Search PubMed⌕ Search

Biomedical subjects

G D Coover

Publications and source records attributed to G D Coover.

At least 19 recordsLinked to original sources
PubMed1997

Effects of small amygdala lesions on fear, but not aggression, in the rat.

The effects of amygdala lesions on passive avoidance of drinking (dPA) and social interactions in a resident-intruder test were examined in two experiments that utilized different lines of Long-Evans hooded rats. The lesions were fairly well restricted to the rostral half of the central nucleus (rACe), or the cholinergically richly innervated basolateral nucleus (ABL) or the medial nucleus (AMe) of the amygdala. In both experiments, dPA deficits indicating disturbances in fear conditioning or fear expression were found with ABL and rACe lesions. The rACe lesions produced a greater deficit. AMe lesions caused no dPA deficit at all, which contrasts with the mild PA deficits reported by others employing larger lesions extending to the cortical nucleus and, perhaps, damaging the central nucleus. Social behavior was not affected by the lesions in any clear manner. In rats from a long-standing home colony, rACe lesions increased a behavior of plowing and kicking the wood-chip cage bedding during social encounters, and AMe lesions increased lateral defense behaviors. Both effects are paradoxical, suggesting increased anxiety in the fear-deficient rACe rats and increased defense with AMe lesions, despite several previous reports of decreased defense. In the second experiment, rats purchased from a supplier showed no lesion effects during social interactions; like the control group, all three lesion groups exhibited increases in offense associated with cohabitation with a female. The ABL lesions, particularly, had no effect comparable to the decreased offense recently reported to occur following neurotoxin lesions.

Aggression↗
PubMed1995

Double dissociation of passive avoidance and milk maze performance deficits with discrete lesions of substantia innominata or globus pallidus of rats.

In three experiments, small bilateral lesions of the substantia innominata (SI), globus pallidus (GP) and central nucleus of the amygdala (ACe) produced deficits in passive avoidance of drinking (dPA) or escape performance in a milk maze (MM). Severe deficits in dPA were produced by electrolytic lesions in lateral SI or rostral ACe, and by electrolytic or ibotenic acid lesions in the heart of the SI. Such lesions produced no effects on MM performance. Lesions of the rostral SI produced no, or mild, deficits in dPA and MM performance. However, lesions of the rostral GP produced an extreme deficit in MM performance but not dPA. The milder MM deficits produced by rSI lesions appeared to reflect a spatial navigation deficit, while the more severe impairment produced by rGP lesions appeared to represent a broader disruption of instrumental behavior. SI lesions also produced a temporary cessation of drinking and a chronic decrease in body weight, both of which were associated with impaired oromotor function. Eating and drinking deficits were less severe when lesions were more lateral or rostral in SI, and absent with lesions in rostral GP or amygdala. The most important finding, however, was a double dissociation of MM performance deficits following rostral GP lesions versus passive avoidance deficits produced by SI lesions.

Animals↗
PubMed1992

Subtotal lesions of the amygdala: the rostral central nucleus in passive avoidance and ulceration.

Rats received small bilateral electrolytic or ibotenate lesions of the rostral part of the amygdaloid central (rACE) or lateral (rAL) nuclei, or caudal part of the basolateral nuclei (cBL), or electrolytic lesions of the dorsal hippocampus (HIPP). All groups were tested in a drinking passive avoidance (PA) task that appears less sensitive to deficits in acquisition/retention or activity/spatial perception than are many other PA tasks, and more specifically sensitive to deficits in generation of fear. Consistent with this interpretation, performance in the task was facilitated, not deficient, in the HIPP group. Electrolytic lesions of rAL produced a mild deficit in PA, but ibotenate lesions did not, and neither did the more caudal lesions of the cBL groups. Ibotenate lesions of rACE did produce a deficit in PA, consistent with views of a role of this part of the amygdala in fear. Electrolytic lesions of rACE produced a very profound PA deficit and also blocked the rapid development of gastric erosions by water-restraint stress, effects that were not found with ibotenate lesions in this location. This suggests a particular contribution of fibers passing through rACE to some of the more marked effects of electrolytic lesions of rostrodorsal portions of the amygdala.

Amygdala↗
PubMed1986

Corticosterone, free fatty acid and glucose responses of rats to footshock, fear, novel stimuli and instrumental reinforcement.

