Figure 9. Physiological properties of a type V neurone.

Aa, elevation or reduction of arterial blood pressure (AP, mmHg) using aortic occlusion (AOc) or sodium nitroprusside (SNP) does not alter the discharge rate of this neurone. Ab, hypothalamic stimulation (arrow) applied outside the critical period after occurrence of a spontaneous spike (s) elicits an antidromic spike (a, top four traces) which frequently fails to invade the soma (IS in the second and fourth traces from top). Hypothalamic stimulation applied within the critical period after the spontaneous spike fails to elicit an antidromic spike (bottom three traces). Ac, left column, spontaneous spike (s), antidromic spike (a) and initial segment of antidromic spike (IS). Ac, right column, superposition of spontaneous and antidromic spike (top) and superposition of antidromic spike and antidromic initial segment (bottom). Ba, toe pinch elicits small increases in arterial blood pressure but fails to alter unit discharge consistently. Bb, cardiopulmonary receptor stimulation with phenylbiguanide (PBG, 10 μg kg⁻¹, i.v.) has no consistent effect on discharge rate.