Contribution of ingestive behaviors to taste-aversion learning in the rat.

Conducted 3 experiments with male Sprague-Dawley rats (N = 132). Ss tasting but not ingesting a flavored solution prior to toxicosis acquired weaker aversions to the flavor than Ss that actively consumed the CS during conditioning. Taste was isolated from ingestion either by curarizing the Ss or by infusing a flavored solution very rapidly into the oral cavity of non-water-deprived Ss. Control groups showed that the facilitatory effect of ingestion on taste-aversion learning did not depend on the consumption of very much of the CS solution. (20 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Demonstrations of neophobia and enhanced neophobia in the albino rat.

Studied the conditions under which neophobia and enhanced neophobia occur in the albino rat in 5 experiments with a total of 160 male albino rats. Neophobia to a .1% saccharin solution was demonstrated in a 10-min single-bottle test. This neophobia was enhanced by pairing water ingestion with a radiation exposure of 100 r or an injection of LiCl 24 hrs prior to the saccharin test. In addition, it was found that the differences in consumption of saccharin in a 10-min single-bottle test due to neophobia and enhanced neophobia were produced by consistent differences in drinking rates which appeared early in the 10-min period. The disappearance of neophobia and enhanced neophobia in a 1-hr single-bottle test suggested that the effects of neophobia and enhanced neophobia are short-lived and are best measured in a brief single-bottle test. Enhanced neophobia was not found when 2 days of water drinking were interposed between LiCl poisoning and saccharin testing. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Taste salience depends on novelty, not concentration, in taste-aversion learning in the rat.

Conducted 2 experiments with 12 rat litters of albino-hooded-Brown-Swarthmore strain derivation. Ss formed stronger aversions to solutions that were either more concentrated or more novel than other solutions. From the results it is proposed that the data can be reinterpreted in terms of just one of these factors-novelty-since the more concentrated solution is also ordinarily more novel. When Ss were poisoned after drinking 2 concentrations of the same solute, Ss reared on water acquired aversions mainly to the more concentrated solution. Ss reared on a still more concentrated solution acquired aversions mainly to the less concentrated solution which for them was more novel. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

DNA fragmentation in rat brain after intraperitoneal administration of kainate

Cell death occurs in many neuropathological conditions. However, the mechanisms governing this process(es) remain generally unknown. In this report we studied whether excitotoxic neuronal death evoked by kainic acid (KA) in rat brain is associated with ladder-like DNA fragmentation. DNA was isolated from hippocampi, entorhinal and sensory cortices at various times following intraperitoneal KA (10 mg kg-1) injections. Typical oligonucleosome-sized DNA fragmentation was observed in all three structures at 18 h and 72 h following KA administration. These findings were further confirmed by in situ nick-translation. DNA fragmentation is believed to be diagnostic for apoptosis. The clear ladders of DNA fragmentation appeared after 18 h, although slight degradation was observed as early as 12 h after KA administration.     

"Learned safety" as a mechanism in long-delay taste-aversion learning in rats.

Notes that rats learn taste aversions with unusually long CS-UCS delays. The hypothesis was tested that the CS-UCS delay gradient is a learning curve: During the delay, a rat gradually learns that a taste is "safe." In 2 experiments with female white rats, a solution which an S drank only once became safe and resistant to learned aversions for at least 3 wks, suggesting a learned safety mechanism. If an S drank a solution twice (within the effective CS-UCS interval) before a single poisoning, it learned less aversion than if it received only the 2nd presentation. The learned-safety theory explains this result; a trace-decay or interference model cannot. (34 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Anatomical studies of DNA fragmentation in rat brain after systemic kainate administration

Rats treated systemically with kainate develop stereotyped epileptic seizures involving mainly limbic structures that may last for hours. This model of limbic status epilepticus has been widely studied using classical neuropathological techniques. We used in situ nick translation histochemistry to examine patterns of DNA fragmentation in this model. We found a stereotyped and reproducible pattern of neuronal populations that demonstrate evidence of DNA fragmentation from 24 h to one week after kainate treatment. Neither blockade of new protein synthesis nor blockade of the N-methyl-D-aspartate-type glutamate receptors significantly altered this response. Moreover, we saw no evidence of the regular internucleosomal cleavage of DNA that produces a characteristic laddered appearance of 180-200 bp DNA fragments after gel electrophoresis in samples obtained from microdissected affected regions. These studies suggest that DNA fragmentation after systemic kainate-induced seizures is not the result of programmed cell death. This assay may be useful for quantitative testing of both neuroprotective agents and mechanistic hypotheses.     

