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Biomedical subjects

P M McCabe

Publications and source records attributed to P M McCabe.

At least 55 records · Page 3Linked to original sources
PubMed1989

Auditory cortex lesions prevent the extinction of Pavlovian differential heart rate conditioning to tonal stimuli in rabbits.

The present study examined the role of the auditory cortex in the extinction of differentially conditioned heart rate (HR) responses in rabbits. Lesions were placed bilaterally in either the auditory cortex or the visual cortex. Three days after recovery from surgery, the auditory cortex lesion group and the visual cortex lesion control group were habituated to the tonal conditioned stimuli (CSs), and then given 2 days of Pavlovian differential conditioning (60 trials per day) in which one tone (CS+) was always paired with the unconditioned stimulus and another tone (CS-) was never paired with the unconditioned stimulus. Animals that had demonstrated reliable differential conditioning (CS+ response at least 5 beats greater than the CS- response) were placed on an extinction schedule for 7 days. The extinction schedule was identical to the differential conditioning schedule with the exception that shock never followed the CS+. The results of the study indicate that auditory cortex lesions prevent the extinction of differential bradycardia conditioned responses (CRs) to tonal CSs. Whereas the bradycardia responses to the CS+ quickly extinguished in the group that had control lesions in the visual cortex, the auditory cortex lesion group continued to exhibit significantly larger bradycardiac HR CRs to the CS+ relative to the CS- during all 7 days of extinction. These results suggest that the animals in the auditory cortex lesioned group did not inhibit responses to a previously reinforced stimulus (i.e., CS+) as well as animals with control lesions in the visual cortex.

Acoustic Stimulation↗
PubMed1989

New signal processing techniques for improved precision of noninvasive impedance cardiography.

Impedance cardiographic determination of clinically important cardiac parameters such as systolic time intervals, stroke volume, and related cardiovascular parameters has not yet found adequate application in clinical practice, since its theoretical basis remains controversial, and the precision of beat-to-beat parameter estimation has until recently suffered under severe shortcomings of available signal processing techniques. High levels of noise and motion artifacts deteriorate signal quality and result in poor event detection. To improve the precision of impedance cardiography, new techniques for event detection and parameter estimation have been developed. Specifically, matched filtering and various signal segmentation and decomposition techniques have been tested on impedance signals with various levels of artificially superimposed noise and on actual recordings from subjects in a laboratory study of cardiovascular response to a cognitive challenge. Substantial improvement in the precision of impedance cardiography was obtained using the newly developed signal processing techniques. In addition, some preliminary evidence from comparisons of the impedance cardiogram with invasive aortic electromagnetic flow measurement in anesthetized rabbits is presented to address questions relating to the origin of the impedance signal.

Animals↗
PubMed1989

Microcomputer servo-controlled bicycle ergometer system for psychophysiological research.

Steady state exercise is widely used for psychophysiological studies in which a constant heart rate at a predetermined level is desired. We have developed a microcomputer servo-controlled bicycle ergometer system that can be used for administering steady state exercise. Fourteen healthy male subjects, with a wide range of fitness levels (measured by VO2max) were exercised to either a fixed workload (130 watts) or a predetermined heart rate level (servo-heart rate) of 122 bpm (i.e., 65% of maximum calculated heart rate for the sample). Servo-heart rate was implemented using a feedback loop that automatically adjusted workload to compensate for immediate variations in heart rate, resulting in a more consistent heart rate. Heart rate varied from the predetermined value by 17 bpm during fixed workload but only 3 bpm during servo-heart rate (p less than .05). Therefore, by using the microcomputer servo-controlled bicycle ergometer, heart rate was maintained at a predetermined level regardless of the subject's fitness level. VO2max and workload during servo-heart rate were significantly correlated (r = .85, p less than .05). Therefore, the workload necessary to maintain heart rate at a constant level may provide an approximate index of aerobic fitness level.

Adult↗
PubMed1988

Cardiovascular responses elicited by electrical and chemical stimulation of the rostral medullary raphe of the rabbit.

Electrical stimulation of the rostral medullary raphe (RMR) of the rabbit elicited pressor responses that were accompanied by tachycardia or bradycardia. Stimulation of dorsal sites (the dorsal raphe obscurus) evoked a pressor/tachycardia response and stimulation of ventral sites (the ventral raphe obscurus, raphe magnus and raphe pallidus) produced a pressor/bradycardia response. Electrical stimulation of the RMR after sinoaortic denervation led to an increase in the magnitude of the pressor response elicited from all stimulation sites, a decrease in the magnitude of the bradycardia produced by stimulation at the ventral sites, but had no effect upon the magnitude of the tachycardia observed from stimulation of the dorsal sites. These findings suggest that electrical stimulation of the dorsal sites leads to inhibition of the cardiomotor component of the baroreceptor reflex. The results of vagal blockade experiments demonstrated that baroreceptor attenuation of the pressor responses at ventral sites was mediated primarily by parasympathetic input to the heart. Chemical stimulation of the RMR with L-glutamate also led to a pressor/tachycardia response at the dorsal sites and a pressor/brachycardia response at the ventral sites. This finding provides evidence that neuronal cell bodies, not axon of passage, mediated the responses elicited by electrical stimulation.

