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T L Davidson

Publications and source records attributed to T L Davidson.

At least 19 recordsLinked to original sources
PubMed2003

The effects of selective ibotenate lesions of the hippocampus on conditioned inhibition and extinction.

Previously, Solomon (1977) reported that aspiration lesions of the dorsal hippocampus in rabbits had no effect either on the acquisition of Pavlovian conditioned inhibition or on performance during a subsequent retardation test. The present experiment confirmed and extended these findings by showing that rats with ibotenate lesions of the complete hippocampus (the dorsal and ventral hippocampus and the dentate gyrus) were also unimpaired on the same types of tasks. Additional tests with the same rats showed that removing the hippocampus significantly impaired extinction of responding to a stimulus that had been previously trained with an appetitive unconditioned stimulus. The performance of the lesioned rats on a summation test was also marginally, but not significantly, different from that of controls. The data are discussed with reference to the idea that the hippocampus is involved with the formation of some, but not all, types of inhibitory associations.

Animals↗
PubMed2002

Transfer across unconditioned stimuli in serial feature discrimination training.

The transfer of conditioned modulation across conditioned stimuli (CS) and unconditioned stimuli (US) was examined in 3 experiments that used Pavlovian appetitive training procedures with rats. In Experiment 1, after training in a positive patterning discrimination (X-->A+/X-/A-), X increased conditioned responding elicited by another trained-then-extinguished CS as long as that CS had been trained with the same US as was used in discrimination training. In Experiment 2, after training with a feature-negative discrimination (X-->A-/A+), X inhibited conditioned responding elicited by another trained-then-extinguished CS as long as that CS had been trained with the same US. Experiments 1 and 2 used a between-groups design, whereas Experiment 3 used a more powerful within-groups design. In Experiment 3, rats were trained in a feature-positive discrimination (X-->A+/A-). In transfer tests, X increased conditioned responding elicited by another CS trained then extinguished with the same US from training. This increase was greater than the X increased conditioned responding elicited by another CS trained then extinguished with a different US from training. The results supported the suggestion that features trained in serial discrimination tasks influence behavior indirectly by transiently raising or lowering the threshold for activation of the US representations by its target stimuli and by any other stimuli that may be associated with that US. Other interpretations of the findings were also considered.

Animals↗
PubMed2001

The hippocampus and motivation revisited: appetite and activity.

After reviewing the available data regarding the various effects of manipulating (e.g. lesions, chemical or electrical stimulation) the hippocampal formation, Jarrard concluded that this structure likely played a role in motivated behaviors, specifically in general behavioral activation and incentive motivation. Since that time there have been technical advances in lesion techniques and conceptual advances in theories of motivation and learning. Here, we present more recent data that demonstrates the effects of hippocampal lesions on general activity, the utilization of interoceptive state cues, ingestive behaviors, and appetitive responding. We critically evaluate several theories of hippocampal function that have been proposed to explain these data, including the hippocampus as an inhibitor of general activation, as a processor of energy state signals and as a mediator of reward valuation. Finally, we propose that these findings may also be accounted for based on a role for the hippocampus in the learned inhibition of appetitive behaviors. We conclude that, while the specific mechanism of hippocampal involvement may not yet be determined, it is clear that this structure is involved in food-related behaviors and we caution researchers to consider this as a possible confound in studies of learning and memory processes.

Animals↗
PubMed2001

Reconsideration of the role of the hippocampus in learned inhibition.

The purpose of this article is to reconsider the role of the hippocampus in learning tasks that require suppression or prevention of memories or responses. This type of learning has generally been referred to as inhibitory learning. Although early theories proposed that the hippocampus was important for inhibitory learning, these ideas have generally fallen out of favor. However, new developments in the conceptual understanding of inhibition along with recent experimental evidence require that we review these conceptual changes with regard to hippocampal function. We review three general categories of 'inhibition' that have been used with reference to hippocampal function: neural inhibition, inhibition of attention and associative or learned inhibition. We then consider recent developments in the field of animal learning that call for changes in the early conceptualizations of learned inhibition. Specifically, current findings suggest that different types of learning paradigms can yield conditioned inhibitors that are embedded in different associative structures, at least some of which can co-exist with conditioned excitation. Next we proceed to review a number of recent experiments from our laboratory as well as others that encouraged renewed interest in the role for the hippocampus in inhibitory learning. We then conclude by considering some of the implications of the idea that the hippocampus is involved with performance of conditioned responses based on cues that are concurrently embedded in inhibitory and excitatory associations.

Animals↗
PubMed1999

Lesions of the amygdala central nucleus abolish lipoprivic-enhanced responding during oil-predicting conditioned stimuli.

