Gary C. Sieck

Pneumotaxic area neuronal discharge during sleep-waking states in the cat.

We examined the spontaneous activity of single neurons within the nucleus parabrachialis medialis (NPBM; pneumotaxic center) of unanesthetized, unrestrained cats in relation to the respiratory cycle during different sleep-waking states. State-related changes were found in the mean discharge rate of NPBM neurons and in the relationship of their activity to the respiratory cycle. These changes in pneumotaxic center neuronal activity paralleled the variations in respiratory patterns associated with different sleep-waking states. State-related changes in NPBM neuronal activity could partially account for the different respiratory patterns of each sleep-waking state by modulating inspiratory-expiratory phase transitions.

A new technique for acute and chronic recording of crural diaphragm EMG in cats.

We have developed a percutaneous technique for placement of electromyogram electrodes in cat diaphragmatic crura. The technique is convenient and relatively atraumatic. Guided by external landmarks, small gauge hypodermic needles are used to advance electrodes through implant sites within or in contact with the crural portions of the diaphragm. Satisfactory EMG is reliably obtained from both acute and chronic preparations.

Respiratory inhibition induced by transient hypertension during sleep in unrestrained cats

The effects of transient blood pressure elevation, induced by intravenous injection of phenylephrine, were studied in drug-free, unrestrained cats during sleep and waking. Transient hypertension evoked an increase in respiratory cycle duration (Ttot), an effect which was most prominent during quiet sleep. Transient hypertension evoked no overall change in inspiratory duration (Tdi) during any sleep-waking state, although reduction of diaphragmatic EMG amplitude was observed. Thus, the ratio of diaphragmatic activity time to total respiratory cycle duration (Tdi/Ttot) was decreased following blood pressure elevation. Apneic episodes occasionally occurred, and these occurrences were more frequent during sleep states. Apneas induced during quiet sleep were often associated with transient or sustained arousal.

Discharge correlations between neurons in the nucleus parabrachialis medialis during sleep-waking states

Spontaneous activity from simultaneously recorded pairs of neurons in the nucleus parabrachialis medialis(NPBM) was examined in unanesthetized, unrestrained cats during each sleep-waking state. Functional interconnections between pairs of neurons were studied with cross-correlation techniques. A total of 40 neuronal pairs were studied, 38 of which were recorded on separate, but proximal electrodes, and two pairs of which were recorded on the same electrode. Of the 40 pairs of neurons examined, 22 showed short delay (< 4 msec) peaks in the cross correlogram of their spike activity. These correlations tended to be highest in quiet sleep (QS). Increased probability of shared discharge with intermediate delays in the peaks of the cross-correlogram (5-150 msec) was observed in 16 of 40 pairs. The increase in correlation at intermediate delays followed a period of decreased shared activity. Activity at intermediate delay peaks was reduced during rapid eye movement (REM) sleep, and appeared with a shorter delay during that state. Long delay correlation peaks ranging from 0.5 to 6 sec appeared in 23 of 40 neuronal pairs, but only in waking and in REM sleep.

TrkB gene therapy by adeno-associated virus enhances recovery after cervical spinal cord injury

Unilateral cervical spinal cord hemisection at C2 (C2SH) interrupts descending bulbospinal inputs to phrenic motoneurons, paralyzing the diaphragm muscle. Recovery after C2SH is enhanced by brain derived neurotrophic factor (BDNF) signaling via the tropomyosin-related kinase subtype B (TrkB) receptor in phrenic motoneurons. The role for gene therapy using adeno-associated virus (AAV)-mediated delivery of TrkB to phrenic motoneurons is not known. The present study determined the therapeutic efficacy of intrapleural delivery of AAV7 encoding for full-length TrkB (AAV-TrkB) to phrenic motoneurons 3 days post-C2SH. Diaphragm EMG was recorded chronically in male rats (n=26) up to 21 days post-C2SH. Absent ipsilateral diaphragm EMG activity was verified 3 days post-C2SH. A greater proportion of animals displayed recovery of ipsilateral diaphragm EMG activity during eupnea by 14 and 21 days post-SH after AAV-TrkB (10/15) compared to AAV-GFP treatment (2/11; p=0.031). Diaphragm EMG amplitude increased over time post-C2SH (p<0.001), and by 14 days post-C2SH, AAV-TrkB treated animals displaying recovery achieved 48% of the pre-injury values compared to 27% in AAV-GFP treated animals. Phrenic motoneuron mRNA expression of glutamatergic AMPA and NMDA receptors revealed a significant, positive correlation (r(2)=0.82), with increased motoneuron NMDA expression evident in animals treated with AAV-TrkB and that displayed recovery after C2SH. Overall, gene therapy using intrapleural delivery of AAV-TrkB to phrenic motoneurons is sufficient to promote recovery of diaphragm activity, adding a novel potential intervention that can be administered after upper cervical spinal cord injury to improve impaired respiratory function.

