Bidirectional regulation of the cAMP response element binding protein encodes spatial map alignment in prism-adapting barn owls

Hunting increases phosphorylation of calcium/calmodulin-dependent protein kinase type II in adult barn owls

Juvenile barn owls readily adapt to prismatic spectacles, whereas adult owls living under standard aviary conditions do not. We previously demonstrated that phosphorylation of the cyclic-AMP response element-binding protein (CREB) provides a readout of the instructive signals that guide plasticity in juveniles. Here we investigated phosphorylation of calcium/calmodulin-dependent protein kinase II (pCaMKII) in both juveniles and adults. In contrast to CREB, we found no differences in pCaMKII expression between prism-wearing and control juveniles within the external nucleus of the inferior colliculus (ICX), the major site of plasticity. For prism-wearing adults that hunted live mice and are capable of adaptation, expression of pCaMKII was increased relative to prism-wearing adults that fed passively on dead mice and are not capable of adaptation. This effect did not bear the hallmarks of instructive information: it was not localized to rostral ICX and did not exhibit a patchy distribution reflecting discrete bimodal stimuli. These data are consistent with a role for CaMKII as a permissive rather than an instructive factor. In addition, the paucity of pCaMKII expression in passively fed adults suggests that the permissive default setting is "off" in adults.

Rapid and widespread effects of 17β-estradiol on intracellular signaling in the male songbird brain: a seasonal comparison

Across vertebrate species, 17β-estradiol (E(2)) acts on the brain via both genomic and nongenomic mechanisms to influence neuronal physiology and behavior. Nongenomic E(2) signaling is typically initiated by membrane-associated estrogen receptors that modulate intracellular signaling cascades, including rapid phosphorylation of ERK. Phosphorylated ERK (pERK) can, in turn, rapidly phosphorylate tyrosine hydroxylase (TH) and cAMP response element-binding protein (CREB). Recent data suggest that the rapid effects of E(2) on mouse aggressive behavior are more prominent during short photoperiods (winter) and that acute aromatase inhibition reduces songbird aggression in winter only. To date, seasonal plasticity in the rapid effects of E(2) on intracellular signaling has not been investigated. Here, we compared the effects of acute (15 min) E(2) treatment on pERK, pTH, and pCREB immunoreactivity in male song sparrows (Melospiza melodia) pretreated with the aromatase inhibitor fadrozole during the breeding and nonbreeding seasons. We examined immunoreactivity in 14 brain regions including portions of the song control system, social behavior network, and the hippocampus (Hp). In both seasons, E(2) significantly decreased pERK in nucleus taeniae of the amygdala, pTH in ventromedial hypothalamus, and pCREB in mesencephalic central gray, robust nucleus of the arcopallium, and caudomedial nidopallium. However, several effects were critically dependent upon season. E(2) decreased pERK in caudomedial nidopallium in the breeding season only and decreased pCREB in the medial preoptic nucleus in the nonbreeding season only. Remarkably, E(2) decreased pERK in Hp in the breeding season but increased pERK in Hp in the nonbreeding season. Together, these data demonstrate that E(2) has rapid effects on intracellular signaling in multiple regions of the male brain and also demonstrate that rapid effects of E(2) can be profoundly different across the seasons.

Activation of extracellular signal-regulated kinases in social behavior circuits during resident-intruder aggression tests

Using a variety of experimental methods, a network of brain areas regulating aggressive behaviors has been identified in several groups of vertebrates. However, aggressive behavior expressed in different contexts is associated with different patterns of activity across hypothalamic and limbic brain regions. Previous studies in rodents demonstrated that short day photoperiods reliably increase both male and female aggression versus long day photoperiods. Here we used immunohistochemistry and western blots to examine the effect of photoperiod on phosphorylation of extracellular signal-regulated kinases 1 and 2 (ERK) in male California mice (Peromyscus californicus) during resident-intruder tests. Phosphorylated ERK (pERK) can alter neuronal activity in the short term and in the long term acts as a transcription factor. In the posterior bed nucleus of the stria terminalis (BNST) males tested in aggression tests had more pERK positive cells when housed in short days but not long days. This result was replicated in western blot analyses from microdissected BNST samples. In the medial amygdala (MEA), immunostaining and western analyses showed that pERK expression also was generally increased in short days. Immunostaining was also used to examine phosphorylation of cyclic AMP response element binding protein (CREB). CREB can be phosphorylated by pERK as well as other kinases and functions primarily as a transcription factor. Intriguingly, aggressive interactions reduced the number of cells stained positive for phosphorylated CREB in the infralimbic cortex, ventral lateral septum and MEA. This effect was observed in mice housed in long days but not short days. Overall, these data suggest that different (but overlapping) networks of aggressive behavior operate under different environmental conditions.

Auditory processing, plasticity, and learning in the barn owl

The human brain has accumulated many useful building blocks over its evolutionary history, and the best knowledge of these has often derived from experiments performed in animal species that display finely honed abilities. In this article we review a model system at the forefront of investigation into the neural bases of information processing, plasticity, and learning: the barn owl auditory localization pathway. In addition to the broadly applicable principles gleaned from three decades of work in this system, there are good reasons to believe that continued exploration of the owl brain will be invaluable for further advances in understanding of how neuronal networks give rise to behavior.

Endocannabinoid-mediated long-term depression in the avian midbrain expressed presynaptically and postsynaptically

Here, we examined long-term synaptic plasticity in the avian auditory midbrain, a region involved in experience-dependent learning. We found that coactivation of N-methyl-D-aspartate receptors (NMDAR) and type 1 cannabinoid receptors (CB1R) induces long-term depression (LTD) at the synapse between the central shell and the external portion of the inferior colliculus of the chicken. Although endocannabinoids are commonly thought of as presynaptic modulators, recent reports have suggested that they can also modulate the postsynaptic site. In the avian midbrain, we found that LTD is mediated by both presynaptic and postsynaptic changes. The presynaptic mechanism consists of a decrease in neurotransmitter release, whereas a depression of NMDAR-mediated current takes place on the postsynaptic side. Both the presynaptic and the postsynaptic effects depend on CB1R activation. The reduction of postsynaptic NMDAR currents represents a novel role of endocannabinoids in synaptic modulation.