Masae Hosogai

Projection of respiratory neurons in rat medullary raphé nuclei to the phrenic nucleus

The present study was undertaken to investigate firing patterns, locations, and projections to the phrenic motor nucleus of respiratory neurons in medullary raphe nuclei of rat. Experiments were performed on spontaneously breathing rats anesthetized with sodium pentobarbital. Extracellular spikes of single respiratory neurons were explored in midline medullary tegmentum. A total of 107 respiratory neurons was recorded in the raphe magnus, obscurus and pallidus. They were classified into the following eight types based on the relation of their firing patterns to the phase of respiration: (1) Inspiratory (I) throughout (n = 42); (2) I-late (n = 9); (3) I-decrementing (n = 1); (4) Pre-I (n = 2); (5) I-frequency modulated (n = 13); (6) Post-I (n = 12); (7) Expiratory (E) (n = 23) and (8) E-frequency modulated neurons (n = 5). Twenty of the 45 respiratory neurons examined were antidromically activated from the phrenic motor nucleus at the C4 spinal level with thresholds of 2-58 microA and latencies of 0.4-2.4 ms. Among the 20 neurons, 11 neurons were I-throughout, five were I-frequency modulated and four were E neurons. These results suggest that there is a population of neurons in the medullary raphe nuclei that projects to the phrenic motor nucleus at the C4 spinal level. It is possible that this projection may, in part, mediate the control of the diaphragmatic muscle motor neurons located in the C4 segments.

Ascending projections of posterior canal-activated excitatory and inhibitory secondary vestibular neurons to the mesodiencephalon in cats

The axonal projections of 62 posterior canal (PC)-activated excitatory and inhibitory secondary vestibular neurons were studied electrophysiologically in cats. PC-related neurons were identified by monosynaptic activation elicited by electrical stimulation of the vestibular nerve and activation following nose-up rotation of the animals head. Single excitatory and inhibitory neurons were identified by antidromic activation following electrical stimulation of the contralateral and ipsilateral medial longitudinal fasciculus, respectively. The oculomotor projections of identified neurons were confirmed with a spike-triggered averaging technique. The axonal projections of the identified neurons were then studied by systematic, antidromic stimulation of the mesodiencephalon. Excitatory neurons showed two main types of axonal projections. In one type, axonal branches were issued to the interstitial nucleus of Cajal, central gray, and thalamus including the ventral posterolateral, ventral posteromedial, ventral lateral, ventral medial, centromedian, central lateral, lateral posterior, and ventral lateral geniculate nuclei. The other type was more frequently observed, giving off axon collaterals to the above-mentioned regions and to Forels field H as well. Inhibitory neurons issued axonal branches to limited areas which included the central gray, interstitial nucleus of Cajal, its adjacent reticular formation and caudalmost part of Forels field H, but not the rostral part of the Forels field H and the thalamus. These results suggest that PC-related excitatory neurons participate in the genesis of vertical eye movements and in the perception of the vestibular sensation, and that PC-related inhibitory neurons seem to take part only in the genesis of vertical eye movements.

Inspiratory neurons with decrementing firing pattern in raphe nuclei of feline medulla

Extracellular spikes of single inspiratory (I) neurons with decrementing firing pattern were recorded in the medullary raphe nuclei in decerebrated or Nembutal anesthetized cats. A total of 23 neurons with decrementing firing patterns during the I phase were recorded in the raphe obscurus and pallidus at the levels of 2.0-4.0 mm rostral to the obex. The respiratory neurons fired in the I phase during a brief stop of the ventilator, indicating that their respiratory-related activities were central in origin. The effect of electrical stimulation of the recording site of the respiratory neuron on diaphragm EMG was examined: both the diaphragm EMG activity and the respiratory frequency were increased. None of six neurons tested for projections to the cervical spinal cord was antidromically activated by electrical stimulation. The present results suggest that cat I-decrementing neurons in the medullary raphe nuclei receive inputs from the central respiratory rhythm generator and may modify the respiratory activity of supraspinal neural structures.

Posterior canal-activated vestibulocortical pathways in cats

This study was undertaken to investigate vestibulothalamocortical pathways in anesthetized cats. Synaptic connections of posterior canal-activated excitatory vestibuloocular relay (PC) neurons to thalamic neurons were examined by a spike-triggered averaging technique. The averaged potentials evoked in the ventrobasal complex of the thalamus revealed a negative wave with latencies from 0.8 to 1.5 ms. Thirty-six thalamic neurons, which were activated by nose-up head rotation and by contralateral labyrinth stimulation, were mainly located in the ventrobasal complex. Thirteen of these neurons were antidromically activated from the anterior suprasylvian sulcus or postcruciate dimple of the cortex. These results suggest that the PC neurons participate, at least in part, in the vestibulocortical pathways contributing to spatial orientation.

Posterior Canal-Activated Excitatory Vestibuloocular Relay Neurons Participate in the Vestibulocortical Pathways in Cats

We have previously reported that axon collaterals of posterior canal-activated excitatory vestibular (PC) neurons project to the contralateral oculomotor nucleus, and rostrally to the thalamus. To elucidate the vestibulothalamocortical pathways we investigated the synaptic connections of the PC neurons with the thalamic neurons by post-spike averaging of compound potentials triggered by spikes of the PC neuron in anesthetized cats. The averaged field potential evoked in the ventrobasal complex (VBC) revealed a spike followed by a negative wave. Latencies of the wave ranged from 0.8 to 1.5 ms. Next, we examined the location and axonal projection of 36 thalamic neurons which were activated by nose-up head rotation and by contralateral labyrinth stimulation. Most of them were located in the VBC and some in the medial geniculate body. Thirteen of the 36 neurons were antidromically activated from the anterior suprasylvian sulcus or postcruciate dimple of the cortex. These results suggest that the PC neurons participate, at least in part, in the vestibulocortical pathways contributing to spatial orientation.

