Immunohistochemical distribution of AMPA-type label in the pigeon (C. livia) hippocampus.

The avian hippocampal formation (HF) is reported to have a role equivalent to that of the mammalian hippocampus, which may involve the glutamatergic system as well. In the present paper we offer evidence of the occurrence and distribution of the subunits composing AMPA-type glutamate receptors on neurons in the hippocampus region of the pigeon brain. The experiment analyzed the immunolabeling of glutamate receptor (GluR)(1)(,) GluR(4,) and GluR(2/3) receptor subunits in adult pigeons and found consistent evidence that neurons located in the five main areas of the avian HF have these AMPA-type subunits, but their incidence varies according to position and neuro-type. About 20%-35% of the irregular and 35%-70% of the triangular neurons on the lateral and medial "V" arms contain GluR(1) and GluR(2/3), while GluR(4) was found only at rounded neurons. The majority of the triangular neurons (over 90%) and about half of the irregular neurons in the medial area contain GluR(1) and GluR(2/3,) whereas the rounded neurons contain primarily GluR(4) (95%). Labeling revealed GluR(1) (40%-60%) and GluR(2/3) (30%) in the dorsomedial and lateral areas but only in irregular neurons, while 60%-80% of the rounded neurons synthesize GluR(4). While triangular and irregular neurons appear to match the description of projecting neurons, rounded ones seem to participate in local circuits. A discussion of the functional significance of the avian HF concentrates on a postulation of the "V" arms as equivalent to the dentate gyrus and the dorsomedial area being similar to the Ammon's horn.

Calcium-binding proteins in the circadian centers of the common marmoset (Callithrix jacchus) and the rock cavy (Kerodon rupestris) brains.

The hypothalamic suprachiasmatic nucleus (SCN) and the thalamic intergeniculate leaflet (IGL) are considered to be the main centers of the mammalian circadian timing system. In primates, the IGL is included as part of the pregeniculate nucleus (PGN), a cell group located mediodorsally to the dorsal lateral geniculate nucleus. This work was carried out to comparatively evaluate the immunohistochemical expression of the calcium-binding proteins calbindin D-28k (CB), parvalbumin (PV), and calretinin (CR) into the circadian brain districts of the common marmoset and the rock cavy. In both species, although no fibers, terminals or perikarya showed PV-immunoreaction (IR) into the SCN, CB-IR perikarya labeling was detected throughout the SCN rostrocaudal extent, seeming to delimit its cytoarchitectonic borders. CR-IR perikarya and neuropil were noticed into the ventral and dorsal portions of the SCN, lacking immunoreactivity in the central core of the marmoset and filling the entire nucleus in the rock cavy. The PGN of the marmoset presented a significant number of CB-, PV-, and CR-IR perikarya throughout the nucleus. The IGL of the rocky cavy exhibited a prominent CB- and CR-IR neuropil, showing similarity to the pattern found in other rodents. By comparing with literature data from other mammals, the results of the present study suggest that CB, PV, and CR are differentially distributed into the SCN and IGL among species. They may act either in concert or in a complementary manner in the SCN and IGL, so as to participate in specific aspects of the circadian regulation.

Monoaminergic markers in the optic tectum of the domestic chick.

The avian optic tectum has become a reliable model system to study the basic mechanisms that underlie the computation of visual stimuli. Many aspects of its cytoarchitecture, chemoarchitecture, connectivity and development are thoroughly characterized. However, knowledge about its monoaminergic innervation is still incomplete. As a prerequisite to understand a possible functional role of the monoaminergic neurotransmitters, the serotonergic, noradrenergic, and dopaminergic innervation of the optic tectum as well as the distribution of serotonin 2A receptors, the dopamine- and cAMP-regulated phosphoprotein DARPP-32 and calbindin D-28K was studied in domestic chicks by immunohistochemical techniques. Serotonergic, noradrenergic, and tyrosine hydroxylase positive axons and axon terminals were present in all layers of the optic tectum. Generally, the highest densities of serotonergic, noradrenergic, and tyrosine hydroxylase positive fibers were found in the superficial tectal layers 1-8, whereas only moderate densities of serotonergic, noradrenergic, and tyrosine hydroxylase positive fibers became obvious in the deep tectal layers 9-15. Serotonergic fibers were particularly abundant in layers 4, 5a and 7 and serotonin 2A receptors in layer 13. Noradrenergic fibers were densest in layers 4 and 5a, whereas tyrosine hydroxylase positive fibers showed a slightly different distribution pattern with additional dense labeling in layer 7. As revealed by double-labeling immunohistochemistry, serotonergic fibers were closely related to the cell bodies of calbindin-positive horizontal cells in layer 5b and tyrosine hydroxylase positive fibers often contacted DARPP-32+ dendritic shafts in layers 9 and 10. These findings indicate that the catecholaminergic innervation of the optic tectum consists of a noradrenergic and a dopaminergic component and that the noradrenergic, serotonergic, and dopaminergic system may be potentially involved in the modulation of retinal input in the superficial layers of the optic tectum as well as in the modulation of tectal output via the deep tectal layers.