Representations of odors in the rat orbitofrontal cortex change during and after learning.

Cells in the orbitofrontal cortex (OF) respond to odors and their associated rewards. To determine how these responses are acquired and maintained, the authors recorded single OF units in rats performing an odor discrimination task. Approximately 64% of all cells differentiated between rewarded and nonrewarded odors. These odor valence responses changed during learning in 26% of all cells, and these changes were positively correlated with improving performance, supporting the idea that the information provided by these cells is used in learning the task. However, changes in odor valence responses were also observed after learning, and included not only increases in odor discrimination, but also decreases or mixed increases and decreases. Thus, only some of the changes in firing reflected acquisition of the task. The results suggest that learning triggers a continuing reorganization of OF neural ensembles representing odors and their rewards. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Unilateral striatal grafts induce behavioral and electrophysiological asymmetry in rats with bilateral kainate lesions of the caudate nucleus.

Rats (n?=?11) with bilateral kainate lesions of the caudate nucleus and subsequent unilateral transplantation of embryonic striatal tissue into the damaged area preferred 4 months later to reach for food with the forepaw contralateral to the graft. No such asymmetry was observed in lesioned, nontransplanted (n?=?8) or unoperated (n?=?5) control rats. Good integration of the graft with the host brain was indicated by the finding that cortical spreading depression did not enter the lesioned caudate nucleus but did penetrate into the lesioned caudate with the graft almost as regularly as in intact rats. Behavioral asymmetry produced by unilateral grafts in bilaterally lesioned animals reveals the effects of transplantation with more sensitivity than the graft-induced compensation of the asymmetries caused by unilateral lesions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Autoshaping and instrumental learning in the rat.

Conducted 2 experiments to compare the effectiveness of P. L. Brown and H. M. Jenkins's (see record 1968-06958-001) autoshaping procedure with that of instrumental conditioning in the establishment and maintenance of instrumental responding. Ss were 40 male and 32 female Long-Evans rats. In a leverpressing situation, with presentation of the lever signaling trial onset, the 2 procedures were equally effective. When illumination of a key signaled trial onset and the response was pressing the key, the instrumental-training procedure was superior to the autoshaping procedure in establishing and maintaining instrumental responding. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Chemical sympathectomy and avoidance learning in the rat.

Reports results of 5 experiments with male Wistar rats (N = 108). Depletion of peripheral sympathetic noradrenaline induced by administration of 6-hydroxydopamine, ip, led to significant decrements in escape and avoidance responding when the required response was difficult, but not when it was relatively easy to acquire. Results are similar to previous findings obtained with adrenal-demedullated Ss. Findings clarify the role of the sympathetic nervous system in the motivation of behavior elicited by aversive stimulation. Implications for 2-process theory and the "Kamin effect," or "learned helplessness," are discussed. (40 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Locomotor and exploratory behavior in the rat following bilateral vestibular deafferentation.

Despite many studies of the postural and ocular reflex deficits caused by chronic bilateral vestibular loss in rats and guinea pigs, there have been few systematic studies of the effects of vestibular loss on locomotor activity and exploratory behavior over a period of several months following the lesion. In this study, the authors quantified locomotor and exploratory behavior in an open field maze at 3 weeks, 3 months, and 5 months following bilateral vestibular loss in rats. As a result of bilateral surgical vestibular lesions, rats exhibited a persistent increase in locomotor velocity, duration, and distance traveled, with a marked tendency for increased inner field activity and reduced thigmotaxis. Rats without balance-sense were also found to spend less time exploring the environment, as indicated by a decreased frequency and duration of wall-supported rearings. These results suggest that sudden and complete loss of balance-sense has persistent and complex effects on the way that rats navigate through and explore the environment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of ingestion in odor-toxicosis learning in the rat.

Conducted 2 experiments with 32 and 34 male Charles River albino rats, in which Ss evidenced aversions to an odor paired with toxicosis in both drinking and exploratory behavior tests. Ingestion during odor-toxicosis conditioning in Exp I resulted in stronger aversions only in tests involving drinking the same solution as had been ingested during training, despite the absence of enhanced aversions to the flavor of the solution used. This result is interpreted as evidence that Ss drinking during conditioning acquired aversions not only to the CS odor but also to additional cues arising from an interaction of the CS odor and the flavor of the ingested solution. Exp II showed that these interaction cues were not the result of a flavor imparted to the ingested substance by dissolved molecules of the odorizing agent. (15 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Position of the ventral pallidum in the rat prefrontal cortex-basal ganglia circuit

