The supramammillary nucleus (SuM), or supramammillary area, is a thin layer of cells in the brain that lies above the

mammillary bodies The mammillary bodies are a pair of small round bodies, located on the undersurface of the brain that, as part of the diencephalon, form part of the limbic system. They are located at the ends of the anterior arches of the fornix. They consist o ...

. It can be considered part of the

hypothalamus The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamu ...

and

diencephalon The diencephalon (or interbrain) is a division of the forebrain (embryonic ''prosencephalon''). It is situated between the telencephalon and the midbrain (embryonic ''mesencephalon''). The diencephalon has also been known as the 'tweenbrain in ol ...

. The nucleus can be divided into medial and lateral sections. The medial SuM, or SuM_M, is made of smaller cells which release

dopamine Dopamine (DA, a contraction of 3,4-dihydroxyphenethylamine) is a neuromodulatory molecule that plays several important roles in cells. It is an organic compound, organic chemical of the catecholamine and phenethylamine families. Dopamine const ...

and give input to the lateral septal nucleus. The lateral SuM, or SuM_L, is made of larger cells that project to the

hippocampus The hippocampus (via Latin from Greek , 'seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic system, a ...

Functions

Although the exact function of the supramammillary nucleus is still not clear, it is known that the SuM plays a role in modulating

theta Theta (, ; uppercase: Θ or ; lowercase: θ or ; grc, ''thē̂ta'' ; Modern: ''thī́ta'' ) is the eighth letter of the Greek alphabet, derived from the Phoenician letter Teth . In the system of Greek numerals, it has a value of 9. Gr ...

frequencies. Because of its role in modulating hippocampal theta, it is implicated in spatial and emotional memory formation. The axons of SuM neurons make monosynaptic connections to granule cells and GABAergic interneurons in the

dentate gyrus The dentate gyrus (DG) is part of the hippocampal formation in the temporal lobe of the brain, which also includes the hippocampus and the subiculum. The dentate gyrus is part of the hippocampal trisynaptic circuit and is thought to contribute ...

. The SuM projects it's afferent signals exclusively to the dentate gyrus and CA2 region of the hippocampus. These SuM neurons will co-release

glutamate Glutamic acid (symbol Glu or E; the ionic form is known as glutamate) is an α-amino acid that is used by almost all living beings in the biosynthesis of proteins. It is a non-essential nutrient for humans, meaning that the human body can syn ...

and GABA, but these inputs will not fully excite the granule cells. Although it will not cause an

action potential An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, ...

alone, SuM neurons can have excitatory impact on granule cells with the help of perforant path inputs. The

perforant path In the brain, the perforant path or perforant pathway provides a connectional route from the entorhinal cortex to all fields of the hippocampal formation, including the dentate gyrus, all CA fields (including CA1), and the subiculum. Though it a ...

way are fibers that connect the

entorhinal cortex The entorhinal cortex (EC) is an area of the brain's allocortex, located in the medial temporal lobe, whose functions include being a widespread network hub for memory, navigation, and the perception of time.Integrating time from experience in the ...

with the hippocampus. This pathway accounts for the major inputs to the hippocampus and

. Ultimately, the SuM will modulate the granule cell outputs causing it to influence the dentate gyrus information processing.

References

Neurons {{Neuroanatomy-stub