RESUMO
A defining feature of the amniote tecto-fugal visual pathway is a massive bilateral projection to the thalamus originating from a distinct neuronal population, tectal ganglion cells (TGCs), of the optic tectum/superior colliculus (TeO/SC). In sauropsids, the thalamic target of the tecto-fugal pathway is the nucleus rotundus thalami (Rt). TGCs axons collateralize en route to Rt to target the nucleus pretectalis principalis (PT), which in turn gives rise to bilateral projection to the TeO. In rodents, the thalamic target of these TGCs afferents is the caudal division of the pulvinar complex (PulC). No pretectal structures in receipt of TGC collaterals have been described in this group. However, Baldwin et al. (Journal of Comparative Neurology, 2011;519(6):1071-1094) reported in the squirrel a feedback projection from the PulC to the SC. Pulvino-tectal (Pul-T) cells lie at the caudal pole of the PulC, intermingled with the axonal terminals of TGCs. Here, by performing a combination of neuronal tracing, immunohistochemistry, immunofluorescence, and in situ hybridization, we characterized the pattern of projections, neurochemical profile, and genoarchitecture of Pul-T cells in the diurnal Chilean rodent Octodon degus. We found that Pul-T neurons exhibit pretectal, but not thalamic, genoarchitectonical markers, as well as hodological and neurochemical properties that match specifically those of the avian nucleus PT. Thus, we propose that Pul-T cells constitute a pretectal cell population hidden within the dorsal thalamus of mammals. Our results solve the oddity entailed by the apparent existence of a noncanonic descending sensory thalamic projection and further stress the conservative character of the tectofugal pathway.
Assuntos
Octodon/anatomia & histologia , Pulvinar/anatomia & histologia , Animais , Feminino , Masculino , Vias Neurais/anatomia & histologia , Vias Neurais/metabolismo , Neurônios/citologia , Neurônios/metabolismo , Octodon/metabolismo , Pulvinar/metabolismo , Teto do Mesencéfalo/anatomia & histologia , Teto do Mesencéfalo/metabolismoRESUMO
Despite the implication of fronto-striatal circuits in attention-deficit/hyperactivity disorder (ADHD), there is a lack of information on the role of these regions, especially the thalamus, in the heterogeneity of ADHD. We assessed the (1)H-magnetic resonance spectroscopy profile in ventromedial prefrontal cortex (VMPFC)-thalamic-striatal regions bilaterally in three groups of subjects (age range 18-24 years old): ADHD inattentive type (ADHD-I; n = 9), ADHD combined type (ADHD-C; n = 10) and non-ADHD controls (n = 12). The peaks of N-acetylaspartate, Choline (Cho), myo-inositol (mI), creatine (Cr) and glutamate-glutamine-GABA (Glx) to Cr were calculated. Subjects with ADHD-C showed lower mI/Cr ratio in the right VMPFC than controls, higher Cho/Cr ratio in the left thalamus-pulvinar than the ADHD-I group and higher Glx/Cr ratio in left putamen than individuals with ADHD-I and controls. This metabolic profile suggests a disruption of fronto-striato-thalamic structures in the ADHD-C as a result of lower neuronal energetic metabolism.