in dorsomedial striatum. Interestingly, there was no difference in reversal trials to criterion in methamphetamine- vs. saline-pretreated rats. However, the expression of Arc mRNA in dorsomedial striatum was attenuated in methamphetamine-pretreated animals, particularly in PPE-negative neurons. Furthermore, the correlation between Arc mRNA expression in dorsomedial striatum and learning was abolished in methamphetamine-pretreated animals. These data suggest that methamphetamine-induced partial monoamine loss is associated with disrupted induction of the effector immediate early gene Arc during a behavioral task, particularly in PPE-negative (presumed striatonigral) neurons, as well as with disruption of the relation between Arc mRNA expression in dorsomedial striatum and reversal learning.

No abstract

The murine monoclonal antibody (MAb), designated DF3, reacts with a 300,000-mol wt mammary epithelial antigen. A sequential double-determinant radioimmunoassay (RIA) has been developed to monitor circulating DF3 antigen. Using this assay, we have demonstrated that 33 of 36 normal women had plasma RIA antigen levels < 150 U/mi. In contrast, 33 of 43 patients (76%) with metastatic breast cancer had RIA DF3 antigen levels _ 150 U/ml. The difference between these two groups was statistically significant (P < 0.001). Similar results have been obtained with a double-determinant enzyme-linked immunoassay (EIA). Only 6 of 111 age-matched normal subjects had EIA DF3 antigens levels _ 30 U/ml, while 42 of 58 patients (72%) with breast cancer had levels equal to or above this value. Thus, similar patterns of specificity are obtained with the EIA or RIA. The elevation of circulating DF3 antigen levels in breast cancer patients has been confirmed by transfer blot assays. MAb DF3 reactivity occurred predominantly with circulating antigens of three different molecular weights ranging from 300,000 to -400,000 mol wt. We also demonstrate that patients with both primary and metastatic breast cancer who were free of detectable disease at the time of sampling have DF3 antigen levels that are similar to those obtained from normal subjects. While patients with hepatoma (27%) and ovarian carcinoma (47%) also had elevated circulating DF3 antigen levels, the results suggest that DF3 antigen levels may be useful in distinguishing breast cancer patients from those with esophageal, gastric, colorectal, pancreatic, and lung carcinomas. Furthermore, the results of the RIA, EIA, and transblot analyses demonstrate that the measurement of circulating DF3 antigen levels provides a new and potentially useful marker to follow the clinical course of patients with metastatic breast cancer.

N-methyl-D-aspartate receptors (NMDARs) are comprised of different subunits. NR2 subunits confer different pharmacological and biophysical properties to NMDARs. Although NR2B subunit expression is uniform throughout striatum, NR2A subunit expression is greater laterally. Pharmacologically isolated NMDAR-mediated excitatory postsynaptic currents (NMDAR-EPSCs) were elicited using minimal local stimulation and recorded in the whole cell configuration to test the hypothesis that biophysical and pharmacological properties of NMDAR-EPSCs of striatal neurons would vary as a function of their location in adult rat striatum. We observed that the decay-time kinetics of NMDAR-EPSCs are significantly slower in neurons of ventromedial versus dorsolateral striatum. Whereas ifenprodil did not differentially affect NMDAR-EPSCs in these regions, application of either glycine or D-serine increased the peak current of NMDAR-EPSCs selectively in dorsolateral striatum. These data provide evidence for functionally distinct NMDARs in the same neuron type in the same brain region of the adult rodent brain. These data thus suggest that the nature of synaptic processing of excitatory input is different in the ventromedial and dorsolateral striatum of the adult rodent brain, regions differentially involved in limbic versus sensorimotor processes, respectively.