A Role for PGC-1α in Transcription and Excitability of Neocortical and Hippocampal Excitatory Neurons.

The transcriptional coactivator peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) is a critical regulator of genes involved in neuronal metabolism, neurotransmission, and morphology. Reduced PGC-1α expression has been implicated in several neurological and psychiatric disorders. An understanding of PGC-1α's roles in different cell types will help determine the functional consequences of PGC-1α dysfunction and/or deficiency in disease. Reports from our laboratory and others suggest a critical role for PGC-1α in inhibitory neurons with high metabolic demand such as fast-spiking interneurons. Here, we document a previously unrecognized role for PGC-1α in maintenance of gene expression programs for synchronous neurotransmitter release, structure, and metabolism in neocortical and hippocampal excitatory neurons. Deletion of PGC-1α from these neurons caused ambulatory hyperactivity in response to a novel environment and enhanced glutamatergic transmission in neocortex and hippocampus, along with reductions in mRNA levels from several PGC-1α neuron-specific target genes. Given the potential role for a reduction in PGC-1α expression or activity in Huntington Disease (HD), we compared reductions in transcripts found in the neocortex and hippocampus of these mice to that of an HD knock-in model; few of these transcripts were reduced in this HD model. These data provide novel insight into the function of PGC-1α in glutamatergic neurons and suggest that it is required for the regulation of structural, neurosecretory, and metabolic genes in both glutamatergic neuron and fast-spiking interneuron populations in a region-specific manner. These findings should be considered when inferring the functional relevance of changes in PGC-1α gene expression in the context of disease.

Characterization of a novel transgenic rat carrying human tau with mutation P301L.

We have established a novel transgenic rat line carrying human microtubule-associated protein Tau-40 with mutation P301L. hTau-40/P301L transgenic male and female rats were followed up to 2 years of age. The hTau-40/P301L rats expressed human tau mRNA and protein in the limbic cortex and associated white matter, hippocampus and spinal cord. With increasing age, the staining density for phosphorylated tau increased in all these areas. Neither silver stains nor Fluoro-Jade staining indicated the presence of dying neurons, or axonal degeneration, and there was no evidence of increased gliosis or inflammation. However, some neurons did display dendritic abnormalities, and immunoblots revealed the presence of sarcosyl insoluble tau. A large test battery revealed no behavioral abnormalities in these rats, except a mild hyperactivity in the elevated plus maze. In conclusion, this transgenic tau rat may be a useful model for 'pretangle' pathology, although in this study conditions were not sufficient to induce significant neuronal loss or behavioral deficits.

Knockout of plasminogen activator inhibitor 1 gene reduces amyloid beta peptide burden in a mouse model of Alzheimer's disease.

Accumulation of amyloid beta peptide (Aß) in the brain is a pathological hallmark of Alzheimer's disease (AD); the underlying mechanism, however, is not well understood. In this study, we show that expression of plasminogen activator inhibitor 1 (PAI-1), a physiological inhibitor of tissue type and urokinase type plasminogen activators (tPA and uPA), increases with age in the brain of wild type and Aß precursor protein-presenilin 1 (APP/PS1) transgenic mice as well as in AD patients. Most importantly, we show that knocking out the PAI-1 gene dramatically reduces Aß burden in the brain of APP/PS1 mice but has no effect on the levels of full-length APP, alpha or beta C-terminal fragments. Furthermore, we show that knocking out the PAI-1 gene leads to increases in the activities of tPA and plasmin, and the plasmin activity inversely correlates with the amounts of SDS insoluble Aß40 and Aß42. Together, these data suggest that increased PAI-1 expression/activity contributes importantly to Aß accumulation during aging and in AD probably by inhibiting plasminogen activation and thus Aß degradation.

DHA and cholesterol containing diets influence Alzheimer-like pathology, cognition and cerebral vasculature in APPswe/PS1dE9 mice.

