Biomedical subjects

H Kannan

Publications and source records attributed to H Kannan.

At least 73 records · Page 4Linked to original sources

PubMed1988

Effects of iontophoretically applied cortisol on tuberoinfundibular neurons in hypothalamic paraventricular nucleus of anesthetized rats.

Effects of cortisol on 22 tuberoinfundibular (TI) neurons in the paraventricular nucleus (PVN) of the hypothalamus were examined in urethane-anesthetized rats. Iontophoretically applied cortisol excited 10 (45%) of 22 TI-neurons tested, whereas the cortisol inhibited 4 (31%) of 13 neurons in the periventricular hypothalamic nucleus. Intravenously applied cortisol (0.5 mg in 0.5 ml saline) excited 4 (36%) of 11 TI neurons tested and inhibited 1 (9%). These results suggest that cortisol may have an excitatory effect on TI neurons in the PVN.

Action Potentials↗

PubMed1988

Effects of stimulation of the hypothalamic paraventricular nucleus on blood pressure and renal sympathetic nerve activity.

Effects of electrical and chemical stimulation of the paraventricular nucleus (PVN) of the hypothalamus on blood pressure were examined in rats anesthetized with urethane-chloralose. Focal electrical stimulation (10-25 microA, 50 Hz, 0.5 msec) within the PVN consistently decreased blood pressure. Microinjection of L-glutamate (0.5 M, 80 n1) into the PVN led to a decrease in blood pressure, while the same amount of saline injection had no effect. The depressor response was not affected by cervical vagotomy. In order to obtain direct evidence for involvement of sympathetic nerve activity in the PVN-induced depressor response, effects of PVN stimulation on renal sympathetic nerve activity were examined. Low intensity electrical stimulation of the PVN inhibited renal sympathetic nerve activity, whereas the high intensity stimulation evoked a transient excitation followed by long lasting inhibition in renal sympathetic nerve activity. Latencies of the inhibitory and the excitatory responses were about 200 msec and 50-100 msec, respectively, judged by peristimulus time histograms. The result suggests that activation of PVN neurons produces a decrease in blood pressure due to inhibition of sympathetic outflows.

Adrenergic Fibers↗

PubMed1988

Neural control of blood glucose homeostasis; effect of microinjection of glucose into hypothalamic nuclei on efferent activity of pancreatic branch of vagus nerve in the rat.

Efferent discharges were recorded from the nerve filament dissected from the central cut end of the pancreatic branch of the vagus nerve in the rat. Microinjections of 5% glucose solution (100-200 nl) into the LHA caused an increase in efferent activity, however, those into VMH caused no change in discharge rate. The results of experiments indicate that activation of vagal pancreatic efferents in hyperglycemic situation is originated in LHA and transmitted to the vagal pancreatic motoneurons. The role played by the neural network on blood glucose homeostasis was also discussed.

Action Potentials↗

PubMed1988

A nonlinear amplifier for improving signal-to-noise ratio of single-unit recordings.

A simple electronic circuit is described that suppresses the baseline noise and enhances the amplitude of extracellularly recorded action potentials. The circuit is useful for improving the signal-to-noise ratio of single-unit recordings, especially for potentials recorded by chronically electrodes.

Action Potentials↗

PubMed1988

Neuronal activity of the cat supraoptic nucleus is influenced by muscle small-diameter afferent (groups III and IV) receptors.

In anesthetized cats, responses of single neurosecretory neurons of the supraoptic nucleus to activation of muscle receptors were investigated. Electrical stimulation (1-3 pulses at 200 Hz) of group III and IV pure muscle afferents (gastrocnemius nerve) evoked excitation of greater than 50% of supraoptic nucleus neurons (n = 50), whereas stimulation of group Ia or Ib fibers was ineffective. Baroreceptor stimulation inhibited 95% of these supraoptic nucleus neurons that responded to activation of muscle afferents. Excitation of receptors in the gastrocnemius muscle by intra-arterial injection of chemicals (NaCl, KCl, and bradykinin) increased firing rates of most (84%, 74%, and 80%, respectively) neurosecretary neurons. The magnitude of the excitatory response was dose dependent--bradykinin being the most effective. The response disappeared after muscle denervation. When the gastrocnemius muscle alone was contracted phasically by ventral root stimulation, discharges of the supraoptic nucleus neurons increased, whereas quick stretch of the muscle had no effect. We conclude that activation of muscle receptors by chemical or mechanical stimulus can directly excite neurosecretory neurons in the supraoptic nucleus and that afferent impulses are carried by polymodal fibers of small diameter but not by the largest afferents (group I) from the muscle. The results may relate to increased concentrations of plasma vasopressin during exercise.

