Sprowls, Caitlin (2017-12). Innervation Patterns of Mystacial Vibrissae Support Active Touch Behaviors in California Sea Lions (Zalophus californianus). Master's Thesis.
Thesis
Vibrissae, or whiskers, are highly developed sensory structures found in mammals. The follicles are referred to as Follicle Sinus Complexes (F-SC) due to the blood-filled sinuses. F-SCs are highly innervated compared to pelage. The most wellknown group of vibrissae, mystacial vibrissae, are found around the muzzle in mammals. Pinnipeds have the largest and most innervated vibrissae of any mammal. More aquatic mammals tend to have larger F-SCs and greater innervation investment (axons per FSC). Behavioral performance studies have shown that California sea lions Zalophus californianus (CSL, an otariid) excel at haptics whereas harbor seals Phoca vitulina (a phocid) excel at hydrodynamic trail following. The data presented in this thesis will infer vibrissal function from these studies. To date there has been no thorough investigation of innervation investment in an otariid. The objectives of this study were to investigate the innervation of the largest F-SCs, compare the innervation and microstructure to the most medial F-SCs, and compare the dorsal to ventral F-SCs. Follicles were dissected from tissues obtained from stranding programs and processed for histology. Axons were counted from wet mounted cross-sections. Asymmetry of axon bundles was present in all F-SC cross sections and have not been described before as well as blood vessels seen entering the DC of the LCS. There was a mean of 75+-5 F-SCs per face muzzle. Innervation increased from medial (705 +-125 axons/F-SC) to lateral (1447+-154) as well as from dorsal (541 +- 60) to the ventral F-SCs (1493 +- 327). Lateral F-SCs axon counts were similar to those in other pinniped studies. The total innervation from lateral axon counts (108,525 axons) agree with other studies but total innervation from all six areas (86,042 axons) was 20% less than values from only lateral F-SCs. Axon density of medial F-SCs were significantly more than lateral F-SCs. This finding is congruent with CSL behavioral performance data that suggest they excel at haptic touch. We found no substantial evidence to differentiate which F-SCs fall into micro- or microvibrissae categories. To date no study has investigated the dorsal-ventral micro anatomical and innervation patterns in any pinniped.
