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PubMed1986

Effects of MK-212 (6-chloro-2[1-piperazinyl]pyrazine) on schedule-controlled behavior and their reversal by 5-HT antagonists in the pigeon.

The effects of MK-212 (6-chloro-2[1-piperazinyl]pyrazine), a centrally-active 5-hydroxytryptamine (5-HT; serotonin) agonist, were studied alone and in combination with the 5-HT antagonists, methysergide (0.01-0.1 mg/kg), metergoline (0.01-1.0 mg/kg) and ketanserin (0.01-3.0 mg/kg). Pigeons were maintained under a procedure where key pecks were reinforced under a multiple fixed-interval (FI) fixed-ratio (FR) schedule of food presentation. In the fixed-interval component, the first response after 3 min had elapsed, produced food, while in the fixed-ratio component, the thirtieth response was reinforced. The drug MK-212 (0.1-3.0 mg/kg) produced dose-related decreases in response rates under both components of the schedule. In smaller doses of MK-212 (0.3 and 1.0 mg/kg), the decrease in the response rate was greater in the fixed-interval component than in the fixed-ratio component. Small doses of methysergide (0.03 mg/kg) and metergoline (0.1 mg/kg), which had little effect when given alone, partially blocked the effects of MK-212 (1.7 and 3.0 mg/kg) in decreasing rate. Larger doses of these compounds, which sometimes increased the response rate when given alone, resulted in a more complete restoration of response rates when administered with MK-212. Ketanserin, a selective 5-HT2 antagonist, reversed the effects of MK-212 in some cases, but the patterning of responses remained disturbed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1982

Conditioned aversion to a taste perceived while grooming.

Four experiments were conducted to determine how the characteristics of conditioned taste aversion (CTA), as described from studies conducted in the drinking and feeding contexts, applied in the grooming context. In Experiment 1, sodium saccharin was mixed with a "neutral-tasting" jelly and applied to the fur of male Sprague-Dawley rats. Rats injected with LiCl after the applications strongly avoided saccharin solutions in subsequent 1-hr, 2-choice (Saccharin solution vs water) drinking tests, whereas rats injected with NaCl or given plain jelly on the fur showed only an initial neophobic response to the saccharin solution. Thus, the taste of saccharin was perceived while grooming and the CTA formed in the grooming context generalized to drinking. In experiments 2-4, we obtained evidence that: (a) rats discriminated between one intensity of saccharin applied to the fur and another used in the test solution; and (b) rats differentiated between qualities of the two tastants applied to the fur in that saccharin overshadowed NaCl; and (c) taste qualities were more important than toxic properties when two stimuli (Saccharin, LiCl) were used (saccharin overshadowed NaCl in subsequent drinking tests). We speculate that taste, while grooming might play a role in social communication in some vertebrates. Further, CTA and grooming might have uses in rodent control (e.g., in agricultural situations) not previously considered such as in delivering a non-attractive, low-salience toxin so that the taste of the crop overshadows that of the bait, and induces crop aversion.

Animals↗
PubMed1991

Discriminative properties of aversive electrical stimulations of the so-called "mesencephalic locomotor region": a parametric study.

The classical 2-lever food-reward-reinforced discrimination paradigm, although already successfully applied to study discriminative properties of positively reinforcing electrical brain stimulations (EBS), has not yet been used for negatively reinforcing (aversive) EBS. This study was aimed at assessing if such a discrimination paradigm could be used to demonstrate discriminative properties of aversive EBS of the so-called "mesencephalic locomotor region" (MLR). Fourteen rats were trained for food reward to press one lever in the presence of EBS of the MLR and the other lever in the absence of EBS. Discriminative control by EBS of the MLR was obtained in 11 rats, which were subsequently subjected to a parametric study. It was found that the discriminative properties of EBS of the MLR covaried with changes in the intensity, frequency and pulse duration of the EBS. Our data also suggest that the aversive dimension of the stimulation might constitute a component of the discriminative cue induced by these EBS.

Animals↗
PubMed1992

Malaise can condition avoidance of high-viscosity fluids.

Previous researchers have assumed that malaise-inducing drugs condition aversions to tastes more readily than to textural stimuli. The present report shows that rats given a single injection of lithium chloride after they have sampled a viscous fluid, subsequently showed greater avoidance of that fluid than did control rats. Rats learned this response even when the lithium chloride injection was given 60 min after they sampled the viscous fluid. The generalization gradient for viscous fluids is apparently very broad, because rats trained to avoid 11 or 95 cp fluids subsequently avoided 11 and 95 cp fluids to a similar degree. Nevertheless, this avoidance is based on textural cues because rats injected with lithium chloride after ingesting one viscous fluid subsequently avoided a wide variety of viscous fluids, including those made from carbohydrate polymers (algin, guar, xanthan), a modified carbohydrate (methyl cellulose), and a protein (methyl cellulose). However, the flavors of viscous gums may influence texture aversion.

Animals↗
PubMed1993

Taste prestimulation increases the chorda tympani nerve response to menthol.

