Distribution of the alpha1 subunit of the GABA(A) receptor on midget and parasol ganglion cells in the retina of the common marmoset Callithrix jacchus

The inhibitory neurotransmitter gamma aminobutyric acid (GABA) has been shown to influence the responses of ganglion cells in the mammalian retina. Consistently, GABA(A) receptor subunits have been localized to different ganglion cell types. In this study, the distribution of the alpha1 subunit of the GABA(A) receptor on the dendrites of midget and parasol ganglion cells was investigated quantitatively in the retina of a New World monkey, the marmoset. Ganglion cells were injected with Neurobiotin in a live in vitro retinal whole-mount preparation. Retinal pieces were then processed with an antibody against the alpha1 subunit of the GABA(A) receptor. Strong punctate immunoreactivity indicative of synaptic localization is present in the ON and OFF sublamina of the inner plexiform layer. Many of the immunoreactive puncta coincide with the dendrites of both midget and parasol ganglion cells. Immunoreactive puncta are present on distal and proximal dendrites of ON and OFF cells of both ganglion cell types. On average, parasol cells show a slight increase in the spatial density of immunoreactive puncta with distance from the soma, whereas the density of immunoreactive puncta on midget cells stays even. Parasol ganglion cells show a slightly higher average density of immunoreactive puncta (0.083 puncta/microm dendrite) than midget cells (0.054 puncta/microm dendrite).

Spatial order in short-wavelength-sensitive cone photoreceptors: a comparative study of the primate retina

We compared the spatial distribution of short-wavelength-sensitive (SWS or blue) cone photoreceptors in the retinas of eight primate species. The regularity of the SWS cone array was quantified with a statistic (packing factor) that varies between a random distribution (0) and a triangular array (1). We find wide variability among species, with packing factors varying between 0.06 and 0.3. The SWS cone array in at least two New World monkey species is indistinguishable from a random array. The SWS cone density gradient across the retina was measured in the capuchin monkey Cebus apella and the squirrel monkey Saimiri sciureus. Both species show a peak density of 5,000-8,000 cells/mm2 at the fovea and a 50-fold central-peripheral density gradient. In contrast to the wide variation in local regularity, the spatial density and the topography of SWS cones are well preserved across primates.

Parental care and clutch sizes in North and South American birds

The evolutionary causes of small clutch sizes in tropical and Southern Hemisphere regions are poorly understood. Alexander Skutch proposed 50 years ago that higher nest predation in the south constrains the rate at which parent birds can deliver food to young and thereby constrains clutch size by limiting the number of young that parents can feed. This hypothesis for explaining differences in clutch size and parental behaviors between latitudes has remained untested. Here, a detailed study of bird species in Arizona and Argentina shows that Skutch's hypothesis explains clutch size variation within North and South America. However, neither Skutch's hypothesis nor two major alternatives explain differences between latitudes.

The Arabidopsis embryonic shoot fate map

A fate map has been constructed for the shoot apical region of the embryo of the dicotyledonous plant Arabidopsis thaliana using spontaneously arising clonal albino sectors caused by the chloroplast mutator 1–2 mutation. Chimeric seedlings exhibiting albino sectors shared between the cotyledons and first true leaves revealed patterns of organ inclusion and exclusion. Frequencies of clone sharing were used to calculate developmental distances between organs based on the frequency of clonal sectors failing to extend between different organs. The resulting fate map shows asymmetry in the developmental distances between the cotyledons (embryonic leaves) which in turn predicts the location of the first post-germination leaf and the handedness of the spiral of leaf placement around the central stem axis in later development. The map suggests that embryonic leaf fate specification in the cotyledons may represent a developmental ground state necessary for the formation of the shoot apical meristem.

