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D M Rector

Publications and source records attributed to D M Rector.

35 records · Page 2Linked to original sources
PubMed1996

Ventral medullary neuronal responses to peripheral chemoreceptor stimulation.

Recent findings suggest that carotid chemoreceptor input into the ventral medullary surface intermediate area during hypoxia is inhibitory (Gozal et al., (1994) Neurosci. Lett. 178, 73-76. However, systemic hypoxia is a complex stimulus, and effects of carotid chemoreceptor stimulation per se on intermediate ventral medullary surface neuronal activity are difficult to isolate. Therefore, we studied neural activation of the intermediate ventral medullary surface during peripheral chemoreceptor stimulation by intravenous sodium cyanide using optical procedures in seven pentobarbital-anesthetized cats. Control recordings were also acquired in the suprasylvian cortex of three cats. Images of reflected 660 nm light were collected at l/s with a charge-coupled device camera, triggered by the cardiac R wave, after 0.0, 0.5, 2, 5, 10, 20 and 40 micrograms/kg i.v. sodium cyanide administration before and following carotid sinus denervation. Sodium cyanide doses > 5 micrograms/kg significantly increased ventilation, an effect which was eliminated following carotid sinus denervation. A pronounced, dose-dependent activity decrease within the intermediate ventral medullary surface occurred within seconds of sodium cyanide administration, with subsequent return to baseline. Carotid sinus denervation eliminated rapid-onset neural responses to all sodium cyanide doses. However, at the 40 micrograms/kg dose, a smaller, slower onset (25 s), activity decrease occurred both pre- and postdenervation. In the neocortex, the sodium cyanide-induced fast responses were absent. Intravenous cyanide, acting via a carotid sinus nerve pathway, results in a dose-dependent decrease in neural activity within the intermediate ventral medullary surface of cats. High-dose sodium cyanide also appears to decrease intermediate ventral medullary surface neural activity directly.

Animals↗
PubMed1996

Optical imaging of the ventral medullary surface of developing kittens during ventilatory challenges.

We used large-array optical recording procedures to examine maturation of regional neural activity within the ventral medullary surface (VMS) of anaesthetized kittens during graded hypercapnic and hypoxic challenges. The VMS was exposed through a ventral surgical approach in 10, 20, 30, and 45-day-old kittens and in adult cats under sodium pentobarbital anaesthesia. Arterial pressure, costal diaphragmatic EMG, and ECG were continuously monitored. A coherent image conduit with 12 mu fibre resolution was attached to a charge-coupled-device camera and positioned over the VMS. Reflected 660 nm light was digitized continuously at 2-s intervals during a baseline period, hyperoxic hypercapnia, (3, 5, and 10% CO2 in O2), and poikylocapnic hypoxia (6%, 9%, and 12% O2 in N2), and recovery. Sixty to seventy-five images within each epoch were averaged, and subtracted from baseline. Regional differences within the image were determined by ANOVA procedures (alpha = 0.05). During hypercapnia, an overall decrease in neural activity (increase in scattered light) occurred, which was marginally age-dependent. By 30 days, regional bidirectional reflectance changes in response to CO2 emerged in a small proportion of animals, and were similar to adult responses. Hypoxia induced a dose- and age-dependent decrease in overall scattered light. Transient "on" and "off" responses were common under both ventilatory stimuli. In 20-30-day kittens, marked rebound responses in reflectance accompanied cessation of hypoxic stimuli; such patterns were absent at other ages. At 30 days, a caudal-rostral bidirectionality in response to mild hypoxia (12% O2) began to emerge in a subset of animals. We conclude that dose-dependent response to ventilatory stimuli occur in the VMS at all post-natal ages of the kitten; however, in hypoxia, the magnitude of the overall reflectance changes is diminished relative to adult patterns. Rebound responses to hypoxia are present at particular ages, and older kittens begin to show a topographical organization of neural activation.

