Calcium responses of chicken trigeminal ganglion neurons to methyl anthranilate and capsaicin

Using digital fluorescence imaging, we determined the effects of methyl anthranilate (MA), an avian irritant, and capsaicin (CAP), a mammalian irritant, on intracellular calcium ([Ca2+]i) in chicken trigeminal neurons. Concentration–response functions indicated that the threshold for inducing increases in [Ca2+]i was higher for CAP (30·mmol·l–1) than for MA (10·mmol·l–1). The maximum magnitudes of [Ca2+]i in response to MA and CAP were compared after normalization to 40·mmol·l–1 KCl. At equal concentrations (300·mmol·l–1), trigeminal neurons responded with a greater change in [Ca2+]i to MA (78% of KCl) than to CAP (43% of KCl). Furthermore, at 300·mmol·l–1, 48% of neurons responded to MA whereas only 16% responded to CAP. The increases in [Ca2+]i induced by both MA and CAP were dependent upon extracellular calcium. While the calcium responses to MA were also dependent on extracellular sodium, responses to CAP were not. There were separate but overlapping populations of neurons sensitive to MA and CAP. Taken together, the higher threshold concentration of CAP, the higher response magnitude to MA than CAP and the greater number of neurons sensitive to MA than CAP provide a rationale for the observed behavioral differences of birds to these two compounds. Finally, the findings that the calcium responses to MA and CAP have different ion dependencies and that there are separate populations sensitive to these compounds suggest different transduction mechanisms mediating chicken trigeminal responses to MA and CAP

Thalamic neuromodulation and its implications for executive networks

The thalamus is a key structure that controls the routing of information in the brain. Understanding modulation at the thalamic level is critical to understanding the flow of information to brain regions involved in cognitive functions, such as the neocortex, the hippocampus, and the basal ganglia. Modulators contribute the majority of synapses that thalamic cells receive, and the highest fraction of modulator synapses is found in thalamic nuclei interconnected with higher order cortical regions. In addition, disruption of modulators often translates into disabling disorders of executive behavior. However, modulation in thalamic nuclei such as the midline and intralaminar groups, which are interconnected with forebrain executive regions, has received little attention compared to sensory nuclei. Thalamic modulators are heterogeneous in regards to their origin, the neurotransmitter they use, and the effect on thalamic cells. Modulators also share some features, such as having small terminal boutons and activating metabotropic receptors on the cells they contact. I will review anatomical and physiological data on thalamic modulators with these goals: first, determine to what extent the evidence supports similar modulator functions across thalamic nuclei; and second, discuss the current evidence on modulation in the midline and intralaminar nuclei in relation to their role in executive function

Differences in Response to Serotonergic Activation between First and Higher Order Thalamic Nuclei

Two types of thalamic nuclei have been recognized: first order, which relay information from subcortical sources, and higher order, which may relay information from one cortical area to another. We have recently shown that muscarinic agonists depolarize all first order and most higher order relay cells but hyperpolarize a significant proportion of higher order relay cells. We now extend this result to serotonergic agonists, using rat thalamic brain slices and whole-cell, current- and voltage-clamp recordings from relay cells in various first order (the lateral geniculate nucleus, the ventral posterior nucleus, and the ventral portion of the medial geniculate body) and higher order nuclei (the lateral posterior, the posterior medial nucleus, and the dorsal portion of the medial geniculate body). Similar to the effects of muscarinic agonists, we found that first and most higher order relay cells were depolarized by serotonergic agonists, but 15% of higher order relay cells responded with hyperpolarization. Thus different subsets of higher order relay cells are hyperpolarized by these modulatory systems, which could have implications for the transfer of information between cortical areas

The Chemical Senses in Birds

7.1 CHEMICAL SENSES The chemical senses generally fall into three categories: chemesthesis (irritation and pain), olfaction (smell), and gustation (taste). Traditionally, the emphasis in describing responsiveness to chemical stimuli has been placed on taste and smell. The reality is more complex. For example, the sensory afferents for chemesthetic perception are in close proximity with olfactory receptors in the nasal cavity and with gustatory receptors in the oral cavity. Because external chemical stimuli can be processed by multiple sensory systems, there has been a great deal of confusion in the literature on the importance of individual sensory modalities. Generally, the principal mediating sensory modality may be related to stimulus type, concentration, and presentation. However, when perception of external chemical stimuli occurs via the integrated perception across modalities, the combined perceptual quality is commonly referred to as flavor