Kenyon cells are the intrinsic neurons of the

mushroom body The mushroom bodies or ''corpora pedunculata'' are a pair of structures in the brain of insects, other arthropods, and some annelids (notably the ragworm ''Platynereis dumerilii''). They are known to play a role in olfactory learning and memory. ...

, a neuropil found in the brains of most arthropods and some

annelid The annelids (Annelida , from Latin ', "little ring"), also known as the segmented worms, are a large phylum, with over 22,000 extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecol ...

s. They were first described by F. C. Kenyon in 1896. The number of Kenyon cells in an organism varies greatly between species. For example, in the fruit fly, '' Drosophila melanogaster,'' there are about 2,500 Kenyon cells per mushroom body, while in cockroaches there are about 230,000.

Structure

While the exact features of Kenyon cells can vary between species, there are enough similarities to define their general structure. Kenyon cells have dendritic branches that arborize in the calyx or calyces, cup-shaped regions of the mushroom body. At the base of the calyces, Kenyon cell axons come together and form a bundle known as the pedunculus. At the end of the pedunculus, Kenyon cell axons bifurcate and extend branches into the vertical and medial lobes. Kenyon cells are mainly postsynaptic in the calyces, where their

synapse In the nervous system, a synapse is a structure that permits a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or to the target effector cell. Synapses are essential to the transmission of nervous impulses from ...

s form microglomeruli. These microglomeruli are made up of Kenyon cell dendrites, cholinergic boutons, and

GABAergic In molecular biology and physiology, something is GABAergic or GABAnergic if it pertains to or affects the neurotransmitter GABA. For example, a synapse is GABAergic if it uses GABA as its neurotransmitter, and a GABAergic neuron produces GABA. A ...

terminals. Antennal lobe projection neurons are the source of the cholinergic input, and the GABAergic input is from protocerebral neurons. Kenyon cells are presynaptic to mushroom body output neurons in the lobes. However, the lobes are not only output regions; Kenyon cells are both pre and postsynaptic in these regions. The cells are subdivided into subtypes; for example, those that have their cell bodies outside of the

calyx Calyx or calyce (plural "calyces"), from the Latin ''calix'' which itself comes from the Ancient Greek ''κάλυξ'' (''kálux'') meaning "husk" or "pod", may refer to: Biology * Calyx (anatomy), collective name for several cup-like structures ...

cup are called ''clawed Kenyon cells''.

Development

Kenyon cells are produced from precursors known as

neuroblast In vertebrates, a neuroblast or primitive nerve cell is a postmitotic cell that does not divide further, and which will develop into a neuron after a migration phase. In invertebrates such as ''Drosophila,'' neuroblasts are neural progenitor cells ...

s. The number of neuroblasts varies greatly between species. In ''Drosophila melanogaster'', Kenyon cells are produced from only four neuroblasts, while in the honey bee they are the product of thousands of neuroblasts. Differences in neuroblast number between species are related to the final number of Kenyon cells in an adult. The positioning of Kenyon cells depends on their birth order. The somata of early-born Kenyon cells are pushed outward as more Kenyon cells are created. This results in a concentric pattern of cell bodies, with the somata of the last-born cells in the center, where the neuroblast had been, and the somata of the first-born cells at the outermost margins of the cell body area. Where a Kenyon cell sends its dendrites in the calyces and which lobes it projects its axons to varies based on its birth-order. Distinct types of Kenyon cells form at specific times during development.

Function

Mushroom bodies are essential for

olfactory The sense of smell, or olfaction, is the special sense through which smells (or odors) are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste. In humans, it ...

learning and memory. Odor information is represented by sparse combinations of Kenyon cells. Learning is facilitated by

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 ...

-driven

plasticity Plasticity may refer to: Science * Plasticity (physics), in engineering and physics, the propensity of a solid material to undergo permanent deformation under load * Neuroplasticity, in neuroscience, how entire brain structures, and the brain it ...

of the odor response of Kenyon cells. The cAMP signaling cascade, especially protein kinase A, must function properly in Kenyon cells for learning and memory to occur. Information about odors may be encoded in the mushroom body by the identities of the responsive neurons as well as the timing of their spikes. Experiments in locusts have shown that Kenyon cells have their activity synchronized to 20-Hz neural oscillations and are particularly responsive to projection neuron spikes at specific phases of the oscillatory cycle.

References

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External links

The mushroom bodies
- with a description of the Kenyon cells.

Arthropod anatomy Animal nervous system