Yukitomo Morita

Entladungsmuster pinealer Neurone der Regenbogenforelle (Salmo irideus) bei Belichtung des Zwischenhirns

SummaryMaintained activity in the absence of light was recorded from the exposed pineal organ (Epiphysis cerebri) of the rainbow trout (Salmo irideus) by means of microelectrodes. Inhibitory responses to light were obtained from pineal ganglion cells (single unit responses) as well as from the pineal tract (mass responses) of specimens deprived of their lateral eyes. The most sensitive units responded to white light of 1 sec duration at 3 · 10−5 lm/m2 (mass responses) and with 7 · 10−5 lm/m2 (single units). A still lower light threshold of 2,5 · 10−6 lm/m2 was found when the lowermost steady illumination was determined which raised the dark threshold. During exposure to steady illumination the maintained activity decreases almost linearly with the logarithm of light intensity. A decrease to about 50 per cent was obtained if the illumination was increased to 2.500 lm/m2. The distribution of spectral sensitivity of the inhibitory effect of light varied among different pineal neurons. Curves exhibiting maxima between 500 and 533 mμ were seen. No Purkinje shift was observed during light adaptation. In some experiments inhibitory effects to short wavelengths and excitatory responses to long wavelengths were recorded (chromatic responses).ZusammenfassungMikroelektrodenableitung vom freigelegten Pinealorgan der Regenbogenforelle (Ableitung von einzelnen Ganglienzellen der Epiphysis cerebri bzw. Massenentladung von Nervenfasern des Tr. pinealis) zeigt eine spontane Impulsaktivität, die durch Belichtung gehemmt wird und auch nach Entfernung der Lateralaugen bestehen bleibt. In der Regel ist die Antwort unabhängig von der Wellenlänge des Reizlichts (achromatische Antwort), doch wurden in einigen Versuchen auch chromatische Antworten beobachtet. Die für eine Reihe von Pinealorganen bei Salmo irideus bestimmte absolute (Hemmungs-)Schwelle liegt bei 3 · 10−5 lm/m2 (Massenentladung) und bei 7 · 10−5 lm/m2 (Einzelneurone) gegenüber Lichtreizen von 1 sec Dauer, und bei 2,5 · 10−6 lm/m2 gegenüber Dauerlicht. Dauerlicht vermindert die Frequenz der Spontanaktivität mit einem Halbwert bei 2500 lm/m2. Eine Purkinje-Verschiebung wird nicht beobachtet. Die Maxima der Spektralsensitivität der einzelnen Pinealneurone variieren zwischen 500 und 533 mμ.

Daily rhythm of serum melatonin in patients with dementia of the degenerate type

The daily rhythm in serum melatonin levels was measured in patients with dementia of the degenerate type (Alzheimers disease, Picks disease and senile dementia of the Alzheimer type) by radioimmunoassay. Thirteen patients (age: 69.0 +/- 8.0 years, mean +/- S.D.) were studied. All patients were hospitalized at the time of the study and had a history of sleep-wake disturbances, nocturnal wandering and/or delirium. We also studied 13 age-matched healthy control subjects (control group 1), ten young adults (control group 2), and nine hospitalized patients without dementia (control group 3). Two subjects in the control groups showed no measurable changes in melatonin level throughout the day, while the other 30 control subjects exhibited a clear daily rhythm with the peak concentration occurring during the night. On the other hand, four out of the 13 patients with dementia did not show any melatonin rhythm. Two of the demented patients who did not exhibit melatonin rhythm displayed clinical symptoms of rhythm disorders. One out of the nine patients with melatonin rhythm presented with clinical symptoms, such as delirium and sleep-wake disturbance. Our results suggest that the probability of absent melatonin rhythm is higher in demented patients compared with subjects without dementia. However, a lack of melatonin rhythm is not always associated with symptomatic rhythm disorders. Since the melatonin rhythm reflects that of the suprachiasmatic nucleus, it follows that the SCN function of the patients having a history of rhythm disorders was not always severely damaged.

Daily rhythm of serum melatonin levels and effect of light exposure in patients with dementia of the Alzheimer’s type

BACKGROUND Several studies have suggested that patients with dementia experience a deterioration of biological rhythms. We investigated the daily profile of serum melatonin levels in patients with dementia of the Alzheimers type (AD), since daily melatonin rhythm is thought to reflect the functioning of the biological clock. METHODS Seventeen inpatients with AD, 10 psychiatric inpatients without dementia, and 11 elderly healthy volunteers participated in this study. Serum melatonin was assessed every 3 hours by radioimmunoassay. RESULTS A daily fluctuation of melatonin levels with a significant nocturnal increase was observed in all three subject groups. However, both the AD patients and psychiatric patients without dementia showed significantly higher levels of melatonin in the daytime compared with the healthy subjects. When the effect of bright light exposure on melatonin secretion was investigated in six AD patients and five psychiatric patients without dementia, the daytime levels were markedly decreased in the patients without dementia, while no change was observed in the AD patients. CONCLUSIONS The high levels of melatonin in the daytime associated with a lack of response to light exposure in AD patients may be due to the neurodegenerative process of this disease.

