Search PubMed⌕ Search

Biomedical subjects

S T Inouye

Publications and source records attributed to S T Inouye.

35 records · Page 2Linked to original sources
PubMed1993

Substance P-like immunoreactivity in the suprachiasmatic nucleus of the rat.

The content of substance P (SP)-like immunoreactivity (LI) within the suprachiasmatic nucleus (SCN) of rats was determined by enzyme immunoassay to evaluate the effect of light on SP-LI in the rat SCN. Male rats were kept under various lighting conditions: light-dark cycles, constant darkness, continuous light exposure for 24 h or light pulse interrupting constant darkness. Animals were also subjected to ocular enucleation. The present study showed that SP-LI in the SCN was unaffected by environmental lighting conditions or by bilateral ocular enucleation. Immunohistochemical studies also confirmed that SP immunoreactivity, which was found in the ventrolateral (VL) subdivision of the SCN, was not reduced significantly even after ocular enucleation. These results suggest that, in contrast to other neurotransmitters in the VL portion of the SCN such as vasoactive intestinal polypeptide (VIP), gastrin releasing peptide (GRP) and neuropeptide Y (NPY), SP level in the SCN is quite stable to light and arises from an area other than the retina.

Animals↗
PubMed1993

Endogenous circadian rhythmicity of somatostatin like-immunoreactivity in the rat suprachiasmatic nucleus.

The suprachiasmatic nucleus (SCN) of the hypothalamus has been established as the locus of the circadian pacemaker in mammals. The SCN is histochemically divided into two subdivisions: dorsomedial and ventrolateral subfields. The dorsomedial SCN is characterized, in part, by dense somatostatin-like immunoreactivity (SS-LI), but its functional significance in circadian pacemaking remains unclear. Our previous study revealed that 24 h SS-LI contents of the SCN in rats kept under light-dark (LD) conditions or blinded by orbital enucleation showed a distinct circadian rhythm. In the present study, 24 h SS-LI contents of the SCN in sighted rats kept under constant darkness (DD) conditions for prolonged periods were measured by enzyme immunoassay. Cellular contents of SS-LI exhibited a clear circadian rhythm on the third day of constant darkness (DD) with a peak at circadian time (CT) 5, corresponding to the time of peak levels found in LD conditions and in enucleated animals. This endogenous free-running rhythm continued to oscillate without attenuation of the amplitude even at 14 days in constant darkness. Moreover, SS-LI rhythm was found to be similar to the vasopressin rhythm in the SCN. In summary, these findings further strengthen the idea that the cellular content of SS-LI in the SCN is under the control of the endogenous circadian pacemaker.

Animals↗
PubMed1993

Circadian rhythm of neuropeptide Y-like immunoreactivity in the iris-ciliary body of the rat.

Neuropeptide Y (NPY)-like immunoreactivity (LI) in the iris-ciliary body of rats kept under constant darkness (DD) and in 12 h light-12 h dark cycle (LD) was determined by enzyme immunoassay. NPY-LI contents in the iris-ciliary body were found to oscillate in circadian fashion under DD and LD conditions, with a peak at about circadian time 12 (CT 12) and a trough at around CT 0. Unilateral superior cervical ganglionectomy caused a significant decrease in NPY-LI levels in the sympathectomized eye compare to the contralateral intact eye, independent of lighting phase. These results suggest the presence of an endogenous circadian rhythm in NPY-LI content in the rat iris-ciliary body, and the possible involvement of a sympathetic input from the superior cervical ganglion.

Animals↗
PubMed1993

Photic regulation of peptides located in the ventrolateral subdivision of the suprachiasmatic nucleus of the rat: daily variations of vasoactive intestinal polypeptide, gastrin-releasing peptide, and neuropeptide Y.

