Histologic evaluation of the crop for diagnosis of proventricular dilatation syndrome in psittacine birds.

Histologic sections of crop tissue were evaluated for the presence of lymphoplasmacytic infiltrates within mesenteric ganglia. All birds with proventricular dilatation syndrome that had lymphoplasmacytic infiltrates in crop ganglia had similar infiltrates in the proventricular and/or ventricular ganglia. False-negative crop biopsy results occurred approximately 24% of the time. More invasive procedures, such as proventricular or ventricular biopsy, may be necessary if the crop biopsy is nondiagnostic in a bird with clinical signs of proventricular dilatation syndrome.

Mechanoreceptors in the crop of the domestic fowl.

Electrophysiological "single fiber" experiments were conducted on the vagal nerves of the domestic fowl to confirm the presence of mechanoreceptors in the crop and to study their properties. The afferent activity of the left vagus nerve was recorded in nine anaesthetized laying hens with and without the crop being artificially distended. Twenty-two units were found to respond to the crop inflation, 18 of them being slowly adapting mechanoreceptors. The discharge rate of these slowly adapting units increased as the pressure inside the crop was raised. Twelve units were localized and the responses of three units to different doses of acetylcholine, epinephrine, and norepinephrine were obtained. Mechanoreceptor discharges were enhanced when the crop was distended and during drug-induced contractions of its smooth muscle, suggesting an "in series" location within the muscle layers. Such receptors may provide the afferent limb of a reflex regulating crop motility and may be involved in the regulation of feed intake.

Stimulatory effects on lactotrophs and crop-sac of interleukin-1 and interleukin-2 in pigeons (Columba livia).

The ultrastructural effects of human-recombinant interleukin-1 beta (IL-1 beta) and human-recombinant interleukin-2 (IL-2) on the crop-sac (the target organ for prolactin secretion in birds) and the anterior pituitary lactotrophs, were studied in pigeons (Columba livia). The intraventricular microinfusion of the two interleukins produced maximal crop-sac stimulation with milk-like secretion, as demonstrated by the observation of ultrastructural changes in the lactiferous areas through scanning and transmission electron microscopy of crop-sac mucosa. A marked activation of the anterior pituitary lactotrophs was also observed. Crop-sac and pituitary lactotrophs stimulatory effects were prevented by a previous intraventricular treatment with monoclonal antibodies for IL-1 beta and IL-2 receptors, but not by an intraperitoneal administration of naloxone. The present results show that interleukins possess in pigeons marked stimulatory effects on prolactin secretion and that these are mediated by specific receptors.

Passive immunization against chicken vasoactive intestinal polypeptide suppresses plasma prolactin and crop sac development in incubating ring doves.

Passive immunization of incubating ring doves with daily injections of sheep anti-chicken vasoactive intestinal polypeptide (cVIP) serum prevented the proliferation of crop sac tissue observed in control doves given nonimmune serum. Daily injections of anti-cVIP serum did not prevent crop sac development in nonbreeding doves simultaneously treated with ovine prolactin. The concentrations of plasma prolactin were significantly depressed in birds given anti-cVIP serum although this effect became progressively less pronounced during the course of the 7- or 14-day treatment periods. Body weights and weights of regressed reproductive organs were unaffected by treatment with anti-cVIP serum and did not differ significantly from control birds. Doves showing a decreased prolactin response to anti-cVIP serum treatment developed an immune response to sheep serum which may have immunoneutralized the administered antibody. Concentrations of plasma LH were not consistently affected by anti-cVIP serum administration and were low throughout the study. The depression in plasma LH normally seen in females after their young hatch was not observed in females treated with anti-cVIP serum. No effect of treatment was observed upon the birds' incubation behavior or in their readiness to feed and brood their young. These results suggest that in the ring dove, VIP is the physiological prolactin-releasing factor responsible for stimulating prolactin secretion and consequently the development of the crop sac, during incubation. They further indicate that increased concentrations of plasma prolactin may not be essential for gonadal regression or the maintenance of full incubation and brooding behavior in ring doves under laboratory conditions.

Facilitation of parental behavior in ring doves by systemic or intracranial injections of prolactin.

