Feeding induced by microinjections of NMDA and AMPA-kainate receptor antagonists into ventral striatal and ventral pallidal areas of the pigeon

Update on Feeding Regulation by Ghrelin in Birds: Focused on Brain Network

Ghrelin is known to be a feeding stimulatory hormone in mammals, but in birds, in contrast to mammals, the feeding behavior is regulated in inhibitory manners. This is because the neuropeptides associated with the regulation in the brain are different from those in mammals, i.e., it has been shown that, in chickens, a corticotropin-releasing hormone family peptide, urocortin, which is a feeding-inhibitory peptide, is mainly involved in the inhibitory mechanism. However, feeding is also regulated by various neurotransmitters in the brain, and recently, their interaction with the mechanisms underlying feeding inhibition by ghrelin in birds has been intensively studied and clarified. This review summarizes these findings.

The role of glutamatergic and GABAergic systems on serotonin- induced feeding behavior in chicken

It has been reported that serotonin can modulate glutamate and GABA release in central nervous system (CNS). The present study was designed to examine the role of glutamatergic and GABAergic systems on serotonin- induced feeding behavior in chickens. In Experiment 1 intracerebroventricular (ICV) injection of MK- 801(NMDA receptor antagonist, 15 nmol) performed followed by serotonin (10 μg). In experiments 2, 3, 4, 5, 6 and 7 prior to serotonin injection, chickens received CNQX (AMPA/kainate receptor antagonist, 390 nmol), AIDA (mGluR1 antagonist, 2 nmol), LY341495 (mGluR2 antagonist, 150 nmol), UBP1112 (mGluR3 antagonist, 2 nmol), picrotoxin (GABA A receptor antagonist, 0.5 μg), CGP54626 (GABAB receptor antagonist, 20 ng) respectively. Cumulative food intake was determined at 3 h post injection. The results of this study showed that the hypophagic effect of serotonin was significantly attenuated by pretreatment with MK- 801 and CNQX (p < 0.05) but AIDA, LY341495 and UBP1112 had no effect (p > 0.05). Also, the inhibitory effect of serotonin on food intake was amplified by picrotoxin (p < 0.05) while CGP54626 had no effect (p > 0.05). These results suggest that serotonin as a modulator probably interacts with glutamatergic (via NMDA and AMPA/Kainate receptors) and GABAergic (via GABAA receptor) systems on feeding behavior in chicken.

Fos expression following activation of the ventral pallidum in normal rats and in a model of Parkinson's Disease: implications for limbic system and basal ganglia interactions

The circuit-related consequences of activating the ventral pallidum (VP) are not well known, and lacking in particular is how these effects are altered in various neuropathological states. To help to address these paucities, this study investigated the brain regions affected by VP activation by quantifying neurons that stain for Fos-like immunoreactivity (ir). Fos-ir was assessed after intra-pallidal injections of the excitatory amino acid agonist, NMDA, or the GABA(A) antagonist, bicuculline in normal rats and in those rendered Parkinsonian-like by lesioning dopaminergic neurons with the neurotoxin, 6-OHDA. We hypothesized that activation of the VP will alter the activity state of brain regions associated with both the basal ganglia and limbic system, and that this influence would be modified in the Parkinsonian state. Blocking tonically activated GABA(A) receptors with bicuculline (50 ng/0.5 microl) elevated Fos-ir in the VP to 423% above the contralateral, vehicle-injected side. Likewise, intra-VP NMDA (0.23 microg or 0.45 microg/0.5 microl), dose-dependently increased the number of pallidal neurons expressing Fos-ir by 224 and 526%, respectively. At higher NMDA doses, the density of Fos-ir neurons was not elevated above control levels. This inverted U-shaped profile was mirrored by a VP output structure, the medial subthalamic nucleus (mSTN). The mSTN showed a 289% increase in Fos-ir neurons with intra-VP injections of 0.45 microg NMDA, and this response was halved following intra-VP injections of 0.9 microg NMDA. Of the 12 other brain regions measured, three showed VP NMDA-induced enhancements in Fos-ir: the frontal cortex, entopeduncular nucleus and substantia nigra pars reticulata, all regions associated with the basal ganglia. In a second study, we evaluated the NMDA activation profile in a rat model of Parkinson's Disease (PD) which was created by a unilateral injection of 6-OHDA into the rostral substantia nigra pars compacta. Comparisons of responses to intra-VP NMDA between the hemispheres ipsilateral and contralateral to the lesion revealed that Fos-ir cells in the pedunculopontine nucleus was reduced by 62%, whereas Fos-ir for the basolateral amygdala and STN was reduced by 32 and 42%, respectively. These findings support the concept that the VP can influence both the basal ganglia and the limbic system, and that that the nature of this influence is modified in an animal model of PD. As the VP regulates motivation and cognition, adaptations in this system may contribute to the mood and mnemonic disorders that can accompany PD.

