The Brain And Behavior by Unknown

Author:Unknown
Language: eng
Format: epub
Published: 0101-01-01T00:00:00+00:00

8: Diencephalon: Hypothalamus and Epithalamus

concentrated in the ventromedial hypothalamus (arc-

uate, ventromedial, and dorsomedial nuclei). Leptin is

released into the blood stream following food intake.

Administration of intravenous leptin stimulates arc-

uate nucleus neurons that results in the suppression of

feeding (Saper, 2012). Stereotactic lesions of the ven-

tromedial nucleus have been used in an attempt to

treat alcoholism, drug addiction, and hypersexuality.

Increase in body weight was a common side effect of

these lesions (Nadvornik, Sramka, and Patoprsta,

1975).

Medial Zone: Posterior Level, Mammillary and Posterior

Nuclei

The mammillary nuclei/body marks the caudal

extent of the medial hypothalamus. The largest num-

ber of afferents to the mammillary body comes from

the hippocampus by way of the fornix. This connec-

tion with the hippocampus suggests that the mam-

Figure 8.4 A magnetic resonance image (aT2-weighted)

demonstrated a high-intensity lesion in the right hypothalamus

millary bodies are also involved in emotion as well as

(arrow). (Reprinted with permission from Kostic, Stefanova, Svetel,

memory. Fibers from the mammillary body make up

and Kozic,1998.)

the mammillothalamic tract, which ascends to the

anterior nucleus of the thalamus, a major component

of the limbic thalamus and circuit of Papez

Medial Zone: Tuberal Level, Ventromedial Nucleus

(Figure 11.5).

The ventromedial nucleus is located below the dor-

The mammillary body is important in several

somedial nucleus and just anterior to the mammillary

aspects of memory, including spatial working memory

bodies (Figures 8.2 and 8.3). It receives input from the

and the head-direction network. Vitamin B1 deficiency,

amygdala, ventral tegmental area, and arcuate nucleus

sometimes due to alcoholism, anorexia nervosa, or

of the hypothalamus and is sensitive to a number of

bariatric surgery, can produce cell loss in the mammil-

circulating factors. It projects heavily to the periaque-

lary bodies, resulting in Wernicke–Korsakoff syn-

ductal gray and the nuclei of the basal forebrain

drome with confusion, apathy, confabulation, and

including the basal nucleus (of Meynert).

anterograde amnesia (Sechi and Serra, 2007). In

The ventromedial nucleus is implicated in sex and

addition, the size and number of neurons of the mam-

aggression. It is sensitive to estrogen and oxytocin

millary bodies was found to be less when patients with

levels and is important in producing the lordosis

depression were examined at autopsy (Bernstein et al.,

response in female rats. Projections from the ventro-

2012).

medial nucleus to the periaqueductal gray may be the

The posterior nucleus is important in thermore-

route by which this region of the hypothalamus

gulation (heating). A lesion of the posterior nucleus

induces

sexual

behavior

(Veening,

de

Jong,

results in hypothermia.

Waldinger, Korte, and Olivier, 2015). In rats, expo-

sure to a predator or an aggressive conspecific (fear)

Lateral Zone: Orexin/Hypocretin Neurons

activated the ventromedial nucleus, but exposure to

Large neurons are interspersed among the fibers of

footshock (pain) did not. It also functions in support

the medial forebrain bundle that course through

of aggressive behavior associated with conspecific

the lateral zone of the hypothalamus. The large

social fear (Silva et al., 2013).

neurons contain either melanin-concentrating hor-

The ventromedial nucleus and surrounding area is

mone or orexin/hypocretin and project to all areas

also recognized as the satiety center. A lesion of the

of the cerebral cortex and are involved in appetite

ventromedial hypothalamus results in hyperphagia

and wakefulness. In the human, orexin/hypocretin

and obesity (King, 2006). Leptin receptors are

neurons tend to be concentrated in the posterior

14:30:57

09

8: Diencephalon: Hypothalamus and Epithalamus

zone. Melanin-concentrating hormone promotes

ingestion and sleep. Orexin/hypocretin enhances

The second case is that of a 24-year-old woman

who presented with episodes of explosive behavior,

wakefulness, feeding, and locomotion.

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