Chapter 1: The Astrobiology Primer 3.0.

The Astrobiology Primer 3.0 (ABP3.0) is a concise introduction to the field of astrobiology for students and others who are new to the field of astrobiology. It provides an entry into the broader materials in this supplementary issue of Astrobiology and an overview of the investigations and driving hypotheses that make up this interdisciplinary field. The content of this chapter was adapted from the other 10 articles in this supplementary issue and thus represents the contribution of all the authors who worked on these introductory articles. The content of this chapter is not exhaustive and represents the topics that the authors found to be the most important and compelling in a dynamic and changing field.

Chapter 11: Astrobiology Education, Engagement, and Resources.

Although astrobiology is a relatively new field of science, the questions it seeks to answer (e.g., "What is life?" "What does life require?") have been investigated for millennia. In recent decades, formal programs dedicated specifically to the science of astrobiology have been organized at academic, governmental, and institutional scales. Constructing educational programs around this emerging science relies on input from broad expertise and backgrounds. Because of the interdisciplinary nature of this field, career pathways in astrobiology often begin in more specific fields such as astronomy, geology, or biology, and unlike many other sciences, typically involve substantial training outside one's primary discipline. The recent origin of astrobiology as a field of science has led to strong collaborations with education research in the development of astrobiology courses and offers a unique instructional laboratory for further pedagogical studies. This chapter is intended to support students, educators, and early career scientists by connecting them to materials and opportunities that the authors and colleagues have found advantageous. Annotated lists of relevant programs and resources are included as a series of appendices in the supplementary material.

Evaluating feasibility of an automated 3-dimensional scanner using Raman spectroscopy for intraoperative breast margin assessment.

Breast conserving surgery is the preferred treatment for women diagnosed with early stage invasive breast cancer. To ensure successful breast conserving surgeries, efficient tumour margin resection is required for minimizing tumour recurrence. Currently surgeons rely on touch preparation cytology or frozen section analysis to assess tumour margin status intraoperatively. These techniques have suboptimal accuracy and are time-consuming. Tumour margin status is eventually confirmed using postoperative histopathology that takes several days. Thus, there is a need for a real-time, accurate, automated guidance tool that can be used during tumour resection intraoperatively to assure complete tumour removal in a single procedure. In this paper, we evaluate feasibility of a 3-dimensional scanner that relies on Raman Spectroscopy to assess the entire margins of a resected specimen within clinically feasible time. We initially tested this device on a phantom sample that simulated positive tumour margins. This device first scans the margins of the sample and then depicts the margin status in relation to an automatically reconstructed image of the phantom sample. The device was further investigated on breast tissues excised from prophylactic mastectomy specimens. Our findings demonstrate immense potential of this device for automated breast tumour margin assessment to minimise repeat invasive surgeries.

Acetate non-utilizing mutants of Arabidopsis: evidence that organic acids influence carbohydrate perception in germinating seedlings.

A phenotypic screen was employed to isolate Arabidopsis plants that are deficient in their ability to utilize or sense acetate. The screening strategy, based on resistance to the toxic acetate analogue monofluoroacetic acid, was adapted from one that has been used successfully to identify important metabolic and regulatory genes involved in acetate metabolism in fungi. Following conventions established from the fungal work, the mutants were called acn mutants for acetate non-utilization. Three highly resistant plant lines were the focus of genetic and physiological studies. Mutant acn1 appears to be a true acetate non-utilizing mutant, as it displays increased sensitivity to exogenous acetate. The progeny of the original acn2 mutant did not germinate, even in the presence of sucrose as an exogenous carbon source. The germination of seeds from the F3 generation depended on the sucrose concentration in the medium. Only a small proportion of seeds germinated in the absence of exogenous sucrose and in the presence of 100 mM sucrose, but up to 70% of seeds germinated on 20 mM sucrose. Mutant acn3 exhibited sensitivity to exogenous sucrose, showing significant chlorosis on medium containing 20 mM sucrose, but no chlorosis when grown in the absence of exogenous sucrose. This phenotype was alleviated if acetate was provided. The acn mutants demonstrate that disrupting organic acid utilization can have profound affects on carbohydrate metabolism.

