Jinzo Yamada

Spinocerebellar Tract Neurons with Axons Passing through the Inferior or Superior Cerebellar Peduncles

Using the retrograde horseradish peroxidase (HRP) method, we determined whether axons of the spinocerebellar tract (SCT) neurons pass through the superior (SCP) or the inferior (ICP) cerebellar peduncle in rats. Following bilateral section of either the SCPs or the ICPs, HRP was injected into the cerebellar anterior lobe and lobule VI, and the resulting labeled neurons were quantitatively examined throughout the length of the spinal cord. Almost all SCT neurons in the central cervical nucleus, Clarkes column and lamina VII of the third cervical (C3) to third thoracic (T3) segments and the T11 to fifth lumbar (L5) segments, and the majority of SCT neurons in the ventrolateral part of the anterior horn of the L6 to caudal (Ca) segments and laminae V of the C8-L5 segments and VII of the L6-Ca segments project their axons through the ICPs. The majority of spinal border cells (T11-L5) and a large number of SCT neurons in lamina VII of the C3-T3, T11-L5 and L6-Ca segments project their axons through the SCPs. A nearly equal number of SCT neurons in lamina VIII (C1-L6) send axons through the SCPs or the ICPs. The proportion of SCT neurons projecting via the SCPs versus those projecting via the ICPs was approximately 1:5.

Electrical Stimulation of Hypothalamic Periventricular Nucleus Is Followed by a Large Rebound Secretion of Growth Hormone in Unanesthetized Rats

The effect of electrical stimulation of the hypothalamic periventricular nucleus (PVN) on plasma GH profile was studied in unanesthetized female Wistar rats. A bipolar concentric electrode was implanted into the PVN, hypothalamic ventromedial nucleus (VMH), or intervening area between the PVN and VMH. Serial blood specimens were collected from an indwelling right atrial cannula. Plasma GH levels were reduced significantly during electrical stimulation of PVN, and a large rise of plasma GH levels followed after cessation of stimulation. An identical plasma GH profile was observed in response to the repeated stimulation. This rebound secretion of GH was completely inhibited by the administration of rat GRF antiserum. The effect of electrical stimulation of VMH on plasma GH levels was similar to that of PVN stimulation. However, the stimulation of hypothalamic area intervening between PVN and VMH was not followed by a surge of GH secretion. Since a continuous exposure of somatotrophs to GRF even in a concurrent presence of somatostatin (SS) is known to induce attenuation of the GH response to GRF through receptor effect, the results suggest that the release of endogenous GRF is augmented following the cessation of electrical stimulation of neurons providing hypophysiotropic SS.

Axon collaterals of spinocerebellar fibers terminate in the parabrachial nucleus of the rat

When horseradish peroxidase (HRP) or wheat germ agglutinin conjugated with HRP was injected into the anterior cerebellar vermis or the spinal cord segments in the rat, terminal labeling was seen in the small round area within the dorsal part of the middle one-third of the parabrachial nucleus (PB). When the tracer was injected into the round PB area, many neuronal cell bodies were labeled in the spinal cord segments, but none in the cerebellum. Thus, the terminal labeling in the round PB area was assumed to be that of axon collaterals of spinocerebellar fibers.

Nerve stimulation does not necessarily enhance retrograde HRP labeling of rat motoneuron

The retrograde horseradish peroxidase (HRP) labeling of medial gastrocnemius (MG) motoneurons was not enhanced by electrical stimulation of the sciatic nerve after HRP injection into the MG muscle of the rat. When pulse trains with short intermissions were applied immediately after the HRP injection, the number of labeled MG motoneurons on the stimulated side was even smaller than that on the control side.

Effect of intermittent infusions of somatostatin on growth hormone secretion in unrestrained male rats with hypothalamic deafferentation.