Nucleus accumbens subregions: hodological and immunohistochemical study in the domestic chick (Gallus domesticus)

The nucleus accumbens was identified in avian species some time ago. However, the precise localization and extent of this nucleus is still a matter of controversy. We have used immunolabeling against calbindin, neuropeptide Y, and DARPP-32 (dopamine- and adenosine-related phosphoprotein, 32 kDa) for the selective marking of putative accumbens subdivisions and have followed the anterograde transport of biotinylated dextran amine injected to the nucleus tractus solitarii region of 7-day-old domestic chicks. The nucleus accumbens extending between rostrocaudal atlas coordinates A 10.6 and A 8.8 can be subdivided into the core and shell, the core corresponding to the ventromedial and juxtaventricular medial striatum laterodorsal to the bed nucleus of stria terminalis, and the shell representing an arched region situated ventrally and ventrolaterally to the core. Immunoreactivity to both calbindin and neuropeptide Y is more intense in the shell than in the core division. DARPP-32 immunolabeling does not differ in the two divisions but is markedly weaker in the bed nucleus of stria terminalis, enabling the separation of this nucleus from the surrounding accumbens subdivisions. Fibers from the nucleus solitarius predominantly terminate in the shell division, similar to the situation described in mammals. Whereas the suggested core lies entirely within the boundary of the medial striatum, the shell seems partially to overlap the ventral pallidum. We have been unable to subdivide the remaining part of accumbens lying rostral to A 10.6 into a putative shell and core by the methods employed in the present study. This region probably corresponds to the rostral pole of the nucleus accumbens.

Ingestive effects of NMDA and AMPA-kainate receptor antagonists microinjections into the lateral hypothalamus of the pigeon (Columba livia)

This study examined the ingestive and behavioral effects of NMDA- and AMPA/kainate glutamatergic receptor blockade in the lateral hypothalamic area (LHy) of free-feeding pigeons (Columba livia). Injections of MK-801 (NMDA receptor antagonist; 6 nmol) or CNQX (AMPA/kainate receptor antagonist; 25.8 nmol) into the LHy of free-feeding pigeons induced significant increases in food intake and in feeding duration, as well as reductions in the latency to start feeding. Duration, latency and volume of water intake, as well as duration of sleep-like behavior, alert immobility, locomotion and preening were not changed by these treatments in the LHy. These results indicate that glutamatergic inputs to cells containing NMDA and/or AMPA receptors located in the LHy could modify both the beginning of a feeding bout (or the end of a period of satiety) and its duration (satiation). Our data also suggest that these inhibitory glutamatergic influences on feeding behavior are tonically active in the LHy.

