Hisashi Yokoi

Intracerebroventricular injection of adrenomedullin inhibits vasopressin release in conscious rats

The hypotensive peptide, adrenomedullin (AM), was first isolated from the tissue of human pheochromocytoma. Recently, AM-immunoreactivities have been found in the central nervous system, including the supraoptic and the paraventricular nuclei. In this study, the effect of centrally administered AM on arginine vasopressin (AVP) release was investigated in conscious rats. Intracerebroventricular injection of AM (1.0 microgram/rat) partially but significantly attenuated the plasma AVP increase induced by hyperosmolality (intraperitoneal (i.p.) injection of hypertonic saline (600 mosmol/kg)) at 30 min after the injection. It also significantly attenuated the plasma AVP increase induced by hypovolemia (i.p. injection of polyethylene glycol) at 30 min after the injection. These results suggest that central AM might play an inhibitory role in both osmo- and baro-regulation of plasma AVP.

Central administration of urocortin inhibits vasopressin release in conscious rats.

Urocortin (UCN) is a new mammalian member of the corticotropin releasing factor (CRF) family and supposed to be an endogenous ligand for type 2 CRF receptors. Previous studies have revealed that UCN mRNA exists in the supraoptic nucleus (SON), and that water deprivation increases UCN immunoreactivity in SON. In this study, we examined the effect of centrally-administered UCN on arginine vasopressin (AVP) release in conscious rats. Intracerebroventricular (i.c.v.) injection of UCN (5.0 microg/rat) significantly attenuated AVP release induced by hyperosmolality at 30 min after the injection. In contrast, CRF (5.0 microg/rat) injected i.c.v. had no significant effect on AVP release. These results suggest that central UCN play an inhibitory role in osmoregulation of AVP release.

Age-associated decrease in response of rat aquaporin-2 gene expression to dehydration.

It is well known that urine-concentrating ability decreases with aging and that this decreasing ability results from a reduced sensitivity of the renal collecting duct to arginine vasopressin (AVP). AVP regulates the water channel (aquaporin-2:AQP2) through V2 receptors and increases the water permeability of the collecting duct. To elucidate the mechanism of change with aging in urine-concentrating ability, we investigated the change of V2 receptor and AQP2 mRNA expression in young (8-week-old) and older (7-month-old) rats after dehydration for 2 days. After dehydration, plasma AVP levels in older rats were higher than young rats, and urinary osmolality in older rats was lower than young rats. By Northern blot analysis, there was no significant difference between young and older rats in both V2 receptor and AQP2 mRNA expression before dehydration. After dehydration, V2 receptor mRNA expression in young and older rats decreased in the same degree, suggesting the downregulation of V2 receptors may occur in the mRNA level. Northern blot analysis and in situ hybridization histochemistry showed that AQP2 mRNA expression increased and the increased expression in older rats was less than in young rats. The present study suggests the reduced response of AQP2 mRNA expression to dehydration, observed in 7-month-old rats, might be partially responsible for the decreasing urine-concentrating ability with aging.

Acute bilateral deafness with nephritis: A human temporal bone study†

Temporal bone pathology is described in a 37‐year‐old man who had acute, bilateral, profound sensorineural hearing loss without improvement 4 months before death. The patient had suffered from low complement nephritis, for which he had received prednisolone therapy. Autopsy revealed malignant lymphoma with non‐Hodgkins type, membranous proliferative glomerulonephritis and necrotizing vasculitis of middle and small arteries. In the temporal bone study, pathological changes were limited to the cochlear region. The vestibular structure showed no detectable pathological changes. The changes included total absence of the organ of Corti, atrophy and/or disappearance of the stria vascularis in the upper turns, collapse of Reissners membrane in the middle turn, and new bone formation in the apical turn.

Antiserum Against Neuropeptide FF Augments Vasopressin Release in Conscious Rats

We previously reported that centrally administered neuropeptide FF (NPFF) inhibited arginine vasopressin (AVP) release. In this study, immunoneutralization of central NPFF was performed to evaluate the role of endogenous NPFF in the regulation of AVP release. Intracerebroventricular (ICV) injection of antiserum against NPFF (Anti-NPFF) significantly augmented the plasma AVP increase induced by hyperosmolality [intraperitoneal injection of hypertonic saline (600 mOsm/kg, 2% BW)] at 60 min after ICV injection compared with normal rabbit serum (NRS) (NRS: 4.20+/-0.30 pg/ml, Anti-NPFF: 5.83+/-0.46 pg/ml, p < 0.01). Anti-NPFF did not cause significant change in plasma osmolality, plasma volume or arterial blood pressure. This evidence indicates that endogenous NPFF might be physiologically involved in osmoregulation of the plasma AVP level through its inhibitory action.

A Scanning Electron Microscopic Study of the Guinea Pig Cochlear Aqueduct

The cochlear aqueduct is the duct that connects the perilymphatic space of the scala tympani with the subarachnoid space. However, its functions are not yet fully elucidated. In the present study on t

Morphological Changes in the Cochlear Aqueduct Following Herpes Simplex Virus Inoculation into the Subarachnoid Space

Type 1 herpes simplex virus (HSV-1) was inoculated into the subarachnoid space through the cisterna magna of guinea pigs to study morphological changes of the inner ear and the ability of the cochlear aqueduct to protect the inner ear. Although most of the animals developed clinical manifestations of meningoencephalitis within a few days after inoculation, Preyers reflex remained intact. Scanning electron microscopy revealed some significant changes in the cochlear aqueduct. Lymphocytes and macrophages were predominant, with narrowing of reticular tissue spaces caused by the swelling of the periotic duct tissue. The cribriform structure of the internal orifice of the cochlear aqueduct appeared to be completely obstructed, whereas it was normal in the presence of bacterial infection as previously reported (1). The morphological changes were confined to the cochlear aqueduct.

Defense Mechanism of the Cochlear Aqueduct against Infection

Guinea pigs were used in this study. Physiological saline, india ink, and Staphylococcus aureus were injected into the cisterna magna, and S. aureus was also injected into the scala tympani. Changes in the microstructure of the cochlear aqueduct were observed by light microscopy and also by scanning electron microscopy, mainly by means of fracture preparations. From these experimental results, it could be confirmed that the periotic duct tissue of the cochlear aqueduct reacted especially to bacterial infection.

Primary Malignant Melanoma Arising from the Base of the Tongue

A rare case of malignant melanoma of the base of the tongue in a 65-year-old Japanese woman is described. The primary and metastatic tumors were treated by surgery, chemohormone and immunotherapy. There was no recurrence for 5 years after the initial diagnosis. Electron microscopy suggested that the melanosomes of the melanoma cells in the cervical lymph nodes were less mature than those in the primary melanoma cells; melanosome immaturity was consistent with a more aggressive quality.

Blast injury to sensory hairs: A study in the guinea pig using scanning electron microscopy

SummaryGuinea pigs were exposed to a blast (maximum 1.0 kg/cm2) of nitrous gas for 0.2 s through the external auditory canal. Then, they were either killed immediately, 1 day, 3 days, 1 week, 2 weeks, or 4 weeks after exposure to the blast. The morphological changes of the cochlear sensory hairs were examined by means of a scanning electron microscope. Changes in the sensory hairs of the animals exposed to the blast for 1 s were examined in the same manner. The results of these experiments show that sensory hairs of the basal and the second turns were damaged more markedly than those of the third and subsequent turns. Outer sensory hairs were damaged more than inner ones.