Afferent and efferent connections of the olfactory bulbs in the lizard Podarcis hispanica

Abstract

The connections of the olfactory bulbs of Podarcis hispanica were studied by tract-tracing of injected horseradish peroxidase. Restricted injections into the main olfactory bulb (MOB) resulted in bilateral terminallike labeling in the medial part of the anterior olfactory nucleus (AON) and in the rostral septum, lateral cortex, nucleus of the lateral olfactory tract, and ventrolateral amygdaloid nucleus. Bilateral retrograde labeling was found in the rostral lateral cortex and in the medial and dorsolateral AON. Ipsilaterally the dorsal cortex, nucleus of the diagonal band, lateral preoptic area, and dorsolateral amygdala showed labeled cell bodies. Retrogradely labeled cells were also found in the midbrain raphe nucleus. Results from injections into the rostral lateral cortex and lateral olfactory tract indicate that the mitral cells are the origin of the centripetal projections of the MOB. Injections in the accessory olfactory bulb (AOB) produced ipsilateral terminallike labeling of the ventral AON, bed nucleus of the accessory olfactory tract, central and ventromedial amygdaloid nuclei, medial part of the bed nucleus of the stria terminalis, and nucleus sphericus. Retrograde labeling of neurons was observed ipsilaterally in the bed nucleus of the accessory olfactory tract and stria terminalis, in the central amygdaloid nucleus, dorsal cortex, and nucleus of the diagonal band. Bilateral labeling of somata was found in the ventral AON, the nucleus sphericus (hilus), and in the mesencephalic raphe nucleus and locus coeruleus. Injections into the dorsal amygdala showed that the mitral neurons are the cells of origin of the AOB centripetal projections. Reciprocal connections are present between AOB and MOB. To our knowledge, this is the first study to address the afferent connections of the olfactory bulbs in a reptile. On the basis of the available data, a discussion is provided of the similarities and differences between the reptilian and mammalian olfactory systems, as well as of the possible functional role of the main olfactory connections in reptiles.

Efferents and Centrifugal Afferents of the Main and Accessory Olfactory Bulbs in the Snake <i>Thamnophis sirtalis</i>

“…In Nissl stained sections it appears to form part of the complex of cells that surrounds the aot ( fig. 1A, B), but the fact that it receives a clear olfactory projection through the lot [Martínez-García et al, 1991;present report] suggests that it forms part of the olfactory amygdala.…”

“…On the other hand, the centrifugal projections to the bulbs, although equally important in understanding how chemosensory information is processed, have been reported only in one reptilian species, the lizard Podarcis hispanica [Martínez-García et al, 1991].…”

“…Available studies suggest that in reptiles with an accessory olfactory system the MOB projects mainly to the LC, and to a lesser extent to the amygdala, whereas the AOB projects to different amygdaloid nuclei [Halpern, 1976;Lohman et al, 1988;Martínez-García et al, 1991]. In reptiles with poorly developed (or no) accessory olfactory system (turtles and crocodiles), the MOB has extensive projections to both the LC and the amygdaloid formation Reiner and Karten, 1985].…”

A Golgi Study on the Nucleus Sphericus of the Striated Snake, Elaphe quadrivirgata

“…The AOT fibers travel caudally in a thick bundle through the hilus and are distributed totally within the hilar layer, forming a dense fiber plexus. The AC fibers enter the nucleus from the rostromedial aspect and run in an arched course, emitting numerous fine short collaterals.The nucleus sphericus (NS) is a prominent cellular aggregation located in the caudal portion of the telencephalon in certain families of reptiles, and is known to be one of the main terminal areas of the accessory olfactory tract (AOT) (Heimer, 1969;Halpern, 1976;1980;Ulinski and Peterson, 1981;Martinez-Garcia et al 1991). From a hodological viewpoint, the NS is frequently compared to the posteromedial cortical nucleus of the amygdala in mammals.…”

Proliferation, Migration, and Survival of Cells in the Telencephalon of the Ball Python, Python Regius

“…Following Curwen (1939), snake studies labeled the region lateral to the caudalmost NS as "pDVR" (Halpern, 1980;Krohmer and Crews, 1987b;Ulinski and Rainey, 1980). Subsequently, Martinez-Garcia et al (1991) labeled the region as DLA in lizards, and limited the PDVR to the caudal DVR region without this additional area (Martínez-García et al, 1993). This system has been implemented in many contemporary snake and squamate brain studies (Lanuza and Halpern, 1997b;Lanuza and Halpern, 1998;Martínez-García et al, 2007).…”