Lobus Parolfactorius Research Articles

A quantitative autoradiographic comparison of binding to glutamate receptor sub-types in hippocampus and forebrain regions of a food-storing and a non-food-storing bird

In two species of birds, food-storing marsh tits, P. palustris, and non-storing blue tits, P. caeruleus, quantitative receptor autoradiography was used to localize NMDA ( N-methyl- d-aspartate)-sensitive [ 3H]glutamate, [ 3H]MK801, and [ 3H]AMPA binding sites, in six regions of the forebrain: hippocampus and parahippocampus, hyperstriatum accessorium (vision) and ventrale (sensory integration), neostriatum (auditory), and lobus parolfactorius (basal ganglia). In both species high levels of labelling to both NMDA and AMPA receptors were observed throughout the forebrain. However, a marked difference in receptor labelling was apparent between the two species, with levels of binding to NMDA ion channel sites being significantly lower (20%) in both the hippocampus and parahippocampus, in food storers compared to non-food storers. The levels of binding to other forebrain regions were remarkably similar in the two species. No differences were seen in the binding to AMPA receptors in forebrain regions of either species.

Distribution of glial fibrillary acidic protein and vimentin-immunopositive elements in the developing chicken brain from hatch to adulthood.

The present study describes the distribution of glial fibrillary acidic protein (GFAP) and vimentin-immunopositive structures in the brain of the domestic chicken (Gallus domesticus) from hatching to maturity. The telencephalon is penetrated by a vimentin-immunopositive radial fibre system, representing a modified form of radial glia, in day-old chicks. Numerous fibres of this system persist until adulthood, mainly in the lobus parolfactorius, lamina medullaris dorsalis and lamina frontalis superior. GFAP immunoreactivity also appears in the course of development in these fibres. The distribution of GFAP-immunopositive astrocytes in the post-hatch telencephalon is like that found in adult chicken, except for the ectostriatum, in which an adult-like GFAP-immunostaining only develops during week three. This delay may be associated with a relatively slow maturation of this visual centre. In the diencephalon and in the mesencephalic tegmentum of day-old chicks GFAP-immunopositive astrocytes are confined to the border zone of several nuclei. In these areas as well as in the pons most GFAP positive astrocytes only appear gradually during the first two post-hatch weeks, although radial fibres occur only sparsely at hatch. Summarizing these results, a gradual replacement of radial fibres by astrocytes, typical of mammals, cannot be found in chicken. In the nucleus laminaris we observed a characteristic palisade of non-ependymal glia, reactive to GFAP but not to vimentin, which almost completely disappears by adulthood. We suggest that this glial system is instrumental in the development of the dendritic organisation of this nucleus. The optic tectum displays a dense array of GFAP-immunopositive radial glia at hatching, similar in this to the situation found in reptiles. However, in the tectum of reptiles this radial glia persists for the lifetime, whereas in the chick it disappears from the superficial tectal layers. This phenomenon may reflect the fact that there is no replacement of tectal cells or regeneration of retinotectal pathways in the chicken. In the early stage, the large cerebral tracts were found to contain dense accumulations of GFAP-positive cells, with peculiarly long outgrowths accompanying nerve fibres. No vimentin-immunopositivity was found in these glial elements; however vimentin was present in the glia situated at the optic chiasm, the anterior commissure and at other decussations. These structures, as well as the raphe, displayed the most intense vimentin-immunopositivity in the post-hatch chicken. This characteristic glial population may represent glial elements that have been reported to regulate fibre-crossing at the midline.

The dopaminergic innervation of the pigeon telencephalon: distribution of DARPP-32 and co-occurrence with glutamate decarboxylase and tyrosine hydroxylase