Effects of visual stimuli and a stressor on head pain

This study sought to experimentally validate two reported precipitants of chronic headaches, namely, negative affect (anxiety, anger, depression) and visual disturbance (flicker, glare, eyestrain), and to investigate whether they triggered common or different physiological mechanisms. Twenty-two male and 68 female subjects (46 with migraine, 29 with tension-type headache, and 15 controls) were submitted to antecedent challenges in the laboratory which induced negative affect or visual disturbance and to a control challenge. The results demonstrated that negative affect and visual disturbance can indeed precipitate headaches, and that the physiological responses associated with these antecedents differ, but the findings were not conclusive as to whether one or more physiological mechanisms are operative. Follow-up revealed that the antecedent challenges had significant effects on headache activity 48 to 72 hours after termination.

Automatic 3-D segmentation of internal structures of the head in MR images using a combination of similarity and free-form transformations: Part II, validation on severely atrophied brains

Studies aimed at quantifying neuroanatomical differences between populations require the volume measurements of individual brain structures. If the study contains a large number of images, manual segmentation is not practical. This study tests the hypothesis that a fully automatic, atlas-based segmentation method can be used to quantify atrophy indexes derived from the brain and cerebellum volumes in normal subjects and chronic alcoholics. This is accomplished by registering an atlas volume with a subject volume, first using a global transformation, and then improving the registration using a local transformation. Segmented structures in the atlas volume are then mapped to the corresponding structures in the subject volume using the combined global and local transformations. This technique has been applied to seven normal and seven alcoholic subjects. Three magnetic resonance volumes were obtained for each subject and each volume was segmented automatically, using the atlas-based method. Accuracy was assessed by manually segmenting regions and measuring the similarity between corresponding regions obtained automatically. Repeatability was determined by comparing volume measurements of segmented structures from each acquisition of the same subject. Results demonstrate that the method is accurate, that the results are repeatable, and that it can provide a method for automatic quantification of brain atrophy, even when the degree of atrophy is large.

Cloning and characterization of a gene encoding an antigenic membrane protein from Actinobacillus pleuropneumoniae with homology to ABC transporters

Actinobacillus pleuropneumoniae is a pathogenic bacterium responsible for a highly contagious and often fatal form of bronchopneumonia in swine. Survival from a natural infection generally results in immunity from further infection by all 12 common serotypes, suggesting the presence of common protective antigens. We have identified one of the antigenic membrane proteins from A. pleuropneumoniae serotype 5, and cloned the gene which encodes it. This gene is found in all 12 serotypes, and encodes a protein with a predicted molecular mass of 30 kDa. Sequence analysis revealed that this antigen has a typical signal sequence characteristic of lipoproteins, and is likely to be secreted and inserted into the periplasmic side of the inner membrane. The gene shows high homology to the surface antigen CjaA of Campylobacter jejuni and to solute binding proteins of the ABC transporter family. The probable role of this protein in substrate binding and transport was supported by the presence of an upstream gene with significant homology to ATP binding proteins of the same family. In Escherichia coli, the cloned gene produced a protein which reacted strongly with convalescent sera from swine infected with A. pleuropneumoniae serotype 5, and weakly with sera from swine infected with serotype 1A or from swine vaccinated with a killed bacterin of serotype 1A or 5. It thus appears that this antigen displays some crossreactivity between serotypes, and may be less exposed in bacterins than in live cells. This protein, designated ApaA, may have an important role in nutrient acquisition and in the pathogenesis of infections caused by A. pleuropneumoniae.

Expression of cannabinoid receptors and their gene transcripts in human blood cells

1. This study shows that the human cannabinoid receptors and their gene transcripts can be analyzed in blood samples when combined with polymerase chain reaction. The results also demonstrate that the expression of the cannabinoid receptors is dependent on gender and ethnic background. 2. Normal human volunteers who do not use marijuana have genes that encode for the marijuana (cannabinoid) receptor proteins. 3. Primer pairs from CB1 and CB2 cDNA coding region sequences showed identical amplified DNA band sizes in both DNA-PCR and reverse PCR, with human templates. This suggests that the CB1 and CB2 genes are intronless at least in their coding regions. 4. An advantage of the coding region being intronless may be that the expression of these genes will have one major RNA processing event to skip, thus making the conditions of their expression relatively quick and simple. This advantage may have implications related to the biological functions of these proteins. 5. We therefore concluded that the existence of human cannabinoid receptors and genes along with the discovery of endogenous cannabinoids (endocannabinoids) may be useful markers in elucidating the role(s) and mechanism(s) of action of cannabinoids.