Analysis of Variance↗
PubMed1996

Imaging of VMS activity during blood pressure challenges in awake and anesthetized goats.

We examined scattered-light changes in a rostral ventral medullary surface (VMS) area from five goats after blood pressure challenges during waking and halothane anesthesia. Reflected 660-nm images were digitized at 1/s after baseline; intravenous saline; 5, 10, or 15 micrograms/kg phenylephrine administration; or sodium nitroprusside infusion sufficient to lower blood pressure by 50%. Phenylephrine elicited a dose-dependent, blood pressure elevation during both states and a substantial transient reflectance increase (interpreted as activity decline) during anesthesia, but only a minimal, long-latency, slow-reflectance decrease activity increase) during waking. Sodium nitroprusside elicited lowering of blood pressure and decreased reflectance in the rostral site during anesthesia. The magnitude of the reflectance change to depressor challenge increased 30%, and the onset latency shortened during waking. Isolated regions of enhanced reflectance changes appeared during both challenges. Activity in this rostral VMS site differentially responds to blood pressure elevation or lowering, and state markedly alters the responses. We speculate that VMS responses to depressor challenge represent reflex activation of respiratory regions.

Anesthesia, General↗
PubMed1995

Imaging the dorsal hippocampus: light reflectance relationships to electroencephalographic patterns during sleep.

We assessed the correspondence of 660 nm light reflectance changes from the dorsal hippocampus with slow wave electroencephalographic (EEG) activity during quiet sleep (QS) and rapid eye movement (REM) sleep in four cats. An optic probe, attached to a charge-coupled-device (CCD) video camera, was placed on the dorsal hippocampal surface to collect reflectance images simultaneously with EEG, which was measured by macroelectrodes placed around the probe circumference. Spectral estimates of EEG and light reflectance amplitude indicated that reflectance changes occurred in a similar frequency range as EEG changes. Dividing the image into 10 subregions revealed that reflectance changes at the rhythmical slow wave activity band (RSA, 4-6 Hz) persisted in localized regions during QS and REM sleep, but regional changes showed considerable wave-by-wave independence between areas and from slow wave electrical activity. Peak frequencies for reflectance changes corresponded to fast RSA frequencies observed in the EEG. Optical changes most likely derive from fast-acting physical phenomena, rather than from alterations in blood perfusion, and provide increased spatial resolution over that offered by electrical measurements.

Animals↗
PubMed1995

Rostral ventral medullary surface activity during hypercapnic challenges in awake and anesthetized goats.

Regions within the rostral ventral medullary surface (RVMS) play an important role in cardiorespiratory responses to CO2 during anesthesia. Activity within a RVMS area, in which local cooling elicited marked ventilatory and blood pressure reductions, was measured as 660 nm scattered light changes in 5 goats following 5% CO2 challenges during waking and anesthetic states. During wakefulness, hypercapnia elicited a substantial, short latency transient (1-1.5 min) activity increase, followed by a sustained decrease. Stimulus cessation elicited a large and rapid off-transient activity increase which persisted for approximately 20 min. In contrast, during halothane anesthesia, the initial activation was absent, and the later activity decline and off-response were much reduced. We conclude that biphasic RVMS activity responses emerge to CO2 stimulation, and are state-dependent.

Administration, Inhalation↗
PubMed1995

Ventral medullary surface responses to hypoxic and hyperoxic transient ventilatory challenges in the cat.

Carotid body afferent contributions to activity of the intermediate area of the ventral medullary surface (IVMS) following transient hypoxia and hyperoxia were examined in 6 spontaneously breathing, pentobarbital-anesthetized cats. Two tidal breaths of 100% N2, 100% O2, or room air, were randomly administered before and after carotid sinus denervation (CSD). Images of scattered light from the IVMS showed that activity increased with hypoxia (10.1 +/- 2.4%), and decreased with hyperoxia (4.8 +/- 1.8%). CSD significantly increased the magnitude and delayed the onset of the hypoxic response, but reversed the initial component of the hyperoxic response. We conclude that carotid body afferents modulate the magnitude and timing of IVMS responses to transient respiratory challenges.

