M. M. Beck

Neural sites and pathways regulating food intake in birds: A comparative analysis to mammalian systems

The paper reviews hypotheses explaining the regulation of food intake in mammals that have addressed specific anatomical structures in the brain. An hypothesis, poikilostasis, is introduced to describe multiple, homeostatic states whereby the regulation of metabolism and feeding occur in birds. Examples are given for both wild and domestic avian species, illustrating dynamic shifts in homeostasis responsible for the changes in body weights that are seen during the course of an annual cycle or by a particular strain of bird. The following neural structures are reviewed as each has been shown to affect food intake in birds or in mammals: ventromedial hypothalamic nucleus (n.), lateral hypothalamic area, paraventricular hypothalamic n., n. tractus solitarius and area postrema, amygdala, parabrachial n., arcuate n. and bed n. of the stria terminalis. Two neural pathways are described which have been proposed to regulate feeding. The trigeminal sensorimotor pathway is the most complete neural pathway characterized for this behavior and encompasses the mechanics of pecking, grasping and mandibulating food particles from the tip of the bill to the back of the buccal cavity. A second pathway, the visceral forebrain system (VFS), affects feeding by regulating metabolism and the balance of the autonomic nervous system. Wild, migratory birds are shown to exhibit marked changes in body weight which are hypothesized to occur due to shifts in balance between the sympathetic and parasympathetic nervous systems. Domestic avian species, selected for a rapid growth rate, are shown to display a dominance of the parasympathetic nervous system. The VFS is the neural system proposed to effect poikilostasis by altering the steady state of the autonomic nervous system in aves and perhaps is applicable to other classes of vertebrates as well.

Changes in immunoreactivity to anti-cGnRH-I and -II are associated with photostimulated sexual status in male quail

Abstract. In sexually active males exposed to long-day (LD) photoperiod, perikarya in the olfactory bulb, lobus parolfactorius, n. accumbens, and preoptic region were immunoreactive (ir) to an antiserum against gonadotropin-releasing hormone (anti-cGnRH-I), and a cluster of ir-perikarya was found in the caudal-most septal area. Ir-perikarya in these brain areas of sexually inactive short-day (SD) males were located within more discrete areas than those in LD brain, which were more scattered in appearance. Absolute cell numbers were similar between LD and SD brains. Ir-fibers in LD brains were mostly in the external median eminence, along the lateral ventricle to septum (especially in and about the n. accumbens), in the septal-preoptic area, along the third ventricle, and at the n. commissure palli. There were fewer ir-fibers in SD brain. Many small dark ring-like ir-structures were found in the hyperstriatum, hippocampus, and n. taeniae. Interpreted as being ir-terminals on non-ir perikarya, these were not observed in SD males. cGnRH-II ir-perikarya were observed in only two areas regardless of reproductive status: (1) ventral to the substantia grisea centralis and caudal to the oculomotor complex, and (2) scattered in and about the lateral hypothalamus. Ir-fibers occurred in the habenular area, hyperstriatum, hippocampus, parahippocampal area, cortex piriformis, and n. taeniae. cGnRH-II ir-fibers occurred in the external median eminence but were less intensely stained than cGnRH-I ir-fibers. These fibers in SD males were similar except in the diencephalon, where scattered swellings were observed. Thus, the appearance and distribution of anti-cGnRH-I and -II ir-structures change with the sexual status of male quail, but changes in immunoreactivity to anti-cGnRH-I appear to be more widespread.

Origins of peripheral and brainstem auditory responses in the white leghorn chick

1. Peripheral and central auditory projections were sectioned and far-field recordings measured to determine neural generators of the waveform in the White Leghorn chick. 2. The mesencephalicus lateralis p. dorsalis and more rostral structures do not contribute to the waveform. 3. Activity of N.VIII is reflected in peaks P1A and P2A; N2A appears to be central in origin but may be in part from the central stump of N.VIII. 4. The crossed dorsal cochlear tract but not the trapezoid body is necessary for P3A and P4A; it is therefore functionally homologous to mammalian trapezoid fibres. 5. P1A, P2A, N2A, P2B are not dependent on crossing fibres.

Physiological responses of tom turkeys to temperature and humidity change with age

Abstract 1. 1. Using a 3-factor uniform-precision rotatable central composite design, male turkeys at 5 ages (5–20 weeks) subjected to 5 temperatures (T, 25–40°C) and 5 relative humidities (RH, 40–80%) during 2 h exposure periods were assessed for body temperature (BT), moisture production (MPM), CO 2 production, respiration rate (RR) and heart rate (HR). Prediction equations based on thermal conditions were developed for each physiological response. 2. 2. For the temperature range selected, RH had a stronger effect than T. Maximum RR occurred at lower T and RR was more variable in older, heavier birds. 3. 3. Twenty-week-old birds used compound ventilation in addition to panting, which may have reduced the severity of heat stress and the consequent lack of a significant change in body temperature.

Far-field recordings of short latency auditory responses in the white Leghorn chick

Far-field recordings of short latency auditory responses were characterized in the White Leghorn chick (Gallus domesticus, 2-3 weeks post hatch). Six to twelve positive peaks were normally present within the first 8 ms following the onset of a click stimulus (stimulus intensity = 99.0 +/- 6.3 dB pe SPL, 44.3 +/- 1.2 dB SL). Both cochlear microphonic (CM) and neural response components were distinguished based on functional criteria. Neural responses (P1a-P6b) were readily masked by white noise. CM responses were resistant to masking and inverted when click polarity was reversed. Systemic cooling produced shifts in neural response latencies such that later peaks (e.g. latencies greater than or equal to P3) were delayed to a greater extent than early peaks (P1a and P2a). The latencies of CM components were relatively unaffected by cooling. The mean latencies and amplitudes were described quantitatively for dominant positive peaks. The mean auditory response threshold for 18 animals was 54.5 +/- 7 dB pe SPL. Dominant later components (P3a and the P3b/P4a complex) were the first to disappear after lethal injection of anesthetic. These were followed immediately by earlier neural peaks. CM components were the last to disappear. A working hypothesis is advanced regarding the distinction between central (P3a, P3b and P4a) and peripheral (P1a, P2a) neural components.