Dopaminergic axons arising from midbrain nuclei innervate the mammalian and avian telencephalon with heterogeneous regional and laminar distributions. In primate, rodent, and avian species, the neuromodulator dopamine is low or almost absent in most primary sensory areas and is most abundant in the striatal parts of the basal ganglia. Furthermore, dopaminergic fibres are present in most limbic and associative structures. Herein, the distribution of DARPP-32, a phosphoprotein related to the dopamine D1-receptor, was investigated in the pigeon telencephalon by immunocytochemical techniques. Furthermore, co-occurrence of DARPP-32-positive perikarya with tyrosine hydroxylase-positive pericellular axonal “baskets” or glutamate decarboxylase-positive neurons, as well as co-occurrence of tyrosine hydroxylase and glutamate decarboxylase were examined. Specificity of the anti-DARPP-32 monoclonal antibody in pigeon brain was determined by immunoblotting. The distribution of DARPP-32 shared important features with the distribution of D1-receptors and dopaminergic fibres in the pigeon telencephalon as described previously. In particular, DARPP-32 was highly abundant in the avian basal ganglia, where a high percentage of neurons were labelled in the “striatal” parts (paleostriatum augmentatum, lobus parolfactorius), while only neuropil staining was observed in the “pallidal” portions (paleostriatum primitivum). In contrast, DARPP-32 was almost absent or present in comparatively lower concentrations in most primary sensory areas. Secondary sensory and tertiary areas of the neostriatum contained numbers of labelled neurons comparable to that of the basal ganglia and intermediate levels of neuropil staining. Approximately up to one-third of DARPP-32-positive neurons received a basket-type innervation from tyrosine hydroxylase-positive fibres in the lateral and caudal neostriatum, but only about half as many did in the medial and frontal neostriatum, and even less so in the hyperstriatum. No case of colocalization of glutamate decarboxylase and DARPP-32 and no co-occurrence of glutamate decarboxylase-positive neurons and tyrosine hydroxylase-basket-like structures could be detected out of more than 2 000 glutamate decarboxylase-positive neurons examined, although the high DARPP-32 and high tyrosine hydroxylase staining density hampered this analysis in the basal ganglia. In conclusion, the pigeon dopaminergic system seems to be organized similar to that of mammals. Apparently, in the telencephalon, dopamine has its primary function in higher level sensory, associative and motor processes, since primary areas showed only weak or no anatomical cues of dopaminergic modulation. Dopamine might exert its effects primarily by modulating the physiological properties of non-GABAergic and therefore presumably excitatory units.

Characteristics of the Proopiomelanocortin System in the Outdoor-Bred Domestic Gander: I. ACTH and β-Endorphin Levels in the Brain, Pituitary, and Plasma

Immunoreactive (ir-) adrenocorticotropic hormone (ACTH) and β-endorphin (βE) levels were determined in seven brain regions, in the three pituitary lobes, and in the plasma of the domestic gander by specific radioimmunoassays. In the brain regions studied the relative concentrations of ir-ACTH and ir-βE were the highest in the mediobasal hypothalamus and in the paraventricular nucleus. There were lower levels of these peptides in the supraoptic nucleus, in the septum, and in the dorsal thalamus. Very low ir-ACTH and -βE contents were found in the archistriatum and in the lobus parolfactorius. In the pars distalis of the pituitary gland the cephalic lobe contained about 10 times more ir-ACTH (3596 pmol/lobe) and 4 times more ir-βE (867 pmol/lobe) than the caudal lobe (383 pmol/lobe and 189 pmol/lobe, respectively). Sephadex G-50 chromatography of pooled cephalic and caudal lobe extracts resulted in two distinct ir-βE peaks, with elution volumes corresponding to the mammalian β-lipotropin and βE, and three ir-ACTH peaks, the second one coeluting with mammalian ACTH. In the neural lobe the ir-ACTH/-βE concentrations were similar to those in the hypothalamus. Resting plasma ir-ACTH (12.8±1.47 pmol/ml) but not ir-βE (31.4±1.22 pmol/ml) levels were significantly increased following castration (to 41.4±1.11 pmol/ml). Serial blood sampling indicated pulsatile ir-βE secretion (mean, coefficients of variation, and minimum–maximum range: 17.5, 62.78, and 2.9–49.7, respectively, for gander 1 and 23.3, 62.85, and 5.00–61.5, respectively, for gander 2).

