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The prey localisation model: a stability analysis.

This paper analyzes the "Prey localisation Model" (House 1984), for animals that are unable to verge their eyes. The Prey localisation Model selects a single point or a portion of the scene in its visual space. In particular it imitates the behaviour of frogs and toads of selecting the closer target when two equally attractive prey are presented to it. The model achieves its goal by tightly coupling two prey selection processes, one for each eye, with lens accommodation. In this paper we offer a stability analysis of the model, and show how lens accommodation, i.e. adjustment in the focal length of the lens, biases the selection of the proximal target. We examine the properties of the model that are responsible for its behaviour and derive a set of conditions which guarantees the localisation of the correct target.

Animals↗

Anxiolytic actions of chlordiazepoxide determine its effects on hyponeophagia in rats.

The effects of chlordiazepoxide (0, 5, 15 mg/kg) on eating latency, eating time and amount eaten of familiar and novel foods by rats were assessed. Familiarity with the test apparatus and procedure increased feeding but reduced responsivity to chlordiazepoxide (5 mg/kg). Food deprivation increased feeding and responsivity to 5 mg/kg chlordiazepoxide but attenuated some sedative effects of 15 mg/kg chlordiazepoxide. Preference for familiar food was shown only by food-deprived, test-experienced rats. The time devoted to eating novel food, but not the amount eaten, was increased by chlordiazepoxide. These findings are discussed in the context of anxiolytic and appetitive interpretations of benzodiazepine effects on hyponeophagia , with the conclusion that reduction in apparatus neophobia largely accounts for the results observed.

Animals↗

Long-term effects of barbital on spontaneous activity of rats trained to use the drug as a discriminative stimulus.

This investigation sought to determine if the discriminative stimulus properties of barbital are reflected in the pattern of spontaneous motor activity induced by the drug. Rats were trained in a Skinner box to discriminate the effects of sodium barbital (80 mg/kg), injected 60 min prior to training, from those of saline. Half of the animals (Group I) were taught the drug discrimination by rewarding them for bar pressing only when they were in the drug condition. The other half of the animals (Group II) were rewarded only in the absence of the effects of barbital. Spontaneous motor activity was monitored during the 20 min period from 40--60 min after injection of the drug or saline. After several months of drug discrimination training, the patterns of spontaneous activity displayed by all animals suggested that the treatments had become conditioned to signal the forthcoming availability or non-availability of food in the Skinner box. The data also suggested that chronic exposure to barbital may induced adaptations which allowed the drug to increase spontaneous motor activity.

Animals↗

Effects of scopolamine and alpha-methylparatyrosine upon predatory attack in cats.

The effects of scopolamine were compared with the effects of alpha-methylparatyrosine methyl ester (AMPT) upon several aspects of electrically elicited predatory attack in cats. Thresholds of current necessary to elicit predation increased under both drugs. Furthermore, specific deficits developed in suprathreshold predatory patterns for both drugs compared with nondrug baselines. Scopolamine suppressed all aspects of attack, while AMPT suppressed approach of the attack object while leaving reflexive biting intact.

Aggression↗

Diazepam-induced place preference conditioning: appetitive and antiaversive properties.

The place conditioning paradigm was used to examine the reinforcing properties of diazepam. Rats were injected with diazepam (0.5-5.0 mg/kg, IP) and 30 min later were confined for 30 min to one side of a shuttle box, in which each of the two compartments had distinctive features. On alternate (control) days they received vehicle injections and were confined for 30 min to the opposite side. At almost all doses tested, diazepam produced place preference for the distinctive compartment that had been previously associated with the drug. Preference for the drug side developed regardless of whether diazepam was paired or unpaired with the least-preferred side, and regardless of whether testing was carried out in the undrugged or in the drugged state. The rats preferred the drug side over a novel compartment, but they did not change their initial preference for the side when diazepam was given after removal from the training box. Animals injected with meprobamate (70 mg/kg, PO), a non-benzodiazepine anxiolytic, also developed conditioned preference for the drug side, comparable to that seen following cocaine hydrochloride (10 mg/kg, IP). The diazepam (2.5 mg/kg)-induced place preference was antagonized by CGS 8216 (3 mg/kg, IP), picrotoxin (2 mg/kg, IP) and naloxone (0.8 mg/kg, SC), injected 3 min before and 15 and 20 min after diazepam respectively. Sodium valproate (200 mg/kg, IP) did not influence diazepam (1 mg/kg)-induced place preference. Sodium valproate by itself had marginal effects on place conditioning. Picrotoxin and naloxone, but not CGS 8816, produced place aversion which, in the case of picrotoxin, was due to state dependent learning.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

The effects of chlorpromazine and lithium on appetitive discrimination learning in the rat.

Rats learned one of two appetitive discrimination tasks varying in terms of cognitive difficulty. Contrary to previous reports showing an impairment in the acquisition of avoidance tasks under the effects of either chlorpromazine (CPZ) or lithium, the results of this experiment indicate that neither drug retards the acquisition of appetitive tasks. Instead, at the highest doses used (2 and 3 mg/kg), CPZ decreased the number of trials required for the difficult task. Rats administered CPZ had longer reaction times than rats administered placebo, and therefore might have achieved criterion earlier because they spent more time in front of and on the discriminanda. The contrary results reported with avoidance tests concerning the effects of CPZ are explained in terms of the anxiety-reducing properties of CPZ, which might reduce drive without impairing cognitive ability.

Animals↗

Sensory and associative effects of LSD on classical appetitive conditioning of the rabbit jaw movement response.

Three experiments were conducted to determine the effects of LSD (30 nmol/kg) in classical appetitive conditioning of the rabbit jaw movement response (JMR). In experiment 1, LSD significantly enhanced the acquisition of conditioned responses (CRs). The performance of control groups receiving unpaired presentations of the conditioned stimulus (CS) and unconditioned stimulus (UCS) demonstrated that LSD's enhancing effect on conditioning could not be attributed to an elevation in baseline responding, sensitization, or pseudoconditioning. Accordingly, experiments 2 and 3 were conducted to determine whether LSD's enhancement of conditioning could have arisen from its altering the sensory processing of either the CS or UCS, or both. In experiment 2, LSD was found to have no significant effect on the functions relating UCS magnitude to the frequency, amplitude, or number of sinusoidal peaks comprising each unconditioned response (UCR). In contrast, experiment 3 revealed that LSD significantly enhanced the frequency of CRs to an extended range of CS intensities and lowered the CS intensity threshold. It was concluded that the enhancing effect of LSD on the acquisition of CRs is attributable, at least in part, to the drug's enhancement of the sensory processing of the CS.

Animals↗