T. L. Davidson, A. M. Altizer, S. C. Benoit, E. K. Walls, and T. L. Powley (1997) reported that rats show facilitated responding to conditioned stimuli (CSs) that predict oil, after administration of the lipoprivic agent, Na-2-mercaptoacetate (MA). This facilitation was blocked by vagal deafferentation. The present article extends that investigation to another structure, the amygdala central nucleus (CN). The CN receives inputs from dorsal vagal nuclei, and neurotoxic lesions of this nucleus are reported to abolish feeding in response to lipoprivic challenges. In Experiment 1, rats with ibotenic acid (IBO) lesions of the CN failed to show enhanced appetitive responding during oil-predicting CSs after administration of MA. Experiment 2 used a conditioned taste-aversion procedure to establish that rats with IBO lesions of the CN were able to discriminate the tastes of sucrose and peanut oil and had intact CS-US representations. It is concluded that the amygdala CN is a necessary structure for the detection of lipoprivic challenges.

Amygdala↗
PubMed1997

Encoding and selective activation of "metabolic memories" in the rat.

Experiment 1 used Pavlovian conditioning procedures to show that rats formed distinct memorial representations of 2 (peanut oil and sucrose pellets) unconditioned stimuli (USs) that could be activated by 2 different conditioned stimuli (CSs). After training in Experiment 2, rats injected with the lipid antimetabolite Na-2-mercaptoacetate (MA) responded more to the CS for oil than to the CS for sucrose. This pattern was not shown by rats that received isotonic saline or systemic 2-deoxy-d-glucose (a glucose antimetabolite). By contrast, intracerebroventricular infusion of the glucose antimetabolite 5-thioglucose selectively promoted responding to the CS for sucrose (Experiment 4). Thus, lipoprivic and glucoprivic treatments selectively promoted the activation of the memories of fat and carbohydrate USs, respectively. In Experiment 3, the capacity of MA to augment responding to a CS for oil was abolished for rats that received subdiaphragmatic vagal deafferentation. This indicates that the capacity of lipoprivic signals to selectively activate the representations of fat USs may depend on vagal afferent fibers.

Animals↗
PubMed1996

Prenatal cocaine: effect on hypoxic ventilatory responsiveness in neonatal rats.

The effects of prenatal (embryonic days 7-21) cocaine (30 mg/kg b.i.d., s.c.) exposure on postnatal respiratory and behavioral responsiveness to acute hypoxia were investigated in 5-day-old (P5) rat pups. Control and cocaine-exposed pups were subjected to 20 min of 0.21 FIO2 followed by 20 min of 0.08 FIO2. Although all pups demonstrated the characteristic biphasic response to hypoxia, cocaine-exposed pups exhibited a blunted, initial response in minute ventilation (p < 0.05) and inspiratory drive (p < 0.05) as compared with control pups who showed increases in these measures (p < 0.01 and p < 0.05, respectively). The consequence of this apparent blunted ventilatory response was reflected in blood gas data gathered after 20 min of 0.08 FIO2:PCO2 (p < 0.05) and base-excess (p < 0.05) were increased and HCO3- (p < 0.05) and SO2 (p < 0.01) were decreased relative to control pups. Cocaine-exposed pups also exhibited behavioral evidence of decreased struggling (p < 0.001) in response to the hypoxic challenge. These data in the rat confirm our previous findings of altered ventilatory responsiveness to inspired hypoxia in the rabbit and extend our observations of a decreased ability to successfully compensate and behaviorally arouse following prenatal cocaine-exposure, thus underscoring the potential vulnerability of infants so exposed.

Animals↗
PubMed1996

Interoceptive sensory signals produced by 24-hr food deprivation, pharmacological glucoprivation, and lipoprivation.

The energy antimetabolites 2-deoxy-D-glucose (2-DG) and Na-2-mercaptoacetate (MA) both reliably augment food intake in rats. The present research was designed to assess if they also give rise to interoceptive cues like 24-hr food deprivation. Rats were first trained to discriminate a mild shock based on interoceptive cues arising from 1- and 24-hr food deprivation. They were then tested for generalized control of conditioned responding to interoceptive cues produced by 2-DG, MA, and saline. Results suggest that 2-DG (350 mg/kg) produces interoceptive sensory cues like those following 24-hr food deprivation. Further, no evidence was found to suggest that MA, either alone or in combination with 2-DG (100 mg/kg), produces interoceptive cues like 2-DG or 24-hr food deprivation.

Animals↗
PubMed1995

Discriminative cues produced by NPY do not generalize to the interoceptive cues produced by food deprivation.

