Sei-Ichi Sasaki

Axon branching of medullary expiratory neurons in the lumbar and the sacral spinal cord of the cat

Intraspinal axon collaterals of expiratory (E) neurons in the caudal nucleus retroambigualis extending their desending spinal axons to the lower lumbar (L6-L7) and the sacral (S1-S3) segments were investigated in anesthetized cats. To search for axon collaterals of single E neurons in the lumbar segments, the spinal gray matter was microstimulated from the dorsal to the ventral sites at 100 microns intervals with an intensity of 150-250 microA at 1 mm intervals rostrocaudally along the spinal cord, and effective stimulating sites of antidromic activation in axon collaterals were systematically mapped. In addition, the detailed trajectory of collaterals in the upper lumbar (L1-L3), the middle lumbar (L4-L5), and the sacral (S1-S3) spinal cord was examined by microstimulation at a matrix of points 100-200 microns apart with a maximum stimulus intensity of 50 microA. The trajectory of axon collaterals was reconstructed on the basis of the location of low-threshold foci and the latency of antidromic spikes. Virtually all E neurons examined had 1-7 collaterals at widely separated segments of the lumbar cord. Many axon collaterals were found in the upper lumbar spinal cord as compared to the middle and the lower lumbar spinal cord. The locations of axon collaterals in the upper lumbar spinal cord overlapped with those of abdominal motoneurons. Axon collaterals in the sacral gray matter were found in 3 of 9 E neurons. Axon collaterals were found within the nucleus of Onuf, in the region dorsal to the nucleus of Onuf, and in the intermediate region. The functional significance of the divergent distribution of multiple axon collaterals of single E neurons in different spinal levels of the lumbar and the sacral spinal cord is discussed in relation to the respiratory function of E neurons and other spinal motor activities.

Lower lumbar branching of caudal medullary expiratory neurons of the cat

Extracellular spike activities of medullary expiratory (E) neurons in the caudal ventral respiratory group were recorded in cats anesthetized with sodium pentobarbital. The majority of E neurons extended their axons in the lower lumbar or the sacral segments and distributed collaterals in L5-L7. These results suggest that E neurons are involved not only in respiratory activities but also in the respiratory modulated motor activities of the lower lumbar segments.

Morphology of single primary spindle afferents of the intercostal muscles in the cat

A reconstruction was made of the trajectory of primary spindle afferents from the intercostal muscles in the spinal cord of the cat. Intraaxonal recordings were performed from the primary spindle afferents that were identified by their response to lung inflation and stimulus threshold to activate the action potentials. The afferents were stained by using intraaxonal injection of horseradish peroxidase (HRP). Results were obtained mainly from internal intercostal Ia fibers, which entered the spinal cord and bifurcated into ascending and descending branches. The ascending branches could be traced up to 10.7 mm, and the descending branches could be traced up to 7.3 mm. The ascending branches extended to the next segment. Collaterals ranging from one to six were given off from these branches. The distances between adjacent collaterals ranged from 0.9 mm to 4.7 mm.

The size of motoneurons of the gastrocnemius muscle in rats with diabetes

Alterations in the number and size of motoneurons were studied in the medial gastrocnemius (MG) motor nucleus of diabetic rats (12 or 22 weeks after injection of storeptozotocin) and age-matched controls. Each group contained 6 animals. MG motoneurons were retrogradely labeled by dextran-fluorescein and the number and size of cell bodies were examined. Significantly fewer labeled MG motoneurons were found in the 22-week diabetic rats as compared with age-matched control animals. The mean soma diameter of MG motoneurons was significantly smaller in the 12- and 22-week diabetic animals. Furthermore the soma size for 22-week diabetic animals was smaller than for 12-week diabetic animals. The distribution of average soma diameters in the MG nucleus of control animals was bimodal; cells with larger average diameter were presumed to be alpha-motoneurons and those with smaller diameters were presumed to be gamma. Compared to control animals, the number of smaller MG motoneurons was reduced in 12 week diabetic animals. By 22 weeks, diabetic animals had no small MG motoneurons and the size distribution became unimodal. We conclude that there is a significant decrease in the absolute number and size of MG motoneurons in diabetic rats, with the possibility that the decrease occurred predominantly among the smaller gamma-motoneurons.

Effect of streptozotocin-induced diabetes on motoneurons and muscle spindles in rats

This study examined the alterations in the number and size of motoneurons innervating the medial gastrocnemius (MG) and biceps femoris (BF) motor nuclei in diabetic rats (12 or 22 weeks after injection of streptozotocin) and age-matched controls using retrograde labeling technique. Additionally, morphological alterations of muscle spindles in BF and MG muscles were tested. Significantly fewer labeled MG motoneurons were found in 12- and 22-week diabetic rats as compared with age-matched control animals. In contrast, the number of BF motoneurons was preserved in each group. Compared to control animals, the ratio of larger motoneurons of MG and BF muscle were decreased at 12 weeks, and smaller MG motoneurons were drastically decreased at 22 weeks. Moreover, MG muscle spindle showed reduction of its number and increase of intrafusal muscle fibers; however, BF muscle spindles showed little or no difference from control animals. We conclude that there is an early loss of alpha motoneurons for both MG and BF muscles followed by a later loss of gamma motoneurons in MG muscle in diabetic animals. Moreover, loss of gamma motoneuron might induce atrophy of MG muscle spindles.