Salmon homing: Combined electrophysiological and experimental behavioral approaches

The discovery of glucagon biosynthesis and receptors within mammalian brain has led one to suspect a neurotransmitter role for glucagon. In order to address this hypothesis in birds, we investigated the existence of glucagon receptors in duck brain by radioligand binding on fresh tissue sections and radioautography. Specific high-affinity [125I]glucagon binding sites similar to those in the liver were demonstrated in the avian brain. Mapping of these putative glucagon receptors revealed a discrete distributional pattern. Most of the [125I]glucagon binding capacity in duck brain is concentrated within the telencephalon, mainly in components of motor and limbic systems. Specific labeling densities were associated with avian equivalents of the mammalian pyramidal system (hyperstriatum accessorium; archistriatum intermedium and tractus occipitomesencephalicus) and extrapyramidal system (paleostriatum augmentatum, paleostriatum primitivum and lobus parolfactorius), as well as several limbic structures (hippocampal formation, nucleus taeniae and the caudal part of the archistriatum). Few glucagon-reactive foci were detected in the diencephalon (the nucleus dorsomedialis of hypothalamus, the two circumventricular organs, organum vasculosum of the lamina terminalis and median eminence and the nucleus habenularis medialis). These findings suggest that glucagon might be involved in the central control of somatic motricity and basic behaviors and point therefore to glucagon as a new neuroactive messenger in avian brain. The extensive difference between the distribution of glucagon binding sites observed in duck brain and that previously reported in rat brain suggests that glucagon does not subserve the same physiological role(s) in avian and mammalian brains.

Efferent connections of the domestic chick archistriatum: a phaseolus lectin anterograde tracing study.

The archistriatum of the domestic chick has been implicated in both fear behaviour and learning. However, relatively little is known about its organisation. The efferent connections of discrete anatomical regions of the chick archistriatum were therefore investigated by iontophoresis of the anterograde tracer Phaseolus vulgaris leucoagglutinin into its anterior, dorsal intermediate, ventral intermediate, medial, and posterior parts. The results of this study suggest that the chick archistriatum can be divided into two basic divisions according to whether they project to the following limbic structures: the hippocampal formation, septal areas, lobus parolfactorius, nucleus accumbens, ventral paleostriatum, and dorsomedial thalamus. The limbic archistriatum includes the posterior archistriatum and extends rostrally through the ventral intermediate archistriatum into the anterior archistriatum. The non-limbic archistriatum comprises the dorsal intermediate and medial archistriatum and largely gives rise to specific sensory, somatosensory, and motor telencephalofugal efferents. There may not be distinct borders between these two divisions of the chick archistriatum.

Organization and efferent connections of the archistriatum of the mallard, Anas platyrhynchos L.: an anterograde and retrograde tracing study.

The intratelencephalic and descending connections of the archistriatum of the mallard were studied using anterograde and retrograde tracers. Autoradiography after injections of [3H]-leucine served to visualize the intratelencephalic and extratelencephalic efferent connections of the archistriatum. Horseradish peroxidase (HRP), HRP-wheatgerm agglutinin, and fluorescent tracers were used to identify the precise origin of the projections to the various terminal fields found in the anterograde experiments. Four main regions can be recognized in the archistriatum of the mallard: (1) the rostral or anterior part that is a source of contralateral intratelencephalic projections, in particular to the contralateral archistriatum; (2) the dorsal intermediate archistriatum that is the origin of a large descending fiber system, the occipitomesencephalic tract, with projections to dorsal thalamic nuclei, the medial spiriform nucleus, the intercollicular nucleus, the deep tectum, parts of the mesencephalic and bulbar reticular formation, and the subnuclei of the descending trigeminal tract. There are no direct projections to motor nuclei. This part corresponds to the somatic sensorimotor part as defined by Zeier and Karten (1971, Brain Res. 31:313-326); it also contributes to the ipsilateral intratelencephalic connections and, to a lesser degree, to contralateral intratelencephalic connections. (3) The ventral intermediate archistriatum is another region that is also a source of intratelencephalic projections, in particular of those to the lobus parolfactorius. The most lateral zone sends fibers to the septal area. (4) The caudoventral intermediate and posterior archistriatum is another region that is a source of the projections to the hypothalamus and thus corresponds to the amygdaloid part of the archistriatum as defined by Zeier and Karten; it also contributes a modest component to the occipitomesencephalic tract. The different cell populations are not spatially separated, which makes it impossible to recognize distinct subnuclei within the four main regions of the archistriatum of the mallard.

