Frank Johnson

Circuits, hormones, and learning: Vocal behavior in songbirds

Species-typical vocal patterns subserve species identification and communication for individual organisms. Only a few groups of organisms learn the sounds used for vocal communication, including songbirds, humans, and cetaceans. Vocal learning in songbirds has come to serve as a model system for the study of brain-behavior relationships and neural mechanisms of learning and memory. Songbirds learn specific vocal patterns during a sensitive period of development via a complex assortment of neurobehavioral mechanisms. In many species of songbirds, the production of vocal behavior by adult males is used to defend territories and attract females, and both males and females must perceive vocal patterns and respond to them. In both juveniles and adults, specific types of auditory experience are necessary for initial song learning as well as the maintenance of stable song patterns. External sources of experience such as acoustic cues must be integrated with internal regulatory factors such as hormones, neurotransmitters, and cytokines for vocal patterns to be learned and produced. Thus, vocal behavior in songbirds is a culturally acquired trait that is regulated by multiple intrinsic as well as extrinsic factors. Here, we focus on functional relationships between circuitry and behavior in male songbirds. In that context, we consider in particular the influence of sex hormones on vocal behavior and its underlying circuitry, as well as the regulatory and functional mechanisms suggested by morphologic changes in the neural substrate for song control. We describe new data on the architecture of the song system that suggests strong similarities between the songbird vocal control system and neural circuits for memory, cognition, and use-dependent plasticity in the mammalian brain.

Personality subtyping and bulimia nervosa: psychopathological and genetic correlates

BACKGROUND There is empirical evidence suggesting that individuals with bulimia nervosa vary considerably in terms of psychiatric co-morbidity and personality functioning. In this study, latent profile analysis was used to attempt to identify clusters of bulimic subjects based on psychiatric co-morbidity and personality. METHOD A total of 178 women with bulimia nervosa or a subclinical variant of bulimia nervosa completed a series of self-report inventories of co-morbid psychopathology and personality, and also provided a buccal smear sample for genetic analyses. RESULTS Three clusters of bulimic women were identified: an affective-perfectionistic cluster, an impulsive cluster, and a low co-morbid psychopathology cluster. The clusters showed expected differences on external validation tests with both personality and eating-disorder measures. The impulsive cluster showed the highest elevations on dissocial behavior and the lowest scores on compulsivity, while the affective-perfectionistic cluster showed the highest levels of eating-disorder symptoms. The clusters did not differ on genetic variations of the serotonin transporter gene. CONCLUSIONS This study corroborates previous findings suggesting that the bulimia nervosa diagnostic category is comprised of three classes of individuals based on co-morbid psychopathology and personality. These differences may have significant etiological and treatment implications.

Neurotrophins Suppress Apoptosis Induced by Deafferentation of an Avian Motor-Cortical Region

Studies of the developing nervous system led to the general view that growth factors promote neuronal survival in a “retrograde” manner. For example, release of NGF from postsynaptic peripheral targets followed by uptake and retrograde transport by presynaptic neurons provided a widely accepted conceptual framework for the action of neurotrophins. In contrast, although presynaptic or “anterograde” influences on the survival of developing neurons have been recognized for some time, the mechanisms by which afferent input regulates the survival of postsynaptic cells have received considerably less attention. In the forebrain network for learned vocal behavior in zebra finches, lesions of a cortical region for song control, the lateral magnocellular nucleus of the anterior neostriatum (lMAN), remove presynaptic input to a motor-cortical song region, the robust nucleus of the archistriatum (RA), and cause massive RA neuron death in young birds that are entering the sensitive period for song learning. Here we report that lesions of lMAN followed by infusions of neurotrophins directly into RA completely suppress neuronal apoptosis in RA. Moreover, we show that lMAN neurons are able to transport neurotrophins in the anterograde direction to RA, that neurotrophin-like immunoreactivity is present in cells in lMAN and RA, and that neurotrophin receptor-like immunoreactivity is present in RA. Expression of neurotrophins in lMAN and RA suggests that lMAN presynaptic input could regulate RA neuron survival by synthesizing, transporting, and releasing neurotrophins anterogradely or by regulating the auto/paracrine release of neurotrophins within RA, or perhaps by both. These data provide the first in vivodemonstration that neurotrophins can prevent the death of deafferented cortical neurons, and they raise the possibility that nonretrograde signaling by neurotrophins may be a common means of promoting neuronal survival in the vertebrate telencephalon. Anterograde and auto/paracrine neurotrophin signaling, along with the more established view that neurotrophins regulate neuron survival via retrograde mechanisms, suggests multidirectional neurotrophin signaling in the vertebrate telencephalon.