Analysis of two types of cone bipolar cells in the retina of a New World monkey, the marmoset, Callithrix jacchus

Two types of cone bipolar cells, the blue cone bipolar cell and the diffuse bipolar cell (DB3), were labelled immunohistochemically and investigated in the retina of a New World monkey, the marmoset. Blue cone bipolar cells were labelled with an antiserum against cholecystokinin. Short-wavelength-sensitive (SWS) cones were labelled with an antiserum against the SWS cone opsin. The DB3 cells were labelled with antibodies to calbindin. Blue cone bipolar cells in marmoset do not form a regular mosaic but instead follow the random distribution of the SWS cones. Nevertheless, the SWS cone to blue cone bipolar cell connectivity in marmoset is very similar to that previously described for macaque. In contrast to the blue cone bipolar cells, the DB3 cells form a regular mosaic. The synaptic connectivity of DB3 cells in the inner plexiform layer was analyzed. They make output synapses onto ganglion cells and amacrine cells, and gap junctions with each other. Our results provide further evidence for the existence of parallel bipolar cell pathways in the primate retina and support the view that the retinae of Old World and New World primates have common neuronal connectivity. The random distribution of SWS cones and blue cone bipolar cells is an exception to the general rule of a regular mosaic distribution of cell populations in the retina.

Temporal contrast sensitivity in the lateral geniculate nucleus of a New World monkey, the marmoset Callithrix jacchus

1. The temporal contrast sensitivity of koniocellular, parvocellular and magnocellular cells in the lateral geniculate nucleus (LGN) of nine adult marmosets was measured. The receptive fields of the cells were between 0.3 and 70 deg from the fovea. The stimulus was a large spatially uniform field which was modulated in luminance at temporal frequencies between 0.98 and 64 Hz. 2. For each cell group there was a gradual increase in modulation sensitivity, especially for temporal frequencies below 8 Hz, with increasing distance from the fovea. At any given eccentricity, magnocellular cells had the greatest sensitivity. In central visual field, the sensitivity of koniocellular cells lay between that of parvocellular and magnocellular cells. In peripheral visual field (above 10 deg eccentricity) koniocellular and parvocellular cells had similar sensitivity. 3. The contrast sensitivity of each cell class was dependent on the anaesthetic used. Cells from animals anaesthetized with isoflurane were less sensitive than cells from animals anaesthetized with sufentanil. This effect was more marked for temporal frequencies below 4 Hz. 4. These results are incompatible with the notion that the koniocellular pathway is functionally homologous to a sluggish, W-like pathway in other mammals. At least in terms of their temporal transfer properties, many koniocellular cells are more like parvocellular cells.

Analysis of the short wavelength-sensitive ("blue") cone mosaic in the primate retina: comparison of New World and Old World monkeys

