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Biomedical subjects

S L Buchanan

Publications and source records attributed to S L Buchanan.

35 records · Page 2Linked to original sources
PubMed1986

Autonomic changes elicited by chemical stimulation of mediodorsal nucleus of the thalamus.

Chronic indwelling cannulas were implanted in the mediodorsal nucleus (MD) of the thalamus in New Zealand albino rabbits. Heart rate (HR), blood pressure (BP), respiration and electromyographic activity (EMG) were recorded subsequent to the injection of saline, l-glutamate, or carbachol through the previously implanted cannulas. Dose related decreases in HR and increases in BP were obtained after administration of both l-glutamate and carbachol at doses in the micromolar range. Control injections through cannulas chronically implanted in the overlying hippocampus or adjacent ventricles resulted in dramatic HR and BP baseline changes in a parasympathetic direction (viz HR and BP decreases) suggesting that the effects obtained with MD placements were due to chemical stimulation of MD. Responses elicited from MD in the present experiment were similar, but not identical, to those produced by electrical stimulation of MD, suggesting that the latter effects were not due to stimulation of fibers of passage.

Animals↗
PubMed1985

Intraseptal scopolamine has differential effects on Pavlovian eye blink and heart rate conditioning.

The effects of intraseptal scopolamine hydrobromide injections on Pavlovian (classical) conditioning were evaluated, with tones used as the conditioned stimulus (CS) and a periorbital electric shock train as the unconditioned stimulus (UCS). Eye blink (EB) and heart rate (HR) conditioned responses were concomitantly recorded. Although injections of scopolamine into the medial septum impaired the acquisition of the Pavlovian conditioned eyelid reflex, these injections enhanced the magnitude of accompanying Pavlovian conditioned HR decelerations. However, scopolamine applied to the lateral septal area had no effect on EB conditioning, relative to the vehicle, but, like medial injections, enhanced the magnitude of the accompanying HR decelerations. These results are compatible with those of previous investigations: Medial septal dysfunction impairs somatomotor conditioning but leaves autonomic conditioning intact, and septal dysfunction produces a parasympathetic bias of the cardiovascular system.

Animals↗
PubMed1984

Age-related changes in Pavlovian conditioning: central nervous system correlates.

Two groups of New Zealand Albino rabbits, average age 6 and 40 months, were subjected to Pavlovian conditioning in which eyeblink (EB) and heart rate (HR) responses were assessed. At the end of conditioning biogenic amine content was assessed in several brain areas; dopamine receptor binding was assessed in caudate nucleus. Older animals revealed an impairment in EB conditioning relative to the young animals; the conditioned decelerative HR response was increased in magnitude in the old animals. Significant deficits in cortical norepinephrine and serotonin were observed in the old subjects, but in both old and young animals the magnitude of the bradycardia was positively correlated with forebrain norepinephrine and inversely correlated with serotonin concentration. Receptor binding experiments revealed that 3H-spiroperidol receptor density was decreased in caudate nuclei of old animals; however, receptor affinity was unaffected by age.

Aging↗
PubMed1984

3H-2-deoxyglucose uptake after electrical stimulation of cardioactive sites in anterior medial cortex in rabbits.

The anterior medial cortex is an important integrative area for cardiovascular adjustments occurring during learning and conditioning. The autoradiographic 3H-2-deoxyglucose (3H-2DG) method for regional cerebral metabolic activity was used to identify other forebrain regions associated with cardiovascular adjustments elicited by electrical stimulation of anterior medial cortex. Rabbits that received anterior midline stimulation that produced bradycardia and depressor responses showed increased metabolic activity in the ipsilateral mediodorsal (MD) nucleus of the thalamus and the dorsal aspect of the claustrum. Two additional animals with anterior cortical placements in the infralimbic and anterior limbic areas showed ipsilateral increased activity in perirhinal cortex, but more dorsolateral placements in the precentral agranular area did not produce increased perirhinal activity. Control animals did not show this pattern of activity. These data suggest that MD and claustrum participate in a neural circuit which mediates cardiovascular adjustments similar to those elicited by Pavlovian conditioning contingencies.

Animals↗
PubMed1982

Cingulate damage attenuates conditioned bradycardia.

New Zealand albino rabbits received either sham, midline cortical, lateral cortical, or combined medial-lateral cortical lesions, and were subjected to differential pavlovian conditioning in which tones of different frequencies served as the conditioning stimulus and a brief paraorbital electric shock train served as the unconditioned stimulus. Heart rate conditioned responses were recorded.d Damage to medial but not lateral neocortex abolished the heart rate conditioned response. These data suggest that midline cortical structures may modulate higher level processing of stimulus information.