Photoreception in pineal organs of larval and adult lampreys, Lampetra japonica

SummaryA comparative study of the larval and adult pineal organs, which are sensitive to incident light, was carried out in the river lampreyLampetra japonica, using intracellular recording from the pineal photoreceptors.1.The tissue overlying the larval pineal organ is transparent, whereas that over the adult pineal is translucent. The optical density of this oval pineal window in the adult lamprey was 1.2.2.In order to elucidate the early development of the larval pineal, the ratior of the diameter (μm) of the pineal to the body-length (cm) was measured. The value ofr was 62.5 in a small larva of 2.8 cm, 29.7 in a larger one of 14.3 cm, and 9.3 in an adult of 54 cm body-length.3.The intracellular response to light of the larval pineal was a hyperpolarization, showing fundamentally the same pattern as that of the adult pineal. It was possible to record a typical response even from the pineal of the smallest larva, 2.8 cm in body length, used in this study.4.The intensity-amplitude relationship was analysed after Naka-Rushtons hyperbolic equation. The value ofσ of isolated larval pineals was 0.88 log unit higher than that of adults. The value ofn was larger in larvae, suggesting a sensitive reaction to changing photic stimulus.5.The spectral sensitivity was compared. The peak was at 505 nm in the larva, but 525 nm in the adult. A change of visual pigment in the pineal during metamorphosis is suggested.

Pineal-dependent locomotor activity of lamprey, Lampetra japonica, measured in relation to LD cycle and circadian rhythmicity

SummaryLocomotor activity of the river lamprey, Lampetra japonica, was investigated under a light-dark (LD 12∶12) cycle and under continuous dark conditions. Intact lampreys were entrained to the light:dark cycle. They were active mainly in the early half of the dark period and inactive in light period. The light:dark entrainment continued in 72.7% of lampreys after the removal of bilateral eyes, but additional pinealectomy made the entrainment disappear in all lampreys. When lampreys were pinealectomized with their eyes intact, light: dark entrainment was abolished in most cases. The results indicate that the pineal organ of the lamprey is a photoreceptive organ responsible for synchronizing locomotor activity to LD cycle. Under continuous dark conditions, the locomotor activity began to free-run with a period of 21.3 ± 0.9 h (mean ± SD, n = 53). This circadian rhythmicity was not affected by the removal of lateral eyes but was abolished by pinealectomy. The pineal organ appears to function as an oscillator, or as one of the oscillators, for the circadian locomotor rhythm of lampreys.

Presence of retina-specific proteins in the lamprey pineal complex.

The pineal complex of river lamprey reacted with the antisera raised against retina specific proteins including bovine opsin, chick visinin and frog light-sensitive cyclic GMP phosphodiesterase (PDE). Immunoreactive materials stained with anti-opsin were evenly located at the outer segment of photoreceptor cells in the pineal organ and also found in the parapineal organ. Although anti-visinin stained the pineal and parapineal photoreceptor cells, the immunopositive photoreceptor cells were observed only at the lateral portion and not at the medial portion of the pineal organ. No immunoreactive materials were found in the pineal complex by the anti-PDE, whereas the anti-PDE reacted with photoreceptor cells of the retinal tissue. The data suggest that the pineal and parapineal retinas of lamprey contain opsin- and visinin-like proteins with different distribution in their photoreceptor cell layer as found in the lamprey retinal tissue.

Melatonin Receptors in the Spinal Cord

The pineal hormone, melatonin, plays an important role in the regulation of diurnal and seasonal rhythms in animals. In addition to the well established actions on the brain, the possibility of a direct melatonin action on the spinal cord has to be considered. In our laboratory, we have obtained data suggesting that melatonin receptors are present in the spinal cords of birds and mammals. Using radioreceptor binding and quantitative autoradiography assays with 2-[125I]iodomelatonin as the specific melatonin agonist, melatonin binding sites have been demonstrated in the rabbit and chicken spinal cords. These sites are saturable, reversible, specific, guanosine nucleotide-sensitive, of picomolar affinity and femtomolar density. The linearity of Scatchard plots of saturation data and the unity of Hill coefficients indicate that a single class of melatonin binding sites is present in the spinal cord membranes studied. The picomolar affinity of these sites is in line with the circulating levels of melatonin in these animals suggesting that these sites are physiologically relevant. Autoradiography studies in the rabbit spinal cord show that melatonin binding sites are localized in the central gray substance (lamina X). In the chicken spinal cord, these binding sites are localized in dorsal gray horns (laminae I-V) and lamina X. As lamina X and laminae I-II have similar functions, melatonin may have comparable roles in the chicken and rabbit spinal cords. Moreover, in the chicken spinal cord, the density of 2-[125I]iodomelatonin binding in the lumbar segment was significantly higher than those of the cervical and thoracic segments. The densities of these binding sites changed with environmental manipulations. When chickens were adapted to a 12L/12D photoperiod and sacrificed at mid-light and mid-dark, there was a significant diurnal variation in the density (maximum number of binding sites; Bmax) of melatonin binding sites in the spinal cord. After constant light treatment or pinealectomy, the Bmax of melatonin receptors in the chicken spinal cord increased significantly in the subjective mid-dark period. Moreover, there was an age-related decrease in the 2-[125I]iodomelatonin binding to the chicken spinal cord. Our results suggest that melatonin receptors in the chicken spinal cord are regulated by environmental lighting and change with development. These receptors may play an important role in the chronobiology of spinal cord function. The biological responses of melatonin on spinal cords have also been demonstrated in vitro. Melatonin decreased the forskolin-stimulated cAMP production in the chicken spinal cord explant. Preincubation with pertussis toxin blocked the melatonin effect. Our results suggest that melatonin receptors in the chicken spinal cord are linked to the adenylate cyclase via a pertussis toxin-sensitive G protein and that melatonin binding sites in spinal cords are melatonin receptors with biological functions. These receptors may be involved in the regulation of spinal cord functions related to sensory transmission, visceral reflexes and autonomic activities.