Increased immunogold labelling of neural cell adhesion molecule isoforms in synaptic active zones of the chick striatum 5–6 hours after one-trial passive avoidance training

An area of the chick striatum, the lobus parolfactorius plays an important role in one-trial passive avoidance learning tasks. [16, 19, 20]In the present study we report evidence that 5–6 h post-training, a significantly higher proportion of synaptic active zones in this area contain labelled epitopes of the neural cell adhesion molecule, with the greatest occurrence of labels at the edges of active zone profiles (in both control and trained groups). This suggests that there is a period after training when expression of the neural cell adhesion molecule in synaptic membranes almost doubles, and that events at active zone edges may play a specific role in mechanisms of synaptic adhesion. Cellular mechanisms of long-term memory formation are believed to include alterations in neural circuitry at the synaptic level. The involvement of the neural cell adhesion molecule (NCAM) in functional synaptic modifications has been demonstrated using a number of physiological models. [6, 9, 13]Performance of rats in the Morris water maze, a spatial learning paradigm which requires the hippocampus, is impaired by either intraventricular injection of NCAM antibodies, [1]or injection into the hippocampus of an enzyme which increases homophilic adhesion of the molecule, due to the removal of polysialic acid residuals from extracellular NCAM domains. [3]In addition, intraventricular injections of anti-NCAM antibodies 6–8 h post-training were shown to impair memory for a one-trial passive avoidance task in the rat. [7] An avoidance training model in the one-day-old chick indicates a similar time window, 5–6 h post-training during which memory for the task can be impaired by intraventricular injection of NCAM antibodies. [14, 17]In the hyperstriatum ventrale, a chick forebrain area involved in the passive avoidance task, subtle changes in the distribution pattern, but not density of NCAM molecules in synaptic membranes were revealed 5–6 h post-training. [15]However, on the basis of studies of synaptic morphometry, a region of striatum, the lobus parolfactorius (LPO), appears to play a more important role in longer term memory storage for the task. [14, 16, 20]

Nitric oxide synthase in learning-relevant nuclei of the chick brain: morphology, distribution, and relation to transmitter phenotypes.

Nitric oxide (NO) has been implicated in learning in the hatchling chicken. To examine morphological and neurochemical properties of neurons that contain NO synthase (NOS) in brain regions known to be involved in learning and memory, the NADPH-diaphorase technique was used in conjunction with immunocytochemistry and tract tracing. A distinct cell type was NOS-labeled in the lobus parolfactorius (LPO) in the telencephalon, and neurons were labeled in the area ventralis of Tsai (AVT), the substantia nigra (nucleus tegmenti pedunculo-pontinus, pars compacta, TPc), and the locus coeruleus in the brainstem. Thus, NO may influence processes of learning and memory in the forebrain after release from intrinsic neurons and/or from extrinsic NOS-projections originating from the brainstem. DiI-tracing revealed that most of the NOS-positive neurons in the AVT/TPc project to the basal forebrain. The majority of tyrosine hydroxylase-positive (presumptive dopaminergic) neurons in the AVT and TPc expressed NOS. Double-labeling with antibodies to tyrosine hydroxylase, choline acetyltransferase, somatostatin, and the neurotrophin receptor as a marker for noradrenergic coeruleus neurons showed that NOS was not colocalized with noradrenergic or somatostatinergic neurons, and that less than a third of the cholinergic neurons were double-labeled for NOS. Injections of 6-hydroxydopamine into the brainstem did not reduce the density of NOS-labeled fibers in the LPO, indicating that most of the NO in the LPO originates from intrinsic neurons in the basal forebrain. Thus, NOS-containing presumptive local circuit neurons in the LPO are the most likely source of NO involved in learning of passive avoidance tasks in hatchling chicks.