Animals↗
PubMed1982

Cingulate cortex: its role in Pavlovian conditioning.

Three experiments with New Zealand albino rabbits examined the role of anterior and posterior cingulate cortex in Pavlovian conditioning. Tones served as conditioned stimuli, and paraorbital electric shock served as the unconditioned stimulus. Anterior cingulate lesions attenuated conditioned heart rate (HR) decelerations, relative to posterior cingulate or sham lesions, but enhanced the magnitude of the bradycardiac component of the orienting reflex. Posterior cingulate lesions enhanced the bradycardiac component of the conditioned response, particularly late in training, relative to anterior or sham lesions. Somatomotor eye-blink conditioning, shock thresholds, and HR unconditioned responses were unaffected by cingulate lesions. Electrical stimulation of cingulate cortex revealed effective sites for eliciting heart rate and blood pressure (BP) changes only in anterior cingulate cortex. Relatively large (70-100 beats per minute) HR decelerations accompanied by small (1-5-mm Hg) BP depressor responses were elicited by stimulation of this area; the HR decreases were abolished by atropine methyl nitrate but were unaffected by either propranolol hydrochloride or phentolamine hydrochloride. These results are discussed in terms of cingulate involvement in the mediation of the cardiovascular component of a response pattern related to stimulus processing.

Animals↗
PubMed1981

Age-related changes in classical (Pavlovian) conditioning in the New Zealand albino rabbit.

The groups of New Zealand albino rabbits of approximately six and forty months of age respectively were subjected to Pavlovian conditioning in which a 1216 Hz, 75 dB tone served as the conditioning stimulus and a brief paraorbital electric shock train served as the unconditioned stimulus. Eyeblink and heart rate responses were assessed. Older animals revealed acquisition deficits in the somatomotor eyelid conditioning task compared to the young animals: however, the magnitude of the concomitantly occurring heart rate change was greater in older than in younger animals. These age-related changes appeared to be enhanced in males and were unrelated to general activity differences, or to the unconditioned response to unpaired tones or electric shocks.

Aging↗
PubMed1976

Orienting and classical conditioning in the rabbit (Oryctolagus cuniculus): effects of septal area lesions.

Rabbits with either sham or septal lesions recieved differential classical conditioning training in which tones of different frequencies served as CSs and paraorbital shock served as the UCS. Eyeblink (EB), EMG, and heart rate (HR) CRs were concommitantly assessed. Free field activity was also studied in selected animals. Animals with septal lesions revealed an impaired EB discrimination which resulted from increased responding to the CS-. These animals showed HR CRs of greater magnitude than sham animals. The HR discrimination was, however, unimpaired by septal lesions. Differential EMG activity also occurred, but was unaffected by septal destruction. Septal lesions resulted in greater free-field activity associated with visual stimulation, but no differences were obtained between septal and sham animals in the dark. It is suggested that these results were due to an enhanced reactivity to environmental stimulation, possibly related to dysfunctions of the orienting reflex.

Animals↗
PubMedDate not supplied

Hippocampal lesions and Pavlovian cardiovascular conditioning.

New Zealand albino rabbits received either sham, cortical control, or hippocampal lesions and were subjected to differential Pavlovian conditioning in which tones of different frequencies served as conditional stimuli (CSs), and a brief paraorbital electric shock train served as the unconditional stimulus. Heart rate (HR), blood pressure (BP), and electromyographic (EMG) conditional responses (CRs) were recorded. Animals with cortical and hippocampal damage or animals with cortical damage alone revealed attenuated bradycardiac CRs, but HR CRs of the former two groups did not significantly differ. BP changes were minimal; reliable differences were not obtained between CS+ and CS-. However, these changes consisted of small but reliable depressor responses, which were not affected by either cortical or hippocampal lesions. Few EMG CRs were obtained. These data, combined with those of previous experiments, suggest that forebrain structures may modulate higher level processing of stimulus information, perhaps in terms of assessing the biological significance of such stimulation.

Animals↗
PubMedDate not supplied

Autonomic responses are elicited by electrical stimulation of the medial but not lateral frontal cortex in rabbits.