Extra- und intracelluläre Abteilungen einzelner Elemente des lichtempfindlichen Zwischenhirns anurer Amphibien

ZusammenfassungAn zwölf Arten verschiedener Anuren-Familien (Bufo, Discoglossus, Hyla, Pelobates, Rana) wird ohne Ausnahme eine direkte Lichtempfindlichkeit des Zwischenhirns festgestellt, die nach Entfernung der lateralen Augen und — soweit vorhanden — des Stirnorgans fortbesteht.Die Aktivität einzelner Zellen wird extra- und intracellulär untersucht. Histologische Kontrolle der extracellulär gelegenen Ableitungspunkte zeigt die Elektrodenspitze in der Nähe von Ganglienzellen des Epiphysenschlauches bzw. Nervenfasern des Tractus pinealis. Belichtung führt zu einer Hemmung der Spontanaktivität, bei schwachen Reizen für die Dauer des Reizes, bei starken Reizen bis zu 1 min nach Ende der Belichtung. In einem mittleren Leuchtdichtebereich kommt es außerdem zu off-Entladungen. Helladaptation verkürzt die Dauer der den Reiz überdauernden Hemmung und begünstigt die off-Entladungen.Neben Zellen mit achromatischer Antwort zeigen bei Rana catesbyana zahlreiche Neurone des Epiphysenschlauchs eine chromatische Antwort (Hemmung der Impulsaktivität durch unltraviolette Strahlung, Erregung durch blaugrünes und längerwelliges Licht).Das intracellulär abgeleitete Membranpotential beträgt bis 40 mV. Ihm sind spontane Spike-Entladungen bis zu 20 mV und langsame Belichtungspotentiale bis zu 5 mV superponiert. Die Spike-Aktivität wird durch Belichtung gehemmt, durch Verdunklung verstärkt (off-Entladungen). Die langsamen Potentiale zeigen bei hohem Membranpotential auf Belichtung eine kurzdauernde Hyperpolarisation (1 mV), gefolgt von einer die Reizdauer über anhaltenden Depolarisation (3–5 mV). Nach Belichtungsende tritt, gleichzeitig mit den off-Entladungen, eine plötzliche Repolarisation ein, die von einer Hyperpolarisation gefolgt wird.

Intracellular responses from UV-sensitive cells in the photosensory pineal organ

A new type of cell having high sensitivity in the ultraviolet (UV) range was found in the pineal organ of the river lamprey. Lampetra japonica, by intracellular recordings. This UV-sensitive cell responded to light with graded hyperpolarizations and had the maximum sensitivity at 380 nm. The response of the cell was much slower than that of the usual pineal photoreceptor with the peak spectral sensitivity at 525 nm. Intracellular injection of Lucifer yellow revealed that the cell consists of 3 parts, corresponding to an outer segment, an inner segment and a terminal of photoreceptor cell. The apical part of the cell protruded into the lumen and the inner segment situated in the layer of photoreceptor cells. It was concluded that this UV-sensitive cell was a UV-specific receptor cell.

Photoreceptor cells and neural elements with long axonal processes in the pineal organ of the lamprey, Lampetra japonica, identified by use of the horseradish peroxidase method

SummaryHorseradish peroxidase (HRP) was applied to the transected end of the pineal tract of the lamprey, Lampetra japonica. Distinct reaction products of HRP were observed in 2 types of cell other than ganglion cells. The first type of cell protrudes a knob-like process into the pineal lumen. This type of cell was clearly identified by electron microscopy as a photoreceptor cell; its outer segment was connected to the ellipsoid through a sensory cilium. The other type of cell was located among photoreceptor and supporting cells. The processes of these cells were thin and slender, and they obviously did not represent photoreceptor, supporting, or conventional ganglion cells. The present results indicate that, in the lamprey, some of the photoreceptor cells of the pineal organ project their axon-like processes toward the posterior commissure, but that there is also another type of cell displaying long axonal projections. HRP-containing cells were distributed randomly over the pineal organ and were occasionally also observed in the parapineal organ.