Behavioral effects of 8-OH-DPAT injections into pontine and mesencephalic areas containing 5-HT-immunoreactive perikarya in the pigeon

This study examined the distribution of 5-HT-immunoreactive perikarya (5-HT-IRp) and the effects of local injections of 8-OH-DPAT into 5-HT-IRp-containing pontine and mesencephalic regions on feeding and drinking behaviors in free-feeding pigeons. When infused into the midline 5-HT-IRp-containing areas, 8-OH-DPAT (6.1 nmol) reliably elicited drinking and, to a lesser extent, feeding responses during the first hour after injection. These responses were significantly higher than the ingestive indexes observed (1) after vehicle (ascorbic acid 0.1%, 200 nl) injections at the same sites and (2) after 8-OH-DPAT injections into adjacent sites devoid of 5-HT-IRp. Increases in drinking were proportionally higher than those observed in feeding and a significant negative correlation was observed between water and food after midline 8-OH-DPAT injections. Similar dipsogenic responses were observed after injections of different 8-OH-DPAT doses (0.6, 2.0, and 6.1 nmol). Pretreatment with local injections of p-MPPI (an antagonist of 5-HT1A receptors) attenuated the ingestive responses evoked by 8-OH-DPAT injections. Injections of 8-OH-DPAT into lateral 5-HT-IRp-containing sites evoked only inconsistent and weak ingestive responses. These results indicate that 5-HT1A receptor-mediated circuits located in the midline superior raphe system of the pigeon may play an important role in mechanisms controlling water intake, similar to that observed in mammals.

Immunohistological characterization of striatal and amygdalar structures in the telencephalon of the fire-bellied toad bombina orientalis

The subpallium of the fire-bellied toad Bombina orientalis was studied by means of enzyme-histological detection of NADPH-diaphorase and immunohistological demonstration of aspartate, GABA, calretinin, choline-acetyl transferase, Leu-and Met-enkephalin, neuropeptide Y, 5-hydroxy-tryptamine (serotonin), somatostatin, substance P and tyrosine-hydroxylase. As in other vertebrates, the striato-pallidum is characterized by GABA-, substance P- and enkephalin-immunoreactivity. Neurons and fibers differing in immunoreactivity are arranged in layers. Choline-acetyl transferase-immunoreactive neurons were found in a position corresponding to the mammalian cholinergic cell-group (Ch4-group), which therefore may be homologous to the nucleus basalis of Meynert. Within the amygdaloid complex, the cortical and lateral (vomeronasal) nuclei are similar in calretinin-, GABA-, NADPH-diaphorase-, enkephalin, substance P- and neuropeptide Y-(immuno)histology. The medial and central amygdaloid nuclei reveal a dense peptidergic innervation, and the medial amygdala additionally exhibits serotonergic fibers and cell bodies staining for neuropeptides and tyrosine-hydroxylase. Differences between Bombina and other anuran species exist, such as the absence of cholinergic neurons in the striatum. Our findings corroborate the view based on recent studies on the hodology and cytoarchitecture of the anuran telencephalon that the anuran ventral telencephalon contains most of the structures found in the mammalian brain. This concerns a septal region, a dorsal and ventral striato-pallidum including a nucleus accumbens and an amygdaloid complex consisting of a central, cortical and vomeronasal amygdala. The only major difference appears to concern the lack of a basolateral amygdala.

Ingestive behaviors and metabolic fuels after central injections of 5-HT1A and 5-HT1D/1B receptors agonists in the pigeon

The effects of intracerebroventricular injections of 8-OH-DPAT (a 5-HT1A agonist; 3, 15 or 30 nmol) or GR46611 (a 5-HT1B/1D agonist; 3, 15 or 30 nmol) on feeding, drinking, preening and sleep-like behaviors were investigated in free-feeding (FF) pigeons. The effects of these 5-HT agonists on blood glucose and free fatty acids levels were also examined. Injections of 8-OH-DPAT evoked intense lipolytic and dipsogenic effects, but failed to affect feeding, non-ingestive behaviors and glycemic levels. On the other hand, GR46611 evoked significant increases in food intake (at the higher dose), as well as lipolytic and hyperglycemic effects, but left drinking and other non-ingestive behaviors unchanged. These effects are opposed to those found in rodents, and may be associated with the diverse, species-specific nature and distribution of these receptors, underscoring the need to examine the functional aspects of the 5-HT1 receptor family in a more extensive range of non-rodent species.