Myelinated and unmyelinated baroreceptors: analysis of differential encoding properties

Arterial baroreceplor (UK) activity is highly dependent upon fiber type. Measures of slope and gain as well as baseline activity relative to normal ar terial pressures ( P ) exhibit a spectrum of variability far more heterogeneous for unmyelinated j('-tvpe) than for myeliiiaied (A-tvpe) Bits. 1 he biological factors responsible for these differences are not well understood. Keren! voltage clamp dat.a from our lab indicates a strong correlaiion between ih<> statistical distribution of ion channel kinetic1- and the degree of homogeneity in i lie discharge properties of ('-type and A-tvpe UK neurons. Here, we utili/,1 a inatheniatira.! model of BRs to explore I lie potential mechanisms underlying the differential encoding properties exhibited by each fiber type. The BK model approximates the arterial wall a= a svstem of nonlinear springs and Hit ear viscous elements coupled to neural membrane models of t lie mechanosensitive terminal ending and the spike initiation zone (SIZ). The complete model mimics the static and dynamic discharge patterns off- and A-type UK libers iu response to a range of test P (e.g. steps and ramps). Due to I(K> defer minlstic nature of the equations it is not possible to model the variability in discharge frequency often observed in single fiber BR recordings, a character istir that is also more irregular for ('- than A-type Bits. However, we are able 1 o test the potential contributions of a variety of factors un deriving the rather disparate encoding properties exhibited by ('- and A-type BRs. l'or exam pie. differences across a population of BR libers appear to be related to ion channel kinetics while the intrinsic variability exhibited by a single BK fiber is likely a function of mechanical properties (e.g. coupling, structure) of the terminal ending. This work is part of an integrative effort investigating the signal processing aspects associated with the afferent limb of the barorecepior reflex.