Orlan M. Youngren

Brain stimulation and species-typical behaviour: Activities evoked by electrical stimulation of the brains of chickens (Gallus gallus)

Abstract Responses to electrical stimulation of 1500 brain loci in eighty-seven birds were analysed for: types of motor patterns elicited, ability of single loci to evoke more than one pattern, dependence of evoked responses on external stimuli, and anatomical location of points yielding various motor patterns. Frequencies of occurrence of motor responses are tabulated and the points plotted on drawings of frontal sections. Frequencies of joint occurrence of two patterns at the same site are analysed. The archistriatum and its efferent tract were frequent sites for several components of agonistic behaviour. Complex sequences other than fighting and threat were not elicited, but many elements of such sequences were readily elicited. These were markedly influenced by external cues.

Effects of reproductive status, ovariectomy, and photoperiod on vasoactive intestinal peptide in the female turkey hypothalamus

Vasoactive intestinal peptide (VIP) appears to be a physiologically relevant prolactin (PRL)-releasing factor during the avian reproductive cycle, yet little is known of the factors involved in modulating the hypothalamic concentrations of this neuropeptide. A heterologous chicken VIP radioimmunoassay was developed to examine the effects of reproductive status, ovariectomy, and photoperiod on hypothalamic VIP immunoreactivity in the female turkey. VIP concentrations were highest in the median eminence/infundibular nuclear complex (ME/INF) relative to other subregions of the hypothalamus and changed only in this region during the reproductive cycle. Quiescent, nonphotostimulated hens subjected to stimulatory photoperiod exhibited a 1.6-fold increase in VIP in the ME/INF (quiescent 59.9 +/- 6.0 vs photostimulated 95.8 +/- 7.1 pg/microgram protein). An additional 2-fold increase in ME/INF VIP concentrations was observed in laying hens (183.0 +/- 28.5 pg/microgram protein). Coincident increases in plasma PRL were also observed. In contrast, during incubation and the photorefractory stage, a dissociation between hypothalamic VIP and plasma PRL occurred. No changes were observed in VIP in incubating hens, yet a 6-fold increase in PRL was noted, compared to layers. In addition, ME/INF VIP concentrations exhibited no change during the photorefractory stage, whereas a 28-fold decrease in plasma PRL occurred. VIP concentrations in the ME/INF of laying hens were unaffected by ovariectomy, whereas exposure to short photoperiod reduced VIP by 44%. The inhibitory effects of short photoperiod could not be reversed by administration of exogenous steroids, while steroid treatment reduced VIP concentrations by 45% in the ovariectomized hens. These results provide additional correlative evidence for a modulatory role of VIP in PRL secretion and suggest that the expression of this neuropeptide in the INF may serve as a neural link between photoperiodic mechanisms and PRL release during the avian reproductive cycle.

Unilateral kainic acid lesions reveal dominance of right archistriatum in avian fear behavior

Unilateral injections of 1 microgram of kainic acid in the archistriatum of 5-day-old domestic chicks reduced fear, as expressed by distress calls (peeps), significantly more than did identical injections in the same structure on the left side. This result adds affective behavior to the growing list of functions that have been shown to be differentially controlled by the right and left hemispheres in birds. The directions of the specializations are intriguingly similar to those for verbal and affective functions in human beings.

Repetitive vocalizations evoked by local electrical stimulation of avian brains. I. Awake chickens (Gallus Gallus).

Electrical stimulation of the brain (ESB) through 1178 chronically-implanted electrodes in 128 chickens consistently yielded repetitive vocalizations from 414 sites. Active points were concentrated in two areas, one ventro-medial to the inferior colliculus, and one apparently in tractus occipitomesencephalicus just ventral to nucleus ovoidalis. Call duration, interval between calls, and frequency structure of individual notes all varied continuously both within and between sites. Simultaneous stimulation of two sites yielded facilitation, summation, and occlusion with increasing stimulus intensity. Results are interpreted to suggest a single set of neural mechanisms controlling repetitive vocalizations. Correlation between sites active in awake and anaesthetized birds was 0·996.

Regulation of Prolactin Secretion by Dopamine and Vasoactive Intestinal Peptide at the Level of the Pituitary in the Turkey

