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BRS Neuroanatomy

C. Pineal gland (epiphysis cerebri) ■ contains the highest concentration of 5-HT in the CNS; however, the vast majority (85%–90%) is found in the gut. ■ contains pinealocytes, which convert 5-HT to melatonin.

VI. OPIOID PEPTIDES

A. Endorphins (Figure 21.6) ■ derived from three peptide precursors: (1) pro-opiomelanocortin , the precursor of adrenocorti cotropic hormone; (2) proenkephalin ; and (3) prodynorphin . ■ include beta-endorphin, the major endorphin found in the brain. ■ endorphinergic neurons are found primarily in the hypothalamus (arcuate and premammil lary nuclei). These neurons project to the hippocampus, amygdala, nucleus accumbens, septal area, thalamus, and locus ceruleus (midbrain and pons). ■ major role in endocrine function.

B. Enkephalins (Figure 21.7) ■ all three peptide precursors produce enkephalin.

■ the most widely distributed and abundant opioid peptides. ■ found in highest concentrations in the globus pallidus . ■ synthesized in striatal neurons, which project to the globus pallidus. ■ located mainly in local circuits of the limbic and striatal systems. ■ coexist with dopamine, norepinephrine, ACh, and GABA. ■ role in pain suppression in the posterior horn of the spinal cord.

Endorphins

Septal nuclei

Thalamus

Arcuate nucleus

Fornix

Nucleus accumbens

Amygdala

Hippocampal formation

Locus ceruleus

Copyright © 2023 Wolters Kluwer, Inc. Unauthorized reproduction of the content is prohibited. FIGURE 21.6. Distribution of endorphin-containing neurons and their projections. Endorphinergic neurons are found al most exclusively in the hypothalamus (arcuate nucleus).