Cholesterol and docosahexenoic acid (DHA) may affect degenerative processes in Alzheimer's Disease (AD) by influencing Abeta metabolism indirectly via the vasculature. We investigated whether DHA-enriched diets or cholesterol-containing Typical Western Diets (TWD) alter behavior and cognition, cerebral hemodynamics (relative cerebral blood volume (rCBV)) and Abeta deposition in 8- and 15-month-old APP(swe)/PS1(dE9) mice. In addition we investigated whether changes in rCBV precede changes in Abeta deposition or vice versa. Mice were fed regular rodent chow, a TWD-, or a DHA-containing diet. Behavior, learning and memory were investigated, and rCBV was measured using contrast-enhanced MRI. The Abeta load was visualized immunohistochemically. We demonstrate that DHA altered rCBV in 8-month-old APP/PS1 and wild type mice[AU1]. In 15-month-old APP/PS1 mice DHA supplementation improved spatial memory, decreased Abeta deposition and slightly increased rCBV, indicating that a DHA-enriched diet can diminish AD-like pathology. In contrast, TWD diets decreased rCBV in 15-month-old mice. The present data indicate that long-term dietary interventions change AD-like pathology in APP/PS1 mice. Additionally, effects of the tested diets on vascular parameters were observed before effects on Abeta load were noted. These data underline the importance of vascular factors in the APP/PS1 mouse model of AD pathology.

Subfield and layer-specific depletion in calbindin-D28K, calretinin and parvalbumin immunoreactivity in the dentate gyrus of amyloid precursor protein/presenilin 1 transgenic mice.

The depletion of neuronal calcium binding proteins deprives neurons of the capacity to buffer high levels of intracellular Ca(2+) and this leaves them vulnerable to pathological processes, such as those present in Alzheimer's disease (AD). The aim of the present study was to investigate the expression of the calcium binding proteins, calbindin-D28K, calretinin and parvalbumin in the dentate gyrus (DG) of amyloid precursor protein (APP)/presenilin 1 (PS1) transgenic (Tg) mice and their non-Tg littermates, as well as the relation with the deposition of human amyloid beta (Abeta). We measured the expression of these three proteins at seven different rostro-caudal levels, and in the molecular, granular and polymorphic layers of the DG. We found that, except in the most caudal part of the DG, there is a substantial loss of calbindin-D28K immunoreactivity in all three layers of the DG in APP/PS1 mice compared with the non-Tg mice. Significant loss of calretinin immunoreactivity is present in most of the polymorphic layer of the DG of APP/PS1 mice compared with the non-Tg mice, as well as in the rostral and intermediate part of the inner molecular layer. Compared with the non-Tg mice parvalbumin immunoreactivity is significantly reduced throughout the whole polymorphic layer as well as in the rostral and intermediate part of the granular layer of DG in APP/PS1 mice. The relatively preservation of calbindin immunoreactivity in the caudal part of molecular and granular layers as well as calretinin immunoreactivity in the caudal part of polymorphic layer of the DG is likely related to the lower Abeta expression in those parts of DG. The present data suggest an involvement of calcium-dependent pathways in the pathogenesis of AD and indicate that there exists a subfield and layer-specific decrease in immunoreactivity which is related to the type of calcium-binding protein in APP/PS1 mice. Moreover, it seems that APP expression affects more the calbindin expression then parvalbumin and calretinin expression in the DG of APP/PS1 Tg mice.

Inhibition of cytotoxicity and amyloid fibril formation by a D-amino acid peptide that specifically binds to Alzheimer's disease amyloid peptide.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder. The 'amyloid cascade hypothesis' assigns the amyloid-beta-peptide (Abeta) a central role in the pathogenesis of AD. Although it is not yet established, whether the resulting Abeta aggregates are the causative agent or just a result of the disease progression, polymerization of Abeta has been identified as a major feature during AD pathogenesis. Inhibition of the Abeta polymer formation, thus, has emerged as a potential therapeutic approach. In this context, we identified peptides consisting of d-enantiomeric amino acid peptides (d-peptides) that bind to Abeta. D-peptides are known to be more protease resistant and less immunogenic than the respective L-enantiomers. Previously, we have shown that a 12mer D-peptide specifically binds to Abeta amyloid plaques in brain tissue sections from former AD patients. In vitro obtained binding affinities to synthetic Abeta revealed a K(d) value in the submicromolar range. The aim of the present study was to investigate the influence of this d-peptide to Abeta polymerization and toxicity. Using cell toxicity assays, thioflavin fluorescence, fluorescence correlation spectroscopy and electron microscopy, we found a significant effect of the d-peptide on both. Presence of D-peptides (dpep) reduces the average size of Abeta aggregates, but increases their number. In addition, Abeta cytotoxicity on PC12 cells is reduced in the presence of dpep.

Changes in cerebral blood volume and amyloid pathology in aged Alzheimer APP/PS1 mice on a docosahexaenoic acid (DHA) diet or cholesterol enriched Typical Western Diet (TWD).

