Background: After imipenem was introduced in clinical practice, neurologic adverse effects led to recommendations against its use in patients with neurologic conditions. However, these conclusions were drawn without considering pharmacokinetic variations in such patients. Furthermore, animal studies lack the use of clinically relevant doses and supporting morphological studies in both naïve and disease models. Objectives: We aim to study the effects of imipenem in the hippocampus of naïve animals, evaluating potential behavioral and morphological alterations. Methods: Naïve Wistar rats received a 10-day course of intraperitoneal imipenem (40 mg/kg) while controls received a saline injection. After that, they were put through the Morris water maze, elevated plus maze, open-field test, and then euthanized. We analyzed neurogenesis (using doublecortin immunoreactivity), astrogliosis, and the γ-Aminobutyric acid (GABA)ergic system (using parvalbumin (PV), calretinin (CR) and calbindin (CB) immunoreactive (IR) neurons) in the hippocampus. Results: Interestingly, our results showed no significant alterations in both short and long-term memory, nor in anxiety. There were also no significant changes in the neuronal density of doublecortin-immunoreactive (IR) neurons nor in astrogliosis. Furthermore, the areal density of PV- and CR-IR was preserved in all hippocampal subfields. The density of CB-IR neurons also showed no changes in the dentate gyrus, CA3, and subiculum; however, a significant increase was found in the CA1 region. Conclusions: Our results indicate that in naïve individuals, a clinically relevant dose of imipenem does not seem to cause overt behavioral deficits or widespread morphological alterations in the hippocampus. However, a specific increase in the CB-IR neuronal population in the CA1 region highlights a localized cellular alteration/plasticity induced by the imipenem. Hence, pharmacokinetic factors seem to be the potential contributors of imipenem side effects. Further studies should focus on this as a possible cause and focus on individuals with brain diseases.

Background/Objectives: Adverse neurological events caused by imipenem are usually more frequent in patients with epilepsy. This study investigates the effects of imipenem on hippocampal neurogenesis, astroglial activation, and behaviour in animals with pro-epileptogenic alterations. Methods: Five-month-old Wistar rats were divided into four groups: control (CT), pentylenetetrazol (PTZ), imipenem-treated group (IM), and imipenem after PTZ-kindling (IM-PTZ). Epileptogenesis was induced by PTZ-kindling for 28 days, followed by 10 days of imipenem (40 mg/kg) or saline injections. Rats underwent memory and anxiety tests followed by immunohistochemical analyses of doublecortin (DCX) and glial fibrillary acidic protein (GFAP) in the hippocampus. Results: Both kindled groups displayed comparable impairments in spatial learning and working memory, while imipenem alone did not alter behaviour. The IM-PTZ group failed to reach control-level performance only in the final Morris Water Maze acquisition trials, suggesting a deficit in memory consolidation rather than a total loss of retention, as the probe trial remained comparable across all groups. Although PTZ increased anxiety-like behaviour, no locomotor differences were observed in open-field test, confirming cognitive impairments were not due to motor deficits. These behavioural changes mirrored distinct cellular alterations: while PTZ alone triggered a compensatory increase in DCX neuronal density and astrocytic branching, imipenem co-administration suppressed this neurogenic response, bringing DCX to baseline. Furthermore, combined treatment induced an uncoupling of astrocytic response, marked by increased astrocyte density and reduced process complexity in dentate hilus and Cornus Ammonis 3 (CA3). Conclusions: These results suggest that imipenem modulates the cellular substrate of the pre-sensitized brain, interfering with hippocampal plasticity and glial compensatory mechanisms, rather than directly driving further behavioural deterioration.