We have determined, by enzyme immunoassay, daily and circadian patterns of the concentrations of three peptides, which are located in the ventrolateral subdivision of the suprachiasmatic nucleus (SCN): vasoactive intestinal polypeptide (VIP), gastrin-releasing peptide (GRP), and neuropeptide Y (NPY). The contents of VIP and GRP, which are synthesized in the SCN, did not show circadian rhythms in constant darkness (DD). Under light-dark (LD) conditions, GRP content increased and VIP content decreased over the course of the light period and then gradually recovered during the dark period. Responsiveness of these peptides to light suggests that VIP and GRP may transmit visual information on duration of illumination. NPY, which is transported from the intergeniculate leaflet of the lateral geniculate body, showed a circadian rhythm with a peak at circadian time 12 hr in DD. This endogenous rhythm was remarkably modulated by photic stimulation. Under LD conditions, the NPY content in the SCN exhibited a bimodal rhythm with peaks at both the light-dark and dark-light transition points. Thus, NPY may convey visual information on the transitions. All these results indicate that the levels of VIP, GRP, and NPY are mainly regulated by light stimulation and suggest that peptides in the ventrolateral SCN are involved in the mediation of photic information to the pacemaker.

Animals↗
PubMed1992

Circadian rhythms of vasopressin content in the suprachiasmatic nucleus of the rat.

The suprachiasmatic nucleus (SCN) of the anterior hypothalamus contains a circadian pacemaker in mammals. We determined the circadian profiles of arginine-vasopressin (AVP), a major peptide in the dorsomedial SCN, in rats under light-dark (LD), constant dark (DD) and constant light (LL) conditions. Under LD conditions, AVP levels in the SCN showed circadian rhythmicity with a peak at early light phase and a broad trough during the dark phase. This rhythm in the AVP contents was maintained even after 14 days of free-running under DD conditions and 3 days under LL conditions. These circadian patterns of AVP are similar to those of somatostatin, another peptide in the dorsomedial SCN. This indicates a common mode of regulation for peptides in this subfield of the SCN.

Animals↗
PubMed1991

Circadian rhythms of somatostatin-immunoreactivity in the suprachiasmatic nucleus of the rat.

Twenty-four hour patterns in somatostatin (SS)-like immunoreactivity (LI) within the suprachiasmatic nucleus (SCN) were determined by enzyme immunoassay in rats blinded by bilateral orbital enucleation or kept sighted under light-dark conditions. A remarkable circadian rhythm was found in the concentration of SS-LI in the SCN under blinded conditions. The peak time appeared at about circadian time (CT) 4 in the early subjective day and the trough at around CT 16 or 20 in the subjective night. Light-dark cycles did not alter the circadian patterns of SS-LI observed in the blinded rat SCN. These results indicate the presence of an endogenous circadian rhythm in SS-LI in the rat SCN, independent of environmental lightning cycles.

Animals↗
PubMed1988

Inhibitor of protein synthesis phase shifts a circadian pacemaker in mammalian SCN.

The suprachiasmatic nucleus (SCN) of the hypothalamus contains a circadian pacemaker that regulates many circadian rhythms in mammals. Experimental work in microorganisms and invertebrates suggests that protein synthesis is required for the function of the circadian oscillator, and recent experiments in golden hamsters suggest an acute inhibition of protein synthesis can induce phase shifts in a mammalian circadian pacemaker. To determine whether protein synthesis in the SCN region is involved in the generation of circadian rhythms in mammals, a protein synthesis inhibitor, anisomycin, was microinjected into the SCN region, and the effect on the circadian rhythm of locomotor activity of hamsters was measured. A single injection of anisomycin into the SCN region induced phase shifts in the circadian activity rhythm that varied systematically as a function of the phase of injection within the circadian cycle. These results suggest that protein synthesis may be involved in the generation of circadian rhythms in mammals and that the anatomic site of action of anisomycin is within the hypothalamic suprachiasmatic region.

Animals↗
PubMed1986

Horizontal knife cuts either ventral or dorsal to the hypothalamic paraventricular nucleus block testicular regression in golden hamsters maintained in short days.