High dietary cholesterol and low dietary docosahexaenoic acid (DHA) intake are risk factors for Alzheimer's disease (AD). However, it is unclear how these components influence the course of the disease. We investigated the effects of dietary lipids on beta-amyloid deposition and blood circulation in the brains of 18-month-old APP/PS1 mice. Starting at 6 months of age, mice were fed a regular rodent chow, a Typical Western Diet (TWD) containing 1% cholesterol, or a diet with a high (0.5%) level of DHA for 12 months. Relative cerebral blood volume (rCBV) and flow (CBF) were determined with (2)H MR spectroscopy and gradient echo contrast enhanced MRI. Deposition of beta-amyloid was visualized in fixed brain tissue with immunohistochemistry. The TWD diet increased plaque burden in the dentate gyrus of the hippocampus, but did not significantly reduce rCBV. In contrast, the DHA-enriched diet increased rCBV without changing blood flow indicating a larger circulation in the brain probably due to vasodilatation and decreased the amount of vascular beta-amyloid deposition. Together, our results indicate that the long-term intake of dietary lipids can impact both brain circulation and beta-amyloid deposition, and support the involvement of hemodynamic changes in the development of AD.

Normal induction but accelerated decay of LTP in APP + PS1 transgenic mice.

Mice carrying mutated human APPswe and PS1 (A246E) transgenes (A/P mice) show age-dependent memory impairment in hippocampus-dependent tasks. Moreover, the mice show normal learning in the water maze within a day but impairment across days. We recorded LTP in a slice preparation (CA1) and in chronically implanted animals (dentate gyrus, or DG) at 17-18 months of age. The genotypes did not differ in the basal synaptic transmission. Also, LTP induction and its maintenance over 60 min did not differ between A/P and control mice. However, the fEPSP enhancement in vivo decayed to 77% of its maximum in 24 h in A/P mice while remaining at 96% in control mice. The time course of the LTP decay in the A/P mice corresponds to their behavioral impairment and indicates that Abeta accumulation in the dentate gyrus may interfere with the signal transduction pathways responsible for memory consolidation.

Diffuse amyloid deposition, but not plaque number, is reduced in amyloid precursor protein/presenilin 1 double-transgenic mice by pathway lesions.

Alzheimer's disease (AD) is the most common form of dementia in the elderly, and the characteristic pathological hallmarks of the disease are neuritic plaques and neurofibrillary tangles. The sequence of events leading to the extracellular deposition of amyloidbeta (Abeta) peptides in plaques or in diffuse deposits is not clear. Here we investigate the relation between disrupted axonal transport of amyloid precursor protein (APP) and/or Abeta and the deposition of Abeta in the deafferented terminal fields in APP/presenilin 1 double-transgenic AD-model mice. In the first experiment we ablated entorhinal cortex neurons and examined the subsequent changes in amyloid deposition in the hippocampus 1 month later. We show that there is a substantial reduction in the amount of diffuse amyloid deposits in the denervated areas of the hippocampus. Further, to investigate the effects of long-term deafferentation, in a second experiment we cut the fimbria-fornix and analyzed the brains 11 months post-lesion. Diffuse amyloid deposits in the deafferented terminal fields of area CA1 and subiculum were dramatically reduced as assessed by image analysis of the Abeta load. Our findings indicate that neuronal ablations decrease diffuse amyloid deposits in the terminal fields of these neurons, and, further, that pathway lesions similarly decrease the amount of diffuse amyloid deposits in the terminal fields of the lesioned axons. Together, this suggests that the axonal transport of APP and/or Abeta and subsequent secretion of Abeta at terminals plays an important role in the deposition of Abeta protein in Alzheimer's disease, and, further, that diffuse deposits do not develop into plaques.py>

Differences in lesion-induced hippocampal plasticity between mice and rats.

