Selective olfactory pathway lesions differentially affect runway behavior of the rat

In vivo imaging of functional disruption, recovery and alteration in rat olfactory circuitry after lesion

Compensatory changes following disruption of neuronal circuitry have been indicated by previous imaging studies of stroke and other brain injury, but evidence of the pathways involved in such dynamic changes has not been shown in vivo. We imaged rats before and after lesion-induced disruption of the lateral olfactory tract to investigate the subsequent recovery and/or reorganization of functional neuronal circuitry. Serial magnetic resonance imaging was performed following intranasal administration of a paramagnetic track tracer Mn(2+). Images were analyzed using statistical mapping techniques in the stereotactic coordinate system. At 1 week post-lesion, Mn(2+) transport caudal to lesion was reduced as expected, and more importantly, increased transport through the anterior commissure was seen. At 4 weeks post-lesion, there was recovery of transport caudal to lesion, and increased transport through the anterior commissure extended to the contralateral olfactory cortex. Correlation analysis of regional Mn(2+) transport indicated that contralateral enhancement was not simply due to septal window spillover. This study demonstrates for the first time in vivo evidence of compensatory changes in functional neuronal activity to a contralateral pathway through the commissure following brain injury.

Neurotoxic effects of secalonic acid D in mice during subchronic postnatal exposure

To establish a dose-response of neurotoxic effects to daily oral doses of the mycotoxin secalonic acid D (SAD), as well as to correlate the neonatal behavioral responses to smaller doses of SAD with the attendant neurochemical effects in mice, 5 neonates of each sex were placed with each mother and 4 litters were treated orally with 0 to 5 mg/kg of SAD daily from postnatal day (PND) 3 through 35. Body weights, toxic signs, and mortality were used to arrive at no observable effect level (NOEL). Performance in several behavioral tests and changes in regional norepinephrine and dopamine levels in the brains of neonates treated with SAD at NOEL (1.25 mg/kg/day) or below were evaluated at selected times during SAD exposure. Doses as low as 1.25 mg/kg/day reversibly reduced body weights in both sexes on PND 12 and 13 compared to controls, whereas doses of 2.5 mg/kg/day or greater were lethal (LD50 of 2.5 mg/kg/day). Toxic signs observable in neonates receiving 2.5 mg/kg/day or more of SAD included fine body tremors, uncoordinated movements, hindlimb weakness, circling, loss of righting reflex, paddling, and terminal coma. Ontogeny of cliff avoidance (PND 5, 7, and 9), hindlimb grip response (PND 14, 17, and 20), olfactory discrimination (PND 8 through 11) and swimming (PND 13 through 21) were significantly delayed by SAD exposure: some even at 0.625 mg/kg/day. Dopamine levels significantly increased on PND 13 and decreased on PND 20 only in the olfactory lobe of SAD-exposed neonates. Norepinephrine levels were unchanged in all the brain regions examined.(ABSTRACT TRUNCATED AT 250 WORDS)