Rats were subjected to sessions of footshock, fear stimuli and instrumental reinforcement to assess responses of blood corticosterone, free fatty acids (FFA) and glucose. The corticosterone response to fearful situations exhibited a stimulus generalization decrement, thus demonstrating a contribution of Pavlovian classical conditioning to the activity of the hypothalamo-pituitary-adrenal system. Corticosterone levels were shown to decrease during operant sessions with large water reinforcements, while FFA and glucose levels were increasing, thus dissociating these stress measures. FFA responses to intermittent, intense footshock were found to be quadratic; blood levels of FFA increased within 10 min, decreased by 40 min, and then showed the increase with 80-min long sessions previously reported in the literature. This pattern of response was not influenced by prior food deprivation or different methods of sampling blood. Blood levels of FFA increased generally to novel/fearful situations and instrumental reinforcement sessions, which were stimulus situations less stressful than the footshock sessions. Glucose increases occurred to footshock and instrumental reinforcement sessions under some conditions, depending more than corticosterone and FFA on prior food deprivation and blood sampling method.

Animals↗
PubMed1984

Plasma corticosterone and meal expectancy in rats: effects of low probability cues.

The plasma corticosterone levels of rats were examined prior to their morning meal on Days 1, 7 and 20 of a regimen of 1 hr access daily to food mash and water. The relationship between external cues and meal provision was varied by feeding some groups immediately upon room entry each morning, and others with a variable interval 90-min delay. On Day 1, corticosterone levels of the hungry rats were elevated around the time of light onset, and until 90 min following room entry. On Day 7, corticosterone levels increased in response to room entry in the delay-fed rats, but did not increase further in immediately fed rats. These results were interpreted as indicating that low, but nonzero, expectancy of meal availability elevates corticosterone levels. On Day 20, the immediately fed rats showed a dip in corticosterone levels after room entry, responding to cues highly predictive of imminent meal availability. Delay-fed rats no longer showed an elevation to room entry. The relationship between corticosterone level and meal expectancy is essentially curvilinear in the hungry rat. The corticosterone levels are high when there is uncertainty about whether food is coming or not, and low when there is a very high or very low probability that food is coming.

Animals↗
PubMed1982

Sleep deprivation procedure produces stomach lesions in rats.

Sprague-Dawley male rats were deprived of food for 40 hr and subjected to sleep deprivation by the "flower pot" or handling intervention procedures during the final 24 hr. Five of six rats in the flower pot group exhibited stomach erosions. Only one rat in the handling group, and no rats in a food deprived control group showed such erosions. The flower pot group also had higher levels of corticosterone than the food deprived control group. These findings argue for more serious consideration of the effects of the stress of procedures for sleep deprivation.

Animals↗
PubMed1982

Plasma corticosterone and free fatty acid responses and positive behavioral contrast.

Corticosterone and free fatty acid (FFA) responses during water-reinforced operant sessions were examined in rats subjected to reinforcement schedule shifts which may elicit frustration-induced arousal reactions. Rats were trained on a multiple VI VI-30 sec schedule that was subsequently changed to a multiple VI EXT or multiple VI VI-60 sec schedule. The rats shifted to the multiple VI EXT schedule developed positive behavioral contrast. The corticosterone levels of both groups were elevated by the first postshift session, in which the frequency of reinforcement was halved, but returned to preshift levels by the 8th postshift session, which preceded discriminative performance in the Contrast group. The FFA levels of both groups were elevated by the Multiple VI VI-30 sessions (compared to presession basal levels), but the response decreased with the halving of the reinforcement rate. The present findings were interpreted as evidence that the psychological variables associated with the acquired emotional state of frustration influence the blood concentration of corticosterone, but not FFA. The findings are consistent with such explanations of positive behavioral contrast as positive induction or release-from-inhibition. No evidence was found for a direct energizing effect of frustration to account for positive contrast.

Animals↗
PubMed1980

Plasma corticosterone elevations in rats in response to consumption of concentrated sugar solutions.

The results of three experiments indicated that male hooded rats exhibit marked corticosterone elevations when they freely consume .740 mol/l (23.2% w/w) sucrose in tap water while nondeprived or .298 mol/l (9.8% w/w) sucrose when deprived of water for 36 hr. The magnitude of the corticosterone elevation was increased by lengthening the duration of prior water deprivation (2, 24, or 48 hr) and by raising the sucrose solution concentration (.189, .298, or .470 mol/l). Free ingestion of tap water following sucrose consumption accelerated the decline from peak level of corticosterone during the period 60-120 min following the onset of sucrose consumption. Glucose (.470 or 1.166 mol/l) consumption by 36-hr water-deprived rats also elevated corticosterone levels, but less effectively than equimolar sucrose. These data suggest strongly that the pituitary-adrenal system is activated by rapid, acute dehydration. The effect is surprising, considering the minimal effects of water deprivation per se on corticosterone levels and the interpretation of increased pituitary-adrenal activity as a sign of psychological stress.