Nitric oxide synthase in learning-relevant nuclei of the chick brain: Morphology, distribution, and relation to transmitter phenotypes

Nitric oxide (NO) has been implicated in learning in the hatchling chicken. To examine morphological and neurochemical properties of neurons that contain NO synthase (NOS) in brain regions known to be involved in learning and memory, the NADPH-diaphorase technique was used in conjunction with immunocytochemistry and tract tracing. A distinct cell type was NOS-labeled in the lobus parolfactorius (LPO) in the telencephalon, and neurons were labeled in the area ventralis of Tsai (AVT), the substantia nigra (nucleus tegmenti pedunculo-pontinus, pars compacta, TPc), and the locus coeruleus in the brainstem. Thus, NO may influence processes of learning and memory in the forebrain after release from intrinsic neurons and/or from extrinsic NOS-projections originating from the brainstem. DiI-tracing revealed that most of the NOS-positive neurons in the AVT/TPc project to the basal forebrain. The majority of tyrosine hydroxylase-positive (presumptive dopaminergic) neurons in the AVT and TPc expressed NOS. Double-labeling with antibodies to tyrosine hydroxylase, choline acetyltransferase, somatostatin, and the neurotrophin receptor as a marker for noradrenergic coeruleus neurons showed that NOS was not colocalized with noradrenergic or somatostatinergic neurons, and that less than a third of the cholinergic neurons were double-labeled for NOS. Injections of 6-hydroxydopamine into the brainstem did not reduce the density of NOS-labeled fibers in the LPO, indicating that most of the NO in the LPO originates from intrinsic neurons in the basal forebrain. Thus, NOS-containing presumptive local circuit neurons in the LPO are the most likely source of NO involved in learning of passive avoidance tasks in hatchling chicks.

Synaptic terminals immunolabelled against glutamate in the lobus parolfactorius of domestic chicks ( Gallus domesticus) in relation to afferents from the archistriatum

The lobus parolfactorius (LPO) has been implicated in memory formation associated with passive avoidance training of young posthatch domestic chicks. The anatomical circuitry underlying memory formation in the chick is likely to involve the intermediate medial hyperstriatum ventrale–archistriatum–LPO arc. In the present work, we attempted to combine an ultrastructural characterisation of archistriatal afferent terminals in LPO with a description of the synaptic structure of LPO, in particular those elements that are immunoreactive to glutamate and GABA. Ventral archistriatal regions of 7-day-old domestic chicks were iontophoretically injected with Phaseolus vulgaris leucoagglutinin and the anterograde transport of the tracer was detected in the LPO. Selected samples from these birds, and also from other day-old chicks, were resin-embedded and reacted for l-glutamate or GABA, using the postembedding immunocytochemical method. Glutamate was abundant in the neuropil of LPO and typically seen in axodendritic or axospinous terminals with asymmetrical junctions, often multiple or perforated postsynaptic appositions. Conversely, GABA was often present in aspinous dendrites, probably representing GABAergic local circuit neurons or (putative striatonigral) projection neurons. Archistriatal efferents terminating in LPO formed small en passant or terminal varicosities, with infrequent asymmetrical axospinous synapses. Glutamate was not detected in these boutons. The findings imply that the functional state of LPO, based on powerful glutamatergic excitation, may be modified by a non-glutamatergic archistriatal input.

Evidence for localized and discrete roles for enkephalins during memory formation in the chick.

This study examined effects on memory formation produced by [Leu]enkephalin and [Met]enkephalin administration in 2 regions of the 2-day-old chick brain involved in memory formation: the intermediate medial hyperstriatum ventrale (IMHV) and the lobus parolfactorius (LPO). Basal concentrations of endogenous [Leu]enkephalin and [Met]enkephalin were determined for 5 brain regions, and effects of 1-trial peck-avoidance training on enkephalin concentrations were examined in the IMHV and LPO. [Leu]enkephalin was amnestic when administered in the IMHV but not in the LPO. In contrast, [Met]enkephalin may be amnestic when administered in the LPO but not in the IMHV. Training decreased [Met]enkephalin concentration in the LPO but not in the IMHV. Training had no effect on [Leu]enkephalin concentration in either the IMHV or the LPO. Thus, amnestic effects of [Leu]- or [Met]enkephalin administration are brain-region specific. Regional activity of endogenous [Met]enkephalin during memory formation is consistent with localized amnestic effects produced by [Met]enkephalin administration.

