In the brain, the perforant path or perforant pathway provides a connectional route from 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 ...

to all fields of the hippocampal formation, including 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 ...

, all CA fields (including CA1), and the subiculum. Though it arises mainly from entorhinal layers II and III, the perforant path comprises a smaller component that originates in deep layers V and VI. There is a major dichotomy with respect to the laminar origin and related terminal distribution: neurons in layer II (and possibly layer VI) project to the

and CA3, whereas layer III (and possibly layer V) cells project to CA1 and the subiculum via the temporoammonic pathway. In addition to playing a role in spatial memory learning generally, the temporoammonic branch (TA-CA1) of the perforant path mediates spatial memory consolidation. The temporoammonic pathway has also been implicated in stress-based animal models of depression. It may also play a role in temporal lobe seizures.

In rats

In rats,

pyramidal A pyramid (from el, πυραμίς ') is a structure whose outer surfaces are triangular and converge to a single step at the top, making the shape roughly a pyramid in the geometric sense. The base of a pyramid can be trilateral, quadrilate ...

and stellate cells in layer II of

project through the subiculum of the hippocampus, giving rise to the name "perforant pathway". These

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 ...

rgic fibers form a laminar pattern and terminate in the dentate gyrus and cornu ammonis 3 (CA3) region of the hippocampus. Fibers arising in the lateral portions of the entorhinal cortex show

enkephalin An enkephalin is a pentapeptide involved in regulating nociception in the body. The enkephalins are termed endogenous ligands, as they are internally derived and bind to the body's opioid receptors. Discovered in 1975, two forms of enkephalin ...

immunoreactivity, whereas medial portions appear to contain

cholecystokinin Cholecystokinin (CCK or CCK-PZ; from Greek ''chole'', "bile"; ''cysto'', "sac"; ''kinin'', "move"; hence, ''move the bile-sac (gallbladder)'') is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat an ...

. Additionally, pyramidal cells in layer III of the entorhinal cortex send topographic projections along the perforant pathway which branch into the subiculum and CA1.

In mice

In mice, the projection to CA1, and the subiculum all come primarily from EC layer III. According to Suh et al. (2011 Science 334:1415) the projection to CA3 and dentate gyrus in mice is primarily from layer II of entorhinal cortex, and forms a trisynaptic path with hippocampus (dentate gyrus to CA3 to CA1), distinguished from the direct (monosynaptic) perforant path from Layer III of entorhinal cortex to CA1 and subiculum.

References

* Shepherd, GM. ''The Synaptic Organization of the Brain''. New York: Oxford University Press. 1998.

External links

* http://thebrain.mcgill.ca/flash/a/a_07/a_07_cl/a_07_cl_tra/a_07_cl_tra.html {{Papez circuit Hippocampus (brain)