‘Satiety’ and ‘feeding’ center in the hypothalamus

Satiety center is a group of cells in the ventromedial hypothalamus that when stimulated suppress a desire for food.


Feeding center is a group of cells in the lateral hypothalamus that when stimulated cause a sensation of hunger.

In the hypothalamus, there are two nerve centers whose actions have opposite effects. If one of these, the feeding center, is stimulated, an animal will eat whether he is hungry or not. If the feeding center is removed, the animal will not eat. The other hypothalamic center is called the satiety center. The satiety center tells the organism when he has had enough to eat. Removal of the satiety center causes an animal to eat continuously and he will grow far beyond his normal size.

When we are subjected to certain stimuli, the hunger-producing center initiates the eating response. When we have eaten enough, the satiety center tells us to stop.

Many of the stimuli that tell the hypothalamus that we are hungry originate in the organs of the body. If the nutrient level of the blood is too low, the hypothalamus is alerted and the feeding center, initiates eating behavior. External stimuli can also initiate eating behavior. The sight, sound, and even the thought of food initiate impulses that eventually reach the feeding center in the hypothalamus. Specific hungers are stimulated by specific deficiencies

Neurotransmitter

Neurotransmitters are endogenous chemicals which relay, amplify, and modulate signals between a neuron and another cell.Neurotransmitters are packaged into synaptic vesicles that cluster beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to receptors in the membrane on the postsynaptic side of the synapse. Release of neurotransmitters usually follows arrival of an action potential at the synapse, but may follow graded electrical potentials. Low level "baseline" release also occurs without electrical stimulation.


Criteria to identify neurotransmitter
1. presence in presynaptic nerve terminal

2. synthesis by presynaptic neuron

3. releasing on stimulation (membrane depolarisation)

4. producing rapid-onset and rapidly reversible responses in the target cell

5. existence of specific receptor

5HT receptors in CNS

5 HT receptors in CNS are all G-protein coupled receptors except 5HT3 receptors (ligand gated cation channel).

14 identified sub types.

5HT1 : mainly inhibitory, 5HT1A : autoreceptors that limit rate of firing of cells, widely distributed in limbic system and main target to treat anxiety and depression (5HT1A antagonist, Buspirone used for anxiety).

5HT1B & 5HT1D receptors : in basal ganglia
5HT1D agonists (Sumatriptan): used to treat migraine.

5HT2 (mainly 5HT2A) : excitatory postsynaptic effect and abundant in cortex and limbic system, target of hallucinogenic drugs, 5HT2 antagonists (methysergic) are used for treatment of migraine.

5HT3 : area postrema (in medulla, involved in vomiting) and other parts of brainstem extending to dorsal horn of spinal cord, cortex and PNS. 5HT3 antagonists (Ondansetron) are used to treat nausea and vomiting.

5HT4 : important in GIT, also present in CNS especially in striatum enhancing cognitive performance.

5HT6 : occur only in CNS, in hippocampus, cortex and limbic system, potential target for treatment of cognition and schizophrenia.

5HT7: hippocampus, cortex, thalamus and hypothalamus, blood vessels and GIT. May have thermoregulatory and endocrine function, cognitive function and sleep.