Nondestructive rainbow trout (Oncorhynchus mykiss) freshness estimation by using an affordable open-ended coaxial technique

In the present work, a nondestructive device set up for a rapid and reliable freshness assessment of rainbow trout during 10 days of storage in ice was evaluated. The device was characterized by a vector network analyzer interfaced with an open coaxial probe to be placed in contact with the fish eye. The acquisition of the reflected scattering parameter (S11), which is the ratio between the amplitude of the reflected and the incident signal, was assessed in the 50 kHz-3 GHz spectral range. S11 is composed of a real part and an imaginary part, and both parts were used to predict quality index method for freshness evaluations. Partial least squares regression predictive models of the demerit scores related to fish eye attributes (eye pupil and eye shape) and the day of storage were set up. The main results showed that both the real and imaginary parts of the S11 decrease as a function of storage time. The combination with multivariate analysis allowed to set up predictive models of the storage time and the demerit scores with R² values up to 0.946 (root mean square error [RMSE] = 0.88 days) and 0.942 (RMSE = 3.17 demerit scores related to the fish eyes attributes), respectively (external validation). According to our results, the proposed cheap solution appears a useful tool for the freshness assessment of rainbow trout. PRACTICAL APPLICATION: This work shows that dielectric properties have the potential to discriminate stored fish according to their freshness quality. A device based on this principle can play a significant role in the postharvest processes, contributing to higher product quality and safety and supporting producers and retailers during the qualitative inspections.

Influence of the Physical State of Two Monofloral Honeys on Sensory Properties and Consumer Satisfaction

Honey is a worldwide known and appreciated food product. Its appreciation by consumers is due to both its nutritional properties and the extremely reduced processing. The floral origin, color, aroma and taste are key factors in determining the quality of honey. Nevertheless, rheological properties, as crystallization rate, play a fundamental role in the perceived overall quality. Indeed, crystallized honey is often considered of poor quality by consumers, but a fine-grained or creamy texture is becoming interesting from the producers' side. The purpose of this study was to investigate textural and aromatic properties and consumers' perception and acceptance of two monofloral honeys that were differently crystallized. Liquid and creamy samples were obtained from crystallized samples. Physico-chemical, descriptive and dynamic sensory analysis, as well as consumer and CATA tests, were conducted on the three honey textures. The physico-chemical analysis well-discriminated the crystallization levels and evidenced that, although the honey variety was different, the textural properties of the creamy samples are very similar. Crystallization was shown to affect the honey sensory perceptions: liquid samples were sweeter, but less aromatic. Consumer tests allowed the validation of panel data and confirmed consumers' higher appreciation for liquid and creamy honey.

The Evaluation of the Effects of Dietary Vitamin E or Selenium on Lipid Oxidation in Rabbit Hamburgers: Comparing TBARS and Hexanal SPME-GC Analyses

The effects and specificity of dietary supplementation of EconomasETM (EcoE), mainly consisting of organic selenium (0.15 or 0.30 mg/kg feed; Se) or of vitamin E (100 or 200 mg/kg feed; VE), on lipid oxidation were evaluated in rabbit hamburgers during refrigerated storage. Oxidation data obtained by thiobarbituric acid-reactive substances (TBARS) spectrophotometric analysis and solid-phase microextraction (SPME) coupled with gas chromatography (GC) to determine hexanal content were compared. The relationships between oxidation levels, colour and pH and the discriminability of EcoE- or VE-treatment compared with control were also examined. TBARS content decreased in both VE and EcoE groups, while hexanal showed lower values only in the VE100 dietary group. The colour parameters were compatible with acceptable product quality and seemed to parallel the TBARS values up to the second day storage. Both VE and EcoE improved oxidative stability without affecting the sensory properties, but the VE effect appeared to more specifically hamper lipid oxidation, as evidenced by the determination and quantification of hexanal, a specific product of fatty acid peroxidation.

Effect of dietary antioxidant supplementation on rabbit performance, meat quality and oxidative stability of muscles

<p>The aim of this study was to cast light on the effects of EconomasE™ (EcoE), a patented pre-mixture of nutritional additives consisting mainly of organic selenium (0.15 or 0.30 mg/kg feed; Se) combined with vitamin C (5 and 10 mg/kg feed; VC), compared to DL-α-tocopherol acetate (100 or 200 mg/kg feed; VE) dietary supplementation on rabbit performance and meat quality. In fact, the role of Se supplementation in the rabbit diet has not yet been elucidated in the literature and, more specifically, there are no studies on the possible synergistic action between organic Se compared with VE on lipids, fatty acids (FA) and the oxidative stability of two glycolytic muscles, <em>longissimus lumborum</em> (LL) and <em>biceps femoris</em> (BF). Two hundred and seventy New Zealand White rabbits were divided into five dietary groups of 54 rabbits each: 1) control (basal diet = BD; CTRL); 2) VE100 (BD + VE100 mg/kg); 3) VE200 (BD + VE200 mg/kg); 4) EcoE100 (BD + EcoE100 mg/kg); and 5) EcoE200 (BD + EcoE200 mg/kg). Neither of the antioxidant treatments affected growth performance, carcass traits or meat characteristics. Lipid and fatty acid contents were similar in LL and BF and not influenced by the dietary treatment. Meat oxidative stability was strongly improved by both antioxidants. These findings indicate that both EcoE and VE greatly improved the oxidative stability of LL and BF muscles at the dosage rates which, from an economic point of view, would normally be included in the formulation of feeds for rabbits.</p>

