Grodno State Medical University, 80, Gorkogo St., 230009, Grodno, Republic of Belarus

*Corresponding Author: Lizaveta I Bon, Candidate of Biological Science, Assistant Professor of Pathophysiology Department, D.A. Maslakov, Grodno State Medical University, 80, Gorky St, 230009, Grodno, Belarus; Tel: +375336878764; Email: [email protected]

Received Date: March 7, 2023

Publication Date: March 24, 2023

Citation: Bon EI, et al. (2023). Piriform and Entorhinal Cortex of the Rat Brain – Cyto- And Chemoarchitectonics. Mathews J Case Rep. 8(3):96.

Copyright: Bon EI, et al. © (2023)

ABSTRACT

The piriform (pyriform) cortex is the ancient cortex of the rostral part of the piriform lobe. The name has traditionally been used as a general term for the rostral olfactory nucleus, the primary olfactory (or piriform) cortex, and the entorhinal region, which forms a more or less pear-shaped structure, at least in macrosmatics like the rat.   The entorhinal cortex occupies most of the parahippocampal gyrus and is located on the ventromedial surface of the brain.

The following layers can be distinguished in the entorhinal cortex: molecular, stellate, pyramidal, large cell, small cell, and multiform. The data presented in the article can serve as a fundamental basis for further study of the parts of the rat brain in normal and pathological conditions with further extrapolation of the obtained data to humans.

Keywords: Piriform Cortex, Entorhinal Cortex, Rat, Cytoarchitectonics, Chemoarchitectonics

The Piriform (Pyriform) Cortex

The piriform (pyriform) cortex is the ancient cortex of the rostral part of the piriform lobe.

The name has traditionally been used as a general term for the rostral olfactory nucleus, the primary olfactory (or piriform) cortex, and the entorhinal region, which form a more or less pear-shaped structure, at least in macrosmatics like the rat [4]. Rostrally, the cortex extends into the olfactory tubercle, where it continues into the lateral transition zone of the rostral olfactory nucleus [2-5]. Caudally, it is gradually replaced by the entorhinal region. The cortex is divided into rostral and caudal parts by a transverse line drawn through the caudal pole of the olfactory tubercle [10-14]. The part of the piriform cortex adjacent to the amygdala is sometimes called the periamygdala cortex.

The pear-shaped cortex contains three layers of cells [15-23]. The superficial molecular layer of the piriform cortex contains horizontal neurons, and afferent fibers from the olfactory bulb arrive there [16]. Deeper are the projections of associative fibers from other parts of the piriform cortex and other olfactory areas [20]. Next are the pyramidal and multiform layers (Table 1).

Table 1: Neuronal and transmitter organization of the piriform cortex [28].

Name of neuron	Cortical layer	Mediator
Horizontal neurons	molecular	GABA
pyramidal neurons	pyramidal	aspartate, glutamate, acetylcholine
Polymorphic neurons	granular	GABA

 

 

 

 

 

 

The piriform cortex forms connections with the amygdala [36] and orbitofrontal [22] cortex and pyramidal neurons the processes of remembering olfactory stimuli in rats [23].

Entorhinal cortex

The entorhinal cortex occupies most of the parahippocampal gyrus and is located on the ventromedial surface of the brain.

The following layers can be distinguished in the entorhinal cortex: molecular, stellate, pyramidal, large cell, small cell and multiform. The pyramidal, large cell, and small cell layers are delimited from each other by a separating sublayer [1].

Deeper than the multiform layer is the perforating and alveolar tracts.

The first layer is practically devoid of neurons and contains

transversely oriented nerve fibers.

Layer II mainly contains medium and large stellate neurons. They tend to cluster in clusters (cell islands), caudally they merge to form a continuous layer.

Layer III contains pyramidal neurons.

Layer IV is most pronounced in the caudal entorhinal cortex. In other areas it is fragmentary.

Layer V in the upper part contains sparsely located pyramidal and polymorphic neurons. Then, in its lower sublayer, the neurons lie denser.

Layer VI contains a heterogeneous population of neurons whose perikarya density decreases in the lower regions adjacent to the white matter (Table 2).

Table 2: Neuronal and transmitter organization of the entorhinal cortex.

Name of neuron	Cortical layer	Mediator
Horizontal neurons	molecular, small cell, multiform	GABA
Stellate neurons	stellate, multiform	calretinin
pyramidal neurons	pyramidal, large cell, small cell	aspartate, glutamate calretinin, calbindin
Basket neurons	stellate, pyramidal	GABA, parvalbumin
Candelabra cells	stellate, pyramidal	GABA, parvalbumin
Fusiform neurons	–//–	–//–
Bipolar neurons	small cell, multiforme	calretinin, calbindin somatostatin, substance P
Polymorphic neurons	pyramidal, small cell, multiform	calretinin, calbindin somatostatin substance P

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The entorhinal cortex localized between the association areas of the neocortex [1] and the hippocampus [20].