Animals↗

PubMed1987

gamma-Aminobutyric acid antagonist blocks baroreceptor-activated inhibition of neurosecretory cells in the hypothalamic paraventricular nucleus of rats.

The effects of gamma-aminobutyric acid (GABA) antagonists on baroreceptor-activated inhibition of neurosecretory cells in the paraventricular nucleus (PVN) were examined in urethane-chloralose anesthetized rats. In 11 neurosecretory cells which were inhibited by baroreceptor activation induced by intravenous application of phenylephrine, microiontophoretically applied bicuculline and/or picrotoxin blocked the inhibition (n = 9) completely or partially, whereas strychnine (n = 4) did not. The results suggest that GABA is, at least in part, involved in the baroreceptor-activated inhibition of PVN neurosecretory cells.

Action Potentials↗

PubMed1987

Oxytocin predominantly excites putative oxytocin neurons in the rat supraoptic nucleus in vitro.

To determine the oxytocin (OXT) sensitivity of neurons in the supraoptic nucleus (SON), extracellular recordings were made from the rat hypothalamic slice preparation. OXT added to the bathing medium (3 X 10(-7) M) excited 13 (93%) of 14 cells which fired continuously (average 4.9 +/- 0.7 spikes/s) and 26 (81%) of 32 cells which fired slowly and irregularly (average 1.4 +/- 0.4 spikes/s). By contrast, only 2 (8%) of 26 phasically firing neurons were excited and none of the SON cells tested were inhibited. The excitation was reversibly antagonized by a synthetic OXT analogue, 1-deamino-[2-(O-methyltyrosine), 4-valine, 8-D-arginine]vasopressin. The results suggest that OXT exerts predominantly excitatory effects in the SON and that putative OXT cells are more likely to be affected than putative vasopressin cells.

Action Potentials↗

PubMed1987

Neurons in the paraventricular nucleus projecting to the median eminence: a study of their afferent connections from peripheral baroreceptors, and from the A1-catecholaminergic area in the ventrolateral medulla.

In male rats anesthetized with urethane-chloralose, extracellular recordings were made from tuberoinfundibular (TI) neurons in the paraventricular nucleus (PVN) identified by antidromic stimulation of the median eminence. Activation of baroreceptors induced by intravenous administration of phenylephrine inhibited approximately two-thirds of the 32 TI-neurons tested. Electrical stimulation of the A1-catecholaminergic area in the ventrolateral medulla produced an excitation in one half of the 28 neurons. Microinjection of L-glutamate (40 nl of 0.5 M solution of pH 7.4-7.6) to the same A1-area evoked an excitation in 7 out of 8 TI-neurons tested. The results show that some TI-neurons in the PVN receive inhibitory synaptic inputs from the baroreceptors and excitatory inputs from neurons in the A1-catecholaminergic area.

Adrenergic Fibers↗

PubMed1987

Depolarizing effect of noradrenaline on neurons of the rat supraoptic nucleus in vitro.

Noradrenaline (NA) (1-100 microM) was applied to 41 neurons recorded intracellularly from the supraoptic nucleus (SON) of the rat hypothalamic slice preparation; 34 (83%) neurons showed membrane depolarization which was dose-dependent. The depolarization was frequently accompanied by decreased membrane resistance, increased firing rate and increased fluctuations in membrane potential. Following the application of the alpha-agonist, phenylephrine, 10 out of 11 neurons tested showed similar responses, while the beta-agonist, isoproterenol, caused no changes in 6 out of 7 SON cells. We found no difference in responsiveness between neurons having a 'phasic' or a 'non-phasic' pattern of firing. We conclude that NA depolarized and increased the firing rate of both vasopressin- and oxytocin-containing neurons through an action on alpha-adrenergic receptors.

Animals↗

PubMed1987

Decrease in blood pressure by stimulation of the rat hypothalamic paraventricular nucleus with L-glutamate or weak current.

Animals↗

PubMed1987

Inhibition of renal sympathetic nerve activity by electrical stimulation of the hypothalamic paraventricular nucleus in anesthetized rats.