Co-ordinate regulation of genes involved in storage lipid mobilization in Arabidopsis thaliana.

Molecular genetic approaches in the model plant Arabidopsis thaliana (Col0) are shedding new light on the role and control of the pathways associated with the mobilization of lipid reserves during oilseed germination and post-germinative growth. Numerous independent studies have reported on the expression of individual genes encoding enzymes from the three major pathways: beta-oxidation, the glyoxylate cycle and gluconeogenesis. However, a single comprehensive study of representative genes and enzymes from the different pathways in a single plant species has not been done. Here we present results from Arabidopsis that demonstrate the co-ordinate regulation of gene expression and enzyme activities for the acyl-CoA oxidase- and 3-ketoacyl-CoA thiolase-mediated steps of beta-oxidation, the isocitrate lyase and malate synthase steps of the glyoxylate cycle and the phosphoenolpyruvate carboxykinase step of gluconeogenesis. The mRNA abundance and enzyme activities increase to a peak at stage 2, 48 h after the onset of seed germination, and decline thereafter either to undetectable levels (for malate synthase and isocitrate lyase) or low basal levels (for the genes of beta-oxidation and gluconeogenesis). The co-ordinate induction of all these genes at the onset of germination raises the possibility that a global regulatory mechanism operates to induce the expression of genes associated with the mobilization of storage reserves during the heterotrophic growth period.

Promoter trapping of a novel medium-chain acyl-CoA oxidase, which is induced transcriptionally during Arabidopsis seed germination.

The first step of peroxisomal fatty acid beta-oxidation is catalyzed by a family of acyl-CoA oxidase isozymes with distinct fatty acyl-CoA chain-length specificities. Here we identify a new acyl-CoA oxidase gene from Arabidopsis (AtACX3) following the isolation of a promoter-trapped mutant in which beta-glucuronidase expression was initially detected in the root meristem. In acx3 mutant seedlings medium-chain acyl-CoA oxidase activity was reduced by 95%, whereas long- and short-chain activities were unchanged. Despite this reduction in activity lipid catabolism and seedling development were not perturbed. AtACX3 was cloned and expressed in Escherichia coli. The recombinant enzyme displayed medium-chain acyl-CoA substrate specificity. Analysis of beta-glucuronidase activity in acx3 revealed that, in addition to constitutive expression in the root axis, AtACX3 is also up-regulated strongly in the hypocotyl and cotyledons of germinating seedlings. This suggests that beta-oxidation is regulated predominantly at the level of transcription in germinating oilseeds. After the discovery of AtACX3, the Arabidopsis acyl-CoA oxidase gene family now comprises four isozymes with substrate specificities that encompass the full range of acyl-CoA chain lengths that exist in vivo.

The Arabidopsis acyl-CoA oxidase gene family.

A family of acyl-CoA oxidase isozymes catalyse the first step in the peroxisomal fatty acid beta-oxidation spiral. Our group and others have recently characterized four genes from this family in the model oilseed Arabidopsis. These genes encode isozymes with different acyl-CoA substrate specificities, which together encompass the full range of fatty acid chain lengths that exist in vivo. Here we review the biochemical properties and physiological roles of the acyl-CoA oxidase isozymes.

Long-chain acyl-CoA oxidases of Arabidopsis.