Peripheral and brainstem auditory function in paroxysmal (px) White Leghorn chicks

The paroxysmal (px) chick is a mutant White Leghorn (Gallus domesticus) which appears normal at hatching and during the subsequent week. By ca. 8 days posthatching, various symptoms develop, of which the most obvious are depressed food intake (anorexia) and audiogenic seizures. Histological evidence suggests that central auditory and vestibular nuclei and fiber tracts begin to degenerate prior to seizure onset. This degeneration, which affects central and peripheral components of both systems, becomes increasingly severe over time although auditory stimulation continues to elicit seizures. Characterization and analysis of peripheral and brainstem auditory response to auditory stimuli indicated that major response differences between px and normal chicks exist in peaks reflecting brainstem activity (P3A, P3B, P4A, P5A). In 5 of 8 px chicks, these later response peaks were either grossly abnormal in terms of amplitude and latency (including amplitude input/output functions) or often entirely absent. Early peaks (P1A and P2A), however, in px waveforms were normal in morphology and amplitude, indicating normal function of peripheral auditory structures. Although lower body temperature of px chicks may account for some of the longer latencies observed, other abnormalities (e.g. absence of peaks) could not be produced in normal birds by induced hypothermia.

CSF ion composition and manipulation during thermoregulation in an avian species, Gallus domesticus☆

1. At thermoneutrality (28 degrees C), CSF Na+:Ca2+ in hens was 61.66; under thermal stress (39 degrees C), it changed to 59.38 (30 min), 62.58 (3 hr), and 52.44 (10 hr); no change in ratio occurred at 15 degrees C. 2. ICV Ouabain and/or EGTA increased body temperature (TR) but not respiration rate (RR) at 39 degrees C. 3. At 28 degrees C, Ouabain decreased, and EGTA increased, TR and RR. 4. Ca2+ may be more critical than Na+ in thermoregulation. 5. Heat stress appears to stimulate Na+-transport mechanisms other than Na+-ATPase. 6. RR appears to be a function of TR, not of ion balance.

Thermoregulatory responses of laying hens under cyclic environmental temperature to intraventricular calcium and sodium

1. Hens received ICV injections of Ca2+ (1.98 g/100 ml) or Na+ (7.25 g/100 ml) at 28 degrees C and, following acclimation, at 37 or 20 degrees C, respectively. 2. At 28 degrees C (thermoneutrality), rectal temperature rose (P less than 0.05) following Na+ and fell (P less than 0.05) following Ca2+, similar to mammals and broiler chickens. 3. At 37 degrees C, Ca2+-induced hypothermia did not occur; nor did the Na+-associated hyperthermia at 20 degrees C. 4. Acclimation to a high or low temperature may produce an endogenous shift in CSF ion levels that make additional ion administration ineffective in affecting body temperature.

Biodeterioration of the biosphere: where does wildlife damage management stand?

Degradation of the biosphere with the associated loss of biological integrity is the most critical issue facing humankind today. Wildlife damage management expertise is critically needed in addressing this issue head-on from both traditional and non-traditional approaches. The profession offers a unique combination of both wildlife management training and damage management experience, which helps in understanding a variety of conservation perspectives, especially on private land. Because relationships between damage management and sustainability are often not clearly recognized, and because many traditional wildlife damage management activities are criticized as inappropriate or not needed, we suggest a reassessment of our vision for the future of the profession to include biosphere sustainability as a basic guiding principle. Implications could include greater emphasis in some areas and reassessment in others such as prairie dog management. Greater emphasis might be placed on native ecosystems, impacts of invasive exotic species or overabundant native species, fragmented habitats, nest pests, and, particularly, sustainable agricultural issues. A shift toward greater service to biosphere sustainability will bring both rewards and responsibilities. It will also strengthen the relevance of wildlife damage management and enhance the credibility of the profession for the future.

Development of metabolic response in male quail brain during sexual maturation

Seasonal reproductive activities of Japanese quail Coturnix japonica are induced most obviously by stimulatory effects of long-day photoperiod. This study addressed the metabolic response, as measured by 2-deoxyglucose (2-DG), in brain of male quail during sexual maturation. At 7 weeks of age, reproductively quiescent quail exposed to a short photoperiod of 6L:18D, received 2-DG on day 0 and +3, +6, +9, +12, +15 and +18 days after onset of 16L:8D. Brains were processed for autoradiography; serum testosterone was measured to indicate reproductive response to photoperiod. Circulating testosterone remained low until day 9, then rose sharply, reaching maximum levels at day 18. Heavily labeled nuclei were identified in some discrete neural pathways: both tectofugal and thalamofugal visual pathways, ascending auditory pathway, efferent vocalization pathway, and limbic structures. Metabolic activity of the terminal nucleus (ectostriatum) of the tectofugal pathway increased significantly by day 18, but in the terminal nuclei (the Wulst) of the thalamofugal visual pathway activity did not change significantly. Energy metabolism of some nuclei of the auditory pathway rose significantly by day 3, although in the vocal pathway it did not show augmentation until days 15-18. The metabolic activity of limbic structures also increased. These results suggest that, in Japanese quail, sensory nuclei and some of their integrative areas become sensitive to environmental cues in response to long-day photoperiod. It is possible that the external environmental cues that affect the reproductive activities of quail act through sensory systems.