Hypothalamic etiology in sympathetically induced pathogenic cardiovascular changes in the cat

Transient cardiovascular changes, including angina-like electrographic signs, are inducible by electrical stimulation of discrete sites in the prefornical region of the lateral hypothalamus (LH) of cats. Repeated stimulation may result in neurogenic cardiac infarction and myocardial bleeding. Thirty Swiss breed locally grown cats were studied under alpha-chloralose anesthesia in pairs, one as control and one experimental, with only the latter receiving multiple stimulations. ECG in lead II and arterial blood pressure were recorded on a Grass polygraph (USA). Electrical stimulation was delivered to a LH target at Fr 9.0, L2.5, D-1 to -2, by means of stainless steel wire electrodes. Stimulation consisted of 15-sec trains of square wave pulses at 100 Hz, 0.2-0.5 msec duration, and threshold currents of 0.05-0.1 mAmp. Stimulation at these LH sites induced small blood pressure changes, often with a small increase or no change in heart rate, presumably a manifestation of baroreceptor dysfunction. Repeating this stimulation greater than 6 times was shown to be pathogenic: on gross examination a darkened area was seen, mostly on the upper ventricular surface of the heart. Microscopic examination of such sites revealed subendocardial bleeding and sometimes also microinfarcts. Scanning electron microscopy revealed an unusually large number of contractures of the myofilaments. Biochemical analysis showed diffusion of catecholamines from nerves. Total myocardial blood flow increased following such stimulation, proportional to the stimulus intensity. It is pointed out that this is not contradictory to the sharply localized ischemic changes assumed to be responsible for the cardiopathy.