Activity patterns of the diaphragm during voluntary movements in awake cats

The diaphragm is an important inspiratory muscle, and is also known to participate in the postural function. However, the activity of the diaphragm during voluntary movements has not been fully investigated in awake animals. In order to investigate the diaphragmatic activity during voluntary movements such as extending or rotating their body, we analyzed the electromyogram (EMG) of the diaphragm and trunk muscles in the cat using a technique for simultaneous recordings of EMG signals and video images. Periodic respiratory discharges occurred in the left and right costal diaphragm when the cat kept still. However, once the cat moved, their periodicity and/or synchrony were sometimes buried by non-respiratory activity. Such non-periodic diaphragmatic activities during voluntary movements are considered as the combination of respiratory activity and non-respiratory activity. Most of the diaphragmatic activities started shortly after the initiation of standing-up movements and occurred after the onset of trunk muscle activities. Those activities were more active compared to the normal respiratory activity. During rotation movements, left and right diaphragmatic activities showed asymmetrical discharge patterns and higher discharges than those during the resting situation. This asymmetrical activity may be caused by taking different lengths of each side of the diaphragm and trunk muscles. During reaching movements, the diaphragmatic activity occurred prior to or with the onset of trunk muscle activities. It is likely that diaphragmatic activities during reaching movements and standing-up movements may have been controlled by some different control mechanisms of the central nervous system. This study will suggest that the diaphragmatic activity is regulated not only by the respiratory center but also by inputs from the center for voluntary movements and/or sensory reflex pathways under the awake condition.

An electrophysiological demonstration of axonal projections of single ventral inspiratory neurons to the phrenic nucleus of the cat

Axonal branching patterns of single inspiratory (I) neurons of the nucleus retroambigualis (NRA) were studied electrophysiologically in cat phrenic nucleus (C4-C6). Experiments were performed on Nembutal anesthetized, artificially ventilated cats, and extracellular spikes of I neurons were recorded. The cervical spinal gray matter was microstimulated from dorsal to ventral sites at 100 microns intervals with an intensity of 150-250 microA using a glass insulated tungsten microelectrode. The stimulations were made at 1 mm intervals rostrocaudally along the spinal cord, and effective stimulating sites of antidromic activation in axonal collaterals were systematically mapped. I neurons examined (n = 8) descending contralaterally distributed multiple collaterals in the phrenic nucleus. These collaterals were found throughout the rostrocaudal phrenic nucleus. An I neuron (n = 1) descending ipsilaterally also distributed collaterals in the ipsilateral phrenic nucleus. Axonal collaterals in the contralateral phrenic nucleus occupied 44.2% of the total length of the cervical spinal cord examined. To determine the detailed trajectory of collaterals in the cervical gray matter, microstimulation was performed in and around the collateral arborizations at the maximum intensity of 50 microA. The descending stem axons could be localized in the lateral funiculus in four I neurons and in the ventral funiculus in one I neuron. I neurons distributed axonal collaterals within the phrenic nucleus. Some part of the collaterals ran to the medial region of the gray matter, re-crossed the midline under the central canal and reached the phrenic nucleus ipsilateral to the I neuron. Re-crossed collaterals arborized in the phrenic nucleus, but did not extend to the gray matter more lateral than the phrenic nucleus. Rostrocaudal extension of the re-crossed collaterals was found to be narrow.

Usefulness of galvanic skin reflex monitor in CT-guided thoracic sympathetic blockade for palmar hyperhidrosis

Computed tomography (CT)-guided thoracic sympathetic blockade with ethanol was performed while monitoring sympathetic nerve activity, with an alternating current (AC) galvanic skin reflex (GSR) monitor, in a patient with palmar hyperhidrosis in whom endoscopic thoracic sympathectomy was impossible because of pleural adhesion. Sweating was suppressed after the thoracic sympathetic blockade, and the monitor showed a significant increase in skin resistance. The effect of sympathetic blockade could be evaluated directly and in real time using a GSR monitor.

Discharge patterns of abdominal and pudendal nerves during induced defecation in anesthetized cats

Defecation is thought to be achieved not only by contraction of the colon, but also by a rise in intra-abdominal pressure. In this study we recorded the discharges of nerves innervating the abdominal (Abd) muscles, diaphragm, external anal sphincter (EAS) muscle and pelvic floor (PF) muscles during induced defecation evoked by distention of an expellable balloon to reveal defecation-related muscle activities. The discharges of the Abd muscle and phrenic (Phr) nerves increased when rectal pressure increased. The discharges of the EAS and PF nerves usually increased in proportion to the pressure in the rectum and maintained a constant activity level, although some trials showed inhibition. The results suggest that activities of these muscles increase the intra-abdominal pressure.

Morphological analysis of the external anal sphincter motor nerve and its motoneurons in the cat

To investigate the spinal neural circuitry that controls the tonus of the external anal sphincter (EAS) in the cat, the size distribution of EAS motor fibers and their motoneurons (MN) was examined, and the presence of muscle spindles in EAS musculature was also tested for. The size distribution of EAS motor fibers was examined after degeneration of afferent fibers and that of their MN was measured, after labeling the cells with horseradish peroxidase. Both distributions were unimodal, thereby demonstrating the difficulty of distinguishing between alpha and potential gamma MN; but muscle spindles were not found in the musculature. Mechanisms underlying the spinally controlled tonus of the EAS remain unclear, including the nature and role of spinal reflexes. It is argued that non-spindle sensory receptors in the anal canal may provide the sensory component of a reflex circuit that contributes to this tonus.