Season and Cooking May Alter Fatty Acids Profile of Polar Lipids from Blue-Back Fish

Polar lipids (PoL) represent a new promising dietary approach in the prevention and treatment of many human diseases, due to their potential nutritional value and unique biophysical properties. This study investigates the effects of catching season and oven baking on the fatty acid profiles (FAP) of PoL in four species of blue-back fish widely present in the North Adriatic Sea: anchovy (Engraulis encrasicholus), sardine (Sardina pilchardus), sprat (Sprattus sprattus), and horse mackerel (Trachurus trachurus). PoL levels (427-652 mg/100 g flesh) varied among the four species, with no significant seasonal variations within species. FAP of raw fillets were particularly high in polyunsaturated fatty acid (PUFA), especially docosahexaenoic acid (DHA) and EPA; total PUFA was constant in all species throughout the year, while long-chain n-3 polyunsaturated fatty acid (n-3 PUFA) rose in spring (except in sprat), especially due to the contribution of DHA. The FAP response for PoL to oven baking was species-specific and, among n-3 PUFA, DHA exhibited the greatest heat resistance; the influence of oven baking on FAP was found to be correlated with the catching season, especially for anchovy and sardine, while sprat PoL were not affected by cooking processes. The four species analyzed in this study presented very low n-6/n-3 fatty acid ratios and highly favorable nutritional indices, emphasizing their PoL qualities and promoting their role in increasing human n-3 PUFA intake. The four species can be considered as superior sources of n-3 PUFA and can be employed as supplements in functional food manufacturing and in pharmaceutical and cosmetic industries.

Authentication of European sea bass according to production method and geographical origin by light stable isotope ratio and rare earth elements analyses combined with chemometrics

In this work, stable isotope ratio (SIR) and rare earth elements (REEs) analyses, combined with multivariate data elaboration, were used to explore the possibility to authenticate European sea bass (Dicentrarchus labrax L.) according to: i) production method (wild or farmed specimens); ii) geographical origin (Western, Central or Eastern Mediterranean Sea). The dataset under investigation included a total of 144 wild and farmed specimens coming from 17 different European areas located in the Mediterranean Sea basin. Samples were subjected to SIR analysis (carbon and nitrogen) and REEs analysis (lanthanum, europium, holmium, erbium, lutetium, and terbium). Then, Analytical data were handled by Principal Component Analysis (PCA) and then by Orthogonal Partial Last Square Discriminant Analysis (OPLS-DA), to obtain functional classification models to qualitatively discriminate sea bass according to the conditions under study. OPLSDA models provided good correct classification rate both for production method and geographical origin. It was confirmed that chemometric elaboration of data obtained from SIR and REEs analyses can be a suitable tool for an accurate authentication of European sea bass.

Toward the Authentication of European Sea Bass Origin through a Combination of Biometric Measurements and Multiple Analytical Techniques

The authenticity of fish products has become an imperative issue for authorities involved in the protection of consumers against fraudulent practices and market stabilization. The present study aimed to provide a method for authentication of European sea bass ( Dicentrarchus labrax) according to the requirements for seafood labels (Regulation 1379/2013/EU). Data on biometric traits, fatty acid profile, elemental composition, and isotopic abundance of wild and reared (intensively, semi-intensively, and extensively) specimens from 18 southern European sources ( n = 160) were collected, clustered in six sets of parameters, and then subjected to multivariate analysis. Correct allocations of subjects according to their production method, origin, and stocking density were demonstrated with good approximation rates (94, 92, and 92%, respectively) using fatty acid profiles. Less satisfying results were obtained using isotopic abundance, biometric traits, and elemental composition. The multivariate analysis also revealed that extensively reared subjects cannot be analytically discriminated from wild subjects.

Objective measurements of pork quality: Evaluation of various techniques

Research has been undertaken in which various methods for meat quality evaluation were compared. The measures used were pH (by homogenization and by combined electrode), light scattering conductivity, dielectric loss factor and colour. A very low incidence of PSE (Pale, Soft, Exudative) and DFD (Dark, Firm, Dry) cases was observed and the correlation between pH, as measured by homogenization and by combined electrode, did not appear to be completely satisfactory. Dielectric loss factor, as measured by the MS tester, seems to be specifically suited for PSE diagnosis. On the other hand, higher values of light scattering and conductivity measured at 24 h post mortem, are found to be linked to the rate of pH fall, even outside the range for PSE. Colour measurements, especially of the parameters L(∗), a(∗) and hue angle, have given interesting information. In fact, meat could be classified by colour intensity (a(∗), psychometric chroma), by type of colour (hue angle) and by exudative phenomena (L(∗)). No marked effects of rearing techniques have been observed, whereas the genetic background appears to influence some colour parameters. Slaughter conditions, on the other hand, could affect markedly all the meat quality parameters measured in this research.