Organization of the dopaminergic innervation of forebrain areas relevant to learning: a combined immunohistochemical/retrograde tracing study in the domestic chick.

The mediorostral neostriatum/hyperstriatum ventrale (MNH) and neostriatum dorsocaudale (Ndc) of the domestic chick are crucially involved in auditory filial imprinting, whereas the lobus parolfactorius (LPO) seems to be involved in the emotional modulation of behavior. Because there is evidence that MNH and Ndc are akin to higher association areas in mammals, the present study evaluates the dopaminergic and thalamic input to these areas, as well as to the avian caudate/putamen homologue LPO, by using retrograde pathway tracing, together with dopamine (DA) and tyrosine hydroxylase (TH) immunohistochemistry. By combining DA immunohistochemistry with retrograde fluorescent tracing, we demonstrated that dopaminergic afferents to the MNH and Ndc arise mainly from the area ventralis, whereas the main dopaminergic input to the LPO arises from the substantia nigra. The main thalamic input to the MNH and LPO arises from the dorsal thalamic nuclei, n. dorsomedialis anterior and n. dorsolateralis anterior, whereas the thalamic input to the Ndc arises from the n. dorsolateralis posterior and n. subrotundus. Furthermore, there are reciprocal intratelencephalic connections between distinct parts of the neostriatum caudale and the mediorostral neostriatum. DA-immunoreactive (ir) fibers are present at moderate densities in the MNH and Ndc and at high densities in the LPO. At the ultrastructural level, DA- and TH-ir axon terminals in the MNH and Ndc form predominantly symmetric synaptic contacts with dendritic shafts, which are often situated in close vicinity to unstained terminals. These results indicate that the general organization of dopaminergic afferents to the chick telecephalon is similar to that of the mesotelencephalic dopaminergic subsystems in mammals such as the mesostriatal and mesolimbocortical DA system.

Distribution of choline acetyltransferase and acetylcholinesterase in vocal control nuclei of the budgerigar (Melopsittacus undulatus).

The present study used histochemical methods to map the distributions of choline acetyl transferase (ChAT) and acetylcholinesterase (AChE) in the vocal control nuclei of a psittacine, the budgerigar (Melopsittacus undulatus). The distributions of ChAT and AChE in budgerigars appeared similar to that in oscine songbirds despite evidence that these systems have evolved independently. The magnicellular nucleus of the lobus parolfactorius in budgerigars, like the area X in songbirds, contained many ChAT labeled somata, fibers, and varicosities and stained densely for AChE. In contrast, the robust nucleus of the archistriatum (RA) and the supralaminar area of the frontal neostriatum in budgerigars, like the RA and the magnicellular nucleus of the neostriatum (MAN) in songbirds, respectively, contained few or no ChAT labeled somata, fibers, and varicosities and stained lightly for AChE. The central nucleus of the lateral neostriatum in budgerigars, like the higher vocal center (HVC) in songbirds, contained no ChAT labeled somata, moderate densities of ChAT labeled fibers and varicosities, and moderate levels of AChE staining. Two nuclei, the oval nucleus of the hyperstriatum ventrale (HVo) and the oval nucleus of the anterior neostriatum (NAo), contained no ChAT labeled somata, dense ChAT labeled fibers and varicosities, and moderate to high levels of AChE staining. The HVo and the NAo have no counterparts in songbirds but may be important vocal control nuclei in the budgerigar. Cholinergic enzymes are also described in other regions which may be involved in budgerigar vocal behavior, including the basal forebrain, the torus semicircularis, and the hypoglossal nuclei (nXII).