This study investigated the capability of dopamine (DA) to prevent avian prolactin (PRL) secretion by antagonizing the PRL-releasing factor, vasoactive intestinal peptide (VIP), at the level of the pituitary. To test this hypothesis, combined intracranial and intrapituitary infusions of DA, DA agonists, and VIP, plus electrical stimulation of the medial preoptic area (ES/POM), were used to characterize the actions of DA on PRL secretion in anesthetized laying turkey hens. Infused into the third ventricle at the rate of 10 nmol/min, DA induced a 2.8-fold increase in circulating PRL levels (63.8 ± 15.1 to 181.3 ± 44.3 ng/ml, p < 0.05), similar to the 3.1-fold PRL increase induced by ES/POM (65 ± 10.3 to 199.1 ± 57.3 ng/ml, p < 0.05). Infused into the anterior pituitary at the rate of 15 ng/min, VIP induced a 2.2-fold increase in PRL (78.6 ± 22.9 to 173.6 ± 39.5 ng/ml, p < 0.05). When DA (10 nmol/min) was infused into the anterior pituitary it completely blocked both ES/POM- and VIP-induced PRL secretion. The D2 DA receptor agonist R- (–) -Propylnorapomorphine HCl inhibited VIP-induced PRL secretion at the level of the anterior pituitary, allowing only an insignificant rise in PRL (54.8 ± 14.3 to 73.9 ± 21.6 ng/ml, p > 0.05), while the D1 DA receptor agonist (±)-SKF-38393 HCl failed to prevent VIP-induced PRL release, allowing PRL to rise 2.5-fold (49.1 ± 10.8 to 121.0 ± 34.8 ng/ml, p < 0.05). Pituitary infusion of DA, DA agonists or vehicle alone caused no change in PRL levels. The data showed that DA prevented avian PRL secretion by blocking the action of VIP at the level of the anterior pituitary. DA effected this blockade of PRL via D2 DA receptors residing within the anterior pituitary. The data also suggested that there were no stimulatory D1 DA receptors related to PRL secretion in the avian anterior pituitary.

Expression of D1 and D2 Dopamine Receptors in the Hypothalamus and Pituitary during the Turkey Reproductive Cycle: Colocalization with Vasoactive Intestinal Peptide

The regulation of avian prolactin (PRL) secretion and PRL gene expression is influenced by hypothalamic vasoactive intestinal peptide (VIP), the PRL-releasing factor in avian species. Recent evidence indicates that D1 and D2 dopamine (DA) receptors play a pivotal role in VIP and PRL secretion. The differential expression of DA receptors located on hypothalamic VIP neurons and anterior pituitary cells may affect the degree of prolactinemia observed during the turkey reproductive cycle. The relative expression of D1D and D2 DA receptor subtype mRNA was quantitated using in situ hybridization histochemistry (ISH). D1D and D2 DA receptor mRNA was found expressed throughout the hypothalamus and pituitary. The expression of D1D DA receptor mRNA in the hypothalamus was found to be 6.8-fold greater than that of D2 DA receptor mRNA. Higher D1D DA receptor mRNA content was found in the anterior hypothalamus (3.6-fold), the ventromedial nucleus (2.0-fold), the infundibular nuclear complex (INF; 1.9-fold), and the medial preoptic nucleus (1.5-fold) of laying hens as compared to that of reproductively quiescent non-photostimulated hens. The levels seen in incubating hyperprolactinemic hens were essentially the same as in laying hens, except for the INF where levels were 52% higher. During the photorefractory stage (hypoprolactinemia), the D1D DA receptor mRNA was at its lowest level in all areas tested. No differences were observed in hypothalamic D2 DA receptor mRNA abundance throughout the reproductive cycle, except for an increase in D2 DA receptor mRNA within the INF of photorefractory hens. Also, a marked reduction in D2 DA receptor mRNA was observed in the pituitary of incubating hens. Pituitary D1D DA receptor levels did not change when birds entered the incubating phase. Double ISH revealed that D1D and D2 DA receptor mRNAs were co-expressed within neurons expressing VIP mRNA, predominantly within the lateral hypothalamus and INF. D1D DA receptor mRNA was more highly expressed than D2 DA receptor mRNA. The present findings clearly demonstrate that the expression of stimulatory D1 DA receptor mRNA in the hypothalamus increases in hyperprolactinemic incubating hens, whereas inhibitory D2 DA receptor mRNA increases in the pituitary of hypoprolactinemic photorefractory hens.

Dopamine receptors influence vasoactive intestinal peptide release from turkey hypothalamic explants.

Vasoactive intestinal peptide (VIP) is a significant prolactin-releasing factor (PRF) in avian species, and dopamine (DA) exhibits both a stimulatory and inhibitory influence upon this prolactin (PRL) secretion. The stimulatory effect of DA upon PRL release appears to be mediated by VIP. This study investigated DAergic actions upon VIP release using turkey hypothalamic explants perifused with DA and its agonists or antagonists. VIP release was stimulated by DA in a dose-dependent manner (10 nmol DA/min, from 67.2 +/- 3.9 to 164.3 +/- 3.1 pg/5 min; 100 nmol DA/min, from 70.1 +/- 3.2 to 291.0 +/- 7.5 pg/5 min; 1,000 nmol DA/min, from 72.0 +/- 4.8 to 501.0 +/- 24.7 pg/5 min). The D1 DA receptor antagonist (R+)-SCH-23390 HCl completely negated the stimulatory effect of DA (100 nmol/min) upon VIP release. Perifusion with the D2 DA receptor antagonist S(-)-eticlopride HCl by itself stimulated VIP release from the hypothalamic explants, increasing VIP from 38.1 +/- 5.3 to 161.9 +/- 9.7 pg/5 min, where release stabilized until perifusion was terminated. The D1 DA agonist (+)-SKF-38393 HCl increased VIP release from 52.7 +/- 4.6 to 192.6 +/- 16.9 pg/5 min, and this stimulated release was partially inhibited by the D2 DA receptor agonist R(-)-NPA HCl (from 192.6 +/- 16.9 to 139.7 +/- 13.8 pg/5 min). These results suggest that VIP secretion is in part regulated by possible opposite actions between stimulatory D1 and inhibitory D2 DA receptors in the turkey hypothalamus.

