The present study explored differences in dendritic/spine extent across several human cortical regions. Specifically, the basilar dendrites/spines of supragranular pyramidal cells were examined in eight Brodmann's areas (BA) arranged according to Benson's (1993, Behav Neurol 6:75-81) functional hierarchy: primary cortex (somatosensory, BA3-1-2; motor, BA4), unimodal cortex (Wernicke's area, BA22; Broca's area, BA44), heteromodal cortex (supple- mentary motor area, BA6beta; angular gyrus, BA39) and supramodal cortex (superior frontopolar zone, BA10; inferior frontopolar zone, BA11). To capture more general aspects of regional variability, primary and unimodal areas were designated as low integrative regions; heteromodal and supramodal areas were designated as high integrative regions. Tissue was obtained from the left hemisphere of 10 neurologically normal individuals (M(age) = 30 +/- 17 years; five males, five females) and stained with a modified rapid Golgi technique. Ten neurons were sampled from each cortical region (n = 800) and evaluated according to total dendritic length, mean segment length, dendritic segment count, dendritic spine number and dendritic spine density. Despite considerable inter-individual variation, there were significant differences across the eight Brodmann's areas and between the high and low integrative regions for all dendritic and spine measures. Dendritic systems in primary and unimodal regions were consistently less complex than in heteromodal and supramodal areas. The range within these rankings was substantial, with total dendritic length in BA10 being 31% greater than that in BA3-1-2, and dendritic spine number being 69% greater. These findings demonstrate that cortical regions involved in the early stages of processing (e.g. primary sensory areas) generally exhibit less complex dendritic/spine systems than those regions involved in the later stages of information processing (e.g. prefrontal cortex). This dendritic progression appears to reflect significant differences in the nature of cortical processing, with spine-dense neurons at hierarchically higher association levels integrating a broader range of synaptic input than those at lower cortical levels.

Dendritic neuropil is a sensitive indicator of the aging process and may exhibit regional cortical variations. The present study examined regional differences and age-related changes in the basilar dendrites/spines of supragranular pyramidal cells in human prefrontal (area 10) and secondary occipital (area 18) cortices. Tissue was obtained from the left hemisphere of 26 neurologically normal individuals ranging in age from 14 to 106 years (M(age) = 57 +/- 22 years; 13 males, 13 females). In tissue prepared by a modified rapid Golgi technique, ten neurons were sampled from each cortical region (N = 520) and were evaluated according to the following parameters: total dendritic length, mean segment length, dendritic segment count, dendritic spine number, and dendritic spine density. The effects of age and Brodmann areas were analyzed with a nested multiple analysis of variance design. Despite considerable interindividual variation, several clear findings emerged: 1) Dendritic systems were significantly larger in area 10 than in area 18 across the sampled life span, presumably because of the more integrative function of area 10 neurons. 2) There was a significant age effect, with a substantial decline in dendritic neuropil from the younger (< or =50 years) group to the older (>50 years) group, especially in spine measures, which decreased almost 50%. 3) Dendritic values were relatively stable after 40 years of age, suggesting that dendritic/spine degeneration in older, relatively healthy individuals may not be an inevitable consequence of the aging process. These findings underscore the importance of life-long commitment to a cognitively invigorating environment.

Dendritic neuropil is a sensitive indicator of the aging process and may exhibit regional cortical variations. The present study examined regional differences and age-related changes in the basilar dendrites/spines of supragranular pyramidal cells in human prefrontal (area 10) and secondary occipital (area 18) cortices. Tissue was obtained from the left hemisphere of 26 neurologically normal individuals ranging in age from 14 to 106 years (M(age) = 57 +/- 22 years; 13 males, 13 females). In tissue prepared by a modified rapid Golgi technique, ten neurons were sampled from each cortical region (N = 520) and were evaluated according to the following parameters: total dendritic length, mean segment length, dendritic segment count, dendritic spine number, and dendritic spine density. The effects of age and Brodmann areas were analyzed with a nested multiple analysis of variance design. Despite considerable interindividual variation, several clear findings emerged: 1) Dendritic systems were significantly larger in area 10 than in area 18 across the sampled life span, presumably because of the more integrative function of area 10 neurons. 2) There was a significant age effect, with a substantial decline in dendritic neuropil from the younger (< or =50 years) group to the older (>50 years) group, especially in spine measures, which decreased almost 50%. 3) Dendritic values were relatively stable after 40 years of age, suggesting that dendritic/spine degeneration in older, relatively healthy individuals may not be an inevitable consequence of the aging process. These findings underscore the importance of life-long commitment to a cognitively invigorating environment.

Gigantopyramidal neurons, referred to as Betz cells in primates, are characterized by large somata and extensive basilar dendrites. Although there have been morphological descriptions and drawings of gigantopyramidal neurons in a limited number of species, quantitative investigations have typically been limited to measures of soma size. The current study thus employed two separate analytical approaches: a morphological investigation using the Golgi technique to provide qualitative and quantitative somatodendritic measures of gigantopyramidal neurons across 19 mammalian species from 7 orders; and unbiased stereology to compare the soma volume of layer V pyramidal and gigantopyramidal neurons in primary motor cortex between 11 carnivore and 9 primate species. Of the 617 neurons traced in the morphological analysis, 181 were gigantopyramidal neurons, with deep (primarily layer V) pyramidal (n = 203) and superficial (primarily layer III) pyramidal (n = 233) neurons quantified for comparative purposes. Qualitatively, dendritic morphology varied considerably across species, with some (sub)orders (e.g., artiodactyls, perissodactyls, feliforms) exhibiting bifurcating, V-shaped apical dendrites. Basilar dendrites exhibited idiosyncratic geometry across and within taxonomic groups. Quantitatively, most dendritic measures were significantly greater in gigantopyramidal neurons than in superficial and deep pyramidal neurons. Cluster analyses revealed that most taxonomic groups could be discriminated based on somatodendritic morphology for both superficial and gigantopyramidal neurons. Finally, in agreement with Brodmann, gigantopyramidal neurons in both the morphological and stereological analyses were larger in feliforms (especially in the Panthera species) than in other (sub)orders, possibly due to specializations in muscle fiber composition and musculoskeletal systems.

Polybrominated diphenyl ethers (PBDEs), chemicals commonly used as flame retardants, are ubiquitous in the environment and bioaccumulate in humans and wildlife. However, little is known about their potential toxicological properties. In the present study, male Long-Evans rats orally administered the commercial PBDE mixture DE-71 or corn oil for 1 week, beginning at postnatal day (PND) 6, were tested on a visual discrimination task and two sustained attention tasks. After completion of these tasks, the rats were administered a drug challenge with the muscarinic antagonist scopolamine (0, 0.01, 0.03, 0.05 mg/kg), which was injected subcutaneously 30 min prior to testing on the second sustained attention task. The DE-71-exposed rats demonstrated deficits in learning but not in sustained attention when compared to controls. Scopolamine impaired the animals' ability to detect the brief visual cues in controls, as evidenced by decreases in accuracy and increases in omission errors. However, the DE-71-exposed rats were subsensitive to the effects of scopolamine on omission errors, particularly on trials in which a long delay preceded the cue, suggesting alterations in the cholinergic modulation of sustained attention. For the DE-71-exposed rats, the lack of sustained attention deficits in the absence of the drug, coupled with the subsensitivity to scopolamine's effects on sustained attention, suggest that although this PBDE mixture produced lasting alterations in cholinergic functioning, either (1) these alterations were not of sufficient magnitude to be behaviorally relevant, or (2) behavioral deficits resulting from these alterations were overcome by the development of compensatory neural mechanisms or response strategies in adulthood.