Axonal projections and conduction properties of olfactory peduncle neurons in the armadillo (Chaetophractus vellerosus)

Summary

Extracellular unit recording was employed to study the axonal properties and efferent projections of antidromically identified neurons in the olfactory peduncle (OP) region of a primitive eutherian macrosmatic mammal, the south american armadillo (Chaetophractus vellerosus). Of 72 cells which satisfied the criteria for antidromic invasion, 55 (76%) and 17 (24%) responded to ipsi- and contralateral olfactory bulb (IOB; COB) stimulation, respectively. The absolute refractory period (3.25±0.3 ms; mean±SE) and the conduction velocity (CV; 1.94±0.2 m/s; mean±SE) of IOB and COB driven neurons were negatively correlated (r=-0.52; p < 0.001). In paired-shock tests (8–1950 ms interval), and early supernormal period (SPN) of increased CV and excitability was found following the relative refractory period in 82% of tested cells (N=50); this period was followed by a late subnormal phase (SBN) of decreased CV and increased threshold in 58% of neurons (N=50). Significant correlations were found to exist between: CV and absolute magnitude of latency variation (r=-0.55; p < 0.001; n=43), CV and duration of SPN and SBN periods (r=-0.60; p < 0.002; n=24 and r=0.58; p < 0.02; n=19, respectively) and between duration of SPN and SBN phases (r=0.79; p < 0.001; n=30). Maximum latency variation during the SPN and SBN periods was attained in a gradual, additive manner. 90% of long-latency units (15–30 ms; n=22) showed progressive increases in initial antidromic latency (16–22% of control) when stimulated with pulse frequencies of 2.5, 10,15, 20 or 40 Hz; initial antidromic latency and magnitude of latency increase were positively correlated (r=0.92).