The possible involvement of efferent pathways from the suprachiasmatic nucleus (SCN) in the photoperiodic regulation of reproduction was studied by measuring the testis size of hamsters bearing a horizontal knife cut either ventral or dorsal to the hypothalamic paraventricular nucleus (PVN) that were transferred from photostimulatory long days (light:dark (L:D) 14:10 h) to non-stimulatory short days (L:D 6:18 h). Knife cuts placed either ventral or dorsal to the PVN blocked testicular regression induced by exposure to short days. These results indicate that efferent fibers running dorsally from the SCN to the PVN are involved in relaying photoperiodic information from the SCN to the PVN. Furthermore, recently-defined efferents that leave the PVN dorsally and terminate in the spinal cord appear to be responsible for relaying seasonal information about day-length to the pineal-reproductive axis of hamsters.

Animals↗
PubMed1984

Light responsiveness of the suprachiasmatic nucleus within the island with the retino-hypothalamic tract spared.

To investigate daily variation in responsiveness of the suprachiasmatic nucleus (SCN) to exposure to light, the evoked change in multiple unit activity of the SCN within the retino-hypothalamic island with the retino-hypothalamic tract (RHT) spared, was measured in the rat at 6 h intervals across a 24 h day. It is found that SCN multiple unit discharge rates increase during a 1 h exposure to light which interrupts constant darkness irrespective of the time of day. A non-parametric statistical analysis did not indicate a significant daily variation in light-responsiveness of the SCN. The present results suggest that the phase-dependent shift of the SCN rhythm after a light exposure is induced not by a rhythm in light-responsiveness of the SCN mediated by the RHT, but by a more complicated machinery within the SCN.

Animals↗
PubMed1983

Does the ventromedial hypothalamic nucleus contain a self-sustained circadian oscillator associated with periodic feedings?

Multiple unit activities (MUAs) of the ventromedial hypothalamic nucleus (VMH) were recorded from intact free-moving male rats. Rhythmic activities observed in the VMH were not distinguishable from those recorded in other places of the brain. When exposed to restricted daily feeding schedules, animals with suprachiasmatic nucleus (SCN) lesions developed a rhythm in motor activity and a rhythm of the VMH with a peak of activity immediately after and a trough right before the feeding. While neural activities of the SCN revealed circadian rhythms even after a lesion of the VMH, circadian rhythms in MUA of the VMH were completely abolished by a lesion of the SCN. Although the VMH is involved in the synchronization of rhythms to periodic feeding, the present results indicate that, unlike the SCN which contains an oscillator associated with light, the VMH does not contain another self-sustained oscillator associated with food.

Activity Cycles↗
PubMed1982

Ventromedial hypothalamic lesions eliminate anticipatory activities of restricted daily feeding schedules in the rat.

Anticipatory activities which precede food delivery under restricted daily feeding schedules were compared in rats with septal, suprachiasmatic and ventromedial hypothalamic lesions. Whereas rats with lesions of the septal nucleus and of the suprachiasmatic nucleus showed a normal pattern of increase in activity several hours prior to feeding, the rats with the ventromedial hypothalamic lesions did not show any activity bouts prior to feeding time. The semi-circular knife cut anterior to the ventromedial hypothalamic nucleus also eliminated the anticipatory activities. These findings suggest that the ventromedial hypothalamic nucleus is required to produce the anticipatory activities of restricted daily feeding schedules.

Animals↗
PubMed1981

Reversal of multiunit activity within and outside the suprachiasmatic nucleus in the rat.

Multiunit activity (MUA) in the suprachiasmatic nucleus (SCN) and adjacent hypothalamic areas were compared in albino rats anesthetized with thiopental, immobilized with succinylcholine chloride and artificially respired. During adaptation to light lasting up to 2 h, MUA in the SCN increased gradually, whereas MUA in the other locations outside the SCN decreased. During adaptation to the dark, MUA in the SCN decreased whereas MUA outside the SCN increased. This reversal was apparent not only when recording in the SCN and adjacent hypothalamus simultaneously, but also while advancing an electrode from the optic chiasm through the SCN to the anterior hypothalamus.