Full-length cDNAs coding for two distinct acyl-CoA oxidases were isolated by screening an Arabidopsis cDNA library. The genes for the two acyl-CoA oxidases have been termed AtACX1 and AtACX2. AtACX1 encodes a peptide of 664 amino acids possessing a molecular mass of 74.3 kDa. AtACX2 encodes a peptide of 691 amino acids in length with a molecular mass of 77.5 kDa. Peroxisomal targeting signals were identified in the primary sequences. AtACX1 has a putative PTS1, whereas AtACX2 has a characteristic PTS2. Expression of AtACX1 and AtACX2 in Escherichia coli gave active enzymes for enzymatic and biochemical analysis. AtACX1 was active with both medium-and long-chain saturated fatty acyl-CoAs and showed maximal activity with C14-CoA. Activity with mono-unsaturated acyl-CoAs was slightly higher than with the corresponding saturated acyl-CoA. AtACX2 was active with long-chain acyl-CoAs and showed maximal activity with C18-CoA. AtACX2 activity with mono-unsaturated acyl-CoAs was approximately twice as high as with the corresponding saturated acyl-CoA. Both enzymes have an apparent Km of approximately 5 microM with the preferred substrate. Northern analysis was conducted to determine the expression patterns of AtACX1 and AtACX2 during germination and in various tissues of a mature plant. The two genes showed generally similar expression profiles and steady-state mRNA levels in seedlings and mature tissues, but subtle differences were observed. Enzymatic analyses of plant extracts revealed that AtACX1 and AtACX2 are members of a family that includes acyl-CoA oxidases specific for shorter-chain acyl-CoAs. Through expression of antisense constructs of the individual genes, we were able to decrease long-chain oxidase activity only in antisense AtACX1 plants. Seedlings with long-chain oxidase activity reduced down to 30% of wild-type levels germinated and established normally; however, reduced root growth appeared to be a general feature of antisense AtACX1 plants.

No induction of beta-oxidation in leaves of Arabidopsis that over-produce lauric acid.

Leaves from transgenic Brassica napus L. plants engineered to produce lauric acid show increased levels of enzyme activities of the pathways associated with fatty acid catabolism (V.A. Eccleston and J.B. Ohlrogge, 1998, Plant Cell 10: 613-621). In order to determine if the increases in enzyme activity are mirrored by increases in the expression of genes encoding enzymes of beta-oxidation, which is the major pathway of fatty acid catabolism in plants, the medium-chain acyl-acyl carrier protein (ACP) thioesterase MCTE from California bay (Umbellularia california) was over-expressed under the control of the cauliflower mosaic virus 35S promoter in Arabidopsis thaliana (L.) Heynh. Arabidopsis was the most suitable choice for these studies since gene expression could be analyzed in a large number of independent MCTE-expressing lines using already well-characterized beta-oxidation genes. Levels of MCTE transcripts in leaves varied widely over the population of plants analyzed. Furthermore, active MCTE was produced as determined by enzymatic analysis of leaf extracts of MCTE-expressing plants. These plants incorporated laurate into triacylglycerol of seeds, but not into lipids of leaves as shown by gaschromatographic analysis of total fatty acid extracts. The expression levels of the beta-oxidation and other genes that are highly expressed during developmental stages involving rapid fatty acid degradation were measured. No significant difference in gene expression was observed among MCTE-expressing plants and transgenic and non-transgenic controls. To eliminate the possibility that post-translational mechanisms are responsible for the observed increases in enzyme activity acyl-CoA oxidase activity was also measured in leaves of MCTE-expressing plants using medium and long chain acyl-CoA substrates. No significant increases in either medium- or long-chain acyl-CoA oxidase activities were detected. We conclude that endogenous beta-oxidation is sufficient to account for the complete degradation of laurate produced in rosette leaves of Arabidopsis expressing MCTE.

Identification of women with T1-T2 breast cancer at low risk of positive axillary nodes.

