Jingxi Zhang

Cryogenic blockade of the central nucleus of the amygdala attenuates aversively conditioned blood pressure and respiratory responses

The central nucleus of the amygdala (ACE) was reversibly blocked during extinction of an aversively conditioned cardiorespiratory response in unanesthetized, freely moving cats. Cryoprobes were positioned bilaterally in the ACE of 4 cats and in the nucleus entopeduncularis of 1 cat. Blood pressure typically showed biphasic changes in response to the conditioned stimulus (CS) during non-cooling trials. Blood pressure initially dropped and then rose. Heart rate consistently dropped, and respiratory rate increased in response to the CS. ACE cooling did not alter the pre-CS baseline blood pressure, heart rate or respiratory timing, but changed the cardiorespiratory response to the CS. During ACE cooling, blood pressure and respiratory responses were greatly attenuated or abolished. No significant effect on the heart rate response was observed during ACE cooling. Cooling of a nearby structure, the nucleus entopeduncularis, did not affect blood pressure, heart rate or respiratory responses to the CS. These results support the hypothesis that the ACE plays a role in both cardiovascular and respiratory regulation during conditioned aversive responses. The study also suggests that, in cats, the predominant influence of the ACE on cardiovascular control is on blood pressure rather than on heart rate regulation.

Respiratory modulation of neuronal discharge in the central nucleus of the amygdala during sleep and waking states

The relationship between neuronal discharge in the central nucleus of the amygdala (ACE) and timing of the respiratory cycle was assessed during quiet and active sleep and during the waking state. Of 169 neurons recorded from the ACE in intact, drug-free cats, 22% discharged phasically with the respiratory cycle during at least one sleep or waking state. The dependency between neuronal discharge and the respiratory cycle was typically strong in only one state. Forty-three percent of the respiratory-related neurons were most strongly correlated with the respiratory cycle during the waking state (AW). An additional 30% were most strongly related to the respiratory cycle during quiet sleep (QS), whereas only 11% showed the strongest dependency during rapid eye movement (REM) sleep. Half of the ACE neurons (49%) discharged at frequencies less than 10 spikes per second, and the most common trend in firing rate across states was one in which neurons fired more rapidly during AW and REM than during QS. No relationship between discharge rate of ACE neurons in the three states and propensity for phasic discharge with the respiratory cycle could be demonstrated.

A miniaturized cryoprobe for functional neuronal blockade in freely moving animals.

We have developed a miniature cryoprobe for blockade of neuronal structures. The cryoprobe uses Freon as a cooling medium and consists of concentric double stainless steel cannulae, a shaft heater coil and a tip thermocouple. The cryoprobe tip temperature is controlled by adjusting Freon flow supplying the cryoprobe by an automobile fuel injector and electronic control circuit, and is displayed on a temperature monitor. Tissue temperatures, determined by thermocouples, ranged from 8.5 degrees C near the cryoprobe tip to 20 degrees C 2.5 mm distal to the tip. The cryoprobe shaft is maintained at body temperature by means of a shaft heater coil and a heater control circuit. The cryoprobe offers advantages of ease of construction, and allows cooling of neuronal structures in freely moving animal preparations.

Respiratory-related discharge of periaqueductal gray neurons during sleep-waking states

Extracellular single-unit spontaneous activity was recorded from the periaqueductal gray region (PAG) in undrugged, freely moving cats. Two analyses, cross-correlation histograms and linear regression techniques, were used to examine state relationships of neuronal discharge with respiratory patterning. Of 68 cells recorded, 19 (28%) showed a timing relationship (breath-by-breath dependency), 14 of which were state-dependent. Twenty-three (34%) showed a tonic discharge correlation with the respiratory cycle, and activity of all these cells was state-dependent. These results suggest that a subset of PAG cells may play a role in state-related respiratory patterning.

Cardiovascular-related discharge of periaqueductal gray neurons during sleep-waking states

The periaqueductal gray (PAG) contains topographically organized areas that, upon stimulation or lesion, lead to modifications in blood pressure and heart rate and redistribution of blood flow. We examined patterns of discharge of single neurons in the PAG in 5 undrugged, freely moving cats to determine if cardiovascular patterning changes observed during different sleep states were related to activity in this midbrain region. Cross-correlation histograms and linear regression techniques were used to calculate dependencies between neuronal discharge and cardiac activity. Fifty of 68 cells recorded (74%) showed a discharge timing relationship (cardiac cycle-by-cycle) and/or a tonic discharge correlation with the cardiac cycle. Nearly all (48 or 96%) of these dependencies were state related. The large proportion of neurons showing a state-related cardiac dependency suggests that the PAG may contribute to mediating different cardiac patterns observed in each state.

Cardiac and Respiratory Interactions Maintaining Homeostasis During Sleep

an important aspect of retaining homeostasis during sleep is maintenance of control over two qualitatively different types of musculature: that essential for oxygen exchange and that essential for blood transport. Maintaining coordination of these two motor systems, one supplied by motor control to the somatic musculature (i.e., diaphragmatic, intercostal, abdominal, and upper airway musculature) and the other supplied by motor control to the “autonomic” musculature (i.e., heart and vasculature), is a formidable task during sleep. Activity of the respiratory somatic musculature changes greatly between different sleep states, as do rate and variability of cardiac pumping and the tone of vasculature in different body areas. The respiratory and cardiovascular systems are tightly interrelated, however, and alterations from one sleep state to another in one system are accompanied by changes in the other. The coupling of activity between the two systems is relevant to certain pathological states, since dysfunction in one system can be associated with rapid onset of failure in the other. In addition, activity of both somatic respiratory and autonomic cardiovascular systems is greatly dependent on, and coordinated with, activity in the postural and limb somatic musculature, which in turn is also dependent on sleep state.

Accuracy of MR-Guided Stereotactic Electrode Implantation

The accuracy of stereotactic electrode implantation using MR guidance and a computerized imaging system was compared to the conventional Talairach system, using ventriculography and a stereotactic atl

Dynamic magnetic resonance imaging of human Rolandic cortex

Rolandic cortex was imaged with magnetic resonance (MR) in nine subjects while performing a motor activation task. Imaging was performed by a volumetric, T2-weighted pulse sequence in a conventional 1.5 Tesla scanner during both resting conditions and volitional toe flexion and extension of the dominant foot. Significant changes in MR signal intensity of 7.8 +/- 2.3% (mean +/- s.e.m.) were observed in the medial Rolandic cortex contralateral to the active foot. Changes were maximal in the vicinity of the central sulcus, but were also identified anteroposteriorly, across successive coronal planes. No significant changes were found in the ipsilateral Rolandic cortex or in other brain structures. Volumetric functional MRI strategies may provide an important non-invasive tool for assessment of cortical motor function.

Discharge Relationships of Periaqueductal Gray Neurons to Cardiac and Respiratory Patterning During Sleep and Waking States

Respiratory muscle activity assists many bodily functions for purposes other than mere tissue oxygenation. Respiratory musculature, for example, are used in vocalization, for providing thoracic and abdominal pressure for defecation and urination, and for maintaining thoracic pressure and body position in somatic movements. Respiratory musculature are used heavily in some species for temperature regulation; tachypnea and upper airway dilation, for example, are primary mechanisms used for cooling in selected animals. Use of the respiratory musculature for these actions involves precise coordination of a number of brain structures, and those brain structures incorporate a number of rostral brain regions in addition to the classical brain stem “dorsal” (e.g., nucleus of solitary tract) and “ventral” (e.g., nucleus ambiguus) respiratory groups typically outlined in the respiratory control literature.