Evaluation of 2-alkylcyclobutanones in irradiated cured pork products during vacuum-packed storage

The 2-Alkylcyclobutanones (2-ACBs) content was determined in three Italian cured pork products (salame Milano, coppa, and pancetta) irradiated at different targeted irradiation doses (2, 5, and 8 kGy) during vacuum-packed storage. Among 2-ACBs, three different compounds were investigated, namely, 2-dodecylcyclobutanone, 2-tetradecylcyclobutanone, and 2-(tetradec-5'-enyl)cyclobutanone. 2-ACBs were absent from the nonirradiated samples, whereas their content increased with irradiation dose. Their presence was recorded occasionally at 2 kGy and constantly at higher irradiation doses (5 and 8 kGy). The plot of 2-ACBs content against targeted irradiation doses showed an exponential relationship. The effect of vacuum-packed storage time on the 2-ACBs content was dependent on the irradiation dose. During vacuum-packed storage for up to 60 days, the 2-ACBs content remained unchanged in the cured pork products irradiated at 2 and 5 kGy, whereas a significant increase was observed in the pork products irradiated at 8 kGy.

The effect of journey time and stocking density during transport on carcass and meat quality in rabbits

Four hundred and fifty hybrid commercial rabbits (half males and half females) at the end of their productive cycle (82 days old) were transported in cages (98×52×24cm, length×width×height) at high or low density (75.5 or 49.0kg/m(2) - 15 or 10 animals per cage) on an uncovered truck for 1, 2 or 4h. Live weight before and after transport as well as slaughter data were recorded for each rabbit. A subset of 180 carcasses were evaluated for meat quality on the basis of meat pH, colour (CIELab system), cooking loss, drip loss and shear force. As a representative of the whole carcass muscle/bone ratio, the left hind leg was separated, dissected and its meat analysed in order to determine its water, protein, ash and lipid content. It was found that a longer journey significantly increases the live weight losses (3.3% vs. 2.0% vs. 1.6% for 4, 2 or 1h, respectively; P<0.001), as a result not only of urine and fecal losses, but also of a decrease in carcass weight (P<0.01) during transport. Ultimate pH (pH(u)) was higher and pH drop lower in rabbits transported for 4h compared to those transported for 2h (P<0.05). Moreover, the meat from animals that had undergone the longest journey was more purple-red (P<0.05), darker (P<0.0001), and firmer when raw and showed less cooking loss than meat from those that underwent shorter journeys. Transport density did not influence any of the considered parameters and there was no interaction between transport time and density.

Drug-induced neurobehavioral plasticity: the role of environmental context

Repeated administrations of addictive drugs produce long-lasting changes in brain and behavior. However, drug-induced neurobehavioral plasticity is not a mere function of the neuropharmacological actions of drugs, but the result of complex drug-environment interactions. In the present review we summarize results obtained in a series of studies using an animal model of drug-environment interaction, showing that environmental context and past drug history interact to modulate the effects of amphetamine, cocaine and morphine on behavior, gene expression and structural plasticity. These findings may help shed some light on the conditions necessary for addictive drugs to enduringly alter brain and behavior.

Selected nutrient contents, fatty acid composition, including conjugated linoleic acid, and retention values in separable lean from lamb rib loins as affected by external fat and cooking method

Proximate composition and fatty acid profile, conjugated linoleic acid (CLA) isomers included, were determined in separable lean of raw and cooked lamb rib loins. The cooking methods compared, which were also investigated for cooking yields and true nutrient retention values, were dry heating of fat-on cuts and moist heating of fat-off cuts; the latter method was tested as a sort of dietetic approach against the more traditional former type. With significantly (P < 0.05) lower cooking losses, dry heating of fat-on rib-loins produced slightly (although only rarely significantly) higher retention values for all of the nutrients considered, including CLA isomers. On the basis of the retention values obtained, both techniques led to a minimum migration of lipids into the separable lean, which was higher (P < 0.05) in dry heating than in moist heating, and was characterized by the prevalence of saturated and monounsaturated fatty acids. On the whole, the response to cooking of the class of CLA isomers (including that of the nutritionally most important isomer cis-9,trans-11) was more similar to that of the monounsaturated than the polyunsaturated fatty acids.

Environmental context and drug history modulate amphetamine-induced c-fos mRNA expression in the basal ganglia, central extended amygdala, and associated limbic forebrain

The context in which amphetamine is administered modulates its ability to induce both behavioral sensitization and immediate early gene expression. When given in a novel test environment amphetamine produces greater levels of c-fos and arc mRNA expression in many brain regions relative to when it is given in the home cage. The purpose of the current study was to determine if environment and drug history interact to influence amphetamine-induced c-fos mRNA expression. Rats with a unilateral 6-hydroxydopamine lesion were treated for 7 days with saline or 0.5 mg/kg of d-amphetamine (i.v.) in a distinct and relatively novel test environment (Novel), or in their home cage (Home). Following a 10-12-day withdrawal period, a challenge injection of either saline or 0.5 mg/kg d-amphetamine was administered. In situ hybridization histochemistry was used to examine c-fos mRNA expression in several regions of the basal ganglia, the central extended amygdala, and limbic forebrain. In most brain regions amphetamine given in the Novel environment produced greater c-fos mRNA expression than when given it was given at Home, and drug history had no effect on amphetamine-induced c-fos mRNA expression. However, within the subthalamic nucleus, substantia nigra reticulata, and central nucleus of the amygdala prior experience with amphetamine in the Novel but not Home environment enhanced the effect of an amphetamine challenge injection on c-fos mRNA expression. In contrast, there was a decrease in c-fos mRNA expression in amphetamine-pretreated animals, regardless of environmental context, in the ventral portion of the far caudal striatum. Reexposure to an environment previously paired with amphetamine produced a conditioned increase in c-fos mRNA expression in portions of the caudate-putamen, the subthalamic nucleus, the nucleus accumbens shell and a conditioned decrease in c-fos mRNA expression in the central nucleus of the amygdala. We conclude that environmental context and drug history interact to alter the basal ganglia and central extended amygdala circuitry engaged by subsequent exposure to amphetamine, or exposure to an environment previously paired with amphetamine.

