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Biomedical subjects

G D Coover

Publications and source records attributed to G D Coover.

16 recordsLinked to original sources
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↗
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↗