Facial nerve sensory responses recorded from the geniculate ganglion ofGallus gallus var.domesticus

Biophysical properties and responses to glutamate receptor agonists of identified subpopulations of rat geniculate ganglion neurons

The goal of the current study was to evaluate the electrophysiological properties and responses to glutamate receptor agonists of rat geniculate ganglion (GG) neurons innervating the tongue. Subpopulations of GG neurons were labeled by injecting Fluoro-Gold (FG) or True Blue chloride into the anterior tongue and soft palate (AT and SP neurons) and applying FG crystals to the posterior auricular branch of the facial nerve (PA neurons). Three to 12 days later, the GG neurons were acutely isolated and patch clamped. Although many biophysical properties of the AT, SP and PA neurons were similar, significant differences were found among these groups in properties related to cell excitability. For example, the average amount of current necessary to elicit an action potential was 61 pA in AT neurons (n=55), 90 pA in SP neurons (n=41) and 189 pA in PA neurons (n=35, P<0.001). In addition, AT neurons tended to fire significantly more action potentials during depolarization as well as following hyperpolarizing pulses than SP or PA neuron types. Most GG neurons responded to application of glutamate receptor agonists. The neurons responded with a depolarization accompanied by a reduction in input resistance. These results suggest that subpopulations of neurons in the geniculate ganglion have distinct biophysical properties and express functional glutamate receptors. The differing biophysical properties of GG neurons is possibly related to their functional heterogeneity and glutaminergic neurotransmission may function in the processing of gustatory, and other sensory information, within the geniculate ganglion and its projections.

Ultrastructure of palatal taste buds in the perihatching chick

Palatal taste buds of perihatching chicks were examined by electron microscopy. Four intragemmal cell types were characterized. 1) Light: with voluminous, electron-lucent cytoplasm containing scattered free ribosomes, rough and smooth endoplasmic reticulum, plump mitochondria, sparse perinuclear filaments, occasional Golgi bodies, and numerous clear and dense-cored vesicles. Clear vesicles sometimes aggregate in a presynaptic-like configuration apposed to an axonal profile. These cells contained large, spherical, uniformly granular nuclei with one nucleolus. 2) Dark: with dense cytoplasm containing filamentous bundles surrounding the nucleus, occasional clear vesicles, centrioles, rough endoplasmic reticulum, and compact mitochrondria. The apical cytoplasm noticeably lacks dense secretory granules. Irregular to lobulated nuclei are densely granular, and contain scattered clumps of chromatin, adhering especially to the inner leaflet of the nuclear membrane, and at least one nucleolus. Cytoplasmic extensions of dark cells envelop other intragemmal cell types and nerve fibers. Light and dark cells project microvilli into the taste pore. 3) Intermediate: contain gradations of features of light and dark cells. 4) Basal: darker than the other intragemmal cell types and confined to the ventral bud region. Putative afferent synapses in relation to light cells, and axo-axonal contacts are described. While the appearance of axo-axonal contacts may be a transient developmental event, other bud features are consonant with observations in adult chickens and suggest that the peripheral gustatory apparatus is mature at hatching in this precocial avian species.

Physiological and behavioural responses associated with feather removal in Gallus gallus var domesticus

Electroencephalographic, cardiovascular and behavioural parameters were examined in Gallus gallus var domesticus in response to feather removal. The progressive removal of feathers resulted in marked changes in the bird's behaviour from an alert agitated response following the initial removals to periods of crouching immobility following successive removals. During the periods of immobility the birds showed a high amplitude low frequency EEG pattern and successive removals resulted in a progressive increase in the total duration of this activity in the two minutes after removal. The heart rate response to feather removal was variable whereas the blood pressure always increased and this increase was followed by a gradual return to pre-stimulus levels. There were no consistent cardiovascular responses related to the immobility. It was concluded that feather removal is likely to be painful to the bird and feather removal by flockmates can be categorised as a welfare problem.