Environmental context modulates the ability of cocaine and amphetamine to induce c-fos mRNA expression in the neocortex, caudate nucleus, and nucleus accumbens

We reported previously that environmental novelty enhances the acute psychomotor activating effects of amphetamine, its ability to induce behavioral sensitization, and its ability to induce c-fos mRNA in the striatum and other structures, relative to when amphetamine is given in the home cage. The purpose of the present experiment was 2-fold: to determine (1) whether environmental novelty has a similar effect on the ability of cocaine to induce c-fos mRNA, and (2) whether this effect is seen in neurologically-intact rats (in previous experiments we studied the intact hemisphere of rats with a unilateral 6-OHDA lesion). In the dorsal portion of the caudate putamen, core and shell of the nucleus accumbens, and in several cortical regions, both amphetamine (1.5 mg/kg) and cocaine (15 mg/kg) induced higher levels of c-fos mRNA expression when administered in a novel environment, relative to when they were administered in the home cage. The ability of environmental context to modulate psychostimulant drug-induced immediate early gene expression may be related to its ability to modulate forms of drug experience-dependent plasticity, such as behavioral sensitization.

The ability of environmental context to facilitate psychomotor sensitization to amphetamine can be dissociated from its effect on acute drug responsiveness and on conditioned responding

Doses of amphetamine or cocaine that fail to induce psychomotor sensitization when given to a rat in its home cage can produce robust sensitization if given immediately following placement into a relatively novel, distinct environment. A drug-associated context can serve as a conditioned stimulus, and therefore may promote robust sensitization by facilitating associative learning processes. We examined this hypothesis by habituating rats to the test environment for 1 or 6--8 hr prior to each drug injection, which degrades the ability of environmental context to serve as an effective conditioned stimulus. When 0.5 mg/kg of amphetamine was administered intravenously immediately after placement into a distinct environment there was a large acute psychomotor response (rotational behavior) on the first test day, and robust sensitization developed with repeated daily injections. When the same treatment was administered in the home cage, there was a small acute response and no sensitization developed. The enhanced acute response seen in the distinct environment was significantly attenuated by 1 hr of habituation to the test environment, and completely abolished by 6--8 hr of habituation. Also, as little as 1 hr of habituation completely prevented the development of a conditioned rotational response. In contrast, neither 1 nor 6--8 hr of habituation had any effect on the ability of amphetamine to induce robust behavioral sensitization. It is concluded that the ability of a distinct environment to facilitate sensitization to amphetamine can be dissociated from its effect on acute drug responsiveness and from the ability of drug-associated environmental stimuli to elicit a conditioned response. Possible mechanisms by which a distinct environment facilitates sensitization are discussed.

Amphetamine and cocaine induce different patterns of c-fos mRNA expression in the striatum and subthalamic nucleus depending on environmental context

In the dorsal striatum, there are two major populations of medium spiny projection neurons. One population is positive for dynorphin mRNA (DYN+), and these cells project preferentially to the substantia nigra, forming the so-called 'direct pathway'. A second population is positive for enkephalin mRNA (ENK+), and these cells influence the substantia nigra indirectly, via the globus pallidus and subthalamic nucleus. Psychostimulant drugs, such as amphetamine and cocaine, are reported to induce immediate early genes (IEGs) in only one subpopulation of dorsal striatal projection neurons, DYN+ cells. However, this apparent selectivity appears to be a function of environmental context. We found that when given in the animal's home cage, amphetamine and cocaine increased expression of the IEG, c-fos, almost exclusively in DYN+ cells. However, when given in a novel environment, amphetamine and cocaine increased c-fos mRNA in both DYN+ and ENK+ cells. Furthermore, amphetamine and cocaine increased c-fos mRNA expression in the subthalamic nucleus when administered in the novel environment, but not when given at home. We conclude that the neural circuitry engaged by psychostimulant drugs, and their ability to induce specific patterns of gene expression, are determined by the environmental context in which they are experienced. This may be related to the ability of environmental novelty to facilitate psychostimulant drug-induced neuroplasticity.

Tolerance and sensitization to the behavioral effects of drugs

Tolerance and sensitization are relatively simple manifestations of learning and memory that refer to decreases and increases in the strength of a response to a stimulus induced by past experiences with the same or related stimuli. In the context of the study of drugs, tolerance refers to the decreased effectiveness of a given drug with repeated administration; sensitization to the increased effectiveness with repeated administration. Tolerance usually involves active adjustments or adaptation to the drug-induce disturbances of function, either within cells or within a neural system. In situations involving inter-neuronal events, these processes of adjustment may take the form of learned modifications that can be re-evoked on future occasions by events that co-occurred at the time of the original modifications. Sensitization, defined as the enhancement of a directly elicited drug effect, though adaptive, appears to represent facilitation within a system, making the effect easier to elicit on future occasions. Like tolerance, sensitization of a drug effect can become linked to the events that co-occurred when the effect was originally elicited, making it possible for sensitization to come under selective event control. This paper is concerned with factors that affect whether tolerance and/or sensitization to the various effects of drugs will develop and be expressed, and with the variety and levels of mechanisms responsible for tolerance and sensitization under different conditions of exposure.

