Chronic administration of citalopram in olfactory bulbectomy rats restores brain 5-HT synthesis rates: an autoradiographic study.

Rationale: The olfactory bulbectomized (OBX) rat model is widely accepted as an animal model of depression with a proposed serotonergic imbalance in the brain.

Objective: To study the effects of chronic administration of citalopram on serotonin (5-HT) synthesis rates.

Method: Serotonin synthesis was evaluated using the alpha-[(14)C]methyl-L: -tryptophan (alpha-MTrp) autoradiographic method in OBX rats. Citalopram was administered continuously (10 mg kg(-1) day(-1)) for 14 days using a subcutaneous osmotic minipump.

Results: The OBX rats treated with citalopram (OBX-CTP) have the same 5-HT synthesis rates as the sham-operated rats treated with citalopram (Sham-CTP). The OBX-CTP rats, relative to the OBX rats treated with saline (OBX-SAL), showed a reduction in the majority of the terminal brain structures, suggesting a normalization of 5-HT synthesis in the OBX-CTP rats following treatment. The OBX-SAL rats have significantly greater synthesis than the Sham-SAL rats in a majority of the terminal structures, but lower rates in the dorsal raphe. A few structures in the OBX-CTP group have lower synthesis than in the Sham-SAL group (e.g., dorsal raphe, hippocampus, amygdala). The data suggest that receptors in some brain areas are likely still responsive to the elevated levels of the extracellular 5-HT produced by citalopram.

Conclusion: There is no significant global or individual structure difference in the synthesis between the Sham-CTP and OBX-CTP groups. The similarity in the synthesis between the OBX-CTP, Sham-CTP and Sham-SAL groups is likely a result of changes in the sensitivity of the receptors through which 5-HT synthesis is controlled. Because of some of the differences in the synthesis between the Sham-CTP and Sham-SAL groups, the data suggest that receptors throughout the brain are not fully desensitized.