The distribution of short wavelength-sensitive (SWS or "blue") cone photoreceptors was compared in primates with dichromatic ("red-green colour blind") and trichromatic colour vision. We compared a New World species, the marmoset (Callithrix jacchus), with an Old World species, the macaque monkey (Macaca nemestrina). The SWS cones were identified by their immunoreactivity to an antiserum against the human SWS cone opsin. A single retina from a male capuchin monkey (Cebus apella) also was studied. The SWS cones make up less than 10% of all cone photoreceptors throughout the retina of all animals studied. In marmoset, the peak spatial density of SWS cones is close to 10,000/mm2 at the foveola. In macaque, the peak spatial density of SWS cones, close to 6,000/mm2, is at the fovea, but SWS cones are absent within 50 microm of the centre of the foveola. In both species, the density of SWS cones is higher on the nasal retinal axis than at corresponding eccentricities on the other retinal axes. The SWS cones in macaque are arranged in a semiregular array, but they are distributed randomly in marmoset. There is no difference in the spatial density or local arrangement of SWS cones between dichromatic and trichromatic marmosets. The results suggest that the SWS cone photoreceptor system is subject to different developmental and evolutionary constraints than those that have led to the formation of the red-green photoreceptor systems in primate vision.

Ganglion cells of a short-wavelength-sensitive cone pathway in New World monkeys: morphology and physiology

We have studied the morphology and physiology of retinal ganglion cells of a short-wavelength-sensitive cone (SWS-cone) pathway in dichromatic and trichromatic New World anthropoids, the capuchin monkey (Cebus apella) and tufted-ear marmoset (Callithrix jacchus). In Old World anthropoids, in which males and females are both trichromats, blue-ON/yellow-OFF retinal ganglion cells have excitatory SWS-cone and inhibitory middle- and long-wavelength-sensitive (MWS- and LWS-) cone inputs, and have been anatomically identified as small-field bistratified ganglion cells (SB-cells) (Dacey & Lee, 1994). Among retinal ganglion cells of New World monkeys, we find SB-cells which have very similar morphology to such cells in macaque and human; for example, the inner dendritic tree is larger and denser than the outer dendritic tree. We also find blue-on retinal ganglion cells of the capuchin to have physiological responses strongly resembling such cells of the macaque monkey retina; for example, responses were more sustained, with a gentler low frequency roll-off than MC-cells, and no evidence of contrast gain control. There was no difference between dichromatic and trichromatic individuals. The results support the view that SWS-cone pathways are similarly organized in New and Old World primates, consistent with the hypothesis that these pathways form a phylogenetically ancient color system.

Colour processing in the primate retina: recent progress

Colour vision in the majority of humans is trichromatic, relying on a comparison of the quantal absorption in three different types of cone photoreceptors. The first steps in this comparison process take place at an early level of the visual system, in the retina. This topical review will highlight recent experiments which have advanced our understanding of how cone signals are compared to generate cone-opponent responses in the primate retina.

Image-guided MR spectroscopy volume of interest localization for longitudinal studies

Longitudinal magnetic resonance spectroscopy (MRS) studies require accurate repositioning of the volume of interest (VOI) over which measurements are made. In this work we present and evaluate a method for the image-guided repositioning of brain volumes of interest. The point-based registration technique we developed allows the repositioning to be performed on-line (i.e. while the patient is in the scanner). MR image volumes were acquired from six subjects, three scans each over the course of a month. During the first scan, two spectroscopy VOIs are visually selected: one in the frontal white matter, the other in the superior cerebellar vermis. The coordinates of 13 internal brain landmarks are also identified. During both subsequent scans, the same 13 landmarks are identified, and the transformation that registers the first set of landmarks to the subsequent set is computed. This result is used to automatically map the position of the spectroscopy VOIs from the first volume to the current volume. For the six subjects evaluated to date, we show an average repositioning error of the spectroscopy VOIs in the order of 1 mm. This accuracy allows us to conclude that any variations in the MR spectra are unlikely to be due to repositioning error.