Modulation of food intake by the kappa opioid U-50,488H: evidence for an effect on satiation

The main goal of the present study was to test the hypothesis that the prophagic effect of the kappa opioid agonist U-50,488H (U50) is primarily due to an effect on satiation. In Experiment 1, the feeding effects of U50 (2.0 and 4.0 mg/kg, i.p.) was tested in animals with ad libitum access to ground food and to three sucrose solutions (1, 4, and 20%). In Experiment 2, a classical "one-bottle" test was utilized to test for the effect of U50 (4.0 mg/kg, i.p.) on the intake of five different sucrose solutions (1, 4, 16, 32, and 40%) over a 30-min period. Finally, in Experiment 3 we evaluated the effect of U50 (2.0, 4.0, and 6.0 mg/kg, i.p.) on extracellular dopamine (DA) concentration in the nucleus accumbens. In Experiment 1, U50 enhanced the intake of ground food but not of sucrose. In Experiment 2, U50 increased the intake of high concentration sucrose solutions whereas it decreased that of low concentration solutions. In Experiment 3, U50 produced a dose-dependent decrease in DA concentrations in the absence but not in the presence of food. The most likely explanation for the present results is that U50 enhances feeding by activating mechanisms that block satiety and satiation. In contrast, we found little evidence for an effect of U50 on palatability.

Environmental novelty differentially affects c-fos mRNA expression induced by amphetamine or cocaine in subregions of the bed nucleus of the stria terminalis and amygdala

The environmental context in which amphetamine or cocaine are administered modulates both their acute psychomotor activating effects and their ability to induce sensitization. Here we report that environmental context differentially affects patterns of amphetamine- and cocaine-induced c-fos mRNA expression in the bed nucleus of the stria terminalis (BST) and amygdala of male rats. In the medial amygdala and medial posterior BST, exposure to novelty resulted in a marked increase in c-fos mRNA. Amphetamine given at home did not induce c-fos mRNA, and when given in the novel environment, did not increase levels beyond that observed for novelty alone. In the basolateral and lateral amygdala, amphetamine or cocaine at home or exposure to novelty induced c-fos mRNA. When amphetamine or cocaine was given in a novel environment the c-fos mRNA response was significantly enhanced. In the central nucleus of the amygdala (CEA) and oval subnucleus of the BST (BSTov), amphetamine administration at home produced a robust increase in c-fos mRNA expression, whereas exposure to novelty had little effect. In contrast to other brain regions examined, the c-fos mRNA response to amphetamine in a novel versus home environment was significantly smaller. In both "home" and "novel" amphetamine groups, c-fos mRNA in the BSTov and CEA was predominantly expressed in enkephalin-containing cells; coexpression with corticotropin-releasing hormone was rare. These data suggest that the context in which psychostimulants are given powerfully and differentially alters the response of limbic structures that have been functionally implicated in drug reinforcement and emotional behaviors.

The role of contextual versus discrete drug-associated cues in promoting the induction of psychomotor sensitization to intravenous amphetamine

The environmental context in which psychostimulant drugs are administered can have a large effect on both their acute psychomotor activating effects and their ability to induce the psychomotor sensitization associated with repeated drug administration. For example, the acute effects of amphetamine and the development of psychomotor sensitization to amphetamine and cocaine are enhanced when they are administered in a distinct and relatively novel test environment, relative to when they are given in the home cage, in the absence of any environmental stimuli predictive of drug administration. The experiments reported here were designed to further examine this phenomenon and to test the hypothesis that the ability of a distinct context to promote robust psychomotor sensitization is due to its ability to reliably signal (cue) drug administration. Specifically, we compared the ability of contextual cues (a distinct test environment) and discrete cues (light, tone and/or odor), which both reliably predict drug administration, to promote the induction of sensitization. The psychomotor stimulant effects (rotational behavior) of repeated intravenous infusions of 0. 5 mg/kg amphetamine were assessed in rats for whom drug treatments were signaled either: (1) by placement into a distinct test environment; (2) by presentation of discrete cues; or (3) rats for whom drug treatments were given in the home environment in the absence of any environmental cues. Amphetamine produced robust sensitization when given in association with placement into a distinct test environment. The same treatment failed to produce sensitization when the drug was given unsignaled in the animal's home cage. Most importantly, signaling drug administration by presenting discrete cues was not sufficient to promote the robust sensitization seen when treatments were given in a distinct test environment. These results confirm that the induction of psychomotor sensitization can be powerfully modulated by environmental context and further establish that, although contextual stimuli associated with a distinct test environment promote robust sensitization, discrete cues that merely predict drug administration do not have this property. Possible reasons for the difference in the ability of contextual versus discrete environmental cues to promote sensitization are discussed.

