Unit activity in rat diencephalic islands — the effect of anaesthetics

Abstract

SUMMARY1. Unit activity was recorded with steel micro-electrodes from 486 hypothalamic neurones in rat diencephalic island preparations.2. The histograms of firing frequencies for populations of hypothalamic units from unanaesthetized preparations and from those under urethane anaesthesia were not significantly different. The firing rates of both were significantly faster than those observed in intact brains under urethane.3. The mean distance between stable units in unanaesthetized island preparations did not differ significantly from that in preparations anaesthetized with urethane.4. The response of individual neurones to intravenous injections of urethane was variable, and apparently not associated with the onset or maintenance of anaesthesia. Some showed transient acceleration, some deceleration and some no change in rate or pattern of discharge.5. All neurones tested were slowed or stopped by intravenous injections of subanaesthetic doses of sodium methohexitone (Brietal). The responses were highly reproducible and dose-dependent.6. Brietal also produced a fall in arterial pressure and depressed respiration. Inhalation of amyl nitrite evoked larger hypotensive responses but did not affect unit activity; nor did inhalation of C02 (hypercapnia) or N20 (hypoxia).7. It is concluded that urethane anaesthesia is not associated with any direct action on hypothalamic neurones. The depression of firing rate in hypothalamic neurones induced by Brietal may represent an important forebrain mechanism in anaesthesia by this agent.

Cortical pyramidal tract interneurones and their sensitivity to L‐glutamic acid

“…The animals were anaesthetized with urethane (25 % solution in physiological saline) 5 ml./kg, which, according to several authors, leaves activity in the brain hardly distinguishable from that of unanaesthetized (encephale isole) preparations (Holmes & Houchin, 1966;Cross & Dyer, 1971;Bradley & Dray, 1972).…”

Electrophysiological evidence for the activation of supraoptic neurones during the release of oxytocin

“…Extracellular action potentials were recorded via steel micro-electrodes, insulated with Insl-X (Insl-X Products, N.Y.) and capacity coupled to a preamplifier (Grass Model P16) with a pass band set at 160 Hz-4 kHz. The output of the preamplifier was distributed to various pieces of instrumentation and permanent records of spike data were obtained on film, magnetic tape and on an ink-writing polygraph (Lincoln, 1967;Cross & Dyer, 1971).…”

INHIBITION BY PENTOBARBITONE AND URETHANE OF THE in vitro RESPONSE OF THE ADENOHYPOPHYSIS TO LUTEINISING HORMONE‐RELEASING HORMONE IN MALE RATS

“…There is some evidence that pentobarbitone is a more potent drug than urethane (e.g. Cross & Dyer, 1971;Dyball & McPhail, 1974;Dyer, ter Haar & Mayes, 1978) and it has been questioned whether urethane significantly interferes with the neural processes controlling ovulation (Haller & Barraclough, 1968;Lincoln & Kelly, 1972). Pentobarbitone has been reported to have a direct inhibitory action on the adenohypophysis (Wuttke, Gelato & Meites, 1972) but there are no data about the influence on the anterior pituitary of concentrations of urethane and pentobarbitone likely 0007-1188/79/100277-05 $01.00 to be encountered in neuroendocrine experiments.…”