Animals↗
PubMed1988

Anatomical and functional connections of neurons of the rostral medullary raphe of the rabbit.

Single cell recordings were made from neurons in the rostral medullary raphe (RMR) of the rabbit. The recording sites were ones that had been shown to yield pressor responses from electrical stimulation and by pressure injections of glutamate. Electrical stimulation of the intermediolateral (IML) region of the spinal cord led to antidromic activation of 12 of the 100 cells studied. Eleven of these cells were located in raphe pallidus or raphe magnus, and one cell was located in raphe obscurus. These findings were consistent with the results of horseradish peroxidase (HRP) histochemistry experiments. Injections of HRP into the IML led to heavy cell body labeling in raphe pallidus and raphe magnus, but sparse labeling in raphe obscurus. Cells in the RMR could be orthodromically activated by electrical stimulation of the putative defense area of the periaqueductal (PAG) but not by stimulation of putative defense areas in the hypothalamus. Most of these cells were located in raphe pallidus or raphe magnus. Similarly, HRP injections into raphe pallidus and raphe magnus led to heavy cell body labeling in the PAG but not the hypothalamus; no cell body labeling was found in the PAG when injections were made into raphe obscurus.

Action Potentials↗
PubMed1988

Role of auditory cortex in the acquisition of differential heart rate conditioning.

Previous findings from our laboratory indicate that lesions of the auditory cortex disrupt the retention of differentially conditioned bradycardiac responses to tonal stimuli in rabbits. In the present experiment, the effect of lesions of the auditory cortex on the acquisition of differential bradycardiac conditioning was examined. The effect of lesions in the auditory cortex were compared to the effect produced by control lesions in the visual cortex. After 7 days of recovery, animals received 7 days of differential Pavlovian bradycardiac conditioning in which one tone (CS+) was paired with the unconditioned stimulus, and another tone (CS-) was never paired with the unconditioned stimulus. All animals demonstrated differential conditioning during the first 3 days of conditioning. On days 4-7, however, auditory cortex lesioned animals did not exhibit significant differential heart rate (HR) conditioning, whereas control animals with lesions in the visual cortex showed no loss of conditioning during this period. The loss of differential conditioning in animals with lesions in the auditory cortex appears to be due to an increase in the magnitude of the response to the CS-. These data support the hypothesis that the auditory cortex serves to inhibit the response to the CS- in differential conditioning of bradycardia to acoustic stimuli, and that the inhibition may be mediated by a descending corticothalamic or corticolimbic pathway.

Animals↗
PubMed1987

Involvement of cortical and thalamic auditory regions in retention of differential bradycardiac conditioning to acoustic conditioned stimuli in rabbits.

Our previous findings indicate that lesions in the medial division of the medial geniculate nucleus (mMGN) prevent the acquisition of differential conditioning of bradycardia to acoustic stimuli in rabbits. In the present experiment, the effect of lesions in mMGN on retention of differential bradycardiac conditioning was examined. In addition, the possible involvement of auditory cortex in differential conditioning was investigated. Electrodes were chronically implanted in mMGN, the ventral division of the medial geniculate nucleus (vMGN), or auditory cortex. After 7 days of recovery, animals received one differential Pavlovian conditioning session. At the end of the session, lesions were produced through the implanted electrodes. All animals demonstrated differential bradycardiac conditioning during the prelesion session. Animals with vMGN lesions also demonstrated differential conditioning during the postlesion session. However, mMGN and auditory cortex lesion animals failed to demonstrate differential conditioning during the postlesion session due to an increased response magnitude to the unpaired tone (CS-). These data support the hypothesis that mMGN plays a role in differential conditioning of bradycardia to tonal stimuli. In addition, these findings suggest that a possible corticothalamic pathway may be involved in the inhibition of the response to the CS-.

Acoustic Stimulation↗
PubMed1986

Ibotenic acid lesions in the medial geniculate region prevent the acquisition of differential Pavlovian conditioning of bradycardia to acoustic stimuli in rabbits.

The present study examined the effect of ibotenic acid lesions in the medial portion of the medial geniculate nucleus (mMGN) on differential heart rate (HR) conditioning to acoustic stimuli in rabbits. Lesions in mMGN prevented the acquisition of differential HR conditioned responses but not bradycardiac responses to the conditioned stimuli. The data suggest that cells in this region play an important role in the discriminative component of HR conditioning.

Acoustic Stimulation↗
PubMed1986

Sinoaortic denervation does not prevent differential Pavlovian conditioning of bradycardia in rabbits.

