Organization of the Zone of Transition between the Pretectum and the Thalamus, with Emphasis on the Pretectothalamic Lamina

Abstract

The zone of transition between the pretectum, derived from prosomere 1, and the thalamus, derived from prosomere 2, is structurally complex and its understanding has been hampered by cytoarchitectural and terminological confusion. Herein, using a battery of complementary morphological approaches, including cytoarchitecture, myeloarchitecture and the expression of molecular markers, we pinpoint the features or combination of features that best characterize each nucleus of the pretectothalamic transitional zone of the rat. Our results reveal useful morphological criteria to identify and delineate, with unprecedented precision, several [mostly auditory] nuclei of the posterior group of the thalamus, namely the pretectothalamic lamina (PTL; formerly known as the posterior limitans nucleus), the medial division of the medial geniculate body (MGBm), the suprageniculate nucleus (SG), and the ethmoid, posterior triangular and posterior nuclei of the thalamus. The PTL is a sparsely-celled and fiber rich flattened nucleus apposed to the lateral surface of the anterior pretectal nucleus (APT) that marks the border between the pretectum and the thalamus; this structure stains selectively with the Wisteria floribunda agglutinin (WFA), and is essentially immunonegative for the calcium binding protein parvalbumin (PV). The MGBm, located medial to the ventral division of the MGB (MGBv), can be unequivocally identified by the large size of many of its neurons, its dark immunostaining for PV, and its rather selective staining for WFA. The SG, which extends for a considerable caudorostral distance and deviates progressively from the MGB, is characterized by its peculiar cytoarchitecture, the paucity of myelinated fibers, and the conspicuous absence of staining for calretinin (CR); indeed, in many CR-stained sections, the SG stands out as a blank spot. Because most of these nuclei are small and show unique anatomical relationships, the information provided in this article will facilitate the interpretation of the results of experimental manipulations aimed at the auditory thalamus and improve the design of future investigations. Moreover, the previously neglected proximity between the MGBm and the caudal region of the scarcely known PTL raises the possibility that certain features or roles traditionally attributed to the MGBm may actually belong to the PTL.

The nucleus pretectalis principalis: A pretectal structure hidden in the mammalian thalamus

“…In a recent exhaustive report of the cytoarchitecture and neurochemistry of the pretecto‐thalamic transition zone, Márquez‐Legorreta, Horta‐Júnior, Berrebi and Saldaña () identify the pretectothalamic lamina as the border that separates several posterior thalamic structures, including the medial division of the MGB, the suprageniculate and ethmoid nuclei, from the anterior pretectal nucleus. The band formed by the Pul‐T cells is located dorsally and caudally to the pretectothalamic lamina, and may constitute an extension to visual areas of the border formed by the pretectothalamic lamina, which surrounds mainly auditory nuclei (Márquez‐Legorreta et al, ).…”

Evaluation of medial division of the medial geniculate (MGM) and posterior intralaminar nucleus (PIN) inputs to the rat auditory cortex, amygdala, and striatum

“…Linke and colleagues (Linke, ; Linke et al, ; Linke & Schwegler, ) agreed with this scheme with the exception of the exact positions of MGM relative to PIN. Subsequent additional cytoarchitecture, myeloarchitecture and molecular marker evidence (Marquez‐Legorreta et al, ) further modified these positions. Figure a illustrates these differences.…”

“…The medial division of the medial geniculate (MGM) and the posterior intralaminar nucleus (PIN) also known as PIL (Paxinos & Watson, ) are situated immediately medial to the ventral division of the medial geniculate (MGV) and ventral to the boundary between MGV and the dorsal division of the medial geniculate (MGD). Although there are disagreements as to their exact borders relative to one another in the rat (see Bordi & LeDoux, , ; Lanuza, Moncho‐Bogani, & Ledoux, ; Linke, ; Linke & Schwegler, ; Marquez‐Legorreta et al, ) both MGM and PIN are classified as association nuclei of the acoustic thalamus (Ledoux, Ruggiero, Forest, Stornetta, & Reis, ; Winer & Morest, ; Winer, Morest, & Diamond, ). Regardless of these boundary disagreements, there are several common anatomical and physiological features linking cells in this region.…”

Adenosine A1 Receptor mRNA Expression by Neurons and Glia in the Auditory Forebrain

“…The division between MGm and the suprageniculate nucleus (Sg) was approximated in figures, but their cell counts were combined, as definitive borders between the two divisions were ambiguous in these preparations, and because transcript distributions were typically uniform across the region. The difficulties in delineation of Sg in mouse have been noted previously, (Jones, ; Watson et al, ), and identification varies across studies (Cruikshank et al, ; Anderson et al, ; Lu et al, ; Anderson and Linden, ; Marquez‐Legorreta et al, ).…”

“…The difficulties in delineation of Sg in mouse have been noted previously, Abbreviations: ms, mouse; rb, rabbit; G/g, goat, Ch, chicken. (Jones, 2007;Watson et al, 2012), and identification varies across studies (Cruikshank et al, 2001;Anderson et al, 2009;Lu et al, 2009;Anderson and Linden, 2011;Marquez-Legorreta et al, 2016).…”