Biomedical subjects

M F Roitman

Publications and source records attributed to M F Roitman.

9 recordsLinked to original sources

PubMed2001

Dopamine mediation of the feeding response to violations of spatial and temporal expectancies.

The present studies were aimed at further characterizing the role of DA in motivation. Rats, conditioned to expect food in one environment and no food in another, all received food on the test night. Those in the environment in which food was unexpected ate four times as much as those eating where food was expected. The overeating was eliminated by administration of the D2 antagonist raclopride. Another expectancy, timing of light offset in rats entrained to a fixed light--dark cycle, was violated by unexpectedly turning the lights off 1 h early. This provoked an elevation in food intake, which was also eliminated by the administration of raclopride. Feeding in two other situations not involving violation of expectancies (food deprivation; normal light offset) was unaffected by DA antagonism. These findings support the idea that DA signals errors in expectancy and that DA signaling is necessary for certain behavioral responses to unexpected events.

Animals↗

PubMed1999

Sodium depletion and aldosterone decrease dopamine transporter activity in nucleus accumbens but not striatum.

Motivated behaviors, including sodium (Na) appetite, are correlated with increased dopamine (DA) transmission in the nucleus accumbens (NAc). DA transporter (DAT) modulation affects DA transmission and may play a role in motivated behaviors. In vivo Na depletion, which reliably induces Na appetite, was correlated with robust decreases in DA uptake via the DAT in the rat NAc with rotating disk electrode voltammetry [1,277 +/- 162 vs. 575 +/- 89 pmol. s-1. g-1; Vmax of transport for control vs. Na-depleted tissue]. Plasma aldosterone (Aldo) levels increase after in vivo Na depletion and contribute to Na appetite. Decreased DAT activity in the NAc was observed after in vitro Aldo treatment (428 +/- 28 vs. 300 +/- 25 pmol. s-1. g-1). Neither treatment affected DAT activity in the striatum. These results suggest that a direct action of Aldo is one possible mechanism by which Na depletion induces a reduction in DAT activity in the NAc. Reduced DAT activity may play a role in generating increased NAc DA transmission during Na appetite, which may underlie the motivating properties of Na for the Na-depleted rat.

Aldosterone↗

PubMed1999

Amiloride-sensitive sodium signals and salt appetite: multiple gustatory pathways.

In the rat, the ionic specificity of Na+ appetite is thought to rely on amiloride-sensitive Na+ signals conveyed by the chorda tympani (CT) nerve. We evaluated whether robust Na+ appetite relies exclusively on CT-mediated amiloride-sensitive Na+ signals. Amiloride dramatically reduced sham drinking of NaCl (41.9 +/- 9.0 vs. 6.9 +/- 3.7 ml, 0.1 M NaCl without vs. with 100 microM amiloride), which resulted in intake that was not different from intake of a non-Na+ salt solution (8.8 +/- 2.3 ml, 0.15 M KCl). In addition, intake of 0.1 M NaCl in CT-transected (CTX) rats was reduced (35.8 +/- 13.3 vs. 8.67 +/- 3.4 ml, sham-operated vs. CTX rats), but the addition of amiloride (100 microM) further reduced intake in CTX rats (0.5 +/- 0.29 ml). These data support the idea that amiloride-sensitive Na+ channels are the critical gustatory substrate for Na+ identification during Na+ appetite in the rat. However, the data indicate that these amiloride-sensitive signals are not conveyed exclusively by the CT nerve but by an additional afferent pathway.

Amiloride↗

PubMed1998

Learned tolerance to ethanol-induced c-Fos expression in rats.

With c-Fos immunoreactivity as a marker for neural activity, we examined whether environmental cues associated with ethanol injection influence the expression of tolerance to ethanol-induced c-Fos activation. Over 24 training days, male Long-Evans rats received ethanol injection (2.5 g/kg) in one environment and saline injection in a different environment. Relative to rats that received ethanol for the first time, ethanol-induced c-Fos expression in the paraventricular nucleus of the hypothalamus (PVN) and the locus coeruleus (LC) was significantly reduced in rats that had received multiple prior ethanol administrations. However, tolerance was partially reversed when ethanol was given in the saline-paired, rather than the ethanol-paired, environment. Results suggest that tolerance to ethanol, as indexed by c-Fos expression in the PVN and the LC, is mediated in part by Pavlovian conditioned responses to cues that predict ethanol administration.

Animals↗

PubMed1997

Dopamine and sodium appetite: antagonists suppress sham drinking of NaCl solutions in the rat.

Sodium (Na) ingestion in rats depleted of Na is a strong, motivated behavior that is enhanced further when depleted rats are sham drinking. Dopamine plays a critical role in motivation, including reward associated with consumption of palatable tastes. The present studies assessed the role of dopamine in real and sham drinking of NaCl solutions after Na depletion with the diuretic furosemide (10 mg/kg). Dopamine (D2) receptor antagonists were evaluated (Haloperidol [0.1 mg/kg] and raclopride [0.2 mg/kg]), for their effects on sham and real drinking of 0.3 M NaCl. Sham drinking was markedly reduced by both antagonists whereas real drinking was unaffected. These effects did not appear to be due to malaise or suppression of motor behavior because drug-treated animals were able to increase ingestion substantially when offered less concentrated NaCl (0.1 M). These results suggest that the positive motivating properties of NaCl stimulation in depleted, sham-drinking rats are mediated by central D2 receptors.

