title: Antidromic activation of spikes with bimodal and trimodal latencies in the olfactory bulb of rabbits.
abstract: Spikes with bimodal and occasional trimodal latencies were recorded from neurons in the olfactory bulb of rabbits in response to lateral olfactory tract (LOT) stimulation at one site. Among neurons with bimodal spike latencies, two types have to be distinguished. In the case of type I neurons long-latency second-mode spikes were suppressed by short-latency first-mode spikes. Due to this suppression the long-latency second-mode spike could be investigated only, when its threshold was lower than that of the short-latency spike. In the case of type II neurons the long-latency second-mode spike was not suppressed. The collision test was applied to type I bimodal spikes. All short-latency first-mode and long-latency second-mode spikes were suppressed by spontaneous spikes. The suppression time indicated the likelihood of collision in most cases, but one could not entirely exclude the possibility, that short-latency first-mode spikes were suppressed due to refractoriness and long-latency second-mode spikes due to inhibition. To allow a more definite interpretation of collision a multiple collision test was applied, by stimulating axons at several LOT sites. A parallel rise of latency values and suppression time values was measured for 3 and more axonal spikes with different latencies, indicating collision and antidromic activation more definitely. Antidromically activated short-latency first-mode spikes were interpreted to be due to axonal stimulation and antidromically activated long-latency second-mode spikes to be due to axon collateral stimulation. No evidence for any postsynaptic activation of type I short-latency first-mode or long-latency second-mode spikes was gained. An indicator for collision of an antidromic spike with a spontaneous spike is the value collision time minus latency (c-l). The c-l values of axonal spikes ranged from 0.2 to 1.8 ms with a mean of 0.7 ms (n = 25), and c-l values of axon collateral spikes from 0.2 to 2.5 ms, with a mean of 1.1 ms (n = 13). The interpretation of c-l values is discussed. In the multiple collision test the c-l deviations from the lowest c-l value of each neuron ranged for axonal spikes between 0.0 and 0.7 ms (n = 25), with 38% not exceeding 0.1 ms and 81% not exceeding 0.4 ms. Spikes activated via axon collaterals had c-l deviations between 0.0 and 2.0 ms (n = 13). The c-l deviations above 2 ms were remote from other values and considered to be possibly inhibitory.(ABSTRACT TRUNCATED AT 400 WORDS)
mesh_terms: D000344:Afferent Pathways / Q000502:physiology; D000818:Animals; D001370:Axonal Transport; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000187:drug effects; D005703:Gallamine Triethiodide / Q000494:pharmacology; D009474:Neurons / Q000502:physiology; D009830:Olfactory Bulb / Q000502:physiology*; D011817:Rabbits
chemical_list: D005703:Gallamine Triethiodide