We studied the differences between mice and rats in lesion-induced sprouting in the hippocampus. The entorhinal cortex was unilaterally lesioned with ibotenic acid in adult, female mice and rats. Four weeks later the subsequent axonal sprouting in the dentate gyrus was analysed, by measuring the density of the synaptophysin immunohistochemical and acetylcholinesterase histochemical staining in the termination area of the entorhinal cortex axons. The data demonstrate that both mice and rats display a significantly increased density of staining for synaptophysin and acetylcholinesterase in the molecular layer of the dentate gyrus, indicative of axonal sprouting. Both species also show an upregulation in the density of staining for acetylcholinesterase in the molecular layer of the dentate gyrus. Further, rats, but not mice, show a significant upregulation of synaptophysin staining in stratum lacunosum moleculare of CA1 following the lesions. However, whereas rats show significant shrinkage of the molecular layer of the dentate gyrus, mice do not show any shrinkage of that layer following entorhinal cortex lesions. Taken together, these data indicate that whereas the process of reinnervation in the hippocampus is similar between the mouse and the rat, the hippocampal response to denervation shows clear differences between these two species.

Altered auditory-evoked potentials in mice carrying mutated human amyloid precursor protein and presenilin-1 transgenes.

Transgenic mice carrying human APPswe and PS1-A264E transgenes (A/P mice) have elevated levels of the highly fibrillogenic amyloid Abeta(1-42) (Abeta) and develop amyloid plaques around the age of 9 months. Our aim was to find whether the gradual accumulation of Abeta in these mice can be detected with long-term recording of auditory-evoked potentials. The A/P double-mutant mice had impaired auditory gating and a tendency toward increased latency of the cortical N35 response, but these changes were not age-dependent between 7 and 11 months of age. In a control experiment that included also APP and PS1 single-mutant mice, the A/P double-mutant mice had weaker auditory gating than either APP or PS1 mice. In contrast, increased N35 latency was found in both A/P and APP mice compared with nontransgenic or PS1 mice. The Abeta40 and Abeta42 levels were robustly increased in A/P mice and Abeta40 moderately increased also in APP mice. Plaques were deposited only in A/P mice. We conclude that the impaired auditory gating is associated with the overproduction Abeta42 but does not reflect its amount. In contrast, increased N35 latency is related to the APP genotype independent of Abeta42 production.

The effects of long-term treatment with metrifonate, a cholinesterase inhibitor, on cholinergic activity, amyloid pathology, and cognitive function in APP and PS1 doubly transgenic mice.

Recent studies in cell cultures have shown that modulating the cholinergic activity can influence the processing and metabolism of amyloid precursor protein (APP). To investigate whether acetylcholinesterase inhibitors (ChEIs) could decrease production of amyloid beta-peptide (A(beta)) and slow down the accumulation of A(beta) also in vivo, we chronically administered metrifonate (100 mg/kg, po), a second-generation ChEI, to 7-month-old doubly transgenic APP+PS1 mice and their nontransgenic littermate controls for 7 months. Behavioral studies, including open field test, T maze, and water maze, were conducted after 6 months treatment with metrifonate, and the mice were sacrificed at the age of 14 months for biochemical and histological analyses. The long-term treatment with metrifonate failed to inhibit the marked overproduction and deposition of A(beta) in the APP+PS1 mice; in contrast, it increased both A(beta)40 and A(beta)42 levels in the hippocampus. However, the A(beta)42 to 40 ratio was significantly reduced by the treatment. In addition, the number of amyloid plaques in the hippocampus did not differ between the treatment and the control groups. Tolerance to cholinesterase inhibition might be induced in the mouse brain because the inhibition rate of AChE was attenuated from about 80 to 50% during the experiment in both APP+PS1 and nontransgenic mice. The metrifonate treatment did not affect cognitive testing parameters but reduced swimming speed and locomotor activity in both genotypes. Our results do not support the idea that ChEIs would slow down the progression of amyloid pathology in Alzheimer's disease.

Brain prolyl oligopeptidase activity is associated with neuronal damage rather than beta-amyloid accumulation.

Prolyl oligopeptidase (POP) have been suggested to participate in the pathogenesis of Alzheimer's disease (AD). In this study the activity of POP is evaluated in AD patients and in transgenic mice with substantial deposits of beta-amyloid (Abeta). In AD cases, the POP activity displayed a significant negative correlation with the scores of senile/neuritic plaques and neurofibrillary tangles but not with Abeta-load. The transgenic mice with high levels of Abeta did not have altered POP activity compared to wild type mice. Based on our results, the low POP activity in AD seems to be associated with neuronal degeneration rather than to Abeta accumulation.

Entorhinal cortex of the mouse: cytoarchitectonical organization.