Estrogen modification of feeding behavior in the female rat: Influence of metabolic state

Abstract The effects of estrogen on feeding behavior and body weight regulation of adult ovariectomized rats were observed after 48 hr of food deprivation. The depletion of body nutrient stores caused by food deprivation resulted in an attenuation of the effects of estrogen treatment on food intake, eating time, meal size, meal duration and the number of meals. Nevertheless, estrogen treatment in fasted animals did shorten the interval between meals immediately after access to food was restored. Indices of the satiating effects of individual meals and the deprivation effects of intervals between meals were calculated for selected times. These indices also indicated an influence of estrogen even in the fasted condition. Estrogen diminished the satiety produced by the first meal after food access was restored, while the deprivation effects of the interval between the first and second meals were enhanced. During the dark period on the first day of refeeding, the satiating effects of food remained reduced in the fasted condition, and estrogen did not appear to further affect satiety compared to oil treatment, but estrogen did lower the deprivation effects of intermeal intervals compared to oil treatment. Estrogen treatment in non-fasted animals lowered both satiety and deprivation effects during the dark period. The varying influence of estrogen on the deprivation effects of intermeal intervals suggests that the influence of estrogen depends upon the long-term effects of an animals metabolic state.

Absence of high-frequency oscillations in the discharge of pneumotaxic neurons in intact, unanesthetized cats

The discharge of neurons in the nucleus parabrachialis medialis (NPBM) was examined for the presence of high-frequency oscillations (HFOs) by autocorrelation analysis. HFOs were not observed in NPBM activity during any sleep-waking state. In contrast, HFOs were found in the activity of medullary respiratory neurons. It is concluded that the NPBM is not the source of HFOs in the respiratory system.

Respiratory-Related Heart Rate Variation during Sleep and Waking States in Cats

Respiratory-related heart rate variation was examined during sleep and waking in cats with time series analysis techniques. Extent (magnitude) and coherence (degree of correlation between heart rate variation and respiratory activity) were calculated from cardiac and respiratory activity spectra. State-related differences in extent and coherence were found. Coherence appeared to be the most appropriate indicator of respiratory arrythmia differences between sleep and waking states. Overall coherence was greatest during quiet sleep, least during quiet wakefulness, and intermediate during rapid eye-movement sleep. Overall extent was also greatest during quiet sleep and least during rapid eye-movement sleep and quiet wakefulness.

Nocturnal feeding pattern in the prepubertal rat: influence of the ventromedial hypothalamus (VMH)

Abstract Daily feeding patterns, food intake and changes in body weight of male and female prepubertal rats were observed across a period from 21 to 50 days of age. Light/dark differences in feeding were found for both males and females throughout the recorded period, with feeding occurring predominantly during the dark period. The light/dark difference in feeding behavior gradually increased as the animals developed. Bilateral lesions placed in the VMH of female rats at 21 days of age disrupted the light/dark differences in feeding behavior primarily by decreasing dark period feeding. These lesions further resulted in a period of hypophagia and retarded body weight gain as well as a delay in pubertal onset. These data indicate that prepubertal rats regulate their feeding behavior so that food intake occurs principally during the dark period and that the integrity of the VMH is necessary for this regulation.

Regulation of feeding behavior in the prepubertal female rat

Abstract Responses to challenges of long-term regulation of feeding behavior were compared between adult and weanling female rats. Adulteration of a high fat diet with NaCl caused both adult and weanling rats to reduce their food intake, but neither group refused to eat. Food deprivation for 24 hr was followed by an increase in feeding for both adult and weanling animals during a period when food intake is normally very low. Continued limited food access to 2 hr during the light period was compensated for by an increase in the normal food intake for this period for both adult and young female rats. It was observed that both adult and weanling rats showed a marked preference for the more dilute glucose solution when given a choice. In addition, both groups maintained a constant caloric intake during presentation of the glucose solutions by adjusting their intake of a solid food source. In each challenge of long-term regulation of feeding behavior, the response of weanling animals was as good or superior to that shown by adults. It is concluded that weanling female rats regulate their feeding just as adults to maintain long-term energy balance. It was also observed that bilateral lesions placed in the ventromedial hypothalamus (VMH) at 21 days of age resulted in reduced daily food intake and retarded body weight gain. Furthermore, young rats with VMH lesions failed to respond to 24 hr of food deprivation or limited food access. These data suggest an important role for the VMH in the long-term regulation of feeding in young rats.