Segregation of receptive field properties in the lateral geniculate nucleus of a New-World monkey, the marmoset Callithrix jacchus

The lateral geniculate nucleus (LGN) in humans and Old-World monkeys is dominated by the representation of the fovea in the parvocellular (PC) layers, and most PC cells in the foveal representation have red-green cone opponent receptive field properties. It is not known whether these features are both unique to trichromatic primates. Here we measured receptive field properties and the visuotopic organization of cells in the LGN of a New-World monkey, the marmoset Callithrix jacchus. The marmoset displays a polymorphism of cone opsins in the medium-long wavelength (ML) range, which allows the LGN of dichromatic ("red-green color blind") and trichromatic individuals to be compared. Furthermore, the koniocellular-interlaminar layers are segregated from the main PC layers in marmoset, allowing the functional role of this subdivision of the LGN to be assessed. We show that the representation of the visual field in the LGN is quantitatively similar in dichromatic and trichromatic marmosets and is similar to that reported for macaque; the vast majority of LGN volume is devoted to the central visual field. ON- and OFF-type responses are partially segregated in the PC layers so that responses are more commonly encountered near the external border of each layer. The red-green (ML) opponent cells in trichromatic animals were all located in the PC layers, and their receptive fields were within 16 degrees of the fovea. The koniocellular zone between the PC and magnocellular layers contained cells that receive excitatory input from short wavelength sensitive cones ("blue- cells") as well as other nonopponent cells. These results suggest that the basic organization of the LGN is common to dichromatic and trichromatic primates and provide further evidence that ML and SWS opponent signals are carried in distinct subdivisions of the retinogeniculocortical pathway.

cyk-1: a C. elegans FH gene required for a late step in embryonic cytokinesis

A maternally expressed Caenorhabditis elegans gene called cyk-1 is required for polar body extrusion during meiosis and for a late step in cytokinesis during embryonic mitosis. Other microfilament- and microtubule-dependent processes appear normal in cyk-1 mutant embryos, indicating that cyk-1 regulates a specific subset of cytoskeletal functions. Because cytokinesis initiates normally and cleavage furrows ingress extensively in cyk-1 mutant embryos, we propose that the wild-type cyk-1 gene is required for a late step in cytokinesis. Cleavage furrows regress after completion of mitosis in cyk-1 mutants, leaving multiple nuclei in a single cell. Positional cloning and sequence analysis of the cyk-1 gene reveal that it encodes an FH protein, a newly defined family of proteins that appear to interact with the cytoskeleton during cytokinesis and in the regulation of cell polarity. Consistent with cyk-1 function being required for a late step in embryonic cytokinesis, we show that the CYK-1 protein co-localizes with actin microfilaments as a ring at the leading edge of the cleavage furrow, but only after extensive furrow ingression. We discuss our findings in the context of other studies suggesting that FH genes in yeast and insects function early in cytokinesis to assemble a cleavage furrow.

The distribution of calcium-binding proteins in the lateral geniculate nucleus and visual cortex of a New World monkey, the marmoset, Callithrix jacchus

Antibodies directed against the calcium-binding proteins, parvalbumin and calbindin, can be used to label distinct neuronal subgroups in the primate visual pathway. We analyzed parvalbumin immunoreactivity (P-IR) and calbindin immunoreactivity (C-IR) in the lateral geniculate nucleus (LGN) and visual cortex of the marmoset, Callithrix jacchus. We compared marmosets which were identified as having dichromatic or trichromatic color vision. Within the LGN, the density of P-IR neurones is highest in the parvocellular and magnocellular laminae, but C-IR neurones are found mainly in the koniocellular division of the LGN, that is, the interlaminar zones and S laminae. Not all interlaminar zone cells are C-IR. In the visual cortex, P-IR neurones are present in all laminae except lamina 1, in areas V1 and V2. Neurones which are strongly C-IR are mainly located in laminae 2 and 3 in V1 and V2. Lightly C-IR neurones are concentrated in lamina 4, and are more numerous in V1 than in V2. Quantitative analysis showed no differences in the density or distribution of IR neurones in either LGN or visual cortex when dichromat and trichromat animals were compared. We conclude that this functional difference is not associated with differences in the neurochemistry of calcium-binding proteins in the primary visual pathways.