Animals↗
PubMed1978

Behavioral effects of neurotoxic lesions of the ascending monoamine pathways in the rat brain.

Intracranial microinjections of 6-hydroxydopamine or 5,6-dihydroxytryptamine into six ascending monoamine pathways produced the expected patterns of depletion of telencephalic serotonin, dopamine, and norepinephrine. Serotonin level was specifically lowered after dorsal or median raphe lesions but not after mesolimbic or nigrostriatal system lesions which lowered both norepinephrine and dopamine. Lesions in the locus coeruleus or ventral nor-adrenergic bundle lowered only norepinephrine, and locus coeruleus lesions elevated serotonin level. Behavior was examined in an open field, one-way active avoidance, and two passive avoidance tasks, and measures were taken of water consumption and body weight. Dorsal raphe lesions had no effect on any of the measures; the other five lesion groups exhibited deficient acquisition of the one-way active avoidance task. In the appetitive passive avoidance task, only the substantia nigra lesion group exhibited a deficiency. In the step-through passive avoidance task, both the substantia nigra and the median raphe groups exhibited a deficit, with the median raphe group exhibiting hyperactivity in the start box during testing. Water consumption was decreased by lesions in the ventral noradrenergic bundle during the first postoperative week and was increased in the median raphe group by the fourth postoperative week. Lastly, lesions in the locus coeruleus dramatically decreased activity in the open field. The results are discussed in regard to the search for specificity of behavioral functions of the distinct ascending monoamine pathways.

5,6-Dihydroxytryptamine↗
PubMed1977

Conditioning decreases in plasma corticosterone level in rats by paring stimuli with daily feedings.

This study examined the nature of a stimulus-induced decrease in the plasma corticosterone levels of rats. Rats maintained on a 23-hr food and water deprivation regimen were fed each morning immediately upon entrance of the experimenter into the otherwise isolated animal quarters. After only 14 feeding trials, the rats showed a marked decrease in corticosterone levels within 10 min of the experimenter's entrance whether fed and watered or not. The acquisition of this decrease was then examined over training trials and by comparing the conditioned animals (Group CD) with a group designed to control for pseudoconditioning, sensitization, and habituation (Group PC) during the use of the more distinctive conditioning stimulus of placing the rat's cage in a sound-attenuating chamber. During training. Group CD was fed .5-6 min after placement in the chamber, and Group PC was fed 1.5-2.5 hr before or after placement. After one training trial, the CD and PC groups showed an increase in corticosterone levels in response to chamber placement when not fed or watered. However, after 14 training trials the CD group exhibited a significant decline, whereas the PC group exhibited a rise in corticosterone levels. The results indicate that external stimuli can cause a decrease in corticosterone level by virtue of prior association with feeding and drinking. This strongly suggests an acquired inhibition of the pituitary-adrenal system.

Adrenal Glands↗
PubMed1976

Deficient passive and one-way active avoidance acquisition following medial forebrain bundle lesions in rats.

Cathodal electrolytic lesions of the medial forebrain bundle (MFB) at posterior hypothalamic levels in male hooded rats produced a mild, transient hypodipsia and lowered jump thresholds to footshock. The lesions produced marked deficits in passive avoidance performance in a paradigm that paired discrete, linearly incrementing footshock intensities with contact of a water spout following 48 hr of water deprivation. Intraperitoneal injections of DL-5-hydroxytryptophan (75 mg/kg), the immediate metabolic precursor of serotonin, had no effect on the passive avoidance performance of either experimental or operated control subjects. Lesions of the MFB also resulted in deficient acquisition in a one-trial step-through passive avoidance paradigm not using motivation to drink and caused a severe acquisition deficit in a one-way active avoidance task. Lesions of the septal nuclei produced lowered jump thresholds but did not affect acquisition in the first passive avoidance task. The results are interpreted as indicating a lesion-induced deficiency in fear learning, independent of the serotonergic functions of the MFB.

5-Hydroxytryptophan↗