The neuroanatomical organization and chemosensory response characteristics of the olfactory bulb in the sea lamprey (Petromyzon marinus).

摘要

Olfactory information is utilized for a variety of behaviours including feeding, migration and spawning. The olfactory bulb is the initial site of odour information processing in the central nervous system. The OB organizes this information along parallel processing pathways using topographic and temporal coding. In general, little is known about the neural substrate involved in transforming olfactory information into behavioural responses. In the sea lamprey (Petromyzon marinus) the responses of olfactory sensory neurons in the peripheral olfactory organ are transmitted along two distinct pathways to the medial and non-medial regions of the OB. The neural substrate for olfactory-locomotor transformation was recently identified in the sea lamprey, and demonstrated that projection neurons (PNs) in the medial OB region initiated movements by connecting to locomotor control centers. In contrast, PNs in the non-medial OB region projected to forebrain regions including the pallium. This thesis examines previously unknown anatomical and physiological characteristics of PNs in these medial and non-medial OB regions and relates the findings to these functionally distinct parallel output pathways. The medial PNs were anatomically isolated within the glomerular neuropil, exhibited varied somal shape, and had larger somata than non-medial PNs. Furthermore, the bulbar region containing these medial PNs responded to several different classes of odours with local field potentials (LFPs) being a mixture of transient and sustained responses and relatively short multiunit responses. The somata of non-medial PNs were below the glomerular neuropil and also exhibited varied shapes, but were smaller than the somata of the medial PNs. The LFP and multiunit recordings suggested that within the non-medial OB region, the dorsal territory responded differentially to lamprey sex pheromones and migratory pheromones while lateral recordings exhibited sustained LFP responses and long multiunit responses largely to basic amino acids. These findings suggest that neural organization in the medial OB may be optimized for the initiation of olfactory-locomotor movements in response to diverse odours, while the nonmedial regions exhibit odour specificity and may be optimized for other functional processes such as odour information integration.