Rhythmic patterns of discharge in hypothalamic neurosecretory neurons of cats and dogs

Recent studies in rats suggest that vasopressin- and oxytocin-secreting neurons in supraoptic nuclei and paraventricular nuclei of the hypothalamus show two different patterns of activity: one a "bursting" or rhythmic pattern and the other, irregular continuous discharges. This possibility was investigated in cats and dogs anesthetized with chloralose or Nembutal by recording electrical activity of single supraoptic and paraventricular neurons. Only some of the "identified" neurosecretory cells showed rhythmic, intermittent discharges ("bursting" cells in rats); the majority showed an irregular continuous firing pattern. Furthermore, the pattern of discharge sometimes changed from one ot the other during long periods of observation. This occurred without apparent stimulus in certain instances; in others, the rhythmic firing was associated with fluctuation in blood pressure and heart rate and was likely to be caused by changes in baroreceptor activity. Possible origins of rhythmic discharges and the physiological importance of such patterns in terms of hormone secretion are discussed.

Radio-iron uptake of rat hepatoma

Iron uptake rate of the tumor tissues of the rat liver was compared with that of the nontumor tissues of the same rat liver. Ferric[59Fe] citrate was injected to rats bearing hepatoma induced by the administration of diethylnitrosamine. The tumor and nontumor tissues were enucleated from the liver and radioactivity (cpm/10 mg tissue) of the individual tissue was calculated to estimate the iron uptake rate of the tissue. Eleven rats were finally available for the study. Population mean of radioactivity of the tumor group was larger than that of the nontumor group when examined 6 hr after the injection, so far as the specimens of both groups were sufficient in number, more than 19. The variance of radioactivity of the tumor group was always larger than that of the nontumor group, probably in part due to cytological and histological varieties of the tumor tissues. These results suggest that the tumor tissues can take up more iron than the nontumor tissues.

Influence of carotid and aortic baroreceptors on neurosecretory neurons in supraoptic nuclei

(1) The effects of arterial baroreceptor stimulation on the activity of 'identified' neurosecretory cells in supraoptic nuclei (SON) of the hypothalamus were investigated in anesthetized cats. (2) Stimulation of baroreceptors by distension of an 'isolated' carotid sinus greatly inhibited SON activity. A linear relationship was found to exist between stimulus intensity (an increase in the sinus pressure) and the degree of inhibition of SON neuron activity. This inhibitory effect was abolished by section of the sinus nerve. (3) The inhibitory effect of baroreceptors on SON neuron activity was most pronounced in the first 5 sec during stimulation, and the effect became less when the stimulus lasted for a long period. At the end of stimulation there was a transient reversal of the response. (4) The excitation of aortic baroreceptors by occluding descending aorta strongly inhibited SON neuron activity. (5) Occlusion of carotid arteries augmented the SON neuron activity. Electrical stimulation of the sinus nerve caused an excitation or an inhibition of SON neurons, depending on the stimulus intensities. Apparently these stimuli produced different degrees of excitation in baro- and chemoreceptors. (6) Combination of chemo- and baroreceptor stimulations revealed that the excitatory effect exerted by chemoreceptor stimulation on SON neurons was reversed or blocked by baroreceptor activation, indicating the powerful inhibitory influence of baroreceptors.

Influence of atrial stretch receptors on hypothalamic neurosecretory neurones

1. The effects of stimulation of atrial receptors on hypothalamic neurosecretory cells were investigated in anaesthetized dogs and cats. Atrial receptors were activated by stretching the left and the right atria while action potentials of individual neurosecretory neurones in the supraoptic (s.o.n.) and paraventricular (p.v.m.) nuclei of the hypothalamus were recorded. 2. Stretching the left atrium markedly decreased firing frequencies of 'antidromically identified' s.o.n. and p.v.n. neurones in dogs and cats; 98% of neurones in dogs and 70% in cats were thus inhibited. Heart rate accelerated following a transient reflexly induced deceleration. The blood pressure was not affected. The magnitude and duration of inhibitory effects produced by atrial stretch on s.o.n. and p.v.n. neurones paralleled changes observed in heart rate. Approximately one third of 'unidentified' cells in s.o.n. and p.v.n. (those which could not be activated antidromically) were inhibited by left atrium stretch. 3. Bilateral vagotomy abolished the effects on neurosecretory neurones as well as on heart rate produced by left atrial stretch, indicating that the vagus nerves carry afferent impulses responsible for the observed changes. 4. Stretching the right atrium did not produce changes in firing frequencies of s.o.n. and p.v.n. neurones in dogs and cats, although cardiac rate was increased considerably by such stretch. Stimulation of the left and right atria was tested in the same animal in succession to permit comparison of the diverse results. 5. Interaction of responses originating from atrial receptors, baro- and chemoreceptors were studied. During carotid occlusion or stimulation of chemoreceptors activity of the neurosecretory cells was greatly augmented. Left atrial stretch when then applied evoked slight or no reduction in activity in s.o.n. and p.v.n. neurones. These results were interpreted to mean that the influence of baro- or chemoreceptors on neurosecretory neurones probably is stronger than that originating from atrial receptors. 6. Unlike the observations made in rats, no rhythmically bursting neurones (phasic cells) were found in dogs and cats. However, atrial stretch sometimes evoked a rhythmic bursting pattern which appeared only during stretch. 7. It is concluded that activation of left atrial receptors, through afferent impulses carried mainly by vagus nerves, inhibits neurosecretory neurones in s.o.n. and p.v.n. The implications of this finding in relation to the role of ADH in the maintenance of blood volume control were discussed.

