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Biomedical subjects

Y Sakuma

Publications and source records attributed to Y Sakuma.

At least 235 records · Page 13Linked to original sources
PubMed1979

Facilitation of the lordosis reflex of female rats from the ventromedial nucleus of the hypothalamus.

1. Effects of electrical stimulation of hypothalamic ventromedial nucleus (v.m.n.) on the lordosis reflex of female rats were examined in ovariectomized and oestrogen-primed animals with chronically implanted electrodes. 2. Lordosis triggered either by manual cutaneous stimulation or by male mounting, was facilitated by electrical stimulation of the v.m.n. 3 A gradual increase in lordosis performance followed a relatively long period of stimulation; never less than 15 min and usually about 1 hr of stimulation was necessary for maximum facilitation. Following the termination of stimulation, the performance returned gradually to the control level during a 5--8 hr period. 4. The optimal frequency of stimulation was between 10 and 30 Hz. Threshold for effective facilitation was, on the average, 12.5 microA. 5. Stimulation tended to induce larger facilitation when applied to the lateral side of v.m.n. 6. Pre-treatment with oestrogen was necessary to obtain facilitation by v.m.n. stimulation. The threshold dosage of oestrogen was 2.5 microgram per animal. 7. Stimulation was effective in adrenalectomized rats, in dexamethasone-primed animals, and in rats pre-treated with exogenous progesterone. Thus, adrenal prodesterone release is not required for the v.m.n. facilitation of lordosis. 8. Medial preoptic stimulation with the same parameters suppressed the lordosis reflex. 9. The v.m.n. participates in the control of lordosis by a facilitatory output. The delay before facilitation implies that the v.m.n. is not in the direct reflex-arc for the execution of lordosis. Rather, a summation or interaction process with an unusually long time course is involved.

Animals↗
PubMed1979

Deficit in the lordosis reflex of female rats caused by lesions in the ventromedial nucleus of the hypothalamus.

1. The effect of electrolytic lesions of the ventromedial nucleus of the hypothalamus (v.m.n.) on the lordosis reflex has been investigated on ovariectomized female rats. Lesions were made through chronically implanted platinum-iridium electrodes. 2. V.m.n. lesions did not disrupt lordosis immediately, but induced a gradual decline in the reflex. Lordosis performance reached it minimum no less than 12 hr after the lesion, and typically after 36--60 hr. 3. The magnitude of the lordosis deficit was related to the amount of v.m.n. damage. Destruction of other hypothalamic regions was without appreciable relation to the deficit. Within v.m.n., lesion size in the lateral, but not medial portion was significantly correlated with lordosis deficit. 4. Because of the slow time courses of v.m.n. lesions and stimulation (Pfaff & Sakuma, 1978) effects, it is postulated that the v.m.n. is not part of the direct reflex-arc for lordosis. Rather, neurones in v.m.n. are likely to exert a tonic hormone-dependent bias on brain stem reflex paths for this behaviour.

Animals↗
PubMed1978

Effects of estrogen and aminergic drugs on thresholds of medial basal hypothalamic axons in the median eminence of the rat.

Antidromic responses were induced in the medial basal hypothalamus (MBH) of female rats by median eminence (ME) stimulation, and thresholds were measured under various endocrine conditions. Two different types of antidromic response were recognized. In 83 out of 97 responses, repetitive shocks to the ME at 20--40 Hz induced a fractionation of antidromically-driven spikes into A- and B-components. In the remainder, the antidromically activated spikes were stable to stimulation at high frequency. The threshold tended to show higher values in proestrus than in diestrus-I in both types of response. However, only in the former type of response, application of conditioning electrical shocks to the ME was effective in decreasing the threshold for successive test pulses. A decrease in the threshold lasted for 150--200 msec following the conditioning, with the lowest threshold at about 60 msec after the shock. Effects of the conditioning persisted in animals with chronic complete deafferentation of the MBH but were abolished in intact rats by reserpine treatment. Dopamine, but not norepinephrine or serotonin, mimicked the threshold-decreasing effect of the conditioning when applied to the ME. The results suggest the possibility of a depolarizing effect of some dopaminergic neural mechanism projecting from the MBH to the ME and acting on the axons of a particular type of MBH neuron characterized by fractionating spikes.

Animals↗
PubMed1977

[Two autopsy cases of adult central nervous system toxoplasmosis: light and electron microscopic studies (author's transl)].

Two autopsy cases of adult central nervous system toxoplasmosis were reported. Two cases treated with immunosuppressive agents and corticosteroids under a diagnosis of Hodgkin's disease were considered to be an acquired CNS toxoplasmosis associated with the underlying diseases. The first case, a 73 year old woman with Hodgkin's disease, showed toxoplasma lesions in the cerebrum. The second case, a 22 year old man with pulmonary tuberculosis, showed toxoplasma lesions in the cerebrum, basal ganglion, thalamus, cerebellum, pons, and medulla oblongatta. Each toxoplasma lesion showed small hemonecrotic softening. Toxoplasma cysts were seen around the hemonecrotic lesion. Encysted toxoplasma organisms were examined in detail with electron microscope.

Adult↗
PubMed1976

[Antidromic identification of hypothalamic neurosecretory cells which participate in the anterior pituitary control (author's transl)].