Conscious rabbits received electrical stimulation of the anterior midline frontal cortex or lateral somatosensory and motor cortex, through chronically-implanted electrodes. Active sites for cardiovascular responses were found in the anterior midline cortex, but stimulation of the frontolateral sensory-motor cortex either did not elicit cardiovascular changes or elicited only small and variable changes when stimulated. The heart-rate response elicited was, in all cases, bradycardia. All blood pressure changes consisted of depressor responses. Stimulation of the lateral frontal cortex almost always resulted in increases in EMG activity, although many placements were observed in the medial frontal cortex that were unaccompanied by movement. In all cases in which depressor responses and bradycardia were elicited, increases in respiration rate and decreases in depth also occurred. The active area from which bradycardia and depressor responses were elicited forms the medial portion of the cortical projection area of the mediodorsal nucleus of the thalamus and thus may be involved in the autonomic accompaniments of the behavioral activities, i.e. learning and memory processes, associated with this nucleus.

Animals↗
PubMedDate not supplied

Age-related changes in associative learning: studies in rabbits and rats.

Two experimental models for studying age-related changes in associative learning are described. One involves classical (Pavlovian) conditioning of eyeblink and heart rate in the rabbit. The second involves Pavlovian leg flexion and heart rate conditioning in the rat. Advantages and disadvantages of each model are discussed. Results with both models suggest differential effects of aging on acquisition of autonomic and somatomotor responses, thus underlining the utility of assessing multiple response systems to adequately characterize age-related changes in learning and memory.

Aging↗
PubMedDate not supplied

Leg flexion conditioning in the rat: its advantages and disadvantages as a model system of age-related changes in associative learning.

Twelve- and 28-month-old Fischer 344 rats of both sexes received five 60-trial sessions of Pavlovian conditioning in which the CS was a 75 dB, 10,000 Hz tone, and the US was a 0.5-mA, 0.5-sec duration footshock. Right foreleg flexion was measured as the conditioned response (CR). Other animals received a random sequence of unpaired tones and footshock and served as pseudoconditioning control groups. Interstimulus intervals (ISIs) of 1.5 and 3.5 sec were studied. The longer ISI resulted in higher rates of responding in both the conditioning and pseudoconditioning groups. However, with the exception of the young males, all animals showed significantly higher levels of responding in the conditioning groups. Females also showed faster acquisition and higher levels of responding than males. A significant sex by age by sessions interaction occurred, suggesting that old males may be somewhat retarded in acquiring the leg flexion CR compared to the other groups of animals. Old males were also slower to reach a criterion of 5 successive CRs than either young males or young or old females.

Aging↗
PubMedDate not supplied

Multiple- and single-unit activity in area 32 (prelimbic region) of the medial prefrontal cortex during Pavlovian heart rate conditioning in rabbits.

Data from both brain lesion and brain stimulation experiments suggest that area 32 of the medial prefrontal cortex (prelimbic area) participates in the acquisition and/or expression of conditioned bradycardia. This report describes experiments designed to determine whether cells in this area of the brain exhibit changes in neural activity during classical conditioning that can be related to these learned heart rate changes. Thus, multiple- and single-unit activity was recorded from area 32 in rabbits during Pavlovian heart rate (HR) conditioning. In the first experiment, neuronal discharge recorded from chronically implanted multiple-unit electrodes in the superficial and deep layers of area 32 increased systematically in response to the presentation of tone conditioned stimuli (CS) paired with paraorbital electric shock as the unconditioned stimulus (US). This tone-evoked increase in multiple-unit activity (MUA) closely paralleled the acquisition of the decelerative HR conditioned response in animals that received paired CS/US presentations, but was of smaller amplitude in animals given unpaired CS/US presentations. Tone-evoked increases in MUA also occurred during tone-alone presentations prior to training, but this activity declined over trials. During extinction, CS-evoked MUA increases also declined over trials. These findings suggest that the CS-evoked increase in neuronal activity in area 32 was associatively produced. A second experiment examined the CS-evoked response of single units (n = 98) in area 32 during differential Pavlovian conditioning, in which one tone (CS+) was consistently followed by the paraorbital shock US and a second tone (CS-) was not. Four types of cells were found: (1) 32% of the cells studied showed no change in response to either CS+ or CS- presentation, (2) 48% showed CS-evoked increases to either CS+ or CS-, (3) 14% showed CS-evoked decreases to CS+ or CS-, and (4) 7% showed a biphasic response, in which an increase was followed by a decrease in activity. These cell types are similar to those previously found in the more dorsal anterior cingulate cortex (area 24) and frontal eyefields (area 8). However, a major difference between the present findings and those of our previous studies of areas 8 and 24 is that in several instances changes in CS-evoked activity in area 32 were significantly greater in response to the CS- than to the CS+, suggesting that some cells in the prelimbic region may code the absence of aversive stimulation, that is, a period of relative "safety."

Acoustic Stimulation↗