BACKGROUND AND OBJECTIVES: The diagnostic and therapeutic significance of axillary dissection has been questioned. We sought to define a subgroup of patients with early-stage breast cancer who are at low risk for positive axillary nodes. METHODS: Between 1970 and 1995, 1,598 women with stage I and II breast cancer underwent level I-II axillary dissection with a minimum of 10 nodes removed. The following factors were examined in univariate analysis for predicting positive nodes: race, method of detection, location of the primary tumor, age, menopausal status, obesity, ER status, PR status, pathologic tumor size, lymphatic vascular invasion, tumor grade, and histology. RESULTS: Four hundred and forty-five of the 1,598 patients (27.8%) had histologically positive axillary nodes. Significant factors in univariate analysis for positive nodes included: tumor size, lymphatic vascular invasion, grade, method of detection, primary tumor location, and age. The only group of women with a 0% risk of axillary nodes were those in whom the pathologic tumor size was < or = 5 mm and mammographically detected. A 5-10% risk of positive axillary nodes was identified in women with (1) pathologic tumor size 6-10 mm, mammographically detected, and age < or = 40 years, and (2) tubular carcinoma < or = 10 mm. Tumors detected on physical examination with or without mammography and women < or = 40 years had a significantly increased risk of nodes. In multivariate analysis lymphatic vascular invasion (P < 0.001), method of detection (P = 0.026), location (P = 0.01), and pathologic tumor size (P = 0.002) were significant predictors of positive axillary lymphadenopathy. CONCLUSIONS: The decision to forego an axillary dissection should be considered in (1) tumors mammographically detected and < or = 5 mm (2) mammographically detected, pathologic size 6-10 mm, age > 40 and (3) tubular carcinoma < or = 10 mm. All other groups had a > 10% risk of nodes and may benefit from axillary dissection.

Higher-plant medium- and short-chain acyl-CoA oxidases: identification, purification and characterization of two novel enzymes of eukaryotic peroxisomal beta-oxidation.

Medium- and short-chain acyl-CoA oxidases were identified in and subsequently purified from dark-grown maize plantlets. The oxidase showing preference for medium-chain fatty acyl-CoAs (C10-C14) was purified to homogeneity. The oxidase showing preference for short-chain fatty acyl-CoAs (C4-C8) was purified over 150-fold. Various catalytic properties confirmed these enzymes to be true acyl-CoA oxidases. They produced trans-2-enoyl-CoA and H2O2 from the saturated acyl-CoA, as verified by various independent assay techniques. They also exhibited FAD-dependent activity; i.e. removal of loosely bound FAD by gel filtration markedly reduced activity, which could be restored upon re-addition of FAD. They showed apparent Km values between 2 and 10 microM for the acyl-CoA substrate giving maximal activity, no activity with the corresponding free fatty acid, high pH optima (8.3-8.6) and a peroxisomal subcellular location. The medium-chain acyl-CoA oxidase was determined to be a monomeric protein with a molecular mass of 62 kDa. The short-chain acyl-CoA oxidase was shown to have a native molecular mass of 60 kDa, but exhibited a labile multimeric structure, as indicated by the elution of multiple peaks of activity during several chromatographic steps, and ultimately by the purification of a subunit of molecular mass 15 kDa. The medium- and short-chain acyl-CoA oxidases were demonstrated to be distinct from the maize equivalent of the cucumber glyoxysomal long-chain acyl-CoA oxidase previously purified and characterized [Kirsch, Loffler and Kindl (1986) J. Biol. Chem. 261, 8570-8575]. The maize long-chain acyl-CoA oxidase was partially purified to permit determination of its substrate specificity; it showed activity with a broad range of acyl-CoAs of chain length greater than C8, and maximal activity with C16. The implications of the existence of multiple acyl-CoA oxidases in the regulation of plant peroxisomal beta-oxidation are discussed.

Involvement of the ventral tegmental area in locomotion elicited from the nucleus accumbens or ventral pallidum.