The present study describes the cytoarchitectonical and chemoarchitectonical organization of the entorhinal cortex of the mouse (C57BL/6J strain). The entorhinal cortex is medially bordered by the parasubiculum, and laterally by the perirhinal cortex; rostrally and medially it is bordered by the piriform cortex, whereas caudally and dorsally it is bordered by the postrhinal cortex. The entorhinal cortex is divided into two main areas, i.e., the lateral entorhinal area (LEA) and the medial entorhinal area (MEA). Both entorhinal areas are further divided into subfields, i.e., LEA is divided into DLE (dorsolateral entorhinal field), DIE (dorsal intermediate entorhinal field), and VIE (ventral intermediate entorhinal field), whereas MEA is divided into CE (caudal entorhinal field) and ME (medial entorhinal field). Cytoarchitectonically, the main difference between LEA and MEA is displayed by layer II neurons: while these are in a dense layer in LEA, they are more dispersed in MEA. Further, in LEA there is a relatively cell-free zone between layers II and III; this zone is not present in MEA. Histochemically, in acetylcholinesterase (AChE)-stained material, MEA is characterized by darker-stained bands in the superficial layer (i.e., layer I) and in the lamina dissecans, in contrast to LEA, which is more evenly stained for AChE. Further, both the border with the perirhinal cortex and the border with the parasubiculum are characterized by dark-stained bands of AChE. The border between the entorhinal cortex and perirhinal cortex is also easily distinguished in parvalbumin-stained material; while the entorhinal cortex is darkly stained, the perirhinal cortex is lightly stained. In contrast, in sections stained for calretinin, the entorhinal cortex is more lightly stained than the parasubiculum, which has a darkly stained superficial layer, and a densely stained group of neurons in layer III.

Chronic, severe hypertension does not impair spatial learning and memory in Sprague-Dawley rats.

This study tested the hypothesis that long-term hypertension impairs spatial learning and memory in rats. In 6-wk-old Sprague-Dawley rats, chronic hypertension was induced by placing one of three sizes of stainless steel clips around the descending aorta (above the renal artery), resulting in a 20-80-mm Hg increase of arterial pressure in all arteries above the clip, that is, the upper trunk and head. Ten months later, the rats were tested for 5 d in a repeated-acquisition water maze task, and on the fifth day, they were tested in a probe trial; that is, there was no escape platform present. At the end of the testing period, the nonsurgical and sham control groups had similar final escape latencies (16 +/- 4 sec and 23 +/- 9 sec, respectively) that were not significantly different from those of the three hypertensive groups. Rats with mild hypertension (140-160 mm Hg) had a final escape latency of 25 +/- 6 sec, whereas severely hypertensive rats (170-199 mm Hg) had a final escape latency of 21 +/- 7 sec and extremely hypertensive rats (>200 Hg) had a final escape latency of 19 +/- 5 sec. All five groups also displayed a similar preference for the correct quadrant in the probe trial. Together, these data suggest that sustained, severe hypertension for over 10 mo is not sufficient to impair spatial learning and memory deficits in otherwise normal rats.

Age-related decline in water maze learning and memory in rats: strain differences.

Rats display an age-related impairment in learning and memory; however, few studies have systematically examined this relationship in multiple strains. The present study used a repeated acquisition water maze task to test the hypothesis that age-related decreases in learning and memory occur at different rates in three strains of rats, i.e. Sprague-Dawley (SD), spontaneously hypertensive (SHR), and Wistar Kyoto (WKY) rats. All three strains of rats displayed age-related decreases in spatial learning and memory; however, the rate of decline differed between the strains. Compared to young rats of the same strain, only SHR were significantly impaired at 12 months of age. All three strains displayed moderate impairment in learning the task at 18 months of age, and at 24 months of age all three strains of rats were severely impaired in the task, but SD performed best at 18 and 24 months of age. Further, SD and SHR displayed a probe trial bias at 3 months of age, but only SD had a bias at 12 months of age and none of the rats showed the bias at later ages. Thus, in these three strains, age-related impairment of spatial memory proceeds at different rates.

Distribution of neurons in the anterior hypothalamic nucleus activated by blood pressure changes in the rat.