Animals↗

PubMed1997

Reward comparison in chronic decerebrate rats.

The simultaneous contrast paradigm was used to evaluate responsiveness to a low (0.05 M) and a high (0.5 M) concentration of sucrose under two conditions in intact and chronic decerebrate rats. In one condition the low concentration was presented on one day and the high concentration on another. In the other condition presentation of the two concentration was alternated within the same daily session. In each case there was a total of 40 trials/day during which the stimulus was delivered intraorally for 2 s at a rate of 1.5 ml/min with a 30-s intertrial interval. The results showed that the intact rats always licked more for the high than for the low concentration of sucrose but that the magnitude of the effect was larger when given the opportunity to compare the two concentrations within the same daily session. The decerebrate rats produced a similar pattern, but the concentration effect was evident only when the stimuli were alternated within the same daily session. These data stand as the first evidence that the isolated caudal brain stem is adequate for the expression of a behavior that depends on comparison processes involving short-term memory.

Animals↗

PubMed1996

c-Fos induction in rat brainstem in response to ethanol- and lithium chloride-induced conditioned taste aversions.

When consumption of a novel taste (conditioned stimulus; CS) is followed by exposure to a toxin, organisms will avoid consumption of that taste in the future. This learned response, known as a conditioned taste aversion (CTA), can be demonstrated using a variety of drugs, including lithium chloride (LiCl) and ethanol. c-Fos immunohistochemistry was used to examine neural activation in the rat brainstem associated with drug administration and with a CS taste previously paired with these drugs. Relative to saline controls, animals injected with either LiCl (76 mg/kg) or ethanol (3.5 g/kg) displayed greater c-Fos expression in area postrema, nucleus of the solitary tract (NTS), and lateral parabrachial nucleus. At these doses, LiCl- and ethanol-injected groups did not differ from each other. For establishing a CTA, intraoral infusion of a 0.15% saccharin solution was followed by injection of either LiCl or ethanol. Both LiCl and ethanol produced quantitatively similar CTAs. Relative to unpaired control groups, saccharin paired with either drug induced significant c-Fos expression in NTS. Thus, like LiCl, ethanol and tastes that have become aversive by virtue of their association with ethanol activate brainstem regions hypothesized to play a role in CTA learning.

Animals↗

PubMed1996

A new taste reactivity analysis of the integration of taste and physiological state information.

We used conjoint manipulation of taste and physiological state to address the theoretical issue of signal integration. The interaction between taste (glucose concentration) and state (food deprivation) was evaluated using the taste reactivity method in which oral motor responses elicited by direct intraoral infusion are measured. The time frame of the typical taste reactivity paradigm, where observation is limited to the infusion period, was expanded to include the postinfusion interval. In each test session, rats received a series of trials consisting of 15-s intraoral infusions and 45-s postinfusion observation intervals. Two experiments were run in which glucose concentration was varied and rats were run nondeprived and after 24 h food deprivation. In experiment 1, glucose concentrations (0, 3.2, 6.25, 12.5, and 25%) were randomly presented during each test session. In experiment 2, individual glucose concentrations (0, 6.25, or 25%) were presented during separate sessions. For both, a deprivation condition was flanked by nondeprived (baseline) sessions. Concentration-response functions were comparable in both experiments. In each experiment, the shape of the concentration-response function was dramatically different during and after infusions. During infusions, there were no increases in glucose-elicited rhythmic oral responses beyond a very dilute concentration. After infusions, the concentration-response functions appeared linear across the concentration range. In both experiments, deprivation elevated responding only in the after-infusion periods. In experiment 1, the concentration-response function was uniformly elevated (on average, 27%) by deprivation, which if taken at face value would suggest an additive combination of taste and state feedback signals. In experiment 2, however, deprivation increased responding (approximately 30%) for 6.25%, but not for 0 or 25%, suggesting a stimulus specificity of the taste-state integration. Clearly then, the taste-state profiles differed as a function of experimental design. In the GENERAL DISCUSSION, we suggest that the uniform elevation of responding to all glucose concentrations, and to water, seen in experiment 1, may be an artifact of the random presentation of all stimuli during individual sessions. Experiment 2, in which stimuli were presented in a between-sessions design, may provide a truer reflection of the underlying integrative process.

Animals↗

PubMed1995

Ingestive taste reactivity as licking behavior.

In ingestive taste reactivity analysis, the rhythmic oral motor responses observed during intraoral infusion of fluids normally ingested by rats are categorized and counted. These rhythmic movements can be likened to spout-licking in several respects. Both are emitted in the same frequency range (5-8 Hz), organized in a burst/pause pattern, and serve the function of intraoral transport of fluid into position for swallowing. The parallel suggests that a temporal pattern analysis, based on the spout-licking literature, can be fruitfully applied to the rhythmic movements that attend intraoral infusion. We provide a demonstration of such an analysis using an electromyographic (EMG) recording-based method for automated event detection. Eight rats received a 37.5% glucose solution (1.0 ml/min) in a series of 120 s infusion trials (45 s intertrial intervals) that was extended until the fluid was rejected. Movement counts declined 19.1% from the first to the last complete trial. Parameters derived from the pattern analysis (number of bursts, mean burst duration, pause durations, coefficient of variation for the distribution of within-burst intermovement intervals) were affected to a greater extent. The results indicate the potential value of temporal pattern analysis for various applications of the taste reactivity paradigm.

Animals↗