Neonatal excitotoxic ventral hippocampal damage alters dopamine response to mild repeated stress and to chronic haloperidol

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Abstract
The effects of neonatal excitotoxic ventral hippocampus (VH)lesions on dopamine release in response to repeated stress (saline injections) and to chronic haloperidol treatment were investigated in Sprague‐Dawley rats infused with ibotenic acid or vehicle into the VH on day 7 of postnatal life (PD7). Beginning on PD35, lesioned and sham‐operated rats were injected i.p. with saline (INJ) once daily for 3 weeks or were not treated (NO INJ). Another cohort of rats was given haloperidol (HAL, 0.4 mg/kg, i.p.) or vehicle beginning on PD35 and thereafter once daily for 3 weeks. 3‐Methoxytyramine (3‐MT) was measured by combined gas chromatography/mass spectrometry in the frontal cortex (FC), nucleus accumbens (NAcc), and striatum (STR) at PD56 following MA0 inhibition with pargyline. At baseline (NO INJ), 3‐MT was reduced in STR of lesioned rats. Repeated saline injections resulted in a further 3‐MT reduction in STR, FC, and NAcc of lesioned animals, but had no effect in sham rats. Chronic HAL, compared with vehicle, suppressed locomotor activity, and increased 3‐MT accumulation in the FC, NAcc, and STR in sham and lesioned rats. This increase was enhanced in the FC of lesioned rats. These data show that mild repeated stress attenuates dopamine release in FC, NAcc, and STR of lesioned rats, while chronic HAL augments it in FC of lesioned animals versus controls. We conclude that the neonatal excitotoxic lesion of VH alters the functioning of midbrain dopamine systems during environmental and pharmacological challenge.