Properties of respiratory neurons in medullary raphe nuclei of rats

The external anal sphincter (EAS) is the orbicular striated muscles which is located in the distal colon and innervated by pudendal nerve, and act as a closure muscle of the anal canal. Several physiological studies reported that EAS is normally in a state of contraction and completely relax during defecation. It is known that activities of EAS muscle disappear by an increase in the colonic pressure in spinal animals. This reflex appeared that the afferent impulses from the colon receptors initiate the inhibition of the tonic activity of EAS, and considered this reflex is one of the basis of defecation. This reflex, however, was recorded only in spinal animals and functional significance of this reflex in a normal condition is still unclear. We recorded and analyzed the nervous activity during defecation in the condition of the intact braimstemspinal cord. Experiments were performed on adult cats anesthetized with urethane-chloralose. The pudendal nerve divides into three branches: the EAS nerve of the external anal sphincter, the perineal nerve of the pelvic floor muscles, and the dorsal nerve of the penis of the external urethral sphincter muscle. The bipolar cuff electrodes were put in the EAS nerve and the perineal nerve for recording nerve dicharges. The defecation reflex was evoked by increasing the pressure of the balloon in the rectum, and the pressure in the rectum was recorded. After the experiment, the pressure in the rectum and the activity of each nerve discharge were analyzed. It was clear that the discharges of the EAS nerve and the perineal nerve increased in proportion to the pressure of the rectum, and maintain a constant activity level though the discharge decreased during the defecation reflex. Our data suggest that the EAS and the pelvic floor muscles do not slack completely but act to some degree and adjust the defecation reflex. Research fund: KAKENHI (22500482).

Evidence for central chemoreception of medullary raphe respiratory neurons

To drive rapid thermoregulatory responses to maintain body temperature during changes in ambient temperature, thermal information from the skin ascends to the preoptic area (POA), which then sends command signals to peripheral effectors. Here, we show that a population of neurons in the dorsal part of the lateral parabrachial nucleus (LPBd) is activated by skin warming and projects directly to the POA. Mimicking skin warming, activation of rat LPBd neurons inhibited the spontaneous activity of cutaneous vasoconstrictor (CVC) component of the sural sympathetic nerve and increased tail skin temperature–responses consistent with increased body heat dissipation. Inactivation of LPBd neurons or blockade of glutamate receptors in the LPBd eliminated the skin warming-induced inhibition of the spontaneous sural CVC activity. These results indicate that neurons in the LPB mediate the afferent pathway for warm signaling from the skin to the POA that is required to defend body temperature in hot environments.

25. Neuronal properties of medullary raphe nuclei to hypercarbic ventilatory challenge

The auditory event-related potentials were studied in 40 patients with Parkinson’s disease (PD) diagnosed on the basis of UK Parkinson’s disease society brain bank criteria to clarify the possible relationship between cognitive function and response to levodopa. The patients with PD were divided into two groups: good response (=50%) (n = 21, mean age 62 years) and mild response (<50%) (n = 19, mean age 68 years) according to response to levodopa. Significant difference was found in P300 latency between the two groups (P = 0.003), whereas there were no differences in N200, P200 and N100 latencies. No differences were shown in MMSE score, duration of illness and Yahr stage between the two groups although the mean age in the good response group was significantly younger than that in the mild response group (P = 0.04). Present results suggest that levodopa response may be decreased in patients with cognitive impairment shown by prolonged P300 latency.

Origin of respiratory activities in the medullary raphe nuclei of rats

In the isolated brain stem-spinal cord-rib preparation from 0to 3-day-old rats, activities in C4 ventral roots and internal intercostal muscles (IIM) were recorded simultaneously. Rhythmic inspiratory motor activities consistently appeared in C4 ventral roots while there was no expiratory activity in IIM in most preparations under superfusion of modified Krebs solution (24-26’C, equilibrated with 95% 02 and 5% CO2, pH 7.4). When pH of the superfusate was changed from 7.4 to 7.0, the frequency of the C4 inspiratory rhythm was increased and rhythmic motor activities in IIM appeared. In most cases, the rhythmic burst in IIM started just after the cessation of the C4 inspiratory burst, and coincided with the movement of the rib towards caudal direction. These results suggest that the expiratory pattern generating mechanisms are preserved in the in vitro preparation. Strychnine (5-l OuM), a glycine receptor antagonist, changed such alternating motor pattern between C4 ventral root and IIM to a synchronous one indicating that the glycinergic inhibitory system plays an important role in the coordination between inspiratory and expiratory muscles during respiration.

1619 Firing pattern and projection to phrenic nucleus of respiratory neurons in rat medullary raphe nuclei

Axonal projections of pump neurons (P-cells) of the nucleus of the solitary tract (NTS) were studied in Nembutal-anesthetized, paralyzed, and artificially ventilated cats. Extracellular recordings were made from single P-cells, which were orthodromically activated by low-threshold electrical stimulation of the ipsilateral cervical vagus nerve with latencies of 3-5 msec (n=l3) . The P-cells were distributed in the NTS in close proximity to the solitary tract at the level from 1 mm rostra1 to 1 mm caudal to the obex. Antidromic mapping by electrical stimulation of the medulla showed that the P-cells sent their axons along the longitudinal column of the ipsilateral ventrolateral medulla. Fine axonal branches suggestive of projections were found in the respiration-related areas in the vicinity of the retrofacial, ambiguus and retroambigual nuclei. Some of the P-cells had axon collaterals to the contralateral NTS as well. These projection patterns were similarly observed in both P-cells located medially to and those laterally to the solitary tract.