Recent findings suggest that descending projections from the amygdaloid central nucleus (ACE) to the nucleus of the solitary tract (NTS) may modulate the baroreceptor reflex and thereby facilitate the expression of the bradycardiac conditioned response (CR) in rabbits. The purpose of the present study was to examine the role of the afferent limb of the baroreceptor reflex in differential Pavlovian conditioning of bradycardia in rabbits. Animals received either aortic denervation, sinoaortic denervation or sham denervation. After recovery from surgery, animals received one differential Pavlovian conditioning session per day over the next 6 days. Sinoaortic denervation abolished the baroreceptor reflex as assessed by intravenous injections of phenylephrine. In addition, sinoaortic denervation increased baseline heart rate (HR), altered the topography of the HR unconditioned response, but did not abolish the HR orienting response or prevent the acquisition of bradycardiac CRs. The findings of the present study suggest that afferent barosensory input is necessary for the expression of the HR CR in rabbits. However, descending ACE projections may still play a role in the HR CR by directly affecting NTS neurons.

Amygdala↗
PubMed1986

The role of the medial geniculate region in differential Pavlovian conditioning of bradycardia in rabbits.

The present study examined the role of the medial geniculate region (MGN) in differential Pavlovian conditioning of bradycardia and corneo-retinal potential (CRP) to acoustic stimuli in rabbits. Injections of horseradish peroxidase into the amygdala central nucleus, an area that mediates the bradycardia-conditioned response (CR), produced cell body and fiber labeling at the ventral and medial borders of the MGN. Then, bilateral electrolytic lesions were made at the medial border of the MGN or in control sites dorsal and/or rostral to the MGN. Ten days after surgery, lesioned and unoperated control animals were subjected to 7 days of differential Pavlovian conditioning. In the control lesion and unoperated groups, the CS+ consistently elicited larger bradycardia responses than the CS-. However, animals with bilateral lesions in the medial MGN did not demonstrate differential bradycardia CRs. Bradycardia response magnitude in MGN lesion animals was not affected. Evidence of CRP differential conditioning was present in each group. The present findings suggest that a region just medial to the MGN is involved in bradycardia differential conditioning in rabbits. The fact that bradycardia responses were still present after medial MGN lesions suggests that other auditory regions may also be involved in the mediation of the bradycardia CR.

Acoustic Stimulation↗
PubMed1986

The role of amygdaloid central nucleus in the retention of differential pavlovian conditioning of bradycardia in rabbits.

The present study examined the role of the amygdaloid central nucleus (ACE) in the retention of differential pavlovian conditioning of bradycardia in rabbits. Electrodes were implanted bilaterally in ACE or in control sites just dorsal and rostral to ACE. Following recovery, animals were subjected to differential pavlovian conditioning in which one tone (CS+) was paired with periorbital shock and a second tone (CS-) was presented alone. Subsequent electrolytic lesions abolished the heart rate (HR) conditioned response (CR), yet had no effect on HR orienting response, unconditioned response, or baseline. In a follow-up experiment, corneoretinal potential (CRP) and HR were recorded. Bilateral ACE lesions profoundly attenuated or abolished the HR CR without abolishing CRP CRs. The major finding of this study is that bilateral lesions of ACE selectively attenuate the HR CR while not necessarily abolishing other CRs.

Amygdala↗
PubMed1986

Lateral subthalamic area as mediator of classically conditioned bradycardia in rabbits.

This study was conducted to examine whether a central efferent pathway passing through the lateral zona incerta (LZI) of the subthalamus selectively mediates the bradycardia conditioned response (CR) in rabbits. Electrodes were implanted bilaterally in LZI or in control sites just dorsal or ventral to LZI. Two days following surgery, animals were subjected to Pavlovian conditioning or to pseudoconditioning. Subsequent bilateral electrolytic lesions did not influence the heart rate (HR) orienting response, unconditioned response, baseline, or lack of response to pseudoconditioning. Bilateral LZI lesions alone abolished the HR CR. In a follow-up experiment, the corneoretinal potential (CRP) CR and HR were recorded. Bilateral LZI lesions following conditioning to a criterion of 65% CRP CRs abolished the HR CR without affecting CRP CRs. The present findings indicate that LZI is part of an efferent pathway that selectively mediates the HR CR in rabbits.

Amygdala↗
PubMed1985

Nucleus reticularis lateralis involvement in the pressor component of the cerebral ischemic response.

Lesions of the ventromedial portion of the nucleus reticularis lateralis (NRL) of the medulla oblongata in the rabbit significantly and markedly reduced the pressor component of the cerebral ischemic response (CIR) without altering vasomotor tone. Use of horseradish peroxidase as an anterograde and retrograde tracer indicated that the ventromedial NRL projects to the intermediolateral cell column (IML) of the upper thoracic spinal cord. Injections of glutamate into ventromedial NRL elevated blood pressure (BP), indicating that neuronal cell bodies in this area are capable of eliciting BP elevations when stimulated. These findings suggest that cell bodies in the ventromedial NRL are capable of eliciting pressor responses during the CIR via direct projections to sympathetic preganglionic cell bodies.

Animals↗