The ventral pallidum receives major inputs from the nucleus accumbens, a striatal region related to the prefrontal cortex. The ventral pallidum, through its projections to the mediodorsal nucleus of the thalamus, has been considered as the main output structure of the prefrontal-basal ganglia circuits. However, as shown recently, the ventral pallidum also sends efferents to the subthalamic nucleus and the substantia nigra, suggesting that it could participate in intrinsic basal ganglia circuits. The aim of the present investigation was to determine the position of the ventral pallidum in the prefrontal-basal ganglia circuit originating from the prelimbic and medial orbital areas. Following injections of biocytin (an anterograde tracer) into the region of the core of the nucleus accumbens receiving excitatory inputs from the prelimbic and medial orbital areas, axonal terminal fields were observed in a delineated dorsal region of the ventral pallidum. When the biocytin injections were made into this ventral pallidal region, anterogradely labelled fibres were observed in both the dorsomedial substantia nigra pars reticulata and the medial subthalamic nucleus, but not in the mediodorsal nucleus of the thalamus. Confirming these anatomical observations, electrical stimulation of the core of the nucleus accumbens induced an inhibition of the spontaneous activity (D=34.9+/-13.3 ms, L=9.2+/-3.3 ms) in 46.5% of the ventral pallidal cells. Among these responding cells, 43% were antidromically driven from the subthalamic nucleus, 30% from the substantia nigra pars reticulata and only 6% from the mediodorsal nucleus of the thalamus. These data demonstrate that the region of the ventral pallidum involved in the prefrontal cortex-basal ganglia circuit originating from the prelimbic and medial orbital areas represents essentially a ventral subcommissural extension of the external segment of the globus pallidus since it exhibits similar extrinsic connections and functional characteristics. In conclusion, in this prelimbic and medial orbital channel, the ventral pallidum cannot be considered as a major output structure but is essentially involved in intrinsic basal ganglia circuits.     

Function and protective capacity of Treponema pallidum subsp. pallidum glycerophosphodiester phosphodiesterase

Infectious syphilis, caused by the spirochete bacterium Treponema pallidum subsp. pallidum, remains a public health concern worldwide. The immune-response evasion mechanisms employed by T. pallidum are poorly understood, and prior attempts to identify immunoprotective antigens for subsequent vaccine design have been unsuccessful. Previous investigations conducted in our laboratory identified the T. pallidum glycerophosphodiester phosphodiesterase as a potential immunoprotective antigen by using a differential immunologic expression library screen. In studies reported here, heterologous expression of the T. pallidum glycerophosphodiester phosphodiesterase in Escherichia coli yielded a full-length, enzymatically active protein. Characterization of the recombinant molecule showed it to be bifunctional, in that it exhibited specific binding to human immunoglobulin A (IgA), IgD, and IgG in addition to possessing enzymatic activity. IgG fractionation studies revealed specific binding of the recombinant enzyme to the Fc fragment of human IgG, a characteristic that may play a role in enabling the syphilis spirochete to evade the host immune response. In further investigations, immunization with the recombinant enzyme significantly protected rabbits from subsequent T. pallidum challenge, altering lesion development at the sites of challenge. In all cases, animals immunized with the recombinant molecule developed atypical pale, flat, slightly indurated, and nonulcerative reactions at the challenge sites that resolved before lesions appeared in the control animals. Although protection in the immunized rabbits was incomplete, as demonstrated by the presence of T. pallidum in the rabbit infectivity test, glycerophosphodiester phosphodiesterase nevertheless represents a significantly immunoprotective T. pallidum antigen and thus may be useful for inclusion in an antigen cocktail vaccine for syphilis.     

Changes in rat brain muscarinic receptors after inhibitory avoidance learning

It is widely accepted that cerebral acetylcholine is necessary for learning and memory, but little is known about the type of muscarinic receptors involved in these functions. To investigate this problem, [3H]-N-methyl-scopolamine which binds to different types of muscarinic receptors, [3H]-Pirenzepine an M1 receptor antagonist, and [3H]-Oxotremorine-M which binds mainly to M2 receptors, were used as ligands to look for possible changes in muscarinic receptor density in neostriatum (NEO), hippocampus (HIP), amygdala (AMY), and temporo-parietal neocortex (CTX), after testing for retention of inhibitory avoidance, trained with high or low footshock intensities. After low reinforcement there was an M1 postsynaptic receptor up-regulation in NEO, HIP, and CTX, and an M2 presynaptic receptor down-regulation in HIP, which suggests a concerted pre- and postsynaptic cholinergic activation in this area. An up-regulation of both M1 and M2 receptors was detected in CTX of low and high footshocked animals, which indicates the presence of a cortical postsynaptic M2 receptor.     