Distribution of choline acetyltransferase and acetylcholinesterase in vocal control nuclei of the budgerigar (Melopsittacus undulatus)

The present study used histochemical methods to map the distributions of choline acetyl transferase (ChAT) and acetylcholinesterase (AChE) in the vocal control nuclei of a psittacine, the budgerigar (Melopsittacus undulatus). The distributions of ChAT and AChE in budgerigars appeared similar to that in oscine songbirds despite evidence that these systems have evolved independently. The magnicellular nucleus of the lobus parolfactorius in budgerigars, like the area X in songbirds, contained many ChAT labeled somata, fibers, and varicosities and stained densely for AChE. In contrast, the robust nucleus of the archistriatum (RA) and the supralaminar area of the frontal neostriatum in budgerigars, like the RA and the magnicellular nucleus of the neostriatum (MAN) in songbirds, respectively, contained few or no ChAT labeled somata, fibers, and varicosities and stained lightly for AChE. The central nucleus of the lateral neostriatum in budgerigars, like the higher vocal center (HVC) in songbirds, contained no ChAT labeled somata, moderate densities of ChAT labeled fibers and varicosities, and moderate levels of AChE staining. Two nuclei, the oval nucleus of the hyperstriatum ventrale (HVo) and the oval nucleus of the anterior neostriatum (NAo), contained no ChAT labeled somata, dense ChAT labeled fibers and varicosities, and moderate to high levels of AChE staining. The HVo and the NAo have no counterparts in songbirds but may be important vocal control nuclei in the budgerigar. Cholinergic enzymes are also described in other regions which may be involved in budgerigar vocal behavior, including the basal forebrain, the torus semicircularis, and the hypoglossal nuclei (nXII). © 1996 Wiley-Liss, Inc.

Light and electron microscopic immunohistochemical study of dopaminergic terminals in the striatal portion of the pigeon basal ganglia using antisera against tyrosine hydroxylase and dopamine

A dopaminergic projection from the midbrain to the striatal portion of the basal ganglia is present in reptiles, birds, and mammals. Although the ultrastructure of these fibers and terminals within the striatum has been studied extensively in mammals, little information is available on the ultrastructure of this projection in nonmammals. In the present study, we used immunohistochemical labeling with antibodies against tyrosine hydroxylase (TH) or dopamine (DA) to study the dopaminergic input to the striatal portion of the basal ganglia in pigeons (i.e., lobus parolfactorius and paleostriatum augmentatum). At the light microscopic level, the anti-TH and anti-DA revealed a similar abundance and distribution of numerous labeled fine fibers and varicosities within the striatum. In contrast, the use of an antidopamine beta-hydroxylase antiserum (which labels only adrenergic and noradrenergic terminals) labeled very few striatal fibers, which were restricted to visceral striatum. These results demonstrate that anti-TH mainly labels dopaminergic terminals in the striatum. At the electron microscopic level, the anti-TH and anti-DA antisera labeled numerous axon terminals within the striatum (15-20% of all striatal terminals). These terminals tended to be small (with an average length of 0.6 microns) and flattened, and their vesicles tended to be small (35-60 nm in diameter) and pleomorphic. About 50% of the terminals were observed to make synaptic contacts in the planes of section examined, and nearly all of these synaptic contacts were symmetric. Both TH+ and DA+ terminals typically contacted dendritic shafts or the necks of dendritic spines, but a few contacted perikarya. No clear differences were observed between TH+ and DA+ terminals within medial striatum (whose neurons project to the nigra in birds) or between TH+ and DA+ terminals within lateral striatum (whose neurons project to the pallidum in birds). In addition, no differences were observed between medial and lateral striata in either TH+ or DA+ terminals. Thus, there is no evident difference in pigeons between striatonigral and striatopallidal neurons in their dopaminergic innervation. Our results also indicate that the abundance, ultrastructural characteristics, and postsynaptic targets of the midbrain dopaminergic input to the pigeon striatum are highly similar to those in mammals. This anatomical similarity is consistent with the pharmacologically demonstrable similarity in the role of the dopaminergic input to the striatum in birds and mammals.

Development of dopamine receptors in the forebrain of the domestic chick in relation to auditory imprinting. An autoradiographic study