Systemic administration of ovine prolactin (PRL) has been previously reported to stimulate parental feeding behavior toward 7-day-old foster squabs by nonbreeding ring doves with previous breeding experience. The first of the present experiments reexamined this claim in experienced, nonbreeding birds given test squabs of different ages. Each visually isolated male and female dove was given twice-daily subcutaneous injections of ovine PRL or vehicle for 7 days and then tested for parental responses toward a single 1-3, 6-8, or 11- to 13-day-old foster squab. Prolactin significantly increased the incidence or frequency of parental regurgitation-feeding episodes in tests with all three squab age groups and, in addition, increased the incidence of parental feeding invitations (squab-oriented bill openings) in tests with 6- to 8-day-old squabs. A second study explored the degree to which PRL can act directly on the central nervous system to facilitate parental activity in the absence of peripheral cues generated from PRL-induced changes in other target organs, such as those associated with crop sac growth and distension. In this experiment, 6- to 8-day-old test squabs were used to determine if parental behavior is enhanced by twice-daily intracerebroventricular (ICV) injections of PRL in doses below those required to stimulate peripheral target organs. Injection schedules and behavior testing procedures were the same as those used in Experiment 1. However, half of the ICV PRL-treated and ICV vehicle-treated birds were food deprived for 16 hr before and during the test in order to control for PRL-induced hyperphagia and resulting crop sac distension, which could confound the results by generating peripheral stimuli conductive to the display of regurgitation-feeding behavior. Intracranial injections of prolactin significantly increased the incidence of feeding behavior, parental feeding invitations, and crouching or sitting in the nest in food-deprived doves but not in freely fed animals. Empty crop sac weights of freely fed and food-deprived PRL-treated birds were not increased above control values, thus indicating that ICV PRL treatment did not result in significant stimulation of peripheral target organs. These results demonstrate a facilitative action of PRL on regurgitation-feeding responses and associated parental behaviors that is not restricted to squabs of one particular age range. They also indicate that PRL is capable of acting directly on the brain to promote these activities in the absence of PRL-induced changes in the crop sac and other peripheral target organs.

Effect of electrical field stimulation on muscle strips from chicken crop.

The effect of electrical field stimulation (EFS) on smooth muscle strips from the chicken crop was investigated. The EFS (5 Hz, 2 ms, 400 mA; 10 Hz, 2 ms, 400 mA; 5 Hz, 2 ms, 500 mA; 10 Hz, 2 ms, 500 mA) produced contractions in all preparations. Atropine (10(-5) mol l-1) diminished muscle contraction in response to EFS. Tetrodotoxin (5 X 10(-6) mol l-1) fully suppressed the contractile responses to EFS. A serotonin antagonist (methysergide, 10(-4) mol l-1) did not alter contractions elicited by EFS. Propranolol (10(-5) mol l-1) led to an increase of contractions induced by EFS. Noradrenaline (10(-6)-10(-4) mol l-1) reduced acetylcholine-induced (1.1 X 10(-6) mol l-1) contraction of the crop smooth muscle strips. Propranolol (10(-5) mol l-1) abolished noradrenaline-induced relaxation almost fully. Tetrodotoxin (5 X 10(-6) mol l-1) did not change the relaxing effect of noradrenaline. These results suggested that the responses of crop smooth muscle to EFS involve excitatory cholinergic and non-cholinergic (probably peptidergic) as well as inhibitory adrenergic nerves.

Topographic representation of visceral target organs within the dorsal motor nucleus of the vagus nerve of the pigeon Columba livia.

Our previous work (Katz and Karten, '83a J. Comp. Neurol. 217:31-46 demonstrated that the dorsal motor nucleus of the vagus nerve (DMN complex) in the pigeon is composed of cytoarchitecturally distinct subnuclei that are distinguished by the size, shape, position, and cytochemical characteristics of their constituent neurons. In view of the diversity of target organs innervated by the vagus nerve, we sought to determine whether the subnuclear heterogeneity of the DMN complex is related to the pattern of target innervation. To test this possibility, retrograde tracing techniques were used to define the subnuclear localization of vagal motoneurons that innervate individual vagal target organs. The distribution of horseradish peroxidase (HRP)-labeled motoneurons within the DMN complex was studied following application of HRP to the cut central end of individual vagal nerve branches and after injection of the tracer into vagal target tissues. In addition, we examined the distribution of acetylcholinesterase depletion within the DMN complex following transection of individual vagal branches. Our data demonstrate that individual vagal target organs have discrete and topographic representations within cytoarchitecturally distinct subnuclei of the DMN complex. Therefore, in the pigeon, the subnuclear distribution of vagal motoneurons plays a critical role in the organization of descending vagal motor pathways. Segregation of visceral representations within the DMN complex may provide a mechanism for organizing functionally diverse afferent inputs to target-specific populations of vagal motoneurons.

Lead induction of crop dysfunction in pigeons through a direct action on neural or smooth muscle components of crop tissue.

