Neurochemistry and circuit organization of the lateral spiriform nucleus of birds: A uniquely nonmammalian direct pathway component of the basal ganglia.

We used diverse methods to characterize the role of avian lateral spiriform nucleus (SpL) in basal ganglia motor function. Connectivity analysis showed that SpL receives input from globus pallidus (GP), and the intrapeduncular nucleus (INP) located ventromedial to GP, whose neurons express numerous striatal markers. SpL-projecting GP neurons were large and aspiny, while SpL-projecting INP neurons were medium sized and spiny. Connectivity analysis further showed that SpL receives inputs from subthalamic nucleus (STN) and substantia nigra pars reticulata (SNr), and that the SNr also receives inputs from GP, INP, and STN. Neurochemical analysis showed that SpL neurons express ENK, GAD, and a variety of pallidal neuron markers, and receive GABAergic terminals, some of which also contain DARPP32, consistent with GP pallidal and INP striatal inputs. Connectivity and neurochemical analysis showed that the SpL input to tectum prominently ends on GABAA receptor-enriched tectobulbar neurons. Behavioral studies showed that lesions of SpL impair visuomotor behaviors involving tracking and pecking moving targets. Our results suggest that SpL modulates brainstem-projecting tectobulbar neurons in a manner comparable to the demonstrated influence of GP internus on motor thalamus and of SNr on tectobulbar neurons in mammals. Given published data in amphibians and reptiles, it seems likely the SpL circuit represents a major direct pathway-type circuit by which the basal ganglia exerts its motor influence in nonmammalian tetrapods. The present studies also show that avian striatum is divided into three spatially segregated territories with differing connectivity, a medial striato-nigral territory, a dorsolateral striato-GP territory, and the ventrolateral INP motor territory.

Joseph Vincent Brady (1922-2011).

Joseph Vincent Brady was born in New York City on March 28, 1922. Joe died on July 29, 2011. Joe was a pioneer in bringing the methods and philosophy of behavior analysis to the emerging field of behavioral pharmacology. In 1960, with David Rioch, Joe founded the nonprofit Institute for Behavioral Research (later the Institutes for Behavioral Resources, or IBR), which continues to the present day. True to his belief in the importance of the environmental determinants of behavior, when interviewed about his accomplishments in so many varied fields, Joe replied that in each area he had been "the beneficiary of a fortuitous environment."

Visual deprivation reactivates rapid ocular dominance plasticity in adult visual cortex.

Brief monocular deprivation (< or =3 d) induces a rapid shift in the ocular dominance of binocular neurons in the juvenile rodent visual cortex but is ineffective in adults. Here, we report that persistent, rapid, juvenile-like ocular dominance plasticity can be reactivated in adult rodent visual cortex when monocular deprivation is preceded by visual deprivation. Ocular dominance shifts in visually deprived adults are caused by a rapid depression of the response to stimulation of the deprived eye, previously only reported in juveniles, and a simultaneous potentiation of the response to stimulation of the nondeprived eye. The enhanced ocular dominance plasticity induced by visual deprivation persists for days, even if binocular vision precedes monocular deprivation. Visual deprivation also induces a significant decrease in the level of GABAA receptors relative to AMPA receptors and a return to the juvenile form of NMDA receptors in the visual cortex, two molecular changes that we propose enable the persistent reactivation of rapid ocular dominance plasticity.

Spatial contrast sensitivity of birds.

Contrast sensitivity (CS) is the ability of the observer to discriminate between adjacent stimuli on the basis of their differences in relative luminosity (contrast) rather than their absolute luminances. In previous studies, using a narrow range of species, birds have been reported to have low contrast detection thresholds relative to mammals and fishes. This was an unexpected finding because birds had been traditionally reported to have excellent visual acuity and color vision. This study reports CS in six species of birds that represent a range of visual adaptations to varying environments. The species studied were American kestrels (Falco sparverius), barn owls (Tyto alba), Japanese quail (Coturnix coturnix japonica), white Carneaux pigeons (Columba livia), starlings (Sturnus vulgaris), and red-bellied woodpeckers (Melanerpes carolinus). Contrast sensitivity functions (CSFs) were obtained from these birds using the pattern electroretinogram and compared with CSFs from the literature when possible. All of these species exhibited low CS relative to humans and most mammals, which suggests that low CS is a general characteristic of birds. Their low maximum CS may represent a trade-off of contrast detection for some other ecologically vital capacity such as UV detection or other aspects of their unique color vision.