Exogenous administration of neuropeptide Y (NPY) into the third ventricle causes a rapid and robust feeding response in sated rats. The current experiment was designed to assess whether the interoceptive cues produced by exogenous NPY administration generalize to those produced by another orexigenic treatment: 24-h food deprivation. Rats were placed in a chamber after receiving either NPY or saline infused into the third ventricle for a total of six sessions (three after NPY and three after saline). Half of the rats were given a brief foot shock after NPY and not after saline, while the other half received the opposite contingency. The pattern of behavioral immobility for the two groups differed with the rats "freezing" significantly more to the treatment (NPY or saline) paired with shock. Then rats were tested for generalization by placing them in the chamber either after 0- or 24-h food deprivation with no NPY or saline administration or any foot shock. Behavioral immobility during the generalization test of rats that had been trained with shock following saline was greater than that for rats that had been trained with shock following NPY, independent of whether testing occurred when the rats were 0- or 24-h food deprived. This outcome indicates that interoceptive stimuli produced by NPY are no more similar to internal cues produced by 24-h food deprivation than to the stimulus consequences of ad lib feeding. These and other recent findings suggest that food deprivation activates processes or mechanisms different from those that underlie the orexigenic effects of NPY.

Animals↗
PubMed1995

Automated scoring of sleep in the neonatal lamb.

The study of sleep is an important and rapidly expanding area of research that generates large bodies of data. Manual scoring of sleep states from polygraph recordings is a laborious and often subjective task. Even when care is taken, the opportunity for disagreement between investigators and between laboratories remains great. To avoid this difficulty and to reduce the subjectivity of sleep state scoring we have designed a computer-based algorithm for scoring sleep state in the lamb. The algorithm underlying the system relies upon spectral analysis of the electrocorticogram and upon amplitude analysis of the electrooculogram and nuchal electromyogram. Partitioning the spectral power observed within the electrocorticogram (1-4 Hz frequency range) reliably identifies deep quiet sleep. Wakefulness and active sleep are then identified based upon threshold crossings of the electrooculogram and of the electromyogram of the nuchal muscles. We compared the sleep states returned by the algorithm to those scored visually by trained personnel for 1 hour of data collected from each of five 19-day-old lambs. There was good agreement between the two methods of scoring sleep. The percents agreement between the algorithm-derived scores and visual scores were as follows: active wakefulness 97%, quiet wakefulness 87%, quite sleep 85% and phasic active sleep 82%. As such, our algorithm provides a fast, reliable and objective method for scoring sleep state in the young lamb.

Algorithms↗
PubMed1994

Design of an airborne plutonium survey program for personnel protection.

Various options were considered for surveying and real-time monitoring for airborne plutonium for optimum protection of personnel. Placement of samplers, dilution factors, and analysis time were considered in the strategy for achieving regulatory compliance and maintaining internal dose as low as reasonably achievable (ALARA). It was found that protection was relatively insensitive to placement as was sensitivity of detection. It was also found that maximum protection was obtained with few detectors and increasing the number of detectors above the optimum value did not appreciably increase the information about a release nor did it aid in locating the release. It was determined that the best protection was obtained with alarming monitors if the detection sensitivity was sufficiently low. Integrating samplers requiring laboratory analysis can be more sensitive than alarming monitors, but the lack of timeliness limits the amount of protection. The integrating samplers can be used effectively to monitor engineering controls. Personal air samplers also offer little protection but can be very effective in analyzing exposure by craft and job type.

Air Pollutants, Radioactive↗
PubMed1994

Arousal response from sleep to tracheal obstruction in lambs during postnatal maturation.

Experiments were carried out to investigate the arousal response from sleep to tracheal obstruction in lambs during postnatal maturation. Ten fetal sheep were instrumented with electrodes for sleep staging and a tracheotomy was done. After spontaneous vaginal delivery, serial experiments were carried out on the lambs at five postnatal ages: 18-48 h and 4, 6, 11, and 18 d. During an experiment, a 5F balloon-tipped catheter was inserted into the tracheostomy tube so that tracheal obstruction could be produced by inflating the balloon. Measurements were made in quiet sleep and active sleep during control periods of tidal respiration and during experimental periods of tracheal obstruction. Neither sleep state nor age influenced control arterial Hb oxygen saturation (SaO2). SaO2 decreased significantly before arousal during tracheal obstruction in quiet sleep at 18-48 h and in active sleep at all ages. The SaO2 at arousal was always lower in active sleep than in quiet sleep. Overall, however, there were no significant effects of age on the change in SaO2 before arousal in either quiet sleep or active sleep. The time to arousal during tracheal obstruction increased between 18-48 h and 6 d of postnatal life in active sleep but not in quite sleep. Our data provide evidence that the arousal response to tracheal obstruction is functional by 18 h of postnatal life in lambs. The increase in time to arousal after tracheal obstruction in active sleep most likely results from state-specific changes in the factors governing oxygen supply and demand.

Aging↗
PubMed1993

Cholecystokinin, but not bombesin, has interoceptive sensory consequences like 1-h food deprivation.