Lead acetate solutions administered p.o. to pigeons produce crop stasis. Crop dysfunction may be an indirect effect on crop activity by a direct interaction with the cerebellum or some other site associated with lead-induced ataxia. Alternatively, crop stasis may be due to the direct interaction of lead with sites on the smooth muscle or neural elements in crop tissue. A behavioral test for ataxia was performed on pigeons given lead by crop intubation or i.m. injection. Blood lead concentrations were also monitored. Lead-induced ataxia was separable from lead-induced crop dysfunction depending on the route of lead administration, suggesting that lead-induced crop stasis is not secondary to toxicity at a site associated with ataxia. Intramuscular treatment produced crop stasis more readily than did crop intubation. This probably reflects different mechanisms of absorption and metabolism. A Tris-succinate medium was devised which accommodated the solubility characteristics of lead, permitting studies of crop tissue in vitro. Lead chloride added to crop tissue in tris-succinate medium caused a concentration-related reversible relaxation. Crop circular muscle was more sensitive to Pb++ than was longitudinal muscle, in agreement with the effects of other agonists. The EC30 of crop circular smooth muscle in plasma was 1000 microM PbCl2 compared to 3 microM in Tris-succinate medium. The results suggest that lead induces crop dysfunction by acting either directly on crop smooth muscle or on neural elements in crop tissue.

Visceral representation within the nucleus of the tractus solitarius in the pigeon, Columba livia.

This study describes the distribution of organ-specific populations of vagal afferent fibers within the nucleus of the solitary tract (nTS) in the pigeon. The central projections of vagal sensory neurons were visualized by the centripetal and trans-ganglionic transport of horseradish peroxidase from either the central cut ends of peripheral vagal branches or from HRP injection sites in peripheral vagal target tissues. This paper also includes a detailed description of the cytoarchitectural organization of the nTS in the pigeon based on studies of Nissl-stained material. Vagal afferent fibers that innervate different peripheral target organs are partially segregated within cytoarchitecturally distinct subnuclei of the nTS. Gastrointestinal afferents, for example, project primarily to medial subnuclei. On the other hand, pulmonary, and on the basis of earlier studies, cardiovascular afferents, project primarily to lateral subnuclei. Moreover, the rostral to caudal distribution of gastrointestinal afferents corresponds to the rostrocaudal topography of the gastrointestinal tract. In addition, our data demonstrate a projection of gastrointestinal afferents to the lateral descending tract of the trigeminal nerve that appears to terminate in the external cuneate nucleus. The cytoarchitectural organization of visceral representations within the pigeon nTS corresponds closely to recent descriptions of this cell group in mammals. Comparison of our results with studies of the central connections of nTS neurons suggests that the subnuclear distribution of organ-specific vagal afferents within nTS plays a critical role in the organization of ascending and descending visceral afferent pathways.

Nature and location of the receptors for salt-gland secretion in the goose.

1. The nature and location of the receptors which stimulate salt-gland secretion in the goose have been investigated.2. The rapid injection of homologous blood (sufficient to raise the blood volume by 16 and 9%) into the right atrium failed to induce secretion. In contrast, hypertonic sucrose, Na(2)SO(4) and LiCl initiated secretion.3. These results support the theory that osmoreceptors initiate secretion by detecting an increase in plasma tonicity.4. The minimal amount of hypertonic NaCl required to initiate secretion when infusions were made into a carotid artery or into various arteries and veins in the splanchnic region was not less than that required by an I.V. route.5. Cross-circulation and perfusion studies also showed that a raised [NaCl] in the blood perfusing the head was ineffective in evoking secretion and thus that plasma tonicity must be raised elsewhere in the body.6. Secretion in response to salt-loading was abolished or prevented by cutting the vagus nerves or blocking them with local anaesthetic. Stimulation of the cephalic end of the cut vagi in an isolated, perfused decerebrate head induced secretion, indicating that the afferent fibres from the receptors to the C.N.S. lie in the vagus nerves. Cutting the vagi below the heart, however, had no effect on the secretory response.7. Blocking nerves in the crop with local anaesthetic had no effect on secretion induced by salt-loading but when local anaesthetic was injected into the pericardial sac, secretion decreased immediately, stopped, and recovered with a time course similar to that seen after blocking the vagus nerves.8. Section of the vagi in the neck abolished the tachycardia observed in response to the injection of hypertonic NaCl into the right atrium.9. As in other species, stimulation of the ;secretory nerve' induced secretion in anaesthetized or decerebrate geese.10. Hexamethonium given I.V. or applied topically to the ;secretory nerve ganglion' blocked secretion in response to salt-loading or to secretory nerve stimulation.11. It appears that the receptors for salt-gland secretion are located in or near the heart and that afferent fibres from these receptors travel in the vagus nerves to the C.N.S.12. A possible scheme of the secretory reflex which initiates and maintains salt-gland activity is proposed.