Regulation of prolactin secretion by dopamine at the level of the hypothalamus in the turkey.

Avian prolactin (PRL) secretion is regulated by vasoactive intestinal peptide (VIP) neurons residing in the infundibular nuclear complex (INF) of the hypothalamus. This VIPergic activity is modulated by stimulatory dopaminergic inputs. Dynorphin, serotonin (5-HT), dopamine (DA) and VIP all appear to stimulate PRL secretion along a hypothalamic pathway, expressing ĸ opioid, serotonergic, dopaminergic and VIPergic receptors in succession, with the VIPergic system as the final mediator. Electrical stimulation (ES) within the turkey hypothalamus at the level of the medial preoptic area (POA), the ventromedial hypothalamic nucleus (VMN), the INF or the median eminence (ME) results in the release of PRL. When the selective D1 DA receptor antagonist SCH-23390 HCl was infused intraventricularly at the rate of 10 nmol/min, ES in the POA or VMN was unable to increase PRL levels, while ES in the INF and ME did increase PRL to the same level as that of controls. These results were interpreted to suggest that the D1 DA receptors involved in PRL release lie caudally to the VMN and dorsally to the INF. Bilateral microinjections (50 ng) of the D1 DA receptor agonist SKF-38393 HCl into the POA or VMN failed to produce any increase in PRL, while similar microinjections in the INF increased PRL significantly within 15 min. Bilateral microinjections of the D1 DA antagonist (50 ng) into the INF blocked the rise in PRL associated with ES in the POA. Bilateral microinjections of a D2 DA antagonist (50 ng) into the INF failed to block PRL secretion induced by ES in the POA. Tract tracing, using double-label immunocytochemistry, revealed the presence of a monosynaptic dopaminergic pathway projecting from the POA to the INF. These data imply that the only hypothalamic D1 DA receptors involved in the regulation of avian PRL secretion are those residing within the INF in the same region as the VIP neurons known to be involved in PRL secretion.

Involvement of serotonin in prolactin release induced by electrical stimulation of the hypothalamus of the turkey (Meleagris gallopavo)

In anesthetized female turkeys electrical stimulation of the ventromedial nucleus (VMN) for 30 min caused increases in plasma prolactin (Prl); with maximum increase above the prestimulation level being 33.6 +/- 5.7 ng/ml for laying hens and 768.1 +/- 187.6 ng/ml for incubating hens. The possibility that serotonin (5-HT) plays a role in electrical stimulation-induced Prl release was investigated after administration of methysergide, a 5-HT receptor blocker (20 mg/kg), and stimulation in either the VMN or the infundibular nuclear complex-median eminence (INF-ME) region. Electrical stimulation in both the VMN and INF-ME region caused increases (P less than 0.05) in plasma Prl. Pretreatment with methysergide prevented the increase in plasma Prl that follows electrical stimulation in the VMN but had no effect on electrical stimulation-induced Prl release in the INF-ME region. We conclude that Prl release in the female turkey requires the functional integrity of serotonergic neurons within the VMN.

Dopamine infusion into the third ventricle increases gene expression of hypothalamic vasoactive intestinal peptide and pituitary prolactin and luteinizing hormone β subunit in the turkey

Turkey prolactin (PRL) secretion is controlled by vasoactive intestinal peptide (VIP) neurons residing in the infundibular nuclear complex (INF) of the hypothalamus. The VIPergic activity is modulated by dopamine (DA) via stimulatory D(1) DA receptors. DA (10 nmol/min for 40 min) was infused into the third ventricle of laying turkey hens to study its effect on circulating PRL, hypothalamic VIP and pituitary PRL and LHbeta subunit mRNA levels. Plasma PRL was significantly elevated after 20 min of DA infusion and remained elevated 30 min after cessation of infusion. Hypothalamic VIP mRNA content was significantly greater in the INF of DA-infused birds than it was in the INF of vehicle-infused control birds. No increase in VIP mRNA due to DA infusion was noted in the preoptic area. Pituitary PRL and LHbeta subunit mRNAs were increased in DA-infused hens as compared to vehicle-infused controls but the rate of increase was more in PRL than LHbeta subunit. This study demonstrates that exogenous DA activates hypothalamic VIP gene expression and this increased expression is limited exclusively to the avian INF. The increased VIP mRNA in the INF is correlated with increased levels of circulating PRL and PRL and LHbeta mRNAs in the anterior pituitary.