This study was designed to evaluate the role of the circuit containing the nucleus accumbens, ventral pallidum (VP) and ventral tegmental area (VTA) in the motor stimulation produced by the microinjection of dopamine, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) or [D-Ala2, MePhe4,Gly-ol5]enkephalin (DAMGO) into VP or the shell and core compartments of the nucleus accumbens. Initial dose-response curves revealed that dopamine was approximately equipotent at producing motor activity after microinjection into the core and shell, AMPA was more effective in the core, whereas DAMGO was more potent in the shell. A role for the VTA in the motor responses elicited by dopamine, AMPA or DAMGO microinjection into the shell, core or VP was evaluated by microinjecting the tau-aminobutyric acidB agonist baclofen into the VTA to inhibit neuronal activity. Baclofen treatment abolished the motor responses elicited by AMPA from the shell, core and VP. The motor effect of DAMGO in the VP was abolished by baclofen, whereas the response in the shell was attenuated. The motor response to dopamine was unaltered by baclofen, regardless of the injection site. These data indicate that there exist differences between the core and shell of the nucleus accumbens in the capacity of neurotransmitter analogs to elicit motor activity, and that although AMPA-induced motor activity is dependent upon neurotransmission in the VTA after microinjection into the core, shell and VP, DAMGO-induced locomotion only requires such tone after microinjection into the VP and shell.

Cocaine alters glutamic acid decarboxylase differentially in the nucleus accumbens core and shell.

The effects of acute and repeated daily cocaine on the levels of mRNA coding for glutamic acid decarboxylase (GAD), preproenkephalin (PPE), preprotachykinin (PPT), and the dopamine D2 receptor were determined in the striatum, nucleus accumbens core and shell areas (NAcore, NAshell), and medial prefrontal cortex. Rats were given repeated saline or cocaine for 6 days. A cocaine challenge administered 24 h later resulted in an augmented locomotor response in daily cocaine-pretreated rats. Six h after the challenge, rats were sacrificed and Northern blot analysis revealed that acute cocaine increased GAD mRNA levels by 44% in the NAshell, while repeated cocaine prevented the acute cocaine-induced increase. These data suggest that cocaine may differentially regulate GABA release at NA core and shell projection fields.

The role of mesoaccumbens--pallidal circuitry in novelty-induced behavioral activation.

When exposed to an environment for the first time, rats express greater behavioral activation than rats which were previously habituated to that environment. The circuit containing the ventral tegmental area, nucleus accumbens and ventral pallidum is required for the expression of locomotor activity elicited by amphetamine-like psychostimulants. It was hypothesized that this circuit is necessary for the expression of novelty-induced motor activity. Dopamine is a neurotransmitter in the projection from the ventral tegmental area to the nucleus accumbens, while GABA is contained in the projections from the nucleus accumbens to the ventral pallidum and from the ventral pallidum back to the ventral tegmental area. Prior to exposing rats to a novel or habituated environment, they received a microinjection of either saline vehicle or one of the following drugs: fluphenazine (dopamine antagonist) into the nucleus accumbens, muscimol (GABAA agonist) into the ventral pallidum, or baclofen GABAB agonist) into the ventral tegmental area. Each of these pretreatments prevented novelty-induced motor activation without suppressing the activity of habituated animals. In contrast, when these microinjections were made into adjacent motor nuclei of the basal ganglia, including fluphenazine into the striatum, muscimol into the globus pallidus and baclofen into the substantia nigra, they were ineffective in blocking novelty-induced motor activity. These data indicate that the integrity of the circuit that contains the ventral tegmental area, nucleus accumbens and ventral pallidum is required for the manifestation of novelty-induced motor activity.

The relationship between MRNA levels and the locomotor response to novelty.