In an attempt to obtain direct evidence for involvement of sympathetic outflow in paraventricular nucleus (PVN)-induced depressor response, effects of electrical stimulation of the PVN on renal sympathetic nerve activity were examined in urethane-chloralose anesthetized rats. Low intensity stimulation of the PVN inhibited renal sympathetic nerve activity, whereas the high intensity stimulation evoked an excitation followed by long-lasting inhibition in renal sympathetic nerve activity. Latencies of the inhibitory and the excitatory responses were about 200 ms and 50-100 ms, respectively. The result suggests that a decrease in blood pressure induced by low intensity stimulation of the PVN is due to inhibiting the sympathetic outflow.

Animals↗

PubMed1986

[Inhibition of vasopressin secreting neurons of the paraventricular nucleus by gastric distension in rats].

The effects of gastric distension on the neural activity of vasopressin (AVP) secreting neurons of the paraventricular nucleus (PVN) were examined in rats anesthetized with urethane alpha - chloralose. Sixteen putative AVP neurons were identified on the basis of phasically firing patterns. About half of the putative AVP neurons (7/16) were inhibited by gastric distension, while distension of the intraperitoneal balloon had no effect. Severing of the left cervical vagus trunk greatly reduced the inhibitory response. In contrast, the gastric distension had no effect on most non-phasically firing neurons (55/66). These data indicate that sensory information originating from the gastric mechanoreceptors selectively inhibits the activity of PVN AVP secreting neurons and suggest that gastric afferent information is important in the rapid inhibition of AVP release after drinking.

Animals↗

PubMed1986

Electrophysiological properties of neurons in the caudal ventrolateral medulla projecting to the paraventricular nucleus of the hypothalamus in rats.

Extracellular recordings were made from neurons in the caudal ventrolateral medulla in urethane-chloralose-anesthetized rats. Stimulation of the paraventricular nucleus (PVN) in the hypothalamus evoked antidromic action potentials in 71 neurons. On the basis of antidromic spike latencies, these neurons could be divided into fast- (24 neurons) and slow-conducting cell groups (47 neurons). Slow-conducting cells showed irregular and slow spontaneous discharges, while a majority of the fast-conducting cells did not show spontaneous discharges. The spontaneous activity of slow-conducting cells was suppressed by i.v. clonidine administration. The effects of clonidine could be consistently reversed by administration of the alpha 2-adrenergic antagonist, yohimbine. The responses by clonidine and yohimbine remained unimpaired in baroreceptor-denervated rats. Vagus nerve stimulation produced an excitation in 80% of slow-conducting cells tested. Baroreceptor activation induced by i.v. administration of phenylephrine inhibited about half of slow-conducting cells tested. Similar elevation of blood pressure in baroreceptor-denervated rats did not show any effect. These physiological and pharmacological properties of slow-conducting cells were similar to those previously reported for catecholaminergic cells in other parts of the brain. The results show the existence of two different populations among neurons in the caudal ventrolateral medulla which project directly to the PVN, and suggest that the presumed A1 catecholaminergic cells are involved in the afferent pathway from cardiovascular baroreceptors and the vagus nerve to the PVN.

Animals↗

PubMed1986

[Electrophysiological studies on the central control of feeding and drinking under hyperbaric environment].

Increased urinary output, decreased fluid intake and reduction in body weight have been reported in divers exposed to hyperbaric environments. Single unit activity of hypothalamic neurons in the lateral hypothalamic area and paraventricular nucleus which control energy and body fluid balance was recorded with chronically implanted electrodes in rats. Neurons in the prefrontal cortex and central medical thalamus were also recorded for comparison. Out of 33 hypothalamic neurons, 19 reversibly decreased their firing rate to 67%, in average, under high pressure (7 atmospheres absolute) of air compared with precompression control. On the other hand, the remaining 14 neurons and all prefrontal and thalamic neurons tested were unaffected. Decreased hypothalamic unit activity was also found under normobaric hyperoxic environment and normoxic hyperbaric environment. The results suggest that hyperbaric air specifically affected the hypothalamic neurons by means of increased partial pressure of both oxygen and nitrogen.

Animals↗

PubMed1985

Connections of neurons in the region of the nucleus tractus solitarius with the hypothalamic paraventricular nucleus: their possible involvement in neural control of the cardiovascular system in rats.

