Spatial recognition memory deficits without notable CNS pathology in rats following herpes simplex encephalitis

Area of Science:

• Neuroscience
• Virology
• Immunology

Background:

• Survivors of herpes simplex encephalitis (HSE) exhibit cognitive deficits, particularly in memory storage and recall.
• The temporal lobes and limbic system are crucial for memory and are often impacted in HSE.
• Previous research linked herpes simplex virus type-1 (HSV-1) intranasal inoculation in rats to limbic system lesions.

Purpose of the Study:

• To investigate if rats recovered from HSE exhibit memory impairments.
• To determine the relationship between HSV-1 infection, limbic system function, and behavioral deficits.

Main Methods:

• Rats recovered from experimentally induced HSE were assessed using an eight-arm radial maze.
• Behavioral testing included allocentric-spatial location and egocentric-spatial discrimination tasks.
• In situ hybridization was used to detect HSV-1 nucleic acids in neural tissues.

Main Results:

• HSV-1 infected rats performed at chance levels in allocentric-spatial memory tasks, indicating impaired acquisition and retention.
• Infected rats performed similarly to controls in egocentric-spatial discrimination tasks.
• HSV-1 was detected in hippocampal and entorhinal cortex neurons, yet some rats with deficits showed no clear histopathological evidence of infection.

Conclusions:

• HSV-1 infection can lead to significant learning and memory impairments in rats.
• These behavioral deficits can occur without apparent inflammatory injury to the temporal lobe memory system.
• This study provides the first experimental evidence of HSV-1 causing behavioral impairments in the absence of overt CNS inflammation.