Evidence that urocortin is absent from neurons of the Edinger-Westphal nucleus in pigeons.

The Edinger-Westphal nucleus (EWN) is a central preganglionic parasympathetic cell group that gives rise to cholinergic input to the ciliary ganglion, thereby regulating several neurovegetative ocular functions. Recently, the supposed presence of the neuropeptide urocortin (UCN) has been reported in EWN neurons in rodent brain. The purpose of the present study was to examine the distribution of UCN in avian brain and to investigate by immunohistochemical analysis the possible use of this substance as an EWN marker in a non-mammalian class of vertebrates. Brain tissue of pigeons was incubated with a specific antibody against UCN and the results showed labeling of many small neurons, forming a double wing in the dorsal mesodiencephalic transition area. Their size and shape, however, differed from those of EWN neurons, and they were preferentially located rostral to the EWN. Double-label experiments employing an antibody against the enzyme choline acetyltransferase (ChAT) showed that UCN is not localized to the cholinergic cells of the EWN and confirmed the rostral distributionof UCN never overlapping the ChAT+ EWN cells. Taken together, these results suggest that, at least in pigeons, the UCN+ population does not belong to the traditionally defined EWN.

Evidence that urocortin is absent from neurons of the Edinger-Westphal nucleus in pigeons

The Edinger-Westphal nucleus (EWN) is a central preganglionic parasympathetic cell group that gives rise to cholinergic input to the ciliary ganglion, thereby regulating several neurovegetative ocular functions. Recently, the supposed presence of the neuropeptide urocortin (UCN) has been reported in EWN neurons in rodent brain. The purpose of the present study was to examine the distribution of UCN in avian brain and to investigate by immunohistochemical analysis the possible use of this substance as an EWN marker in a non-mammalian class of vertebrates. Brain tissue of pigeons was incubated with a specific antibody against UCN and the results showed labeling of many small neurons, forming a double wing in the dorsal mesodiencephalic transition area. Their size and shape, however, differed from those of EWN neurons, and they were preferentially located rostral to the EWN. Double-label experiments employing an antibody against the enzyme choline acetyltransferase (ChAT) showed that UCN is not localized to the cholinergic cells of the EWN and confirmed the rostral distributionof UCN never overlapping the ChAT+ EWN cells. Taken together, these results suggest that, at least in pigeons, the UCN+ population does not belong to the traditionally defined EWN.

Habituation to sound stimulation in detelencephalated pigeons (Columbia livia)

Habituation to sound stimulation was analyzed in terms of the functional role of the telencephalon in learning. Sixteen pigeons were exposed to 1000-Hz, 83-dB, 1-s sound (stimulus A) at 30-s intervals until there was habituation of the exploratory and pre-exploratory responses. The learning criterion was 10 trials without the occurrence of these responses. Twenty-four hours after habituation to stimulus A the birds were tested with a 500-Hz, 85-dB, 1-s sound (stimulus B). On the day following habituation to stimulus B, the birds of the experimental group (N=8) suffered ablation of the telencephalon and the birds of the control group (N=8) had sham surgery. Retesting with the same sequence of procedures was carried out 10 days after surgery. in the POST-lesion situation there was a decrease of the number of habituation trials to stimulus A (P<0.01) and to stimulus B (P<0.05) by experimental pigeons compared to the PRE-lesion situation. The data suggest an interaction of a facilitatory effect of the lesion and long-term learning effects