Midbrain tegmentum

Figures 4-6 show the cytoarchitectonic subdivisions which contain dopaminergic cells in the ventral midbrain tegmentum, as illustrated in stereotaxic atlases of the rat and mouse brain. These atlases nowadays represent common laboratory tools, especially for young researchers (who may not be necessarily experts in sophisticated neuroanatomical subdivisions and nomenclature). The SN and its different subdivisions (described in Section 2.2.2) are clearly delineated in Figures 4-6. Medially to the SN, the emphasis on the parcellation (or lack of parcellation) into different nuclei varies slightly according to the authors. The VTA is obviously indicated in all atlases, but its extent is rarely delineated, though the boundaries of this region are outlined at rostral levels in Swanson s...

Fig. 5. The plate illustrates the ventral midbrain tegmentum as illustrated in the atlas of the rat brain of Swanson (1992), at levels approximately equivalent to those shown in Fig. 4. B and D are images of Nissl-stained sections. Abbreviations CLI, central linear nucleus of the raphe cpd, cerebral peduncle DGlb, dentate gyrus, lateral blade EW, Edinger-Westphal nucleus fr, fasciculus retroflexus hf, hippocampal fixure IF, interfascicular...

Opioid receptors (and especially p receptor binding) are abundant in all the subregions of the ventral midbrain tegmentum, including the SNr (Fallon and Loughlin, 1995). 

Fiber terminal networks containing substance P, enkephalin and dynorphin are densely distributed in the ventral midbrain tegmentum (reviewed by Fallon and Loughlin, 1985, 1995). Terminal fibers containing substance P and those containing dynorphin are very dense in the SNr, and more sparsely distributed in the VTA and SNc, whereas the terminal fibers containing enkephalin are concentrated in the SNc and in the dorsal portion of the VTA. 

In the context of the present chapter, it is of special interest that orexin/hypocretin-containing hypothalamic neurons innervate in the ventral midbrain tegmentum the VTA and the SNc with a dense plexus of terminal fibers, whereas the SNr is substantially spared (Fig. 15). Consistently with this pattern of orexin/hypocretin innervation, in the rat orexin 1 and orexin 2 receptor mRNAs are very dense in both the VTA and the SNc, whereas no orexin receptor expression has been detected in the SNr (Marcus et al., 2001). 

Dana C, Vial M, Leonard K, Beauregard A, Kitabgi P, Vincent JP, Rostene W, Beaudet A (1989) Electron microscopic localization of neurotensin binding sites in the midbrain tegmentum of the rat. I. Ventral tegmental area and the interfascicular nucleus. J Neurosci 9 2247-2257. 

Aggressiveness results from the failure of inhibitory neurochemical processes or exaggeration of stimulatory processes in brain regions, such as the orbito-ffontal cortex, the septal area, hippocampus, amygdala, caudate nucleus, thalamus, ventro-medial and posterior hypothalamus, midbrain tegmentum, pons, and the fastigial nuclei and anterior lobe of the cerebellum. 

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