Studies of antidromically identified neurosecretory cells of the hypothalamus by intracellular and extracellular recordings

Abstract

SUMMARY1. Neurosecretory neurones in supraoptic (SON) and paraventricular (PVN) nuclei of the hypothalamus of cats, anaesthetized with chloralose, and dogs, anaesthetized with Nembutal, were studied. These neurosecretory neurones were identified by action potentials evoked antidromically following stimulation of the posterior lobe of the pituitary gland. Reactions of 158 such neurones in cats and 228 in dogs were analysed.2. The latencies of antidromic potentials evoked in neurosecretory neurones by posterior lobe stimulation were between 10 and 22 msec for SON and between 14 and 28 msec for PVN cells. Approximate speed of conduction in the axons was 0 4-0 9 m/sec. The absolute refractory period for the soma-dendritic (SD) spike was 5-10 msec. These cells followed repetitive stimulation up to a rate of 100/sec.A notch was generally present on the rising phase of antidromic potentials and when the antidromically conducted signal fell in the relative refractory period of the preceding response, a complete separation between this first small A-spike and later large B-spikes, probably soma-dendritic spike, frequently occurred. Thus, two responses, a small and a large, sometimes appeared with more than 10 msec intervening. When the second antidromic response fell in the absolute refractory period of the first, the B-spike was blocked and only the A-spike appeared.3. Intracellular recordings from neurosecretory cells, mainly from SON in the dog, showed that these neurones possess resting membrane potentials of 50-80 mV, and action potentials of the same magnitude.In spontaneously firing neurosecretory cells separate A-and B-spikes also occurred and could be recorded intracellularly. three spikes with latencies of 10-30 msec. Excitation was followed by an inhibition, of 'spontaneous' discharges as well as of subsequent antidromic excitation, lasting 100-500 msec. Intracellular recordings from neurosecretory cells showed that stimulations of the septal area and RF produced action potentials or EPSPs of short duration followed by long lasting IPSPs. Hyperpolarization was always longer than the preceding EPSP, and its duration was generally 80 msec. Large IPSPs of 20 mV could be recorded occasionally.7. Antidromic excitation of neurosecretory cells by stimulation of the posterior pituitary was followed by the inhibition of 'spontaneous' discharges of the cells. This inhibition usually lasted for 100 msec. A corresponding IPSP was recorded during this inhibitory phase. These findings indicate the existence of recurrent collaterals in neurosecretory cells.8. This conclusion that recurrent collaterals exist was also supported by other evidence, namely, that certain neurones were found in the SON and PVN which responded to a single pulse antidromic stimulation of the posterior pituitary with five to seven discharges at a rate of between 500 and 800/sec. Weaker stimuli produced fewer spikes. Such cells resembled in their behaviour 'Renshaw cells' of the spinal cord. RF stimulation had an inhibitory effect on some of these neur...

Physiological and morphological identification of hypothalamic magnocellular neuroendocrine cells in goldfish preoptic nucleus*

“…2 and 3). I have not as yet found unequivocal physiological evidence which either supports or refutes the finding of i.p.s.p.s from electrical stimulation of the neural lobe (Kandel, 1964;Koizumi & Yamashita, 1972) and suggests a recurrent collateral inhibitory pathway between magnocellular neuroendocrine cells.…”

Phasic bursting activity of rat paraventricular neurones in the absence of synaptic transmission

“…Recurrent synaptic inhibition has been reported to exist in the hypothalamoneurohypophysial system of the goldfish (Kandel, 1964), the cat (Barker, Crayton & Nicoll, 1971;, cat and dog (Koizumi & Yamashita, 1972) and the rat (Kelly & Dreifuss, 1970;Dreifuss & Kelly, 1972a;Negoro & Holland, 1972;Dyball, 1974). Certain cells antidromically activated by electrical stimulation of the posterior pituitary or infundibular stalk, show prolonged after hyperpolarizations that can be enhanced with depolarizing current injections.…”

Intrinsic inhibition in magnocellular neuroendocrine cells of rat hypothalamus.

“…The evidence is derived primarily from extracellular recordings of antidromically activated magnocellular neurones, where reduced spontaneous firing implied inhibition. A period (25-125 ms) of reduced spontaneous firing after an antidromic spike suggested recurrent inhibition in the rat (Dreifuss & Kelly, 1972;Negoro & Holland, 1972), cat (Barker, Crayton & Nicoll, 1971;Koizumi & Yamashita, 1972), and monkey (Hayward & Jennings, 1973 a). Increased stimulus intensity occasionally enhanced and prolonged inhibition.…”