Feline cerebral veins and arteries: comparison of autonomic innervation and vasomotor responses

Abstract

1. The innervation of feline cerebral (pial) vessels by nerve fibres containing noradrenaline, substance P or vasoactive intestinal polypeptide (VIP) has been examined using the Falck—Hillarp histo‐fluorescence method and immunohistochemical techniques. Cerebral veins were shown to be innervated by nerve fibres containing noradrenaline, substance P or VIP. Nerve fibres containing noradrenaline were the most numerous, while fibres containing substance P were observed least frequently in both types of vessel. For each putative neurotransmitter, the density of the innervation of the cerebral veins was less than that of cerebral arteries. 2. The vasomotor responses of individual pial arteries and veins on the convexity of the cerebral cortex to perivascular micro‐injection of noradrenaline, substance P and VIP were examined in twenty‐five cats anaesthetized with α‐chloralose. 3. The perivascular micro‐application of noradrenaline resulted in pronounced dose‐dependent reductions in the diameter of pial veins (maximum calibre reduction: 32±3% noradrenaline 10⁻⁵ M) and arteries (22±3% noradrenaline 10⁻⁵ M). Pial veins were more sensitive to noradrenaline than were pial arteries tested under similar conditions. The reductions in the diameter of cerebral veins and arteries resulting from the administration of noradrenaline could be attenuated by the concomitant micro‐application of phentolamine (10⁻⁶ M). 4. The perivascular micro‐application of substance P effected significant dose‐dependent increases in the calibre of pial veins (maximum calibre increase: 16±4% substance P 10⁻⁷ M) which were of a similar magnitude to those observed in pial arteries in response to this peptide (21±4% substance P 10⁻⁶ M). 5. The perivascular micro‐application of VIP resulted in small increases in the calibre of pial veins (maximum calibre increase: 9±2% VIP 10⁻⁸ M) which were proportionately smaller than those observed in pial arteries in response to this peptide (23±5% VIP 10⁻⁷ M).