Modulation of morphine sensitization in the rat by contextual stimuli

RATIONALE

The repeated administration of addictive drugs, such as amphetamine, cocaine, and morphine, produces a progressive enhancement (sensitization) of their psychomotor activating effects. We have previously shown that administration of amphetamine or cocaine in a distinct test environment promotes more robust psychomotor sensitization than if they are given at home. No information is available, however, on whether this environmental manipulation has a similar effect on sensitization to morphine, a drug that enhances dopamine (DA) release in the striatum indirectly by disinhibiting midbrain DA neurons.

OBJECTIVES

The main goal of present study was to determine whether exposure to a distinct environmental context facilitates morphine sensitization.

METHODS

As an index of psychomotor activation, we used rotational behavior in rats with a unilateral 6-hydroxydopamine lesion of the mesostriatal DA system. There are inconsistencies in the literature regarding the ability of morphine to elicit rotational behavior. Therefore, in experiment 1 we determined the effect of 2.0, 3.0, 4.0, 6.0, and 8.0 mg/kg, IP, of morphine on rotational behavior. In experiment 2, we studied the effect of five consecutive IV infusions of saline or morphine (2.0 mg/kg) in rats treated either in their home cage or in a distinct and relatively novel test environment. After 5 days of withdrawal, all rats received an IV infusion of 2.0 mg/kg morphine (Morphine challenge). The following day all rats received an IV infusion of saline (Saline challenge).

RESULTS

Morphine produced a dose-dependent increase in rotational behavior. Environmental novelty enhanced both the acute psychomotor response to morphine and its ability to induce psychomotor sensitization. Furthermore, a conditioned rotational response was seen only in animals treated in the novel environment.

CONCLUSIONS

Environmental novelty can facilitate the development of sensitization to the psychomotor activating effects of major addictive drugs, such as amphetamine, cocaine, and morphine.

Environmental modulation of the response to amphetamine: dissociation between changes in behavior and changes in dopamine and glutamate overflow in the rat striatal complex

RATIONALE

We have previously shown that environmental novelty enhances the behavioral activating effects of amphetamine and amphetamine-induced expression of the immediate early gene c-fos in the striatal complex, particularly in the most caudal portion of the caudate. In contrast, we found no effect of novelty on the ability of amphetamine to induce dopamine (DA) overflow in the rostral caudate or in the core of the nucleus accumbens.

OBJECTIVES

The twofold aim of the present study was to determine the effect of environmental novelty on (1) amphetamine-induced DA overflow in the shell of the nucleus accumbens and in the caudal portions of the caudate, and (2) glutamate and aspartate overflow in the caudal portions of the caudate.

METHODS

Two groups of rats with a unilateral 6-hydroxydopamine lesion of the mesostriatal dopaminergic system received amphetamine (0.5 mg/kg, i.v.) in physically identical cages. For one group, the cages were also the home environment, whereas, for the other group, they were a completely novel environment. In vivo microdialysis was used to estimate DA, glutamate, and aspartate concentrations.

RESULTS

Environmental novelty enhanced amphetamine-induced rotational behavior (experiments 1-3) but did not alter amphetamine-induced DA overflow in either the shell of the nucleus accumbens (experiment 1) or the caudate (experiment 2). In addition, the ability of environmental novelty to enhance amphetamine-induced behavioral activation was not associated with changes in glutamate or aspartate efflux in the caudate (experiment 3).

CONCLUSIONS

The present data indicate that the psychomotor activating effects of amphetamine can be modulated by environmental context independent of its primary neuropharmacological actions in the striatal complex.

Environmental modulation of amphetamine-induced c-fos expression in D1 versus D2 striatal neurons

We have reported previously that exposure to environmental novelty enhances the behavioral activating effects of amphetamine and its ability to induce the immediate early gene c-fos in the striatum and in other brain regions. In the present study, we used double in situ hybridization histochemistry to study the effect of amphetamine and/or novelty on c-fos expression in two populations of striatal neurons that preferentially express either D1 or D2 dopamine receptor mRNA. When given intraperitoneally to rats in their home cage, amphetamine (2.0 mg/kg) increased c-fos expression only in D1 neurons. In contrast, when the same dose of amphetamine was administered to rats in a novel environment, c-fos was increased in both D1 and D2 neurons. We conclude that the neural populations engaged by amphetamine vary as a function of the circumstances surrounding its administration.

Susceptibility to amphetamine-induced locomotor sensitization is modulated by environmental stimuli

We have previously reported that intravenous (i.v.) administrations of 0.5-1.0 mg/kg of amphetamine in the absence of any environmental stimuli predictive of drug administration failed to induce psychomotor sensitization whereas the same drug did produce robust sensitization when given in association with environmental novelty. These results were obtained by studying rotational behavior in animals with a unilateral 6-OHDA lesion of the mesostriatal dopamine system. The purpose of this study was to determine if environmental novelty has a similar effect on sensitization to the locomotor activating effects of amphetamine in neurologically intact rats. Rats were implanted with i.v. catheters and divided in four groups. Two groups were housed in locomotor activity cages and given seven consecutive i.v. infusions of either saline (SAL-HOME group) or 0.375 mg/kg of amphetamine (AMPH-HOME group), using a remotely activated delivery system. Simultaneously, the other two groups were transported to the test cages and given the same treatment (SAL-NOVEL and AMPH-NOVEL groups). After one week withdrawal, all groups were given an amphetamine challenge (0.375 mg/kg, i.v.). Amphetamine sensitization developed when the drug was administered under NOVEL conditions, as indicated by a progressive increase in amphetamine-induced locomotor activity over test sessions and by a greater response to the amphetamine challenge in the AMPH-pretreated versus the SAL-pretreated group. In contrast, no sensitization was observed under HOME conditions. Similar results were obtained with the analysis of vertical activity.