Blocking in rat serial pattern learning.

Both associative and rule-learning theories have been proposed to account for rat serial pattern learning, but individually they are unable to account for a variety of recent behavioral and psychobiological phenomena. The present study examined the role of rule learning versus discriminative learning in rat pattern learning using a classic associative phenomenon: blocking. Rats learned to press levers in an 8-lever circular array according to a rule-based serial pattern, 123–234–345–456–567–678–781–812, where digits indicate the correct lever in the array for each trial. Each pattern presentation contained a chunk with a final element violation, such as 454 instead of 456. Rats learned in a first phase that a noise signaled the violation chunk; then, a concurrent spatial cue was added in a second phase. A test with spatial cues alone showed that blocking occurred. The results suggest that associative learning mediated cuing of violation elements. Taken together with other behavioral and psychobiological evidence already reported in the literature implicating rule learning when rats learn this pattern in this paradigm, these results implicate multiple concurrent learning processes in rat serial pattern learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned taste aversions and neophobia in rats with hippocampal lesions.

In Exp I extensive hippocampal lesions retarded, but did not prohibit, the conditioning of a strong taste aversion to physiological saline (the CS) in 16 male Holtzman albino rats when illness (the UCS) was induced by apomorphine injection 15 min following ingestion of the saline. In Exp II hippocampal lesions reduced the aversiveness of novelty in a drinking fluid for 21 thirsty Ss. It is suggested that the mild impairment of taste aversion learning in Ss with hippocampal lesions was not the result of destruction of mnemonic mechanisms that serve to span the long CS-UCS interval but rather that the reduced intensity of the aversion resulted from a lesion-altered neophobic disposition that weakened the saliency of the novel flavor CS. (51 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Chemical sympathectomy and two-way escape and avoidance learning in the rat.

Reports 6 studies with male hooded Wistar rats on the effects of 2,4,5-trihydroxyphenylethylamine (6-hydroxydopamine) on 2-way escape and avoidance learning. Ss were tested on either escape or avoidance learning at 80 days of age after chemical sympathectomy at birth or 40 or 80 days of age. Neonatal and chronic sympathectomy (at 40 days), but not acute sympathectomy (at 80 days), resulted in depressed escape learning. Avoidance learning was affected by neonatal sympathectomy and partially by acute sympathectomy. Results have implications for the role of the autonomic nervous system in escape-avoidance learning. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Emotional and motivational changes after bilateral lesions of the globus pallidus.

This study investigated motivational changes in a 44 year-old man (PJ) who developed considerable reduction in spontaneous activity and speech, flat affect, social withdrawal, loss of interest, inability to feel, and lack of concern regarding his medical condition after bilateral, focal, anoxic lesions of the globus pallidus. PJ and 30 male controls performed a task designed to parse hedonic evaluation, or liking, from incentive motivation, or wanting. Affective stimuli were presented on a computer screen and subjects controlled viewing time by pressing keys. PJ's liking and wanting of unpleasant stimuli was similar to that of controls. In response to pleasant stimuli, PJ showed normal ratings of wanting and hedonic appreciation, but significantly reduced viewing time or made no responses. Active withdrawal from liked stimuli could constitute the basic mechanism underlying poor motivation and social withdrawal associated with globus pallidus damage. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

ACTH and ACTH4–20 modification of neophobia and taste aversion responses in the rat.

A series of 6 experiments assessed the effects of ACTH and the ACTH analog ACTH4–20 on drinking in conditioned taste aversion and neophobic situations using a total of 168 male Sprague-Dawley rats as Ss. Both substances delayed the extinction of a conditioned taste aversion established by a single pairing of lithium chloride with milk (Exp I). However, in this situation, the ACTH parent peptide was more potent behaviorally. ACTH supressed milk consumption in Ss with no toxicosis experience (Exp II). This effect was apparently not due to the conditioning of a taste aversion (Exp III) with ACTH serving as a weak aversive UCS. Exogenous ACTH (Exp IV) or ACTH4–20 (Exp V) did not enhance neophobia; however, repeated injections of ACTH suppressed drinking. This ACTH suppression was related to the familiarity/novelty of the substance being consumed. The neophobic response to milk was not accompanied by pituitary-adrenal activation (Exp VI). Both neophobic and conditioned taste aversion situations appear to be useful for assessing peptide effects on consummatory behavior. (36 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)