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H Kannan

Publications and source records attributed to H Kannan.

80 records · Page 5Linked to original sources
PubMed1983

Influences of the limbic system on hypothalamo-neurohypophysial system.

(1) Effects of stimulations of various limbic structures (the olfactory bulb, olfactory tubercle, prepyriform cortex, endopyriform nucleus and various parts of amygdaloid nuclei) on the neurosecretory neurons in the supraoptic (SON) and paraventricular nuclei (PVN) of the hypothalamus were studied. All regions stimulated received strong inputs from the olfactory bulb. (2) Out of 195 "identified' neurosecretory neurons tested one-half or more (49-74%, depending on the structures stimulated) were inhibited by stimuli consisting of 1-3 short pulses. The inhibition occurred immediately after the stimulus in approximately one-fifty of all inhibited neurons, in the remaining four-fifths inhibition occurred after more than 20 ms latency. Inhibition of neurosecretory neuron activity lasted for several hundred milliseconds, often followed by clear post-inhibitory excitation or rebound. (3) In 23 neurons, a distinct "evoked' response of brief duration occurred with a 30 ms latency following stimulation of the lateral and medical amygdala, olfactory tubercle and prepyriform cortex. In another 17 neurons, a general increase in background activity with a longer latency (50-100 ms) occurred following stimulation of nearly all amygdaloid nuclei, olfactory tubercle and the pyriform cortex: lateral amygdala stimulation caused an excitation of the largest proportion of neurosecretory cells (30%) while none was excited by stimulation of the olfactory bulb and endopyriform cortex, except those occurring as post-inhibitory excitation. (4) There was a convergence of afferent impulses on single neurosecretory cells. A large proportion (42%) of the neurons received inputs from 2 to 4 limbic regions. (5) Neurosecretory cells which were influenced by limbic stimuli were also inhibited by baroreceptor activation and excited by osmotic stimulation. "Unidentified' neurons within SON and PVN and "atypical neurosecretory cells' (those responding to pituitary stalk stimulation with varying latencies) were also affected by the forebrain stimulation; some of these were also affected by an osmotic stimulus. A part of this group may send their axons to the median eminence.

Action Potentials↗
PubMed1981

Pathways between the nucleus tractus solitarius and neurosecretory neurons of the supraoptic nucleus: electrophysiological studies.

In anesthetized cats recordings were made from hypothalamo-neurohypophysial neurons in a supraoptic nucleus (SON) of the hypothalamus. The region of the nucleus tractus solitarius in the medulla, identified electrophysiologically as the site of termination of the first relay neurons of the sinus and aortic nerves, was stimulated with single or short trains of pulses (2-3 at 200 Hz). Out of 133 SON neurons 67 were affected by such stimuli. In 14 cells (21% of 'responsive' neurons) the stimulus produced profound inhibition of SON neuron activity after a latency of 10-30 msec. In another 8 neurons (12%) the inhibitory effect was observed after a longer latency of over 100 msec. An increase in intensity of stimulus merely prolonged or increased the inhibitory effect without changing the response qualitatively. The other 45 (67%) SON neurons were excited by stimulation of the nucleus tractus solitarius. In a small proportion of these neurons (5 cells, 7%) the stimulus evoked discharges, even in spontaneously silent neurosecretory cells, after a latency of 10-20 msec with little fluctuation. In the remaining 40 neurons, i.e. 60% of the 'responsive' neurons, the excitatory effect was observed after a latency of 40-120 msec. Again, changes in intensity of stimulation did not alter the nature of this response. The results indicate that both 'fast' as well as 'slow' pathways between the nucleus tractus solitarius and SON neurons exist and impulses travelling through the latter pathway from the carotid sinus or aortic nerve affect the larger proportion of SON neurons.

Afferent Pathways↗
PubMed1981

Pontine neurones: electrophysiological evidence of mediating carotid baroreceptor inputs to supraoptic neurones in rats.

Effects of pressure stimulation of the isolated carotid sinus, of occlusion of the common carotid artery and of tail pinching on the discharge activity of dorsal pontine area neurones and antidromically identified supraoptic neurosecretory neurones were studied in male rats anaesthetized with urethane. Electrical stimulation of the supraoptic nucleus (SON) produced antidromically conducted action potentials in a small number (24/384) of the units recorded in the dorsal pontine area. Pressure pulse stimulation of the isolated carotid sinus inhibited and carotid occlusion facilitated discharge activity in some of the tested dorsal pontine area neurones. In these responsive pontine neurones a transient excitation of grouped discharges was occasionally observed to concur with a small, spontaneous depression of the arterial blood pressure. Tail pinching excited some of these pontine neurones. Histological examination revealed that these responsive neurones were located in the dorsal pontine area close, but ventral and lateral, to the locus coeruleus. Electrical stimulation of the dorsal pons evoked a synaptically mediated excitation in 20 and inhibition in the other seven of the 52 SON units which were identified antidromically after stimulation of the pituitary stalk. Pressure stimulation of the isolated carotid sinus evoked an inhibition of discharge activity in some of th SON units which were excited by dorsal pontine area stimulation. All of the six tested units which showed inhibition after dorsal pontine area stimulation were unresponsive to pressure stimulation. Based on these data, it was concluded that at least some of the neurones which mediate carotid baroreceptor inputs to SON neurosecretory neurones are located in the dorsal pontine area close, but ventral and lateral, to the locus coeruleus and that these dorsal pontine area neurones also mediate converging synaptic inputs originating from somatic pain receptors.

Action Potentials↗
PubMedDate not supplied

The role of cardiovascular and muscle afferent systems in control of body water balance.

Influences of afferent inputs from cardiovascular and muscle receptors on the activities of neurosecretory neurons in the hypothalamus, which secrete vasopressin (ADH) were studied. Recordings were made from identified neurosecretory neurons in the supraoptic (SON) and paraventricular nuclei (PVN) of cats and rats. Activation of baroreceptors in the carotid sinus and aortic arch and atrial receptors inhibited SON and PVN neuron activities, while activation of chemoreceptors in the carotid sinus excited them. Repetitive electrical stimulation of the carotid sinus and aortic nerves showed that weak stimulation produced excitation and stronger stimulation produced inhibition of SON and PVN neurons. Electrical stimulation of these nerves and the nucleus tractus solitarius (NTS) by a single or short train of pulses showed that 'fast' and 'slow' pathways between the NTS and the SON existed, while these two types of pathways were not observed between the NTS and the PVN. Evidence of direct connections from the NTS to the PVN was found by means of antidromic stimulation of the PVN. Electrical stimulations of group I afferent fibers from the gastrocnemius muscle did not change SON neuron discharges, while activation of group III and IV afferent fibers excited them. Injection of chemicals (NaCl, KCl, bradykinin) into arteries supplying the muscle excited SON neurons. The excitation disappeared after section of the muscle nerves. The results indicated that activation of small afferents from the muscle excites the SON neurons, leading to an increase in vasopressin secretion. All these studies show that afferent inputs from receptors in the cardiovascular system and in the muscle have modulatory effects on neurosecretory neurons, and participate in control of body water balance by regulating vasopressin secretion from the neurohypophysis.

Animals↗