Long-lasting sensitization to the accelerating effects of amphetamine on the speed of an internal clock

Drinking in the rat occurs in bursts of rapid licking, a high frequency rhythmic behavior controlled by a neural clock located in the brain stem. We found that 3.0 mg/kg amphetamine increased the speed of licking and shifted to the left the frequency distribution of inter-lick intervals. Repeated amphetamine treatments result in long-lasting sensitization to this effect. Thus, it appears possible to produce enduring changes in the activity of a biological interval clock (or 'stopwatch') by manipulating catecholaminergic transmission. These findings may be important for an understanding of the neural basis of normal and pathological timing behavior.

A comparison of two behavioral measures of psychomotor activation following intravenous amphetamine or cocaine: dose- and sensitization-dependent changes

This paper presents data concerning the dose-effect relationships of intravenously administered amphetamine and cocaine on two widely used measures of psychomotor activation: locomotor crossover activity in neurologically intact rats, and rotational behavior in rats with a unilateral 6-hydroxydopamine lesion. There were marked differences in dose-effect relationships, both as a function of drug and of behavioral measure. Amphetamine produced a linear increase in rotational behavior over a wide range of doses (the highest effective dose was 76.8 times the lowest), but a linear increase in locomotor crossover activity over only a narrow dose range (the highest effective dose was only four times the lowest). In contrast, for cocaine, the dose-effect relationships for the two behaviors were very similar, but for both behaviors the effective dose range was quite narrow, the highest effective dose being only between two and four times the lowest. The data highlight the advantages and disadvantages of these measures as indices of the psychomotor activating effects of psychostimulant drugs.

Amphetamine-induced behavior, dopamine release, and c-fos mRNA expression: modulation by environmental novelty

We have shown recently that the psychomotor activating effects of amphetamine in the rat are much greater when this drug is administered in association with environmental novelty than when it is given in a home environment. The main purpose of the present study was to explore the neural basis of this phenomenon. We found, using in situ hybridization of c-fos mRNA, that the pattern of neuronal activation in the cortex, in the caudate, in the shell and core of the nucleus accumbens, and in other subcortical structures was markedly different when amphetamine (2.0 mg/kg, i.p.) was given in association with exposure to environmental novelty relative to when it was given at home. In most brain regions the magnitude of c-fos expression was over two times greater in rats given amphetamine plus novelty than in rats given amphetamine alone. In contrast, an in vivo microdialysis study indicated that environmental novelty did not affect amphetamine-induced dopamine release in either caudate or nucleus accumbens. Furthermore, a unilateral 6-hydroxydopamine lesion of the mesostriatal dopamine system reduced amphetamine- but not novelty-induced c-fos expression. Finally, we found no differences in the amount of corticosterone secreted after exposure to novelty, amphetamine, or both, suggesting that corticosterone does not play a critical role in the ability of novelty to modulate amphetamine-induced psychomotor activation. In conclusion, it seems that environmental novelty alters the neurobiological effects of amphetamine independently of the primary neuropharmacological actions of this drug in the striatum.

Injection of the protein kinase C inhibitor Ro31-8220 into the nucleus accumbens attenuates the acute response to amphetamine: tissue and behavioral studies

The ability of amphetamine to produce heightened locomotor activity is thought to be due to its ability to enhance dopamine release from mesolimbic dopamine neurons. The mechanism by which amphetamine increases dopamine release is not well understood, but is thought to involve exchange diffusion with synaptosomal dopamine through the dopamine transporter. We recently reported that amphetamine-mediated dopamine release in the striatum is also dependent on protein kinase C activity. In the current study, we investigated the role of protein kinase C activity in the acute neurochemical and behavioral response to amphetamine in the nucleus accumbens. Consistent with previous results in the striatum, amphetamine-stimulated dopamine release from nucleus accumbens tissue was inhibited by the specific protein kinase C inhibitor Ro31-8220, but not by the relatively inactive analog bisindoylmaleimide V. In addition, the effects of protein kinase C activity on the acute behavioral response to amphetamine was examined by injecting Ro31-8220 into the nucleus accumbens 15 min prior to intra-accumbens amphetamine. Pretreatment with Ro31-8220 attenuated the motor-stimulant effects of intra-accumbens amphetamine relative to control subjects pretreated with vehicle. Bisindoylmaleimide V did not significantly inhibit the motor-stimulant effects of intra-accumbens amphetamine. These results suggest that the action of amphetamine in the nucleus accumbens in increasing dopamine release and locomotor activity is dependent on protein kinase C activity.

