The distribution of GABA‐containing perikarya, fibers, and terminals in the forebrain and midbrain of pigeons, with particular reference to the basal ganglia and its projection targets

Abstract

Immunohistochemical techniques were used to study the distributions of glutamic acid decarboxylase (GAD) and gamma-aminobutyric acid (GABA) in pigeon forebrain and midbrain to determine the organization of GABAergic systems in these brain areas in birds. In the basal ganglia, numerous medium-sized neurons throughout the striatum were labeled for GABA, while pallidal neurons, as well as a small population of large, aspiny striatal neurons, labeled for GAD and GABA. GAD+ and GABA+ fibers and terminals were abundant throughout the basal ganglia, and GABAergic fibers were found in all extratelencephalic targets of the basal ganglia. Most of these targets also contained numerous GABAergic neurons. In pallial regions, approximately 10-12% of the neurons were GABAergic. The outer rind of the pallium was more intensely labeled for GABAergic fibers than the core. The olfactory tubercle region, the ventral pallidum, and the hypothalamus were extremely densely labeled for GABAergic fibers, while GABAergic neurons were unevenly distributed in the hypothalamus. GABAergic neurons and fibers were abundant in the dorsalmost part of thalamus and the dorsal geniculate region, while GABAergic neurons and fibers were sparse (or lightly labeled) in the thalamic nuclei rotundus, triangularis, and ovoidalis. Further, GABAergic neurons were abundant in the superficial tectal layers, the magnocellular isthmic nucleus, the inferior colliculus, the intercollicular region, the central gray, and the reticular formation. GABAergic fibers were particularly abundant in the superficial tectal layers, the parvocellular isthmic nucleus, the inferior colliculus, the intercollicular region, the central gray, and the interpeduncular nucleus. These results suggest that GABA plays a role as a neurotransmitter in nearly all fore- and midbrain regions of birds, and in many instances the observed distributions of GABAergic neurons and fibers closely resemble the patterns seen in mammals, as well as in other vertebrates.

Performance of appetitive or consummatory components of male sexual behavior is mediated by different brain areas: a 2-deoxyglucose autoradiographic study

“…49,50,63 The dorsomedial area of the avian hippocampus is rich in GABAergic fibers, that may primarily reflect intrinsic connections and includes the most intense labeling of serotoninergic, cholinergic and catecholaminergic fibers and neuropil of the ascending afferents of the medial fiber tract. 63,84 This is the region where a significant reduction in glucose utilization was detected in this study, following copulatory behavior. The mechanism underlying this decreased activity in the CSB group is not well understood at present but it may represent a specific inhibition of the intrinsic circuits activity.…”

“…The paleostriatum primitivum gives rise to most of the GABAergic sub-telencephalic projections of the paleostriatal complex (counterpart of mammalian pallido-tegmental system), via axons of the ansa lenticularis 60 to nucleus dorsointermedius posterior thalami, nucleus spiriformis lateralis and substantia nigra. 84 However, none of those well-documented projection areas showed any statistically significant metabolic changes, suggesting that metabolic stimulation of paleostriatum primitivum might reflect inhibition of the GABAergic cells in paleostriatum primitivum, 44 which in turn does not affect metabolic activity in its projection areas. These findings are in agreement with studies in primates, that suggest that normal tonic activity of pallidal neurons inhibits their target neurons in the thalamus and mesencephalic tegmentum.…”

“…Tuberculum olfactorium contains a dense accumulation of GABAergic fibers and receives inputs from the olfactory bulb, lobus parolfactorius and lateral septum. 84 One study also briefly reports tuberculum olfactorium projections to the septum, archistriatum, lateral corticoid area, cortex piriformis, area temporo-parieto-occipitalis, hippocampus, medial hyperstriatum ventrale including intermediate hyperstriatum ventrale, dorsomedial thalamic nucleus, entire habenular region and ventral hypothalamic area, 81 but these connections are not fully characterized. The present study provides strong evidence for the participation of tuberculum olfactorium to functional circuits related to reproductive behavior, both in its anticipatory and consummatory phase.…”

“…86,95 The reversed relationship of metabolic changes in nucleus interpeduncularis and hippocampus medial part could imply a possible disinhibition mechanism, supported by the dense GABAergic fibers found in nucleus interpeduncularis. 84 Moreover, nucleus interpeduncularis is known to receive descending cholinergic projections via the fasciculus retroflexus from the medial habenula, which in turn receives input from olfactory areas and regions related to the limbic system. The anatomical connections and the functional involvement of nucleus interpeduncularis in sexual behavior supports the idea that nucleus interpeduncularis in the tegmentum integrates incoming sensory/olfactory information with appropriate motor responses.…”

Revised nomenclature for avian telencephalon and some related brainstem nuclei

“…By means of these projections, SNr neurons are involved in the basal ganglia-mediated control of movement (Reiner et al, 1998a). A similar GABAergic cell population has been identified in birds, lateral to and overlapping the SNc/A9 (Veenman and Reiner, 1994). This cell group was initially called the substantia nigra pars lateralis (Veenman and Reiner, 1994;, and it was shown to receive striatal input from SP/DYN-containing terminals of striatal origin and to project to the tectum and thalamus Anderson et al, 1991;Reiner et al, 1998a).…”