Animals↗
PubMed1980

The statistical analysis of spontaneous transmitter release at individual junctions on cockroach muscle.

1. Miniature excitatory post-synaptic potentials (MEPSPs) were recorded extra- and intracellularly from the coxal depressor muscle of the cockroach, Periplaneta americana. 2. Statistical analysis of the time intervals between MEPSPs showed that the variance-to-mean curve for the extracellular data sets lay significantly above the line predicted for a Poisson process. A shuffling procedure, however, made the series almost random. 3. The serial correlation coefficients for the extracellular data sets exceeded the confidence limits for various lags and most of them were positive. In comparison with the intensity function, the departure from the random process appeared to be mainly due to large positive correlation of intervals. 4. It is concluded that in insect neuromuscular junctions, the spontaneous release of transmitter at individual sites is more clustered than that predicted by a Poisson process.

Acetylcholine↗
PubMed1979

Persistence of circadian rhythmicity in a mammalian hypothalamic "island" containing the suprachiasmatic nucleus.

The experimental work described tested the prosposition that the suprachiasmatic nucleus of the hypothalamus is an autonomous circadian pacemaker. Simultaneous recording from two extracellular electrodes indicated neural (multiple unit) activity at two sites in the brain, one of which is in or near the suprachiasmatic nucleus and the other in one of many other brain locations. Both sites in intact rats displayed clear circadian rhythmicity of spontaneous neural activity. In experimental animals, a Halasz knife was used to create an island of hypothalamic tissue that contained the suprachiasmatic nuclei. In such animals that were also blinded by bilateral ocular enucleation, circadian rhythmicity was lost at all brain locations recorded outside the island, but it persisted within the island that contained the suprachiasmatic nuclei. The rhythmicity of the island is thus not dependent on afferent inputs from elsewhere in the brain.

Action Potentials↗
PubMed1978

The effect of calcium and magnesium on the spontaneous release of transmitter at insect motor nerve terminals.

1. The effect of the extracellular calcium and magnesium concentrations and calcium ionophore, X-537A, on the frequency of miniature excitatory post-synaptic potentials (MEPSPs) was studied in cockroach leg muscle fibres. 2. The frequency of MEPSPs increased as the calcium concentration was increased from 0.1 to 10 mM. In the presence of 10 mM magnesium, however, raising the calcium concentration from 0.1 to 1 mM slightly depressed the frequency. In saline containing elevated potassium (20.8 mM), increasing the calcium concentration produced a much higher frequency than that in the normal potassium saline (10.8 mM) in the absence of magnesium. Raising the extracellular potassium concentration was without effect unless the bathing solution contained calcium. 3. The frequency of the miniature potentials was reduced as the magnesium concentration was raised from 0 to 10 mM, depending on the presence of calcium ions. On the contrary, a slightly increased frequency was observed in the low calcium saline as the magnesium concentration was raised from 1 to 10 mM. The reciprocal relationship between calcium and magnesium and the time course of the effect suggest that both ions act at the same surface sites in the presynaptic membrane. 4. X-537A elicited a transient increase in frequency followed by a fall of the frequency to a very low rate. Further application of the ionophore was without effect. The effect of X-537A on the spontaneous release of transmitter at the insect neuromuscular junction was comparable with that on the spontaneous acetylcholine release in vertebrate neuromuscular junctions.

Animals↗
PubMed1975

The mode of spontaneous transmitter release at the insect neuromuscular junction.

The time intervals between miniature excitatory postsynaptic potentials and the counts of them in the cockroach, Periplaneta americana, were analyzed, using a computer program to test for properties of a Poisson process. The miniature potentials occurred basically in random manner at this neuromuscular junction. Although the distribution of the potentials did not fit the criteria for a Poisson process when the muscle fiber exhibited the short burst of high-frequency discharges, it was suggested that the primary process of such a distribution is Poisson, which is occasionally contaminated by the burst phase of the release rates.

Animals↗