Animals↗
PubMed1995

Pressor-induced responses of the cat ventral medullary surface.

We examined ventral medullary surface activity using light reflectance procedures after blood pressure alterations induced by phenylephrine or sodium nitroprusside in 23 pentobarbital sodium-anesthetized cats. Images of reflected 660-nm light were collected and digitized at 1- to 3-s intervals after baseline and intravenous saline, 5-40 micrograms/kg phenylephrine, or sodium nitroprusside infusion. Carotid sinus nerve denervation (CSD) and bilateral vagotomy were performed in five and three animals, respectively, and challenges were repeated. Phenylephrine elicited a dose-dependent transient blood pressure elevation and reflectance increase (interpreted as activity decline) over the entire ventral medullary surface examined. The increase consisted of an initial rapid transient component, peaking at 45 s, and a 3- to 5-min recovery. CSD enhanced, and vagotomy substantially reduced, the initial transient response to phenylephrine. Sodium nitroprusside-induced lowering of blood pressure was associated with decreased reflectance in rostral sites and increased reflectance in caudal regions. CSD abolished a late component and diminished amplitude of an initial rapidly rising component of changes induced by nitroprusside, a decline further accentuated by addition of vagotomy.

Animals↗
PubMed1995

Maturation of kitten ventral medullary surface activity during pressor challenges.

We used large-array optical recording procedures to examine maturation of regional neural activity within the ventral medullary surface (VMS) of anesthetized kittens during pharmacologically induced blood pressure elevation. Under sodium pentobarbital anesthesia, the VMS was exposed in 10, 20 and 30- to 45-day-old kittens and in adult cats. Arterial pressure, costal diaphragmatic EMG, and ECG were continuously monitored. An imaging camera, composed of a charge-coupled device and a coherent bundle of optic fibers, was positioned over the VMS. Light at 660 nm illuminated the neural tissue, and was collected by the probe. Resulting light-scatter images were acquired at 2-second intervals during a baseline period, and following intravenous administration of phenylephrine at 10, 20 and 40 micrograms/kg. Sixty to seventy-five images within each epoch were averaged, and subtracted from baseline. Regional differences within the image were determined by ANOVA procedures (alpha = 0.05). Phenylephrine elicited dose-dependent elevations of blood pressure accompanied by decreased diaphragmatic EMG activity which were less profound in younger animals. With maturation, responsiveness of respiratory patterning to the pressor response increased. In contrast to adult cats, 10-day kittens increased VMS neural activity in a dose-dependent fashion with pressor stimulation. A progressive transition to adult response patterns was observed with increasing postnatal age, and was established in over half of the kittens by 30-45 days. We conclude that phenylephrine-induced baroreceptor stimulation elicits divergent VMS activity responses in developing and mature animals. Such a developmental pattern may reflect immature function of central and/or peripheral baroreflexes.

Aging↗
PubMed1994

Afferent contributions to intermediate area of the cat ventral medullary surface during mild hypoxia.

The intermediate area of the cat ventral medullary surface activates to mild hypoxia. Carotid body and vagal afferent contributions to this response were examined by recording activity levels, measured as changes in scattered 660 nm light, from the medullary surface in 7 anesthetized, spontaneously breathing cats following 12% O2 in N2 ventilatory challenge. A miniaturized video camera collected images synchronous with the peak of cardiac R wave at 1/s, from a 3.2 mm diameter area, before, and following bilateral carotid sinus denervation (CSD) and vagotomy. In intact animals, hypoxia increased activity; however, greater increases in activity levels followed CSD, while vagotomy elicited a marked reduction of the response. Thus, carotid body afferents exert inhibitory or disfacilitatory influences on intermediate area neurons, while the vagus appears to play an excitatory role.