Electrophysiological recordings of the summated response of the chorda tympani nerve to menthol stimulation of the tongue were obtained from 15 adult Sprague-Dawley rats. The chorda tympani nerve response to menthol was of short duration, ending within 2.5 s after stimulus onset, leaving the receptors in a state of insensitivity to subsequent menthol stimulation. Rinse durations with deionized-distilled water up to 10 min failed to bring the receptors back to their original prestimulus state. Although stimulation with menthol prevented taste receptors from responding to subsequent presentations of menthol, the chorda tympani nerve would respond normally to NaCl, NH4Cl, KCl, sodium acetate, glucose, citric acid, and quinine-HCl solutions. Prior stimulation with one of these taste solutions resulted in the recovery of the menthol response. The magnitude of the recovered menthol response depended on the magnitude of the phasic response elicited by the preceding taste stimulus. A general explanation involving possible reception and transduction mechanisms was offered to account for menthol's unexpected stimulatory effects on the chorda tympani nerve.

Animals↗
PubMed1996

An ear for quality: differential associative characteristics of taste-potentiated auditory and odor avoidance.

This research compared the avoidance behavior of rats exposed to either a taste-tone (NaCl-70 dB, 1800 Hz) or a taste-odor (NaCl-almond) compound that had been paired with LiCl-induced illness. When tested in the presence of either the odor or the auditory cue presented alone it was found that taste potentiated both cues, but stronger initial avoidance and resistance to extinction was shown to the odor cue. A second experiment examined the generalization of potentiated odor and auditory aversions to a novel environment. Rats were exposed to either a taste-odor or taste-tone compound, again followed by illness. Half of each group was tested in the conditioning chamber and half in a novel chamber. Odor aversions were not affected by location, whereas auditory aversions were significantly stronger in the conditioning chamber. Experiment 3 showed that taste-potentiated odor and auditory aversions showed different patterns of extinction when the taste aversion on which they were based was gradually extinguished. These experiments provide evidence that while the taste potentiation of auditory cues is a reliable phenomena, the pattern of effects is different from that of taste-potentiated odor aversions.

Acoustic Stimulation↗
PubMed1992

Spatial localization without visual references.

To explain the veridical percept of the spatial ordering of objects and the generation of eye movements to peripheral targets, Lotze (1885 Microcosmos. Edinburgh: T. & T. Clark) proposed that there is a position label (local sign) for each retinal element. To estimate the precision of local sign information, we measured absolute localization thresholds at various eccentricities in the nasal visual field, in the complete absence of visual references. To eliminate perception of the visual surround, observers viewed a large display screen through a neutral density filter (2.0 log unit) in a dark room. The fixation target was extinguished at various times (interstimulus intervals or ISIs) prior to the onset of the test stimulus. In general, our results show that localization thresholds are proportional to the target eccentricity at all ISIs. At each eccentricity, localization thresholds are elevated after the extinction of the visual reference compared to thresholds when the reference is present. However, relative to the referenced threshold, unreferenced thresholds are elevated by a greater proportion at smaller eccentricities than at larger eccentricities. Our threshold vs ISI data can be adequately modeled on the basis of an intrinsic positional uncertainty, which increases with eccentricity, and additive and multiplicative sources of noise. The additive noise appears to reflect primarily the increasing scatter in eye position when the fixation target is extinguished. Our model's estimate of intrinsic positional uncertainty in the isoeccentric direction appears to reflect primarily the intrinsic positional uncertainty of the peripheral retina (the local sign), being very similar to cumulative cone position uncertainty and to the spacing between ON-P beta ganglion cells. In the isoeccentric direction, the estimated precision of the local sign mechanism across eccentricities is slightly better than the precision of saccadic endpoints, suggesting that noise in the motor system must also contribute to the scatter of saccadic endpoints in the isoeccentric direction. Interestingly, in the radial direction, we find a surprising similarity in our observers' positional uncertainty and the precision of saccadic endpoints.

Fovea Centralis↗
PubMed1978

Brief communication. Generalization of [DAla2]-enkephalinamide but not of substance P to the morphine cue.

Rats were trained to discriminate morphine (7.5 mg/kg, IP) from saline in a two bar positively reinforced lever pressing paradigm on a FR4 schedule. Morphine (IP) showed a naloxone reversible dose-related generalization to the training dose. [DAla2]-Methionine enkephalinamide (DAE) at 1 mg/kg and Substance P (SP) at 0.1 and 0.25 mg/kg showed vehicle appropriate responding after IP injection. DAE (5 mg/kg) disrupted responding completely; SP (0.5 and 0.1 mg/kg) disrupted responding in 50% of the rats. The disruption caused by IP injection of DAE was not naloxone reversible. Intraventricular injection of morphine (5 microgram/rat) and DAE (5 microgram/rat) produced generalization to the opiate cue. The effect of DAE was reversed by naloxone (1 mg/kg, SC). SP (500 and 750 ng/rat, IVT) produced saline-like responding; 1 microgram/rat disrupted responding completely. These data demonstrate that morphine and enkephalin, but not Substance P, share similar discriminative properties.

Animals↗