Neurogenesis in adult canary telencephalon is independent of gonadal hormone levels

Neurons generated in adulthood are found throughout the canary telencephalon. We are interested in the factors that control the rate of proliferation of stem cells that give rise to these new neurons. The rate of incorporation of newly generated neurons into vocal-control regions varies seasonally. This difference could reflect a higher rate of neurogenesis, a lower rate of cell death, or an altered migration. We examined the incidence of thymidine-labeled cells in the telencephalic ventricular zone of adult canaries as a function of variations in gonadal hormone levels. Adult female canaries maintained on a short-day photoperiod were anesthetized and gonadectomized. Four separate groups of birds received systemic exposure to either testosterone, estradiol, a combination of an anti-androgen and an inhibitor of estrogen synthesis, or nothing. All birds were also implanted with an osmotic minipump that released 3H-thymidine for 3 d and were killed 4 or 7 d following the onset of treatment. Analysis of autoradiograms revealed no differences between groups in the incidence of labeling within the ventricular zone either at the level of the anterior commissure or directly adjacent to the vocal-control nucleus HVC (higher vocal center). These results suggest that sex steroids do not regulate the rate of cell division in the ventricular zone. Seasonal differences in the incorporation of labeled cells into HVC may therefore be due to regulation of neurogenesis by photoperiodic factors other than gonadal steroids or to some other cellular mechanism, such as differential migration or survival of neurons.

Estrogen regulation of cell proliferation and distribution of estrogen receptor‐α in the brains of adult female prairie and meadow voles

Adult female prairie (Microtus ochrogaster) and meadow (M. pennsylvanicus) voles were compared to examine neural cell proliferation and the effects of estrogen manipulation on cell proliferation in the amygdala, ventromedial hypothalamus (VMH), and dentate gyrus of the hippocampus (DG). Unlike prior studies, our study focused on the amygdala and VMH, because they are involved in social behaviors and may underlie behavioral differences between the species. Meadow voles had a higher density of cells labeled with the cell proliferation marker 5‐bromo‐2′‐deoxyuridine (BrdU) in the amygdala and DG than did prairie voles. Treatment with estradiol benzoate (EB) for 3 days increased the density of BrdU‐labeled cells in the amygdala, particularly in the posterior cortical (pCorA) and medial (pMeA) nuclei, in meadow, but not prairie, voles. Furthermore, the majority of the BrdU‐labeled cells in the pCorA and pMeA displayed either a neuronal or a glial progenitor phenotype, but no species or treatment differences were found in the percentage of neuronal or glial progenitor cells. To understand better estrogens effects on adult neurogenesis, we also examined estrogen receptor‐α (ERα) distribution. Meadow voles had more ERα‐labeled cells in the pCorA and VMH, but not in the pMeA or DG, than did prairie voles. In addition, more than one‐half of the BrdU‐labeled cells in the amygdala of both species coexpressed ERα labeling. Together, these data indicate that estrogen alters cell proliferation in a species‐ and region‐specific manner, and some of these effects may lie in the specific localization of estrogen receptors in the adult vole brain. J. Comp. Neurol. 489:166–179, 2005.

[30] Introduction to the bioluminescence of medusae, with special reference to the photoprotein aequorin

Publisher Summary This chapter discusses the bioluminescence of Medusae, with special reference to the photoprotein aequorin. The Pholas system has certain points in common with the Aequorea system, and these points tend to place both systems among the photoprotein types, which comprise a different category from that of a substrate–enzyme system in the usual sense. The seeming stability of components of the Aequorea system against drying and autolysis offered sufficient encouragement to the possibility of obtaining cell-flee luminescent extracts and their active components. The protein moiety of spent aequorin can be logically regarded as an enzyme catalyzing a luminescent oxidation of coelenterazine. The aequorin must be considered to represent an enzyme intermediate, as hypothetically suggested by several investigators. Aqueous solutions of aequorin are practically nonfluorescent.

CB1 cannabinoid receptor expression in brain regions associated with zebra finch song control.