Thiamine deficiency decreases steady-state transketolase and pyruvate dehydrogenase but not alpha-ketoglutarate dehydrogenase mRNA levels in three human cell types

Reductions in the levels and activities of enzymes that utilize thiamine diphosphate (ThDP) as a cofactor are thought to be responsible for the tissue damage suffered during thiamine deficiency. Although loss of cofactor can account in part for loss of enzyme activity, thiamine and its phosphorylated derivatives may also regulate the expression of the genes encoding these proteins. To examine this possibility, steady-state mRNA levels for three ThDP-dependent enzymes were measured in human fibroblasts, lymphoblasts and neuroblastoma cells cultured under conditions of thiamine sufficiency and deficiency. In all three cell types, the mRNA levels of transketolase and the E1beta subunit of pyruvate dehydrogenase complex were lower in thiamine-deficient cultures. In contrast, mRNA levels for a ThDP-binding subunit of alpha-ketoglutarate dehydrogenase, the E1 subunit did not differ. These results indicate that thiamine or a thiamine metabolite regulates the expression in humans of some, but not all, genes encoding ThDP-utilizing enzymes.

An assessment of the comprehension of the American Urological Association Symptom Index

PURPOSE

We determine the reading grade level of the American Urological Association (AUA) symptom index, and assessed patient ability to read and understand the index using a standardized reading and IQ test.

MATERIALS AND METHODS

The reading grade level required to read and understand the AUA symptom index was determined using the Spache and Dale-Chall readability formulas. A total of 202 men a mean of 66.1 years old completed the AUA symptom index, Wonderlic personnel test and scholastic level examination, and revised Ohio literacy test. Patients were instructed to report any difficulty in reading or understanding the AUA symptom score.

RESULTS

According to the Spache and Dale-Chall readability formulas, the AUA symptom index requires a grade 6 reading level. Of the 202 patients 30 (14.9%) did not complete the symptom index due to an inability to read it (28, 13.9%) and poor comprehension (2, 1%). Tested mean IQ and reading grade level was 91.7 and 11, respectively.

CONCLUSIONS

A grade 6 reading level is required to read and understand the AUA symptom index. A significant percentage of patients cannot read the index and require assistance from others for its completion. This assistance may introduce significant interviewer bias, potentially altering study outcome.

Effects of food deprivation and a stressor on head pain

This study sought to experimentally validate 2 self-reported trigger factors of headaches, namely negative affect (anxiety, depression, and anger) and hunger, and to investigate whether these triggers activated the same or different physiological mechanisms. Students (38 women and 18 men) who had suffered from frequent headaches (migraine or tension type) for 6 months or more were randomly assigned to 4 conditions, which involved manipulating hunger by means of 19 hr of food deprivation and negative affect by means of a stressor (difficult to solve anagrams). The findings were consistent with self-reports that hunger and negative affect can precipitate headaches in individuals who suffer from both migraine and tension-type headaches. The physiological responses to the experimental conditions differed, but the findings were not conclusive with respect to whether the trigger factors operated by means of a common biological pathway.

Aspartate 155 of human transketolase is essential for thiamine diphosphate-magnesium binding, and cofactor binding is required for dimer formation

Active human transketolase is a homodimeric enzyme possessing two active sites, each with a non-covalently bound thiamine diphosphate and magnesium. Both subunits contribute residues at each site which are involved in cofactor binding and in catalysis. His-tagged transketolase, produced in E. coli, was similar to transketolase purified from human tissues with respect to Km apps for cofactor and substrates and with respect to cofactor-dependent hysteresis. Mutation of aspartate 155, corresponding to a conserved aspartate residue among thiamine diphosphate-binding proteins, resulted in an inactive protein which could not bind the cofactor-magnesium complex and which could not dimerize. The results are consistent with the suggestion that aspartate 155 is an important coordination site for magnesium. In support of this interpretation, binding of cofactor by wild type apo-transketolase required the presence of magnesium. Additionally, monomeric apo-his-transketolase required both magnesium and cofactor binding for dimer formation.

