Characteristics of the sympathetic innervation of the nictitating membrane and of the vasculature of the nose and tongue of the cat

Differential neural activation of vascular alpha-adrenoceptors in oral tissues of cats

The aim of this study was to determine the relative contribution of alpha(1)- and alpha(2)-adrenoceptors involved in sympathetic-evoked vasoconstrictor responses in tissues perfused by the lingual arterial circulation in pentobarbital anesthetized cats. Blood flow in the lingual artery was measured by ultrasonic flowmetry. Laser-Doppler flowmetry was utilized to measure oral tissue vasoconstrictor responses in the maxillary gingiva and from the surface of the tongue. Electrical stimulation of the preganglionic superior cervical sympathetic nerve resulted in frequency-dependent blood flow decreases at all three sites. These responses were stable over time and were uniformly antagonized by administration of phentolamine (0.3 - 3.0 mg kg(-1)). The selective alpha(1)-adrenoceptor antagonist, prazosin (10 - 300 microg kg(-1)), attenuated vasoconstriction in the lingual artery and gingiva, but was ineffective in blocking vasoconstriction in the tongue. Subsequent administration of rauwolscine (300 microg kg(-1)) antagonized remaining vasoconstrictor responses. In contrast, rauwolscine (10 - 300 microg kg(-1)), given alone, blocked evoked vasoconstriction in the tongue, and was without effect on gingival or lingual artery vasoconstrictor responses. Subsequent administration of prazosin (300 microg kg(-1)) largely antagonized remaining neurally elicited responses. These results suggest that neural vasoconstrictor responses in some regional vascular beds in the cat oral cavity are mediated by both alpha(1)- and alpha(2)-adrenoceptors. In contrast, tongue surface vasoconstrictor responses to sympathetic nerve activation appear to be mediated primarily by alpha(2)-adrenoceptors.

Innervation of individual guinea-pig superior cervical ganglion cells by axons with similar conduction velocities

1. Individual neurones in the guinea-pig superior cervical ganglion were studied to determine whether they are innervated by preganglionic axons with similar conduction velocities. 2. Latencies of synaptic responses recorded intracellularly in ganglion cells after stimulation of individual ventral roots varied from 28 to 430 msec. Most of this variability arose from differences in preganglionic conduction velocity. 3. The twelve different axons that on average innervate each ganglion cell tended to have broadly similar conduction velocities; a neurone receiving a rapidly conducting input was usually contacted by other rapidly conducting axons, and vice versa. 4. Preferential innervation of individual neurones by axons with similar conduction velocities was evident even when only axons arising from the same spinal segment were compared. Thus preferential innervation by axons of similar conduction velocity cannot be simply a manifestation of segmental preferences. 5. These results suggest that the mature pattern of innervation in mammalian sympathetic ganglia reflects the functional as well as the positional qualities of the synaptic partners.

Relaxation of smooth muscle following contraction elicited by sympathetic nerve stimulation in vivo

1. A method for studying in vivo the process of neuroeffector transmission in the nictitating membrane and nasal blood vessels of the cat is described. 2. Administration of desmethylimipramine or cocaine caused increases in both the amplitude and duration of the nasal and membrane responses which may be explained by inhibition of neuronal uptake of noradrenaline. 3. Phenoxybenzamine depressed the responses to nerve stimulation, but had little effect on the relationship between response amplitude and rate of recovery. 4. The relationship between response amplitude and rate of recovery is discussed and related to the sigmoid shape of a log concentration-response curve.