Olfactory bulbectomy protects hippocampal pyramidal neurons against excitotoxic death

Fluoxetine modulates hippocampal cell signaling pathways implicated in neuroplasticity in olfactory bulbectomized mice

The olfactory bulbectomy (OB) animal model of depression is a well-established model that is capable of detecting antidepressant activity following chronic drug therapy, and the surgery results in behavioral and biochemical changes that are reminiscent of various symptoms of depression. In the present study, we investigated the degree to which 14 days of p.o. administration of the classic antidepressant fluoxetine (10mg/kg) were able to reverse OB-induced changes in behavior (namely, hyperactivity in the open-field test and reduced motivational and self-care behaviors in the splash test) and in the activation of hippocampal cell signaling pathways that are thought to be involved in synaptic plasticity. OB caused significant increases in ERK1 and CREB (Ser(133)) phosphorylation and in the expression of BDNF immunocontent, all of which were prevented by fluoxetine administration. Moreover, fluoxetine administration also caused a significant decrease in ERK2 phosphorylation in mice that had undergone OB. Neither Akt nor GSK-3β phosphorylation was altered in any experimental condition. In conclusion, the present study shows that OB can induce significant behavioral changes that are accompanied by the activation of hippocampal signaling pathways, namely the ERK1/CREB/BDNF pathway, which is involved in the synaptic plasticity. Conversely, fluoxetine prevented these OB-induced behavioral changes and avoided the activation of ERK1/CREB/BDNF in the hippocampus. Taken together, our results extend the data from the existing literature regarding OB-induced behavioral and neurochemical changes, and suggest a possible underlying mechanism that can account for the antidepressant effect of fluoxetine in this model.

A Cupric Silver Histochemical Analysis of Domoic Acid Damage to Olfactory Pathways Following Status Epilepticus in a Rat Model for Chronic Recurrent Spontaneous Seizures and Aggressive Behavior

The amnesic shellfish toxin, domoic acid, interferes with glutamatergic pathways leading to neuronal damage, most notably causing memory loss and seizures. In this study, the authors utilized a recently developed rat model for domoic acid–induced epilepsy, an emerging disease appearing in California sea lions weeks to months after poisoning, to identify structural damage that may lead to a permanent epileptic state. Sprague Dawley rats were kindled with several low hourly intraperitoneal doses of domoic acid until a state of status epilepticus (SE) appears. This kindling approach has previously been shown to induce a permanent state of epileptic disease in 96% animals within 6 months. Three animals were selected for neurohistology a week after the initial SE. An amino cupric silver staining method using neutral red counterstain was used on every eighth 40 µm coronal section from each brain to highlight neural degeneration from the olfactory bulb through the brain stem. The most extensive damage was found in the olfactory bulb and related olfactory pathways, including the anterior/medial olfactory cortices, endopiriform nucleus, and entorhinal cortex. These findings indicate that damage to olfactory pathways is prominent in a rat model for domoic acid–induced chronic recurrent spontaneous seizures and aggressive behavior.

Locomotor sensitization to cocaine in rats with olfactory bulbectomy

Olfactory bulbectomy in rats has been suggested as a comprehensive animal model of affective disorders associated with an array of behavioral changes, responsivity to chronic antidepressant treatment, and alterations in limbic structures thought to be critical in the pathophysiology of affective disorders. Recent work showing increased motivational responsivity to amphetamine suggests that olfactory bulbectomy could also be a useful animal model of dual diagnosis disorders. To further investigate this possibility, we studied locomotor activity in olfactory bulbectomized rats 14 days postsurgery in response to novelty and upon acute and repeated injections of cocaine (15/mg/kg) or saline. Consistent with prior studies, lesioned animals showed greater locomotor activity in response to a novel environment and significantly heightened locomotor activation upon initial cocaine exposure. Over 7 days of repeated cocaine injections, lesioned animals also showed a presensitized pattern of activity, with a loss of incremental increases in locomotion observed in control animals. Daily saline injections produced no group differences in pre- or postinjection activity, while cocaine-treated bulbectomized rats demonstrated a decline in their daily preinjection activity. These results suggest that neural alterations caused by olfactory bulbectomy produce altered behavioral response patterns to repeated doses of cocaine, and support the study of olfactory bulbectomy as a useful neurobehavioral model for understanding substance use disorder comorbidity in mental illness.