"Wineglass" confabulations among brain-damaged alcoholics on the Wechsler Memory Scale-Revised visual reproduction subtest

Confabulation is a clinically well-documented accompaniment of selective types of memory impairment, especially in brain-damaged alcoholics. This study reports specific occurrences of visual confabulation consisting of spontaneous alterations of Card D of the Visual Reproduction subtest of the Wechsler Memory Scale-Revised. The resemblance of a wineglass was fashioned by a 90-degree rotation into a "bowl and stem", observed in six of 30 brain-damaged alcoholics. There were no such instances in 132 other patients, including alcoholic controls, those with Parkinson's Disease, temporal lobe epileptics (pre- or post-surgery), and those with neurotoxic exposure. When asked, the subjects who identified the figure as a wineglass or similar drinking instrument reported that they had drawn it as originally shown to them. "Wineglass" confabulators had shorter periods of abstinence, longer drinking histories and lower intellectual functioning than their brain-damaged peers or an alcoholic control group. These findings lend support for the association of alcohol-related confabulation with visual, as well as previously-documented verbal material among brain-damaged alcoholics.

Effects of food deprivation and a stressor on head pain

This study sought to experimentally validate 2 self-reported trigger factors of headaches, namely negative affect (anxiety, depression, and anger) and hunger, and to investigate whether these triggers activated the same or different physiological mechanisms. Students (38 women and 18 men) who had suffered from frequent headaches (migraine or tension type) for 6 months or more were randomly assigned to 4 conditions, which involved manipulating hunger by means of 19 hr of food deprivation and negative affect by means of a stressor (difficult to solve anagrams). The findings were consistent with self-reports that hunger and negative affect can precipitate headaches in individuals who suffer from both migraine and tension-type headaches. The physiological responses to the experimental conditions differed, but the findings were not conclusive with respect to whether the trigger factors operated by means of a common biological pathway.

Evidence that blue-on cells are part of the third geniculocortical pathway in primates

Colour vision in primates is mediated by cone opponent ganglion cells in the retina, whose axons project to the dorsal lateral geniculate nucleus in the visual thalamus. It has long been assumed that cone opponent ganglion cells project to the parvocellular layers of the geniculate. Here, we examine the role of a third subdivision of the geniculocortical pathway: the interlaminar or koniocellular geniculate relay cells. We made extracellular recordings in the dorsal lateral geniculate nucleus of the common marmoset Callithrix jacchus, a New World monkey in which the interlaminar cells are well segregated from the parvocellular layers. We found that one group of colour opponent cells, the blue-on cells, was largely segregated to the interlaminar zone. This segregation was common to dichromatic ('red-green colour-blind') and trichromatic marmosets. The result calls into question the traditional notion that all colour information passes through the parvocellular division of the retino-geniculo-cortical pathway in primates.

Song transmission and auditory perception of distance in wood warblers (Parulinae)

The influence of breeding habitat on the evolution of song structure was examined in four wood warbler species of the sub-family Parulinae. The effects of song degradation on the ability of territorial paruline males to estimate distance by means of acoustic cues was also investigated. Song transmission characteristics of paruline breeding habitats were compared in southeastern Ontario, Canada; songs native to the habitat in which they were broadcast did not degrade less than foreign songs. The response of territorial paruline males to playback of 'near' (undegraded) and 'far' (degraded) conspecific songs broadcast from the same position within the territory at the same amplitude were then compared. Males responded to near songs as they would to a conspecific territorial intruder and with less intensity to far songs, suggesting that males may use cues from song degradation to estimate distance to vocal conspecifics. Our results from transmission and playback experiments are discussed with respect to the ranging hypothesis, which proposes that selection should favour males that structure songs to minimize their degradation, so that songs function to disrupt or intimidate rivals by providing unreliable distance cues.