Afferent Pathways↗
PubMed1994

Low-cost acquisition of video images simultaneously with 240 electrophysiological signals.

We developed a low-cost system for simultaneous collection and storage of physiological and video signals. The system samples and multiplexes up to 240 low-bandwidth analog channels with a camera video signal, and outputs a standard composite video signal containing analog and video data. The combined signals can be stored on video tape or can be digitized by an inexpensive framegrabber. The circuitry separates horizontal synchronizing pulses from a camera output; the pulses increment a counter that sequentially selects each electrophysiological channel on a sample-and-hold multiplexer. The intensity of each horizontal scan line from the multiplexer output represents the amplitude of one sample of each physiological channel. This signal is then multiplexed with the video signal, such that a portion of each video horizontal line represents the physiological data. The combined output is stored together, providing a means for synchronizing the two signals during analysis. The design allows easy coordination of electrophysiological events with video images from a standard video camera, avoiding the necessity for separate analog to digital circuitry for physiological and video signal storage on computer media, as well as the need for complex synchronization of the data from different media.

Costs and Cost Analysis↗
PubMed1994

Ventral medullary surface activity during sleep, waking, and anesthetic states in the goat.

We examined activity, measured as changes in reflected light, from the surface of a rostral ventral medullary area that is involved in cardiorespiratory control. We collected images during sleep and waking states and during halothane anesthesia in five adult unrestrained goats. During quiet sleep, overall activity increased and overall variability decreased compared with waking levels, whereas rapid eye movement sleep increased variability, and average activity decreased to near-waking levels. Distinct regions of activation and suppression appeared during sleep states. Deep anesthesia decreased activity and minimized variation. We speculate that alterations in rostral ventral medullary surface activity may play a role in state-dependent changes in cardiorespiratory control mechanisms.

Activity Cycles↗
PubMed1994

Hippocampal reflected optical patterns during sleep and waking states in the freely behaving cat.

We examined reflected light as a measure of neural activity from a 2 mm2 area of dorsal hippocampus and surrounding neocortex in nine freely behaving cats during sleep and waking states. Light reflectance at 660 or 700 nm was measured by a coherent fiber optic probe attached to a charge-coupled device video camera that allowed acquisition of images from subcortical structures. In the dorsal hippocampus, rapid eye movement sleep (REMS) and active waking (AW) resulted in a significant decline (-0.9% +/- 0.3 and -2.0% +/- 0.5, respectively) in overall reflected light from the dorsal hippocampus relative to quiet sleep (QS), while quiet waking (QW) resulted in an overall increase (+2.0% +/- 0.4). In the neocortical probe placement group, reflectance also decreased during AW (-1.6% +/- 0.5) and increased during QW (+1.7 +/- 0.6) as compared to QS. In contrast to the hippocampus, however, overall reflectance increased, rather than decreased, in the neocortex during REMS (+2.7% +/- 1.3). We interpret a decline in reflectance as representing increased activation of underlying neural tissue. Thus, the cat dorsal hippocampus increased overall activity during REMS as compared to QS, while neocortical structures decreased overall activity during the same state. These results concur with expected activity changes based on electrophysiologic and autoradiographic studies. The imaging procedure provided a continuous assessment of spatially organized neural activity changes in the freely behaving animal.

Animals↗
PubMed1993

Imaging of hippocampal and neocortical neural activity following intravenous cocaine administration in freely behaving cats.

