Iodo-QNB cortical binding and brain perfusion: effects of a cholinergic basal forebrain lesion in the rat

Change of central cholinergic receptors following lesions of nucleus basalis magnocellularis in rats: search for an imaging index suitable for the early detection of Alzheimer's disease

Cholinergic system in the central nervous system is involved in the memory function. Thus, because the dysfunction of cholinergic system that project to the cerebral cortex from nucleus basalis of Meynert (nbM) would be implicated in the memory function deficits in Alzheimer's disease (AD), evaluating cholinergic function may be useful for the early detection of AD. In this study, because the nucleus basalis magnocellularis (NBM) in rats is equivalent to nbM in human, we investigated the change in cholinergic receptors in the frontal cortex of rats with unilateral lesion to the NBM to find an appropriate index for the early detection of AD using techniques of nuclear medicine. The right NBM was injected with ibotenic acid. [(18)F]FDG-PET images were obtained 3 days later. Some rats were sacrificed at 1 week, whereas others were subjected to a second [(18)F]FDG-PET at 4 weeks then sacrificed for membrane preparation. The prepared membranes were subjected to radioreceptor assays to measure the density of nicotinic and muscarinic acetylcholine receptors. Glucose metabolism had decreased on the damaged side compared to the control side at 3 days, but at 4 weeks, there was no difference between the sides. Nicotinic acetylcholine receptors had significantly decreased in density compared to the control side at both 1 and 4 weeks. However, muscarinic receptors were not affected. These results suggested that neuronal dysfunction in AD could be diagnosed at an early stage by imaging nicotinic acetylcholine receptors.

Septohippocampal acetylcholine: involved in but not necessary for learning and memory?

The neurotransmitter acetylcholine (ACh) has been accorded an important role in supporting learning and memory processes in the hippocampus. Cholinergic activity in the hippocampus is correlated with memory, and restoration of ACh in the hippocampus after disruption of the septohippocampal pathway is sufficient to rescue memory. However, selective ablation of cholinergic septohippocampal projections is largely without effect on hippocampal-dependent learning and memory processes. We consider the evidence underlying each of these statements, and the contradictions they pose for understanding the functional role of hippocampal ACh in memory. We suggest that although hippocampal ACh is involved in memory in the intact brain, it is not necessary for many aspects of hippocampal memory function.

Cerebral blood flow at one year after controlled cortical impact in rats: assessment by magnetic resonance imaging

Progressive tissue loss and delayed cognitive deficits are seen in rats during the initial year after experimental traumatic brain injury (TBI). As much as 10% of parenchymal volume is lost even in the contralateral hemisphere by 1 year after controlled cortical impact (CCI) in rats. Progressive declines in cerebral blood flow (CBF) are also associated with advanced age and neurodegenerative diseases. Surprisingly, the long-term effects of TBI on CBF remain undefined. CBF was quantified by continuous arterial spin-labeled magnetic resonance imaging (MRI) and measurements of spin-lattice relaxation time in a slice through the plane of injury at 1 year after experimental TBI produced by CCI (n = 4) or sham surgery (n = 4) in rats. CBF was quantified in six regions of interest (ROIs) that were anatomically identified on the control images in each hemisphere and included a medial cortical segment (contusion-enriched, beneath the impact site, on the ipsilateral side) cortex, hippocampus, thalamus, amygdala/pyriform cortex, and hemisphere. At 1 year after injury, CBF was dramatically (96%) reduced in structures within the large cystic lesion that was seen in three of four rats and variably included cortex and hippocampus. Overall, there was an 80% reduction in CBF in the ipsilateral medial cortical segment comparing CCI and sham groups. Similarly, 52% and 67% reductions were seen in CBF in the cortical and hippocampal ROIs ipsilateral to impact (CCI vs. sham), respectively. These are regions both with marked CBF disturbances early after injury and that ultimately suffer considerable tissue loss over the 1-year interval. However, at 1 year after CCI, CBF was not different from sham in other ROIs, including ipsilateral thalamus, or either contralateral hippocampus or hemisphere. We conclude that, at 1 year after CCI, CBF is reduced in anatomic structures at or near the impact site, including injured cortex and hippocampus, and this translates into a reduction in hemispheric CBF. However, despite both significant occult tissue loss ipsilateral and contralateral to the injury and delayed cognitive deficits, widespread reductions in CBF are not observed. This suggests the possibility of remodeling or repackaging of the brain that preserves CBF outside of the cystic lesion.