Study of cardiac sympathetic and vagal efferent activity during reflex responses produced by stretch of the atria

(1) In chloralose anesthetized dogs, effects of the left and the right atrial stretch were studied in the same animal. Stretch of the sino-atrial region of the right atrium produced acceleration of the heart rate during, and reversal of response at the termination of, the stretch. Stretch of the left pulmonary vein-atrial junctional region evoked an initial decrease followed by an increase in heart rate. The responses were similar in all animals, despite initial heart rates ranging from 120 to 200 beats per minute. (2) Activity in vagal and sympathetic nerve branches innervating the heart was recorded simultaneously. Care was taken to identify the vagal fibers innervating the heart, and record their activity without contamination of sympathetic impulses. The right atrial stretch evoked an augmentation of sympathetic activity which reached its peak at 20 sec after the beginning of stimulus. The stimulus slightly increased the vagal activity; this change occurred slowly and reached its peak in about 40-60 sec after stretch. At the release of stretch, sympathetic activity generally showed a reversal of response, i.e. activity was inhibited for 30 sec. (3) Stretch of the left atrium produced biphasic changes in cardiac sympathetic nerves; their activity was strongly inhibited for the first 15 sec, then augmented throughout the remainder of the stretch. This effect lasted 30 sec after the cessation of stimulus. Effects on vagal cardiac nerve fibers were smaller; mild augmentation in activity was produced. The onset of this effect was faster than that seen in case of the right atrium stretch. (4) Reciprocal action between vagal and sympathetic cardiac nerves was obvious only in the early phase of left atrium stretch. Effects on the heart were determined by balances in activity of these antagonistic nerves. In contrast with what occurred in cardiac reflexes, carotid sinus distension even in the same animal produced a large increase in vagal activity, and near complete inhibition of sympathetic nerve activity. Thus, good reciprocal action between the two sets of nerves was demonstrated. A difference in the two types of reflexes was thus revealed. (5) Stretch of the right atrium evoked during carotid sinus distension caused an increase in heart rate from the new low level which was produced by baroreceptor activation. Vagal activity which was greatly augmented by sinus distension was decreased by atrial stretch, while previously inhibited sympathetic activity due to sinus distension was augmented by stretch of the atrium. The effect of stretch on vagal activity seems to depend to a degree on the prestimulus level. It is of interest that the powerful baroreceptor reflexes do not mask the cardiac reflexes studied. (6) The relative importance of sympathetic and vagal efferents to atrial stretch reflexes was discussed.

Aminoglycoside antibiotics. XII. Effect of N-alkylation in kanamycin antibiotics

Four N-ethyl derivatives of kanamycin A and five N-ethyl derivatives of kanamycin B were synthesized. The antimicrobial activity of N-ethyl kanamycin derivatives was determined against aminoglycoside-sensitive and resistant organisms. The structure-activity relationship of these compounds is discussed with reference to the activity of N-acyl kanamycin derivatives.

Comparative studies of non-hemoglobin proteins of adult and newborn red blood cell lysates

It has been known that hemolysate is composed of not only hemoglobin but also non-hemoglobin proteins (NHP). NHP isolated effectively from hemolysate of adult and newborn by CM-Sephadex chromatography was investigated by polyacrylamide disc or slab electrophoresis. It was demonstrated on slab electrophoresis that adult NHP is composed of 4 zones (approximately 14 bands) with different mobilities and that adult NHP shows a considerably different pattern from cord NHP. The difference was observed also on the electrophoresis stained for esterase or lactate dehydrogenase. Rabbit antiserum to adult NHP was adsorbed with cord NHP and specific antiserum for adult NHP was prepared. However, antiserum reacting with only cord NHP was not obtained from anti-cord NHP serum. These results suggested that adult specific components with passable antigenicity were present in adult NHP and that cord NHP had similar antigenicity as adult NHP.

Inhibition and excitation induced by glutamic acid on cerebellar interneurons

Thin sections of guinea pig cerebellum were incubated in an artificial medium and responses of neurons in the granular layer to glutamic acid were studied. About half of these neurons were inhibited by glutamate administered electrophoretically (GI cells) and others were excited (GE cells). The GI cells were also inhibited in a medium containing glutamate. Gamma-amino butyric acid inhibited the GI as well as the GE cells. The inhibition in the GI cells induced by glutamate was not susceptible to picrotoxin or strychnine medication, and was not blocked in a CI-free medium or in a medium containing CA2+ in low concentrations and Mg2+ in high concentrations. Some GI cells showed high-amplitude spikes which were recordable at distances of tens of micrometer from the cell. These observations indicate that at least some of the GI cells were large Golgi cells and that the inhibition induced by glutamate in the GI cells was not mediated by inhibitory interneurons.