Differences in behavioral and neurochemical responses to drugs of abuse and environmental stress have been observed between rats that have a greater locomotor response in a novel environment (high responders: HR) compared to those that have a low response to novelty (low responders: LR). This study examined nuclei associated with the nigrostriatal and mesolimbic systems for differences in mRNA content between HR and LR using Northern blot analysis. These brain regions were chosen because of their role in both drug abuse and stress responses. The mRNAs examined code for either peptide transmitters that interact with the dopaminergic system or components of the dopaminergic system that have not been previously examined for differences between HR and LR. HR rats had approximately 50% lower levels of mRNA for beta-preprotachykinin (PPT) in the core of the nucleus accumbens (NACC) compared to LR. No differences between HR and LR in mRNA levels for dynorphin (DYN), preproenkephalin (PPE), glutamic acid decarboxylase (GAD) or neurotensin (NT) were observed in the core of the NACC. In the shell region of the NACC, HR exhibited a 25% reduction in the level of mRNA for NT compared to LR. No differences between HR and LR in mRNA levels for PPT, DYN, PPE or GAD were observed in the shell of the NACC. In the medial frontal cortex and the dorsal striatum, no differences between HR and LR in mRNA levels for PPT, DYN, PPE, GAD or NT were found. In the substantia nigra and ventral tegmental area no differences between HR and LR in mRNA levels for tyrosine hydroxylase, GAD, cholecystokinin, or NT were noted.(ABSTRACT TRUNCATED AT 250 WORDS)

Individual differences in behavior following amphetamine, GBR-12909, or apomorphine but not SKF-38393 or quinpirole.

Subjects that respond more to a novel environment show a greater locomotor response to drugs of abuse such as cocaine and amphetamine. The current study was performed to examine differences between high (HR) and low (LR) responding rats to a novel environment following administration of amphetamine, a selective dopamine uptake blocker (GBR-12909), a nonselective dopamine agonist (apomorphine), and selective dopamine D1 and D2/D3 agonists. A behavioral checklist and a rating scale were used to determine the behavioral arousal caused by administration of amphetamine (0, 0.5, 2.0, and 8.0 mg/kg), GBR-12909 (0, 1.25, 5.0, and 20.0 mg/kg), apomorphine (0, 0.1, 0.3, and 1 mg/kg), SKF 39393 (0, 2.5, 10, and 40 mg/kg), or quinpirole (0, 0.05, 0.5, and 5.0 mg/kg). The five drugs produced behavioral activation profiles distinct from each other. Following amphetamine administration, both HR and LR subjects showed dose dependent increases in behavioral arousal. The behaviors primarily affected were sniffing, locomotor activity, rearing, and oral activity. HR rats showed a greater overall behavioral response to amphetamine administration compared with LR rats and there were differences in specific behaviors between the two groups. Following GBR-12909 administration, all subjects showed dose dependent increases in sniffing, locomotor activity, and rearing. Differences between HR and LR were observed in sniffing, locomotor activity, and rearing behaviors. HR and LR both showed dose dependent increases in behavior following apomorphine administration. HR showed greater behavioral activation after apomorphine than LR.(ABSTRACT TRUNCATED AT 250 WORDS)

Individual locomotor response to novelty predicts selective alterations in D1 and D2 receptors and mRNAs.

Rats that have a greater locomotor response to novelty (high responders, HR) have differences in measures of presynaptic dopamine transmission compared to low responders (LR) to a novel environment, including altered dopamine release and behavioral response to indirect dopamine agonists. This study examined the role of three dopamine terminal fields, the nucleus accumbens, striatum, and medial prefrontal cortex, in differences between HR and LR. In the first experiment, dopamine was infused directly into the nucleus accumbens (0, 3, 10, and 30 micrograms/side) or the striatum (0, 10, 30, and 100 micrograms/side). HR showed a greater behavioral response to both the 3 and 30 micrograms/side doses infused into the nucleus accumbens compared to LR. No differences between HR and LR were revealed by dopamine infusion into the striatum. In the second experiment, radioligand binding assays were performed to determine if differences exist between high and low responder rats in the Bmax and/or KD of radiolabeled antagonist ligands for the dopamine D1 and/or D2 receptors. There were fewer D2 binding sites in the nucleus accumbens and fewer sites in the striatum in HR compared to LR. High responders showed a greater Bmax for D1 binding sites in the nucleus accumbens than LR. No differences in number of binding sites for D1 receptors were observed between HR and LR in the striatum. No differences between HR and LR in D2 or D1 receptor binding were observed in the medial prefrontal cortex. There were no differences in KD for any of the dopamine receptors in the regions examined.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of cocaine microinjections into the nucleus accumbens and medial prefrontal cortex on schedule-induced behaviour: comparison with systemic cocaine administration.