Attempts were made to identify hypothalamic neurosecretory cells which participate in the anterior pituitary control with a special reference to the effects of ovarian hormones. Wave forms of the antidromically activated action potentials in the hypothalamus were investigated in the female rats of Wistar strain. The animals of different endocrinological environments, that is, proestrus and diestrus-I of 4-day cyclers; ovariectomized, ovariectomized and estrogen primed, ovariectomized and progesterone primed, were used. The operational procedures were performed under light urethane anesthesia. Different two types of craniotomy were adopted for the preparation. For recordings from the medial basal hypothalamus, the ventral surface of the brain was exposed by parapharyngeal approach, and a bipolar silver ball electrode for the application of electrical stimuli was placed on the surface of the median eminence (ME). Another method was used for recordings of the medical preoptic area (MPO) and the periventricular area of the MPO and the anterior hypothalamus (PVA). In the latter, the parietal surface of the brain was exposed and a side-by-side bipolar electrode for the stimulation was inserted to the arcuate (ARC-ME region. All the recordings were performed by using glass pipettes which were filled with 0.5 M sodium acetate solution. The solution was added with pontamine sky blue 6B to allow marking recording sites. Stimulatory pulses of 5 msec duration of variable intensity were generated by an electronic stimulator and applied by the above mentioned bipolar electrodes. The antidromic responses and the intensity of the stimuli were observed and photographed on a synchroscope. ...

Action Potentials↗
PubMed1976

Effects of Limbic stimulation and the microinontophoresis of aminergic drugs on the single unit activity of hypothalamic neurosecretory cells (author's transl).

Attempts were made to investigate the chemical nature of hypothalamic afferents from the extrahypothalamic structures which participate in the control of hypothalamic neurosecretory cells. Experimental procedures were discribed in the preceding report, except that of the electrical stimulation and the microinontophoresis. Some part of data obtained in this study were referred in the preceding report for improvement of statistic reliability. For electrical stimulation, side-by-side bipolar electrodes were placed in the medial preoptic area (MPO), medial amygdala (mAMYG) and dorsal hippocampus (dHPC) from the parietal surface of the brain and fastened to the cranium by dental resin. Microintophoresis of norepinephrine (NE), dopamine (DA) and acetylcholine (Ach) was carried out by using five-barrelled glass pipette on the antidromically activated units in the medical basal hypothalamus by the median eminence stimulation. Extracellular potentials were recorded by the central barrel of each electrode. One of the outer barrels was filled with physiological saline and used for control purpose. (1) Eelctrical stimulation of the MPO with train pulses of 0.2 msec duration and 300 muA intensity in 100 HZ for 5 sec, induced facilitation and inhibition in 26.4% and 9.4% of 106 tests, respectively. By the mAMYG stimulation with 500 muA, facilitation was seen in 18.8% and inhibition in 10.4%, of 96 tests. The HPC stimulation induced facilitation in 10.0% and inhibition in 23.3% of 90 tests. (2) Facilitatory effect of the MPO was most frequently seen in the ovariectomized and estrogen primed rats (58.8% of the tests). In contrast, the inhibitory effect of the dHPC was striking in the diestrus-I (40.0%). (3) Microiontophoresis of NE induced facilitation in 60.0% and inhibition in 10.6% of 66 identified cells. DA induced facilitation in 45%, and inhibition in 11.7% of 60 tests. Ach induced facilitation in 41.4%, and inhibition in 13.8% of 58 tests. (4) By NE infusion, facilitation was most commonly seen in the proestrus (70.6%). Inhibition was most readily elicited by Ach infusion on the diestrus-I (30%). Facilitative effect of DA was eminent in the diestrus-I (81.8%). (5) Successive administration of NE and DA on identical units revealed that in 56.0%, the units were responsive to only one agent and the other was effectless. 25.5% of the units responded to both of NE and DA. (6) The conceidence of effects, either facilitation or inhibition, between that of electrical stimulation of the microinontophoresis, was calculated on 46 units. The facilitatory effect of the MPO was most commonly mimicked by NE infusion (81.8%), and the inhibitory effect of the dHPC by Ach infusion (46.7%). NE also mimicked facilitatory effect of mAMYG stimulation (73.3%). (7) Intraventricular infusion of 20 mug of NE induced significant increase of serum LH (p less than 0.05 to saline) when measured by radioimmunoassay, whereas DA resulted in a decrease of LH (p less than 0.01).

Acetylcholine↗
PubMed1976

Electrophysiological evidences for possible participation of periventricular neurons in anterior pituitary regulation.

Unit activity of neurons in the periventricular area of the third ventricle (PVA), in which the organum vasculosum laminae terminalis is included, was recorded in female rats in proestrus. The units were antidromically driven by electrical stimulation of the arcuate-median eminence region (ARC-ME). In the antidromic responses, a notch was generally observed in the rising phase of the driven wave, and fractionation of A- and B-components at the notch was readily elicited by applying repetitive stimulatory pulses at frequencies higher than 10 Hz, or successive double pulses with intervals less than 3.5 msec. At the same time, ARC-ME efferents to the PVA were suggested by orthodromic responses in the PVA to ARC-ME stimulation. Occasionally, anti- and orthodromic responses appeared in one electrode, indicating a proximate distribution of these two types of neurons in the PVA. Repetitive stimulation of the ARC-ME at 50 Hz facilitated the orthodromically driven units, whereas antidromically driven units were inhibited. This seems to imply that the orthodromic responses might be recorded from an inhibitory interneuron in the ARC-ME efferent pathway to the PVA, judging from the identical time course of the responses of the two types of the units. Both the anti- and orthodromically driven units were tested with microiontophoresis of LH-RH, TRH, LH, FSH and prolactin. Orthodromically driven units showed no response to microiontophoresis of any hormone. In the antidromically driven units, microiontophoresis of LH-RH and FSH elicited inhibition in 15 and 18% of the tests, and facilitation was seen in 15-25% of the tests in response to LH, TRH and prolactin. The demonstration that local application of hypothalamic and pituitary hormones exerts direct effects on the activity of the PVA neurons which send their axons directly to the ARC-ME, provides additional evidence that the PVA may participate in anterior pituitary regulation.

Action Potentials↗