Extracellular recordings were made from 607 spontaneously firing neurons within the nucleus tractus solitarius (NTS) and its vicinity in urethane-anesthetized male rats. Following electrical stimulation of the hypothalamic paraventricular nucleus (PVN) area, 21% of the neurons were orthodromically excited, 6% were inhibited and 2.5% were antidromically activated. The antidromic spike latencies were 22-64 ms. Among those orthodromically responding neurons, 81 neurons were tested by pressure pulse stimulation of the isolated carotid sinus. The pressure stimulation produced excitation in 7 and inhibition in 13 neurons. Of the 8 tested neurons which were antidromically activated, one neuron was excited and another neuron inhibited by the pressure pulse stimulation. These results provide electrophysiological evidence for reciprocal connections between neurons in the NTS region and the PVN, and give support to the hypothesis that the PVN is involved in the neural control of the cardiovascular system.

Animals↗

PubMed1984

Effects of electrical and chemical stimulation of the paraventricular nucleus on neurons in the subfornical organ of cats.

Single unit recordings were made from neurons of the subfornical organ (SFO) in hemispherectomized cats following electrical stimulation in the paraventricular nucleus (PVN) of the hypothalamus. Of 132 neurons tested, 48 (36%) were inhibited, 3 (2.3%) excited and two (1.5%) antidromically activated. In separate experiments the wall of the third ventricle near the PVN was locally perfused with glutamate solution using a concentric push-pull cannula. Of 35 SFO neurons tested, 6 were inhibited, 5 were facilitated and 24 unaffected. The results indicate that one-third of SFO neurons receive synaptic inputs from cells in or near the PVN.

Angiotensin II↗

PubMed1984

Paraventricular neurosecretory neurons: synaptic inputs from the ventrolateral medulla in rats.

Effects of electrical stimulation of the ventrolateral medulla on discharge activity of neurosecretory neurons in the paraventricular nucleus (PVN) were studied in male rats anesthetized with urethane-chloralose. Among 35 phasically firing neurosecretory neurons, stimulation of the lateral reticular nucleus and its vicinity produced excitation in 10 and inhibition in 2. The stimulation also enhanced the activity of 40% of the PVN neurosecretory neurons that fired continuously (n = 81); of these responsive neurons, half of the neurons tested (n = 12) were inhibited by i.v. administration of phenylephrine. The result suggests that both vasopressin- and oxytocin-secreting neurons in the PVN receive mainly excitatory synaptic inputs from the ventrolateral medulla.

Animals↗

PubMed1983

Electrophysiological study of paraventricular nucleus neurons projecting to the dorsomedial medulla and their response to baroreceptor stimulation in rats.

In male rats anesthetized with urethane, extracellular recordings were made from 415 neurons in the paraventricular nucleus (PVN) and adjacent areas. Of these neurons 64 were excited antidromically by stimulation of the dorsomedial medulla but not by stimulation of the pituitary stalk (first group). Seventy-three neurons were antidromically excited by stimulation of the pituitary stalk but not of the dorsomedial medulla (second group, neurosecretory cells). The other 2 neurons were antidromically excited by stimulation of both the dorsomedial medulla and the pituitary stalk (third group). Latencies of antidromically evoked action potentials by stimulation of the dorsomedial medulla and of the pituitary stalk ranged between 8 and 60 ms (mean +/- S.D., 38.5 +/- 9.8, n = 66) and from 7 to 24 ms (mean +/- S.D., 13.0 +/- 3.6, n = 75), respectively, suggesting unmyelinated fiber projections in both instances. PVN neurons of these 3 groups were found to be dispersed throughout the PVN and no difference in specific locations between the neuron groups existed. Their characteristics, however, were different. The first group of neurons discharged at a slower rate and showed no phasic pattern of firing, while 28% of the second group of neurons ('identified' neurosecretory cells) showed phasic patterns of firing and their rates of discharge were higher than those of the first group of neurons. The two neurons belonging to the third group showed irregular spontaneous discharges. The areas within the dorsomedial medulla stimulation of which evoked antidromic excitation of PVN neurons were located within and adjacent to the nucleus of the tractus solitarius (NTS) and the dorsal motor nucleus of the vagus (DMV). Among PVN neurons which were antidromically excited by stimulation of dorsomedial medulla, 51 cells were examined for their responses to excitation of baroreceptors. An increase in pressure of the 'isolated' carotid sinus excited 2 neurons, and inhibited 7 (14%). On the other hand, 27% (11 out of 41) of neurosecretory cells (second group) were inhibited by baroreceptor stimulation. From these results, it was concluded that essentially separate populations of PVN neurons project to the neurohypophysis and to the NTS, DMV and their vicinities, and that some of the caudally-projecting PVN neurons receive synaptic input from carotid baroreceptor reflex pathway, suggesting the possible involvement of these PVN neurons in central cardiovascular regulation.

Afferent Pathways↗