Deficits of Learning and Spatial Memory are Associated with Increased Pyknosis of Pyramidal Neurons of the Hippocampus of Adult Rats with Chronic Hydrocephalus
Authors: Femi-Akinlosotu OM , Shokunbi MT , Olopade FE , Igbong P 
Published: July 2022

Background: The hippocampus is the brain's center for the consolidation of short-term and spatial memory that enables navigation. Hippocampal injury occurs in hydrocephalus and is associated with loss of memory.

Objective: We assessed pyknotic changes in kaolin-induced chronic hydrocephalus in adult rats using qualitative and quantitative means, and related these to memory deficits in the rats.

Methods: Adult rats were randomly divided into control and experimental groups. Hydrocephalus was induced by intracisternal injection of 0.1ml sterile kaolin suspension for 6weeks. Control rats received sham injections. Spatial memory was assessed with the Morris water maze test. Coronal sections of the brains were grouped into either mild or moderate hydrocephalus and then stained with H&E and cresyl violet stains. Thus, there were three groups: control, mild hydrocephalus and moderate hydrocephalus (n=10), respectively.

Results: Shrinking and thinning of the hippocampal tissue, distortion of the pyramidal layer and pyknotic cells were observed in the CA1 and CA3 regions of the hydrocephalic rats. The pyknotic indices in the mild hydrocephalic rat (Cornus Ammonis, CA) CA1, CA2, CA3 (54.30±1.38; 27.62±0.83; 57.61±0.74) and moderate hydrocephalic rat CA1, CA2, CA3 (48.18±0.67; 32.00±0.84; 42.41±1.19) regions were significantly increased compared to the controls' CA1, CA2, CA3 (12.14±0.56; 9.21±0.36; 13.04±0.59).

Conclusion: Chronic hydrocephalus in adult rats was associated with cell death in all the regions of the hippocampus, irrespective of the degree of ventricular enlargement. The extent of cell death corresponded with the severity of learning and memory deficits.

Background: The hippocampus is the center of the brain for the consolidation of short-term memory and spatial memory that enables navigation. Hippocampal damage occurs in hydrocephalus and is associated with memory loss.

Objective: We assessed pyknotic changes in chronic kaolin-induced hydrocephalus in adult rats using qualitative and quantitative means, and related them to memory deficits in rats.

Methods: Adult rats were randomly assigned to control and experimental groups. Hydrocephalus was induced by intracisternal injection of 0.1 ml of sterile kaolin suspension for 6 weeks. Control rats received sham injections. Spatial memory was assessed by the Morris water maze test. Coronal sections of brains were grouped into mild or moderate hydrocephalus and then stained with H&E and cresyl violet. There were therefore three groups: control, mild hydrocephalus and moderate hydrocephalus (n=10), respectively.

RESULTS: Shrinking and thinning of hippocampal tissue, distortion of the pyramidal layer, and pyknotic cells were observed in the CA1 and CA3 regions of hydrocephalic rats. The pyknotic indices in the CA1, CA2 and CA3 regions of mild hydrocephalic rats (Cornus Ammonis, CA) (54.30±1.38; 27.62±0.83; 57.61±0.74) and hydrocephalic rats moderate CA1, CA2 and CA3 (48.18±0.67; 32.00±0.84; 42.41±1.19) were significantly increased compared to the CA1, CA2, CA3 regions of controls (12.14±0.56; 9.21±0.36; 13.04±0.59).

Conclusion: Chronic hydrocephalus in adult rats was associated with cell death in all regions of the hippocampus, regardless of the degree of ventricular enlargement. The extent of cell death corresponded to the severity of learning and memory deficits.

Key words: Chronic hydrocephalus, hippocampus, adult rats, memory, pyknotic cells.

Keywords: Adult rats; Chronic hydrocephalus; hippocampus; memory; pyknotic cells.