Behavioral reactions to gustatory stimuli in young chicks (Gallus gallus domesticus)

Freely-moving, posthatch chicks were individually presented 2 concentrations each of quinine, citric acid, fructose, sucrose, sodium saccharin, and distilled water and their behavioral reactions were videotaped and analyzed. Already during the first posthatch day distinct rejection responses to quinine and citric acid could be recognized. Prolonged head shaking and beak clapping episodes were the most dominant features of these reactions. While responses to water and sweet stimuli could be interpreted as acceptance behaviors, the resolution was generally not fine enough to discriminate between reactions to the 2 different sweet concentrations of these stimuli or between them and water. When only water or sugar solutions were presented to other hatchlings in a single session, there was a suggestion of more definite acceptance behavior to some sweet stimuli as compared to water. It is concluded that the systems mediating aversive gustatory responses are present and functioning in posthatching chicks while acceptance responses, though present, are less discriminative among stimuli.

Cutaneous sensory afferents recorded from the nervus intramandibularis of Gallus gallus var domesticus

The responses of single sensory afferent nerve fibres were recorded from small nerve bundles of the intramandibular nerve of the chicken following thermal and mechanical stimulation of the beak. Thermoreceptors, nociceptors and mechanoreceptors were identified and their responses characterized. Of the thermoreceptors identified 11 units were classified as cold receptors, which responded to cooling the receptive field by increasing the discharge rate and had conduction velocities in the range 0.83 to 4.4 m/s. Only one warm unit was identified. Two classes of nociceptors were identified: mechano-thermal (polymodal) nociceptors and high threshold mechanical nociceptors. The discharge characteristics and stimulus-response curves of both types were described. While the mechano-thermal nociceptors were exclusively C-fibres (c.v. 0.4 to 1.86 m/s), the high threshold mechanoreceptors contained both C and A delta fibres (c.v. 1 to 5.5 m/s). Thermal response thresholds for the mechano-thermal units ranged from 41 to 50 degrees C with mechanical thresholds of 2 to over 50 g. Mechanical thresholds for the high threshold units ranged from 5 to over 50 g. The mechanoreceptors were either slowly or rapidly adapting. The pattern of response together with stimulus-response curves were presented for the slowly adapting units. Conduction velocities of the slowly adapting units varied from 0.7 to 20 m/s and mechanical threshold from 0.1 to 2 g. On the basis of their response to a vibrating, and a ramp-and-hold mechanical stimulus, the rapidly adapting units were divided into Herbst and Grandry units with only the Herbst units responding accurately to the vibrating stimulus. Both units had fibres conducting in the 50 m/s range with thresholds in the 0.1 to 10 g range. The results are discussed in relation to the receptors found in other avian species and mammalian peripheral sensory afferents.

Central distribution and efferent origins of facial nerve branches in the chicken

The central afferent distribution and the origins of visceromotor and somatomotor components of greater superficial petrosal (GSP), chorda tympani (CT), and hyomandibular (Hy) branches of the facial nerve were analyzed by the transganglionic and retrograde transport of horseradish peroxidase. Labelled sensory afferent fascicles of the GSP collected dorsomedial to the spinal trigeminal complex and passed caudally as the tractus solitarius. Fine-grain terminal fields were evident in ipsilateral n. sensorius n. facialis, nuclei ventrolateralis anterior (Vla), centralis anterior and presulcalis anterior of the solitary complex, and n. glossopharyngei et n. motorius dorsalis nervi vagi (n. IX-X). Minor contralateral projections to these nuclei occasionally were observed. CT sensory afferents exhibited similar ipsilateral projections, and specifically, the projection to Vla was qualitatively sparser than that from the GSP. Small multipolar and spindle-shaped somata of visceromotor n. salivatorius were labelled retrogradely from the GSP and CT. Large, oval somatomotor cells of the three subdivisions of the facial motor nucleus were labelled retrogradely from Hy, with no evidence of sensory afferent or visceromotor connections.