A study of the amygdaloid defence reaction showing the value of Althesin anaesthesia in studies of the functions of the fore-brain in cats

Abstract

1. In cats under Althesin (alphaxalone-alphadalone) anaesthesia, sites in the amygdala and brain-stem defence areas have been electrically stimulated by means of monopolar, semi-microelectrodes. 2. Such stimulation evoked a consistent pattern of visceral changes characteristic of the alerting stage of the defence reaction as it has been described by previous workers. This "visceral alerting reaction" included increases in arterial blood pressure, heart-rate and cardiac output with vasoconstriction in kidney, intestines and skin but vasodilatation in the hind limbs. 3. These results differ strikingly from those reported previously n that, under conventional anaesthetics, such as chloralose or barbiturate, the full visceral alerting reaction cannot be evoked by amygdala stimulation, or any other manoeuvre which involves transmission through the brain stem defence areas. 4. The area of the amygdala from which such responses can be elicited under althesin closely resembles that which has been reported to evoke defence reactions in conscious animals. 5. It is concluded that Althesin, used in the manner described, does not distort synaptic transmission in the forebrain in the way that conventional anaesthetics do. It is suggested that this steroid anaesthetic may be invaluable in any studies of fore-brain physiology in the cat.

Cardiovascular and phrenic nerve responses to stimulation of the amygdala central nucleus in the anaesthetized rabbit.

“…sites eliciting bradyeardia. In similar experiments in cats amygdala stimulation has been reported to have variable effects on phrenic activity (Bonvallet & Gary Bobo, 1972), to increase both rate and depth of respiration (Timms, 1981) or to entrain respiratory effort (Harper, Frysinger, Trelease & Marks, 1984). In addition, neurones in the c.n.…”

The effect of kindling of different nuclei in the left and right amygdala on anxiety in the rat

“…Stimulation of the amygdala can alter heart rate and blood pressure (Heinemann et al, 1973;Timms, 1981), respiration (Applegate et al, 1983;Harper et al, 1984), and produce a cessation of ongoing behavior (Applegate et al, 1983). In humans, electrical stimUlation of the central amygdala elicits feelings of fear or anxiety, as well as similar autonomic reactions indicative of fear (Chapman et al, 1954;Gloor et l'Il., 1981).…”

Seasonal variations of LH, prolactin, androstenedione, testosterone and testicular FSH binding in the male blue fox (Alopex lagopus)

“…Samples were taken at least every 20 min for 3-7 h. In addition, two of the males were anaesthetized once in January 1983 (during the period of testicular redevelopment) for 5-6 h. The steroid mixture Saffan (Glaxovet, Greenford, Middlesex, England; 9 mg alphaxalone/ml, 3 mg alphadolone/ml) was used as the anaesthetic to minimize disturbances to neuroendocrine function (Timms, 1981 ;Clarke & Doughton, 1983). The animals were premedicated with 5 mg dexachlorpheniramine maléate (Phenamin, Nyco, Oslo, Norway) given subcutaneously 20 min before induction of anaesthesia to prevent possible histamine release as seen with this anaesthetic in dogs (Child et al, 1971).…”