BRS

Chapter 21 Neurotransmitters and Pathways

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■ shows a significant loss of neurons in Alzheimer and Parkinson diseases. ■ modulates levels of arousal, upregulated in threatening/stressful events, has a role in anxiety and panic disorders in situations of chronic stress. 2. Lateral tegmental area ■ located in the medulla and pons. ■ projects via the central tegmental tract and the medial forebrain bundle to the hypothal amus and thalamus.

V. SEROTONIN (5-HYDROXYTRYPTAMINE)

A. Characteristics ■ mostly localized to gastrointestinal (GI) tract where it regulates GI motility. ■ found in the raphe nuclei of the brainstem—plays a role in pain modulation. ■ role in influencing arousal, sensory perception, emotion, mental status (eg, anxiety and mood), and higher cognitive functions. ■ tricyclic antidepressants and fluoxetine increase 5-hydroxytryptamine (5-HT) availability by reducing its reuptake. B. Major serotonergic pathways (Figure 21.5) ■ 5-HT neurons are found in the raphe nuclei of the brainstem. Raphe nuclei project diffusely to the entire CNS (Figure 21.4). 1. Raphe nuclei of the medulla ■ project to the posterior horns of the spinal cord. 2. Raphe nuclei of the pons ■ project to the spinal cord and cerebellum. 3. Raphe nuclei of the midbrain ■ project to widespread areas of the diencephalon and the telencephalon, including the striatum.

Serotonin

x

Thalamus

e

r t

c o

e o

N

Medial forebrain bundle

C i n

g u l a

t e

g y

r u

s

Fornix

Striatum Septal nuclei Hypothalamus Mammillary nucleus

Nucleus raphe dorsalis

Amygdala Hippocampal formation

Locus ceruleus

Cerebellar cortex

Tryptophan

Tryptophan-hydroxylase

Sup. nucleus centralis

Nuclei raphe obscurus and pallidus

5-Hydroxytryptophan

Nucleus raphe pontis

Copyright © 2023 Wolters Kluwer, Inc. Unauthorized reproduction of the content is prohibited. Spinal cord Aromatic L-amino acid decarboxylase Serotonin (5-hydroxytryptamine) Nucleus raphe magnus

FIGURE 21.5. Distribution of 5-hydroxytryptamine (serotonin)-containing neurons and their projections. Serotonin- containing neurons are found in nuclei of the raphe. They project widely to the forebrain, cerebellum, and spinal cord. The inset shows the synthetic pathway of serotonin.