Amygdalar connections in the lesser hedgehog tenrec

Abstract

The present study analyses the overall extrinsic connectivity of the non-olfactory amygdala (Ay) in the lesser hedgehog tenrec. The data were obtained from tracer injections into the lateral and intermediate portions of the Ay as well as several non-amygdalar brain regions. Both the solitary and the parabrachial nucleus receive descending projections from the central nucleus of the Ay, but only the parabrachial nucleus appears to project to the Ay. There is one prominent region in the ventromedial hypothalamus connected reciprocally with the medial and central Ay. Amygdalar afferents clearly arise from the dorsomedial thalamus, the subparafascicular nuclei and the medial geniculate complex (GM). Similar to other subprimate species, the latter projections originate in the dorsal and most caudal geniculate portions and terminate in the dorsolateral Ay. Unusual is the presence of amygdalo-projecting cells in the marginal geniculate zone and their virtual absence in the medial GM. As in other species, amygdalo-striatal projections mainly originate in the basolateral Ay and terminate predominantly in the ventral striatum. Given the poor differentiation of the tenrec's neocortex, there is a remarkable similarity with regard to the amygdalo-cortical connectivity between tenrec and rat, particularly as to prefrontal, limbic and somatosensorimotor areas as well as the rhinal cortex throughout its length. The tenrec's isocortex dorsomedial to the caudal rhinal cortex, on the other hand, may not be connected with the Ay. An absence of such connections is expected for primary auditory and visual fields, but it is unusual for their secondary fields.

Cholinergic, catecholaminergic, serotonergic, and orexinergic neuronal populations in the brain of the lesser hedgehog tenrec (Echinops telfairi)

“…The majority of the Afrotheria are endemic to the African continent, but they are also found on the island of Madagascar, with the sirens showing a far broader distribution across the Indian, Pacific, and Atlantic oceans. The organization of the brain of the lesser hedgehog tenrec, Echinops telfairi, has been the subject of many studies (Alp ar et al, 2010;Kosaka et al, 2005;Krubitzer et al, 1997;Künzle, 1988Künzle, , 1992Künzle, , 1993Künzle, , 1994Künzle, , 1995aKünzle, ,1995bKünzle, , 1996Künzle, , 1998Künzle, , 2002Künzle, , 2003Künzle, , 2005aKünzle, , 2005bKünzle, , 2006Künzle, , 2009Künzle, , 2012Künzle et al, 2002;Künzle & Radtke-Schuller, 2000a, 2000b, 2001Künzle & Rehkämper, 1992;Künzle & Unger, 1992;Morawski et al, 2010;Radtke-Schuller & Künzle, 2000;Schmolke & Künzle, 1997;Stephan et al, 1981;Wolff & Künzle, 1997), making it one of the most intensely studied Afrotherian brains. To the authors' knowledge, no comprehensive mapping studies of the nuclei forming the cholinergic, catecholaminergic, serotonergic, or orexinergic systems in the lesser hedgehog tenrec have been undertaken, although the dopaminergic neurons of the olfactory bulb have been described (Kosaka et al, 2005).…”