Experimental study of the connections of the telencephalon in the rainbow trout (Oncorhynchus mykiss). II: Dorsal area and preoptic region

Abstract

In this study and the accompanying article (Folgueira et al., 2004a), the fluorescent carbocyanine dye 1,1'-dioctadecyl 3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) was used in fixed tissue to comprehensively analyze the connections of the different regions of the telencephalic lobes and the preoptic region of the rainbow trout. Here, we analyze the connections of the dorsal area (D; pallium) of the telencephalon, and the preoptic region, as well as the telencephalic connections of several structures in the diencephalon and brainstem of juvenile trout. The dorsal plus dorsolateral pallial zone of D (Dd+Dl-d) receives afferents from contralateral Dd+Dl-d, the ventral area of the telencephalon, preoptic nucleus, suprachiasmatic nucleus, medial thalamus, preglomerular complex, anterior and lateral tuberal nuclei, posterior tuberal nucleus, posterior hypothalamic lobe, superior raphe nucleus, and the rhombencephalic central gray and reticular formation, and projects to the central zone of D (Dc), medial thalamus, and some caudomedial hypothalamic regions. The medial zone of D (Dm) maintains reciprocal connections with the preglomerular complex and also receives afferents from the preoptic nucleus, suprachiasmatic nucleus, anterior tuberal nucleus, preglomerular tertiary gustatory nucleus, posterior tubercle, superior raphe nucleus, locus coeruleus, and the rhombencephalic central gray, and reticular formation. Dc receives fibers mainly from Dd+Dl-d, preoptic nucleus, preglomerular complex, and torus semicircularis and projects to several extratelencephalic centers, including the paracommissural nucleus, optic tectum, torus semicircularis, thalamus, preglomerular complex, posterior tubercle nuclei, and inferior hypothalamic lobes. The posterior zone of D (Dp) is mainly connected with the olfactory bulbs, the ventral and supracommissural nuclei of the ventral area (subpallium), the preoptic nucleus, and the preglomerular complex and projects to wide hypothalamic and posterior tubercular regions. The preoptic nucleus projects to the olfactory bulb, to most regions of the telencephalic lobes, and to several diencephalic and brainstem structures. These results reveal complex and specialized connectional patterns in the rainbow trout dorsal telencephalon and preoptic region. Most of these connections have not been described previously in salmonids. These connections indicate that the salmonid telencephalon is involved in multisensorial processing and modulation of brain activity.

The Vertebrate mesolimbic reward system and social behavior network: A comparative synthesis

“…This conserved region contains sex steroid hormone receptors (Forlano et al, 2005(Forlano et al, , 2010Munchrath and Hofmann, 2010), and receives fibers from and projects to the telencephalon and hypothalamus (Folgueira et al, 2004b). There are three subdivisions of the teleost POA based on cell size: parvocellular, magnocellular, and gigantocellular (Braford and Northcutt, 1983).…”

“…The medial part of the dorsal telencephalon (Dm) is currently thought to be the putative blAMY homolog. This region receives olfactory input (Folgueira et al, 2004a) as well as other nonchemosensory inputs (Folgueira et al, 2004b), similar to the mammalian blAMY. However, it should be noted that there are subregions of Dm about which little is known in terms of their function.…”

“…The lateral part of the dorsal telencephalon (Dl) is currently thought to be the homolog of the mammalian HIP based on connectivity to the POA and hypothalamus (Folgueira et al, 2004b), and cell mass criteria (Nieuwenhuys, 2009). There is also support for this region being functionally similar to the mammalian HIP, as lesions lead to deficits in spatial learning, but not emotional or cue learning (Portavella et al, 2002;Rodriguez et al, 2002b).…”

Expanded expression of Sonic Hedgehog inAstyanaxcavefish:multiple consequences on forebrain development and evolution

“…The po is another cholinergic region in mammals and also contains cholinergic neurons in fish and other nonmammalian vertebrates (Marin et al, 1997;Pombal et al, 2001;Rodriguez-Moldes et al, 2002). Moreover, in fish, the po projects to the olfactory bulbs (Folgueira et al, 2004), and these projections might represent the fish counterpart of the pathway from basal forebrain cholinergic nuclei of the diagonal band onto the olfactory bulbs of mammals (Shipley, 1985). Importantly, this cholinergic innervation of the bulbs actively participates in olfactory functions, such as early olfactory learning and discrimination (Fletcher and Wilson, 2002;Linster and Cleland, 2002;Wilson et al, 2004).…”

Non-laminar cerebral cortex in teleost fishes?

“…Descending pathways originate mainly from the Dc (figure 2b), which are mostly directed to the optic tectum, torus semicircularis, nucleus lateralis valvulae, nucleus paracommissuralis and inferior lobes of the hypothalamus (Murakami et al 1983 and Dm also give rise to descending fibres (figure 2b), which are targeted mainly to the inferior lobes of the hypothalamus and preglomerular complex (Folgueira et al 2004;Yamamoto & Ito 2005b, 2008Northcutt 2006;Yang et al 2007). Thus, the Dc seems to give rise to longer descending pathways that reach down to the meso-rhombencephalic level than those originating from the Dl and Dm that mostly end in the diencephalon.…”