A comparison of the interoceptive sensory consequences of cholecystokinin, bombesin, and 1-h food deprivation was conducted in rats. In two experiments, rats were first trained to use stimuli arising from different degrees of food deprivation (1 and 24 h or 1 and 4 h) as discriminative signals for shock, and were then tested for generalized control of discriminative responding (i.e., conditioned freezing) by cues arising from injection of 4 micrograms/kg (Experiment 1 only) and 8 micrograms/kg cholecystokinin (Experiment 1A only), 12 micrograms/kg bombesin (BBS), and isotonic saline, respectively. The effects of these peptides on food intake were also assessed. In both experiments, BBS and cholecystokinin (CCK) each suppressed feeding relative to saline; however, generalization of discriminative responding was obtained only following CCK. Generalization depended on prior learning about food deprivation cues--CCK had little effect on freezing in rats that showed weak discrimination performance (i.e., rats trained with 1- and 4-h deprivation cues). The results indicated that CCK but not BBS produces interoceptive cues like those occurring under 1-h food deprivation.

Animals↗
PubMed1993

A role for hippocampus in the utilization of hunger signals.

The hippocampus is generally regarded as an important anatomical substrate for learning and memory (e.g., Eichenbaum, Otto, & Cohen, Behavioral and Neural Biology, 57, 2-36, 1992; Squire, Psychological Review, 99, 195-231, 1992). In the present research, we provide evidence that the hippocampus is also involved with another function--utilization of hunger state signals. Rats with selective ibotenate lesions of the hippocampus were found to be impaired in their ability to discriminate between the interoceptive sensory consequences of food deprivation and satiation. At the same time the ability of these rats to discriminate between different exteroceptive cues was unaffected. These results suggest that deficits in discriminative performance were specific to interoceptive state stimuli. In addition, hippocampal-damaged rats also seemed unable to use their food deprivation stimuli as signals to engage in normal feeding behavior. Our results argue that although the hippocampus may be important for learning and memory processes, it also deserves consideration as a neural substrate for the regulation of food intake and perhaps other functions which involve interoceptive signals.

Animals↗
PubMed1993

Hippocampal lesions do not impair negative patterning: a challenge to configural association theory.

According to configural association (CAS) theory (Sutherland & Rudy, 1989), an intact hippocampus is required for rats to solve learning problems that are based on "configural" processes. This theory identifies the negative patterning discrimination as a critical example of this type of problem. Rudy and Sutherland (1989) reported disruption of negative patterning following hippocampal formation damage produced by intracranial infusion of a mixture of kainic acid + colchicine (KA + COL). We assessed acquisition of negative patterning in rats with hippocampal damage produced by KA + COL compared with rats with more selective ibotenate lesions of hippocampus. Neither group showed impaired negative patterning relative to controls. A transfer test provided evidence that all groups used configural processes to solve the problem. Thus contrary to CAS theory, the hippocampus is not an important substrate for the operation of configural processes.

Acoustic Stimulation↗
PubMed1993

The nature and function of interoceptive signals to feed: toward integration of physiological and learning perspectives.

The idea that different states of energy need give rise to distinct interoceptive sensations has been basic to many accounts of the physiological and the learned controls of feeding. Yet, a number of difficulties have complicated attempts to provide direct evidence for this view. The present article describes a research strategy that confirms that food deprivation states produce salient interoceptive stimuli in rats. The implications of this research for the physiological origins of energy state signals, the brain structures involved with processing energy state information, and the manner in which signals of energy need influence feeding were considered. The possibility that food deprivation cues influence feeding by modulating the activation of associations involving external events and their postingestive aftereffects was discussed with reference to earlier associative accounts of the function of hunger signals.

Animals↗
PubMed1993

Cl- replacement alters the ventilatory response to central chemoreceptor stimulation.

To determine whether cerebrospinal fluid (CSF) Cl- has a role in determining the stimulus to the central respiratory chemoreceptors under conditions of constant CSF pH, CO2, and HCO3- concentrations, the ventral medullary surface of the anesthetized rat was perfused with mock CSF of various ion composition and pH. Four mock CSF perfusates were used: two normal pH control perfusions and two acidic solutions. One acidic perfusate was formulated in the traditional manner by substituting Cl- for HCO3-. The second acidic perfusate, and one of the normal pH control perfusates, had approximately 15% of the Cl- replaced with isethionate, an impermeant strong anion. When the two acidic solutions were perfused over the ventral medulla, consistently larger increases in both tidal volume and minute ventilation were observed with the isethionate-containing acidic solution, despite conditions of identical pH and PCO2. The unequal ventilatory effects of the two acidic perfusions suggest that Cl- transport may be a factor determining the stimulus to the central respiratory chemoreceptors.

Animals↗