Modulatory effect of environmental stimuli on the susceptibility to amphetamine sensitization: a dose-effect study in rats

In previous studies the repeated administration of 0.5 to 1.0 mg/kg of amphetamine i.v. failed to induce psychomotor sensitization if the drug was administered to animals living in the test environment (at home). The same doses did induce sensitization if animals were transported to the test environment for each drug treatment. The purpose of the present experiment was to determine the extent to which this effect of environment is dose dependent. Rats either lived in test cages or were transported from the animal colony to test cages where they received an i.v. infusion of one of five doses of amphetamine (0.125, 0.5, 1.0, 4.0 or 8.0 mg/kg) or saline each day for 5 consecutive days. Rotational behavior was used as an index of psychomotor activation. After a 6-day drug-free period all animals were challenged with 0.5 mg/kg of amphetamine to determine the pretreatment dose necessary to induce sensitization. The effect of the drug-treatment environment was to shift the dose-effect curve for the induction of sensitization, such that significantly lower doses were necessary to induce sensitization when amphetamine was given in a novel environment. With high doses, however, sensitization occurred regardless of environmental condition. It is concluded that the circumstances surrounding drug administration can powerfully modulate the ability of psychostimulants to induce sensitization, but this effect is dose dependent.

The effect of environment on the changes in calmodulin in rat brain produced by repeated amphetamine treatment

Rats were given repeated infusions of i.v. amphetamine in association with placement in a novel test environment, a protocol that produces behavioral sensitization, or in the home cage, a protocol that fails to induce sensitization. In several brain areas amphetamine altered calmodulin content, but only in the group treated in a novel environment, suggesting that amphetamine-induced alterations in calmodulin may occur only when drug treatments induce behavioral sensitization.

The influence of environment on the induction of sensitization to the psychomotor activating effects of intravenous cocaine in rats is dose-dependent

The acute psychomotor response and development of sensitization to amphetamine is attenuated if i.p. injections are given in the cage where a rat lives relative to when injections are given in a novel but physically identical test environment. Furthermore, when the environmental cues predicting i.p. injections are completely eliminated by using remotely activated i.v. injections in the home cage, 1.0 mg/kg amphetamine produces a very small acute response and no sensitization. The same treatments do produce sensitization if i.v. injections are signaled by placement of the rat in a novel test cage. The present experiment was designed to determine if there is a similar effect of environmental condition on the response to i.v. cocaine, and to what extent the effect may be dose-dependent. This was accomplished by comparing the psychomotor activating effects (rotational behavior) of repeated i.v. administrations of one of eight doses of cocaine (0.0, 0.3, 0.6, 1.2, 2.4, 3.6, 4.8, or 7.2 mg/kg) given in the home cage, with infusions of the same doses given in a novel test cage. There was no effect of environment on the acute psychomotor response to cocaine. There was, however, a significant effect of environment on the induction of sensitization. A higher dose of cocaine was required to induce sensitization when i.v. administrations were given in the home cage than when they were given in a physically identical but novel test environment. At high doses, however, cocaine induced sensitization regardless of environmental condition. The results suggest that the effect of this environmental manipulation is to shift the dose-effect curve for the induction of sensitization, and support the notion that the ability of psychostimulant drugs to induce sensitization can be modulated by the circumstances surrounding drug administration.

Modulation of the induction or expression of psychostimulant sensitization by the circumstances surrounding drug administration

The conditions necessary to induce psychomotor sensitization and to promote its expression are not well understood. Two examples are reviewed here of how the circumstances surrounding drug administration ("set and setting") can powerfully modulate the sensitization produced by psychostimulant drugs, such as amphetamine or cocaine. In the first example it is suggested that repeated exposure to psychostimulant drugs may induce "neural sensitization" (i.e., produce relevant adaptations in the nervous system). The circumstances surrounding drug administration may determine, however, whether neural sensitization is expressed in behavior. In the second example it is suggested that the circumstances surrounding drug administration may determine whether sensitization is induced at all, or at least the rate and extent of sensitization produced by a given dose of a drug. It is concluded that psychomotor sensitization is not an inevitable consequence of exposure to psychostimulant drugs, but is the result of interactions amongst the pharmacological actions of drugs and the circumstances surrounding drug administration.

Enduring enhancement of amphetamine sensitization by drug-associated environmental stimuli

We report on the effect of environment on amphetamine sensitization in rats with a unilateral 6-hydroxydopamine lesion of the mesostriatal dopamine system. The rats were either housed in the test environment (HOME) or exposed to it only during the treatments (NOVEL). In experiment 1, the rats received seven consecutive i.p. injections of either saline or 2 mg/kg amphetamine. After 1 wk withdrawal the rotational response to 2 mg/kg amphetamine i.p. (i.e., amphetamine challenge) was compared in saline- vs. amphetamine-pretreated animals. Although both HOME and NOVEL groups sensitized, the magnitude of sensitization was greater in the NOVEL group. In the NOVEL group there was also a greater conditioned response to drug-related cues. In experiment 2 a dose-effect curve (0.75, 1.5, 3.0 and 6.0 mg/kg amphetamine i.p.) was determined before and after six i.p. injections of 4.0 mg/kg amphetamine. Sensitization was indicated by a parallel shift to the left of the dose-effect curve in both groups, but this shift was 2.6 times greater in the NOVEL group than in the HOME group. Finally, in experiment 3, we found that environment- and sensitization-dependent differences in the psychomotor response to amphetamine were not accompanied by differences in the concentration of amphetamine in the plasma or in the striatum.