The effects of cocaine HCl infusions into either the nucleus accumbens (NACC) or medial prefrontal cortex (PFC) were compared on the performance of schedule-induced polydipsia (SIP) and related behaviours. Food-deprived rats were exposed to a fixed-time 60-s schedule of food delivery in daily 30-min sessions until stable levels of behaviour were obtained (14 days). Rats were then bilaterally infused with cocaine into either the NACC or PFC via chronically indwelling guide cannulae. Each subject received a sequence of five cocaine infusions (0, 12.5, 25, 50, 100 micrograms) according to a Latin Square design. For comparison, following these intracranial infusions each rat received a sequence of five IP injections of cocaine (0, 2.5, 5, 10, 20 mg/kg) also in a counterbalanced order. NACC and PFC infusions of cocaine and IP cocaine dose-dependently reduced SIP. Cocaine infusions into the NACC, but not the PFC, increased locomotor activity but the characteristic temporal profile of locomotor activity during SIP was retained. IP cocaine also increased locomotor activity in a dose-dependent manner, but the temporal profile of activity was flattened following 20 mg/kg cocaine. NACC and PFC infusions of cocaine had little effect on the total number of panel presses to gain access to the food pellets, but did slightly decrease the high rates of responding immediately prior to the pellet delivery. IP cocaine increased the total number of panel presses at the higher doses, mainly by increasing the low rates of responding. The effects of cocaine infusions into the PFC were behaviourally the most selective, as they reduced SIP without having substantial effects either on locomotor activity or panel pressing.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuroanatomy and neurochemical mechanisms of time-dependent sensitization.

Time-dependent sensitization (TDS) is a phenomenon described in rodents as an enhancement in the behavioral and neurochemical responses to intermittent exposure to psychostimulant drugs. Time-dependent sensitization also occurs after repeated encounters with environmental stress. Several features of TDS parallel those of multiple chemical sensitivity (MCS) in humans, and these similarities have led to the hypothesis that MCS may be explained in part by a similar sensitization process that occurs in rodents. In the studies presented here, we discuss some of the critical features of TDS following repeated exposure to cocaine and environmental stress, including the anatomical and neurochemical pathways utilized in expressing TDS. In addition, we discuss the possible neurochemical basis for individual differences in responsiveness to stimuli, including novelty and cocaine. The striking similarities between TDS and MCS suggest it may be possible to develop an animal model of MCS, using TDS in rodents as its basis.

Involvement of dopamine and excitatory amino acid transmission in novelty-induced motor activity.

The increase in locomotor activity expressed by rats in a novel environment demonstrates individual variability, and the present study evaluated an hypothesis that the variability resides, in part, in differences in neurotransmission in the nucleus accumbens, ventral tegmental area or ventral pallidum. Rats were divided into equal groups expressing either a high or low response in a novel open field. Subsequently, dopamine, the excitatory amino acid agonist alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) or the mu opioid agonist [D-Ala2, MePhe4, Gly-ol5] enkephalin (DAMGO) was microinjected into one of the three brain nuclei, and motor activity was monitored. All three drugs produced a dose-dependent elevation in motor activity in all three brain nuclei. However, the motor response elicited by dopamine in the ventral pallidum and nucleus accumbens was significantly greater in the rats demonstrating a high locomotor response to novelty. Similarly, the motor response elicited by AMPA in the ventral pallidum, nucleus accumbens or ventral tegmental area was enhanced in the high versus low responding rats. In contrast, at no dose and in no brain nucleus was the motor response to DAMGO different between high and low responding rats. These data indicate that alterations in dopamine and excitatory amino acid but not enkephalin neurotransmission in the ventral pallidum, nucleus accumbens and ventral tegmental area are associated with differences in motor activity expressed by animals in a novel environment.