The entorhinal cortex plays the role of a link in the exchange of information.

Forms connections with the hippocampus, dentate gyrus, subiculum, anterior cingulate cortex, olfactory bulbs, piriform cortex [13] and is involved in the perception of smells.

The data presented in the article can serve as a fundamental basis for further study of the parts of the rat brain in normal and pathological conditions with further extrapolation of the obtained data to humans.

REFERENCES

1. Bon EI. (2022). The central nervous system of the rat. Bon EI*, Maksimovich NYe, Zimatkin SM - Grodno: GrGMU:226.
2. Gottfried JA, Winston JS, Dolan RJ. (2006). Dissociable codes of odor quality and odorant structure in human piriform cortex. Neuron. 49(3):467-479.
3. Shapiro LA, Ng KL, Kinyamu R, Whitaker-Azmitia P, Geisert EE, Blurton-Jones M, et al. (2007). Origin, migration and fate of newly generated neurons in the adult rodent piriform cortex. Brain Struct Funct. 212(2):133-48.
4. Mouly AM, Di Scala G. (2006). Entorhinal cortex stimulation modulates amygdala and piriform cortex responses to olfactory bulb inputs in the rat. Neuroscience. 137(4):1131-1141.
5. Srinivasan S, Stevens CF. (2018). The distributed circuit within the piriform cortex makes odor discrimination robust/ J Comp Neurol. 526(17):2725-2743.
6. Vessal M, Dugani CB, Solomon DA, Burnham WM, Ivy GO. (2004). Astrocytic proliferation in the piriform cortex of amygdala-kindled subjects: a quantitative study in partial versus fully kindled brains. Brain Res. 1022(1-2):47-53.
7. Nasu M, Shimamura K, Esumi S, Tamamaki N. (2020). Sequential pattern of sublayer formation in the paleocortex and neocortex. Med Mol Morphol. 53(3):168-176.
8. Schaffer ES, Stettler DD, Kato D, Choi GB, Axel R, Abbott LF. (2018). Odor Perception on the Two Sides of the Brain: Consistency Despite Randomness. Neuron. 98(4):736-742.
9. Rigas P, Castro-Alamancos MA. (2004). Leading role of the piriform cortex over the neocortex in the generation of spontaneous interictal spikes during block of GABA(A) receptors. Neuroscience. 124(4):953-661.
10. Gurkova IaO, Kalimullina LB. (2003). Neuronal structure of piriform cortex of anterior amygdaloid body of the rat brain/Morfologiia. 123(1):31-34.
11. Löscher W, Ebert U, Wahnschaffe U, Rundfeldt C. (1995). Susceptibility of different cell layers of the anterior and posterior part of the piriform cortex to electrical stimulation and kindling: comparison with the basolateral amygdala and "area tempestas". Neuroscience. 66(2):265-276.
12. Datiche F, Cattarelli M. (1996). Reciprocal and topographic connections between the piriform and prefrontal cortices in the rat: a tracing study using the B subunit of the cholera toxin. Brain Res Bull. 41(6):391-398.
13. Rosin JF, Datiche F, Cattarelli M. (1999). Modulation of the piriform cortex activity by the basal forebrain: an optical recording study in the rat. Brain Res. 820(1-2):105-111.
14. Chapman CA, Racine RJ. (1997). Converging inputs to the entorhinal cortex from the piriform cortex and medial septum: facilitation and current source density analysis. J Neurophysiol. 78(5):2602-2615.
15. Chen Z, Padmanabhan K. (2022). Top-down feedback enables flexible coding strategies in the olfactory cortex. Cell Rep. 38(12):110545.
16. Heggli DE, Malthe-Sørenssen D. (1982). Systemic injection of kainic acid: effect on neurotransmitter markers in piriform cortex, amygdaloid complex and hippocampus and protection by cortical lesioning and anticonvulsants. Neuroscience. 7(5):1257-1264.
17. KREINER J. (1949). Myeloarchitectonics of the lateral olfactory tract and of the piriform cortex of the albino rat. J Comp Neurol. 91(1):103-127.
18. East BS, Fleming G, Vervoordt S, Shah P, Sullivan RM, Wilson DA. (2021). Basolateral amygdala to posterior piriform cortex connectivity ensures precision in learned odor threat. Sci Rep. 11(1):21746.
19. Zinyuk LE, Datiche F, Cattarelli M. (2001). Cell activity in the anterior piriform cortex during an olfactory learning in the rat. Behav Brain Res. 124(1):29-32.
20. Calu DJ, Roesch MR, Stalnaker TA, Schoenbaum G. (2007). Associative encoding in posterior piriform cortex during odor discrimination and reversal learning. Cereb Corte. 17(6):1342-1349
21. Howard JD, Plailly J, Grueschow M, Haynes JD, Gottfried JA. (2009). Odor quality coding and categorization in human posterior piriform cortex. Nat Neurosci. 12(7):932-938.