Electrophysiological and Fos-like protein immunocytochemical methods were used to identify the number and distribution of anterior hypothalamic neurons that are activated by changes in arterial pressure. First, in anesthetized, male Sprague-Dawley rats, arterial pressure increases and decreases led to differential activation of neurons in the anterior hypothalamic nucleus. Most of the units that responded to a rise in arterial pressure with a decrease in activity (pressor units) were located in the central part of the anterior hypothalamic nucleus, whereas units that increased firing when arterial pressure rose (the depressor units) were found throughout the nucleus. Second, in awake, male Sprague-Dawley rats, Fos-like protein immunoreactivity was mapped following sustained arterial pressure changes. Within the anterior hypothalamus, reduction in arterial pressure increased the number of Fos-labeled neurons primarily in the paraventricular nucleus and to a lesser extent in the anterior half of the anterior hypothalamic nucleus. In contrast, elevation in arterial pressure increased Fos labeling throughout the anterior hypothalamic nucleus and to a lesser extent in the paraventricular nucleus.

Efferent connections of the anteromedial nucleus of the thalamus of the rat.

The projections from the anteromedial nucleus of the thalamus (AM) were investigated using anterograde and retrograde tracing techniques. AM projects to nearly the entire rostrocaudal extent of limbic cortex and to visual cortex. Anteriorly, AM projects to medial orbital, frontal polar, precentral agranular, and infraradiata cortices. Posteriorly, AM projects to retrosplenial granular, entorhinal, perirhinal and presubicular cortices, and to the subiculum. Further, AM projects to visual cortical area 18b, and to the lateral and basolateral nuclei of the amygdala. AM projections are topographically organized, i.e., projections to different cortical areas arise from distinct parts of AM. The neurons projecting to rostral infraradiata cortex (IRalpha) are more caudally located in AM than the neurons projecting to caudal infraradiata cortex (IRbeta). The neuronal cell bodies that project to the terminal field in area 18b are located primarily in ventral and lateral parts of AM, whereas neurons projecting to perirhinal cortex and amygdala are more medially located in AM. Injections into the most caudal, medial part of AM (i.e., the interanteromedial [IAM] nucleus) label terminals in the rostral precentral agranular, caudal IRbeta, and caudal perirhinal cortices. Whereas most AM axons terminate in layers I and V-VI, exceptions to this pattern include area 18b (axons and terminals in layers I and IV-V), the retrosplenial granular cortex (axons and terminals in layers I and V), and the presubicular, perirhinal, and entorhinal cortices (axons and terminals predominantly in layer V). Together, these findings suggest that AM influences a widespread area of limbic cortex.

In mice tonic estrogen replacement therapy improves non-spatial and spatial memory in a water maze task.

We investigated the effects of estrogen replacement therapy on water maze non-spatial and spatial navigation in mice. Three groups of mice were ovariectomized and two of these groups being implanted with s.c. pellets that produce blood levels of estrogen close to those found in estrous (estrogen low, 75-100 pg/ml blood) or proestrous (estrogen high, 300-400 pg/ml). The behavioral assessment was initiated 7 days after pellet implantation. Non-spatial navigation to a clearly visible platform was stimulated by low and high levels of estrogen. However, spatial navigation to a hidden platform was improved by low estrogen levels. We found that estrogen improves two different types of memory processes that depend on striatal (non-spatial navigation) and hippocampal (spatial) memory systems.

Projections from the anterodorsal and anteroventral nucleus of the thalamus to the limbic cortex in the rat.

The present study characterized the projections of the anterodorsal (AD) and the anteroventral (AV) thalamic nuclei to the limbic cortex. Both AD and AV project to the full extent of the retrosplenial granular cortex in a topographic pattern. Neurons in caudal parts of both nuclei project to rostral retrosplenial cortex, and neurons in rostral parts of both nuclei project to caudal retrosplenial cortex. Within AV, the magnocellular neurons project primarily to the retrosplenial granular a cortex, whereas the parvicellular neurons project mainly to the retrosplenial granular b cortex. AD projections to retrosplenial cortex terminate in very different patterns than do AV projections: The AD projection terminates with equal density in layers I, III, and IV of the retrosplenial granular cortex, whereas, in contrast, the AV projections terminate very densely in layer Ia and less densely in layer IV. Further, both AD and AV project densely to the postsubicular, presubicular, and parasubicular cortices and lightly to the entorhinal (only the most caudal part) cortex and to the subiculum proper (only the most septal part). Rostral parts of AD project equally to all three subicular cortices, whereas neurons in caudal AD project primarily to the postsubicular cortex. Compared to AD, neurons in AV have a less extensive projection to the subicular cortex, and this projection terminates primarily in the postsubicular and presubicular cortices. Further, the AD projection terminates in layers I, II/III, and V of postsubiculum, whereas the AV projection terminates only in layers I and V.