Cannabinoids have been used for millennia through various preparations of Cannabis sativa. Despite this long history of use, the physiological significance of cannabinoid signaling in the vertebrate CNS is not well understood. High CB1 cannabinoid receptor densities in mammalian telencephalon and the results of behavioral studies suggest that cannabinoids play a role in cognitive function, learning, and memory. Since a network of discrete brain regions in zebra finch telencephalon controls song learning, we hypothesized that cannabinoid signaling may be relevant to songbird vocal development and behavior. Radioligand binding experiments using the cannabinoid agonist [3H]CP-55940 allowed identification of a dense population of high-affinity cannabinoid binding sites in zebra finch neuronal membranes. Northern blotting and RT-PCR experiments demonstrated expression of a predominant zebra finch CB1 mRNA of approximately 5.5 kb. Expression of this CB1 mRNA appears to change over the course of vocal development within the caudal telencephalon. As zebra finch caudal telencephalon contains the higher vocal center (HVC) and the robust nucleus of the archistriatum (RA), regions involved in song learning and production, we further investigated CB1 expression in these areas using in situ hybridization. In situ hybridization revealed that CB1 mRNA is expressed at high levels within both HVC and RA. Overall, these data demonstrate the presence of CB1 signaling systems within songbird telencephalon, notably within regions known to be involved in song learning and production. High-level CB1 expression in song regions suggests a potential role for cannabinoid signaling in zebra finch vocal development.

Auditory-Dependent Vocal Recovery in Adult Male Zebra Finches Is Facilitated by Lesion of a Forebrain Pathway That Includes the Basal Ganglia

The integration of two neural pathways generates learned song in zebra finches. The vocal motor pathway (VMP) is a direct connection between HVC (proper name) and the robust nucleus of the arcopallium (RA), whereas the anterior forebrain pathway (AFP) comprises an indirect circuit from HVC to RA that traverses the basal ganglia. Partial ablation (microlesion) of HVC in adult birds alters the integration of VMP and AFP synaptic input within RA and destabilizes singing. However, the vocal pattern shows surprising resilience because birds subsequently recover their song in ∼1 week. Here, we show that deafening prevents vocal recovery after HVC microlesions, indicating that birds require auditory feedback to restore/relearn their vocal patterns. We then tested the role of the AFP (basal ganglia circuit) in this feedback-based recovery by ablating the output nucleus of the AFP [lateral magnocellular nucleus of the anterior nidopallium (LMAN)]. We found that LMAN ablation after HVC microlesions induced a sudden recovery of the vocal pattern. Thus, the AFP cannot be the neural locus of an instructive/learning mechanism that uses auditory feedback to guide vocal recovery, at least in this form of adult vocal plasticity. Instead, the AFP appears to be the source of the variable motor patterns responsible for vocal destabilization. In part, auditory feedback may restore song by strengthening the VMP component of synaptic input to RA relative to the AFP component.

Impact of experience-dependent and -independent factors on gene expression in songbird brain

Songbirds provide rich natural models for studying the relationships between brain anatomy, behavior, environmental signals, and gene expression. Under the Songbird Neurogenomics Initiative, investigators from 11 laboratories collected brain samples from six species of songbird under a range of experimental conditions, and 488 of these samples were analyzed systematically for gene expression by microarray. ANOVA was used to test 32 planned contrasts in the data, revealing the relative impact of different factors. The brain region from which tissue was taken had the greatest influence on gene expression profile, affecting the majority of signals measured by 18,848 cDNA spots on the microarray. Social and environmental manipulations had a highly variable impact, interpreted here as a manifestation of paradoxical “constitutive plasticity” (fewer inducible genes) during periods of enhanced behavioral responsiveness. Several specific genes were identified that may be important in the evolution of linkages between environmental signals and behavior. The data were also analyzed using weighted gene coexpression network analysis, followed by gene ontology analysis. This revealed modules of coexpressed genes that are also enriched for specific functional annotations, such as “ribosome” (expressed more highly in juvenile brain) and “dopamine metabolic process” (expressed more highly in striatal song control nucleus area X). These results underscore the complexity of influences on neural gene expression and provide a resource for studying how these influences are integrated during natural experience.

Quantifying song bout production during zebra finch sensory-motor learning suggests a sensitive period for vocal practice

Using an event-triggered recording system, the quantity of daily song bout production was measured weekly in male zebra finches (Taeniopygia guttata) during sensory-motor learning and at one year of age. Our aim was to ask whether the development of a stereotyped vocal pattern involves a practice-driven component. If so, we hypothesized that juvenile males learning song should sing more often than adults reciting a vocal pattern they had already learned, and that greater levels of juvenile singing should be associated with improvement in the quality of the adult song. Across the period measured (36-365 days of age), subjects showed an inverted U-shaped pattern of daily song bout production. Song bout production was lowest during subsong, with increased production associated with plastic song and song crystallization, although individual differences were large. Daily song bout production decreased in adulthood. Higher levels of song bout production during plastic song correlated with fewer sequencing errors in adult song patterns (r(2)=0.77). In contrast, quantity of singing during song crystallization showed no relationship to vocal stereotypy (r(2)=0.002). Our data suggest a sensitive period for vocal practice during zebra finch sensory-motor learning with consequences for the note-sequence fidelity of the adult vocal pattern.