We examined spatial-temporal patterns of neural activity, as inferred from 700 nm light reflectance, from the dorsal hippocampus and surrounding neocortex in seven freely behaving cats following 1.5, 2.5, 3.5 and 5.0 mg/kg intravenous cocaine administration. Images were acquired using a new technique which gathered reflected light from cortical and subcortical structures. Cardiac and respiratory patterning, collected simultaneously with optical images, revealed increased rates and diminished variation after intravenous cocaine administration. Cocaine increased reflectance correlates of hippocampal neural activity in a dose-dependent fashion over a 120 min period, with a lengthening time-to-peak effect (22-76 min). The largest dose resulted in an initial decrease, followed by the greatest enhancement in neuronal activity. Correlates of neural activation in the neocortex displayed an inverse dose-response curve to that found in the hippocampus; the time-to-peak effect was shorter (6-43 min) and the maximal change was reduced. Regional patches and bands of activation occurred during the period of the cocaine response, and were more pronounced in the hippocampus than the neocortex. Procaine, administered in a similar dose, slightly increased neural activity for 10 min in both the hippocampus and neocortex, and elicited a small increase in respiration. Cocaine induces a pronounced enhancement of neural activation in the neocortex and dorsal hippocampus; the time course of activation in the hippocampus parallels an increased respiratory pattern and outlasts the neocortical response. We speculate that hippocampal activation may be related to the profound respiratory acceleration found in response to cocaine.

Animals↗
PubMed1993

Ventilatory CO2-induced optical activity changes of cat ventral medullary surface.

We examined neuronal activation of the ventral medullary surface (VMS) during hypercapnic challenges using optical recording procedures. With a coherent imaging probe, we assessed reflected 700-nm light from 18 VMS sites in 11 spontaneously breathing adult cats and from the suprasylvian cortex in two cats. Video frames were acquired during a baseline period, hypercapnic (3, 5, and 10% CO2 in O2) exposure, and recovery. Hypercapnic exposure elicited overall reflectance changes in all VMS sites, but no changes in the suprasylvian cortex. Light reflectance changes, suggesting altered neuronal activity, were reproducible, occurred as early as 30 s after CO2 exposure, and were dose dependent. The changes persisted approximately 20-25 min beyond the stimulus, but respiratory responses consistently recovered within 2-3 min. Although more rostral VMS sites tended to be associated with decreased activity and caudal regions with increased excitation, no uniform topographical organization was apparent across animals. The variability in VMS optical reflectance patterns across animals during CO2 stimulation may reflect the heterogeneous topographical distribution of responsive neurons in the structure.

Animals↗
PubMed1993

Optical imaging of the ventral medullary surface of cats: hypoxia-induced differences in neural activation.

Large-array optical recording procedures provide the potential to examine simultaneous activity of large numbers of neurons. We applied this technique to examine regional neuronal activation on the ventral medullary surface (VMS) of cats during hypoxic challenges. VMS was exposed through a ventral surgical approach in eight adult cats under pentobarbital sodium anesthesia. Arterial pressure, end-tidal CO2, costal diaphragmatic electromyograms, and electrocardiograms were continuously monitored. A coherent image conduit with 12-microns-fiber resolution was attached to a charge-coupled device camera and positioned over the VMS. Reflected 700-nm light was digitized continuously at 2- to 3-s intervals during baseline period, hypoxic (6, 9, and 12% O2 in N2) exposure, and recovery. Forty images within each epoch were averaged and subtracted from baseline. Regional differences within the image were determined by analysis of variance procedures (alpha = 0.05). In caudal VMS, hypoxic challenges with 12% O2 consistently induced a regional diminution in reflected light (increased neural activity) that was rapid in onset and persisted for approximately 20 min after termination of exposure, well beyond the duration of discernible ventilatory alterations. In contrast, the same challenge resulted in decreased neural activity of similar duration in rostral VMS areas. Challenges with lower inspired concentrations of O2 reversed the pattern of diminished neural activity in rostral regions and led to a dose-dependent increase in neural activity, a dependency also observed in caudal VMS. We conclude that caudal VMS neurons demonstrate a unidirectional dose-dependent response pattern to hypoxic stimuli, whereas rostral VMS regions exhibit a bidirectional response to increasing hypoxic stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