The visual acuity and refractive state of the American kestrel (Falco sparverius).

The pattern electroretinogram (PERG) was used to measure the visual acuity and refractive state of nine American kestrels (Falco sparverius). Visual acuity was determined from psychometric functions of PERG amplitude vs. spatial frequency. Refractive state was measured by finding the trial lens that resulted in the highest acuity. All nine kestrels were found to be emmetropic. Their median visual acuity was 29 c/deg. The PERG, however, underestimates behaviorally determined visual acuity by approximately 37%. When adjusted for this underestimation, the median kestrel acuity was 46 c/deg. The visual acuity of American kestrels is compared to reports in the literature of 17 other species of birds.

Temporal modulation of spatial contrast vision in pigeons (Columba livia).

Spatiotemporal contrast sensitivity (CS) functions were obtained from four White Carneaux pigeons. The spatial frequency for each session was selected randomly from a group of five spatial frequencies ranging from 0.42 to 1.26 c/deg. Within the session, the temporal frequency varied from 1 to 32 Hz. When plotted as a function of spatial frequency, the CS functions peaked in the range 0.7-1.0 c/deg. When compared to data that had been collected at 0 Hz temporal modulation, the temporally modulated spatial CS functions showed reduced CS, especially at the higher spatial frequencies, and reduced peak spatial frequency. When plotted as a function of temporal frequency, the CS functions were flat up to 8-16 Hz. Above 16 Hz, the curves showed a sharp roll off. When plotted as a three-dimensional, spatiotemporal CS surface, the data had a number of characteristics in common with the three-dimensional spatiotemporal model of CS proposed by Burbeck and Kelly (J. Opt. Soc. Am. 70 (1980) 1121).

Nucleus magnocellularis and nucleus laminaris in Belgian Waterslager and normal strain canaries.

Belgian Waterslager (BWS) canaries are characterized by a mean 30% loss of hair cells in the basilar papilla compared to other canaries, and a corresponding increase in behavioral auditory thresholds. In spite of the large number of missing and damaged sensory cells, there is on average only a 12% reduction in the number of fibers in the VIIIth nerve. In this study, we examined cell number and size, and volume of auditory nuclei, specifically in nucleus magnocellularis and nucleus laminaris in Belgian Waterslager canaries. While the overall anatomical structure and organization of these nuclei and the total number of cells in the non-BWS and BWS canaries were comparable, BWS canaries showed a significant decrease in the volume of the auditory nuclei that was attributed to a reduction in cell size. These results provide further evidence in favor of a role of the sensory epithelium in the maintenance of central auditory structures.

Contrast sensitivity in pigeons: a comparison of behavioral and pattern ERG methods.

Contrast sensitivity (CS) is often used to assess spatial and temporal vision in animals. Conventional behavioral psychophysical techniques are both time and labor intensive, whereas measurement of CS functions by means of the pattern electroretinogram (PERG) is considerably more rapid and efficient. Are the two methods comparable, however? To answer this question, contrast-sensitivity functions were obtained using both the PERG and behavioral psychophysics in the same subjects, which were White Carneaux pigeons. The stimuli, in both methods, were phase-reversing, contrast-modulated sweeps of sinusoidal gratings. The PERG-CS functions were recorded via corneal electrodes and the behavioral data were collected using a modified staircase method that used moderate food deprivation and food reward. The results indicated that the PERG-CS functions had comparable bandwidth and peak spatial frequency to the behavioral CS functions. The PERG-CS functions, however, were lower on average than the behavioral curves by about 54%. The visual acuity of the two methods, as estimated from the high-frequency cutoff of the CS functions, differed by 37%. Both of these values are roughly consistent with the square root of 2 advantage of binocular viewing (behavioral method) over monocular viewing (PERG method). In addition, the peak spatial frequency showed a decrease of 0.125 c/deg with the PERG method and bandwidth was reduced by approximately 0.5 octave. These findings suggest that the PERG is an acceptable alternative to behavioral measurement of CS functions, especially in animal psychophysics, if one takes into account the underestimation of CS by the PERG method and the small changes in peak spatial frequency and bandwidth.