The effect of intermittent infusions of somatostatin (SS) on growth hormone (GH) secretion was studied in unrestrained adult male rats deprived largely of SS influence on the medial basal hypothalamus by anterolateral deafferentation (AL-cut). In addition, the influence of hypothalamic surgery on the plasma GH response to beta-endorphin (beta-END) was observed. In sham-operated rats, high-amplitude GH pulses separated by low baseline levels occurred at 185 min intervals. In rats with AL-cut, GH pulses were difficult to identify upon visual appraisal and baseline plasma GH levels became significantly higher than those of sham-operated rats. When AL-cut was performed unilaterally (half-AL-cut), low amplitude GH pulses separated by elevated baseline GH levels occurred at frequent intervals. The amount of GH secreted during 6 h was significantly reduced in rats with AL-cut or half-AL-cut as compared to that of sham-operated rats. The plasma GH response to intracerebroventricular injection of beta-END (4 micrograms) was abolished in AL-cut rats, and the response was significantly reduced in half-AL-cut rats as compared to that of sham-operated rats. When AL-cut rats were subjected to repeated infusions of SS (30 micrograms/kg b. wt./h, 150 min) separated by 30 min control periods, a large rebound of GH secretion was observed after removal and the amount of GH secreted during 6 h became comparable to that of sham-operated rats. The results suggest that SS plays important roles in the dynamic secretion of GH.

Cells of origin of spinopontine fibers in the rat

When wheat germ agglutinin-horseradish peroxidase conjugate was injected into the caudal part of the medial, lateral, ventral and peduncular pontine nuclei in the rat, retrogradely labeled spinal neurons were found contralaterally in the intermediate basilar nucleus (IBN) in the upper two cervical cord segments, and in laminae VI and VII in the lumbar cord segments. The IBN appeared to send fibers mainly to the caudomedial part of the pontine nuclei, while laminae VI and VII of the lumbar cord segments of the caudolateral part of the pontine nuclei.

Effect of hypthalamic ventromedial lesions on plasma growth hormone response to growth hormone-releasing factor in rats

The effect of ventromedial-arcuate (VMH-ARC) nuclei lesions on plasma growth hormone (GH) response to human growth hormone-releasing factor (GRF, 1 microgram/kg b.wt., i.v.) was studied in conscious rats after they had received chlorpromazine (CPZ) or CPZ plus antiserum against somatostatin (ASS). When rats were pretreated with CPZ alone, there was no difference in basal plasma GH level between VMH-ARC lesioned rats and controls. The magnitude of plasma GH response to GRF in 5 out of 6 VMH-ARC lesioned rats exceeded that of controls. When the same observation was repeated using the same rats after they had received ASS and CPZ, basal plasma GH levels of controls were significantly higher than those of VMH-ARC lesioned rats, and the magnitude of the plasma GH response to GRF was augmented in both groups of rats. The plasma GH response to GRF was comparable between two groups, though the peak plasma GH response to GRF was slightly but significantly lower in VMH-ARC lesioned rats as compared to controls. Pituitary GH content was reduced significantly in VMH-ARC lesioned rats as compared to controls. The results demonstrate that the pituitary responsiveness to GRF does not appear to be altered significantly in rats bearing bilateral VMH-ARC lesions. In addition, the placement of electrolytic lesions in VMH-ARC regions causes reduced SS secretion into the hypophyseal portal vessels and leads to an augmentation of plasma GH response to GRF.

Lateral reticular nucleus neurons sending their axons to the contralateral inferior cerebellar peduncle. A horseradish peroxidase study in the rat.

The lateral reticular nucleus of the medulla oblongata (LRN) in the rat was observed after injecting horseradish peroxidase (HRP) bilaterally into the anterior lobe of the cerebellum; the inferior cerebellar peduncle had been cut unilaterally prior to the HRP injections. HRP-labeled neurons were seen bilaterally in the LRN; 89% in the contralateral, and 11% in the side ipsilateral to the pedunculotomy. The labeled neurons in the LRN ipsilateral to the pedunculotomy were assumed to send their axons to the anterior lobe of the cerebellum via the controlateral inferior cerebellar peduncle. Of these neurons, 60, 11 and 29% were distributed in the magnocellular, subtrigeminal and parvicellular divisions of the LRN, respectively.