Serotonergic fibers distribution in the midline and intralaminar thalamic nuclei in the rock cavy (Kerodon rupestris)

Abstract

The thalamic midline/intralaminar complex is part of the higher-order thalamus, which receives little sensory input, and instead forms extensive cortico-thalamo-cortical pathways. The midline thalamic nuclei connect with the medial prefrontal cortex and the medial temporal lobe. On the other hand, the intralaminar nuclei connect with the fronto-parietal cortex. Taking into account this connectivity pattern, it is not surprising that the midline/intralaminar complex has been implicated in a broad variety of cognitive functions, including memory process, attention and orientation, and also reward-based behavior. Serotonin (5-HT) is a neurotransmitter that exerts different post-synaptic roles. Serotonergic neurons are almost entirely restricted to the raphe nuclei and the 5-HT fibers are distributed widely throughout the brain, including the midline/intralaminar complex. The present study comprises a detailed description of the morphologic features and semiquantitative analysis of 5-HT fibers distribution in the midline/intralaminar complex in the rock cavy, a typical rodent of the Northeast region of Brazil, which has been used by our group as an anatomical model to expand the comprehension about phylogeny on the nervous system. The 5-HT fibers in the midline/intralaminar nuclei of the rock cavy were classified into three distinct categories: (1) beaded fibers, which are relatively fine and endowed with large varicosities; (2) fine fibers, with thin axons and small varicosities uniformly distributed in whole axon; and (3) stem axons, showing thick non-varicose axons. Moreover, the density of 5-HT fibers is variable among the analyzed nuclei. On the basis of this diversity of the morphological fibers and the differential profile of optical density among the midline/intralaminar nuclei of the rock cavy, we conclude that the serotonergic system uses a diverse morphologic apparatus to exert a large functional repertory in the midline/intralaminar thalamic nuclei.

Limbic thalamus and state-dependent behavior: The paraventricular nucleus of the thalamic midline as a node in circadian timing and sleep/wake-regulatory networks

“…Thus, PVT receives a dense aminergic innervation from the brain stem: adrenergic innervation from the medulla oblongata (Otake and Ruggiero, 1995;Phillipson and Bohn, 1994), noradrenergic fibers from the locus coeruleus (Jones and Yang, 1985;Krout et al, 2002;Vogt et al, 2008), serotonergic innervation from the median and dorsal raphe (Cropper et al, 1984;de Medeiros Silva et al, 2014;Hsu and Price, 2009;Otake and Ruggiero, 1995;Vertes et al, 2010), dopaminergic fibers which derive primarily from cells of the periventricular and posterior hypothalamic areas (García-Cabezas et al, 2007Hökfelt et al, 1976;Otake and Ruggiero, 1995;Takada et al, 1990). The aminergic innervation of PVT includes histaminergic fibers deriving from the tuberomammillary nucleus of the posterior hypothalamus (Airaksinen and Panula, 1988;Airaksinen et al, 1989;Jin et al, 2002;Panula et al, 1989).…”

The Neurofunctional Model of Consciousness: The Physiological Interconnectivity of Brain Networks

“…On the other hand, the functions of the ILN and the MTN are functionally differentiated, but their activity are highly dependent [91][92][93][94][95]. Regarding consciousness, both nuclei (due to its multiple connections with the ARAS) activate the excitability of the cerebral cortex to maintain vigilance and arousal [42, 58-60, 76, 91].…”