The rostro-medial neostriatum/hyperstriatum ventrale (MNH) and the neostriatum dorsocaudale (Ndc) are forebrain regions which play a role in auditory filial imprinting. Both regions receive a distinct dopaminergic input from the mesencephalon and we were interested to investigate if the dopaminergic system, which is known to play a role in associative learning processes and neuronal plasticity is involved in auditory imprinting. Using ligand autoradiography we studied the distribution and density of dopamine receptors (D 1 and D 2 type) in the forebrain of socially isolated chicks during the first postnatal week and compared these data with the values of age-matched imprinted chicks. D 1- and D 2-receptors were present in the chick forebrain on the day of hatching and they showed in general, the same distribution until postnatal day 7. Between days 0 and 2 the D 2-receptor density increased significantly in the lobus parolfactorius and paleostriatum augmentatum while for D 1-receptor density no significant changes were detectable. The receptor densities in the investigated forebrain regions did not differ significantly between imprinted and control chicks. These results suggest that auditory imprinting does not induce alterations of dopamine receptor density, however, more subtle changes can not be excluded. The presented detailed data about the developmental profile of dopamine receptors within distinct brain regions is a further step towards a more specific interpretation of behavioral effects of dopamine receptor agonists or antagonists at different postnatal ages.

Efferent connectivity of the hippocampal formation of the zebra finch (Taenopygia guttata): An anterograde pathway tracing study usingPhaseolus vulgaris leucoagglutinin

The avian hippocampal formation (HP) is considered to be homologous to the mammalian hippocampus, being involved in memory formation and spatial memory in particular. The subdivisions and boundaries of the pigeon hippocampus have been defined previously by various morphological methods to detect further similarities with the mammalian homologue. We studied the efferent projections of the zebra finch hippocampus by applying Phaseolus vulgaris leucoagglutinin, and three main subdivisions were distinguished on the basis of the connectivity patterns. Dorsolateral injections gave rise to projections innervating the rostralmost extension of the HP, a laminar complex including the dorsal and ventral hyperstriata and the lamina frontalis superior, the rostral lobus parolfactorius, the medial and ventral paleostriatal regions, the lateral septal nucleus, the nucleus of the diagonal band, the dorsolateral corticoid area, the archistriatum posterius, and the nucleus taeniae in the telencephalon. In the diencephalon, labelled axons were seen in the periventricular and lateral hypothalamus, including the lateral mammillary nuclei, and in the dorsolateral and the dorsomedial posterior thalamic nuclei, whereas, in the midbrain, only the area ventralis of Tsai contained hippocampal fibres. With the exception of the bilateral archistriatal efferents, all projections were ipsilateral. Dorsomedial injections gave rise to a local fibre system that was almost completely restricted to the ipsilateral hippocampal formation. In addition, lectin-containing fibres continued in the dorsal septal region and a thin band in the hyperstriatum accessorium, adjacent to the lateral ventricle. Ventral injections gave rise to axons innervating ipsilaterally the dorsolateral subdivision, and bilaterally the medial septal nuclei and the contralateral ventral hippocampus.

Stimulus‐Evoked Increase of Glutamate in the Mediorostral Neostriatum/Hyperstriatum Ventrale of Domestic Chick After Auditory Filial Imprinting: An In Vivo Microdialysis Study

Imprinting in chicks is a form of juvenile learning that has been used to study the basic cellular mechanisms of learning and memory. The forebrain area mediorostral neostriatum/hyperstriatum ventrale (MNH) is a center for acoustic imprinting. Electrophysiological and pharmacological behavioral studies in the MNH have demonstrated that the glutamatergic system and the associated receptors are critically involved in auditory filial imprinting. Accordingly, we investigated the hypothesis that stimulus-evoked glutamate release may be altered after this learning process. Using an in vivo microdialysis technique, we observed a significantly higher increase of extracellular glutamate level in tone-imprinted chicks during exposure to the previously imprinted tone than in socially imprinted control chicks. In a further series of experiments, where we exposed animals from both experimental groups to handling distress, glutamate levels in MNH showed only a slight increase, whereas we observed a pronounced increase of extracellular glutamate in the lobus parolfactorius (LPO), the avian analogue of the basal ganglia. No difference of distress-evoked glutamate release was found in MNH and LPO between tone-imprinted and socially imprinted chicks. The tone-evoked enhanced glutamate response in tone-imprinted chicks suggests that during auditory imprinting glutamatergic synapses develop the potential to increase transmitter release in response to the imprinting stimulus.

Organization of afferent and efferent projections of the nucleus basalis prosencephali in a passerine, Taeniopygia guttata.

The connections of nucleus basalis (NB) of the rostral forebrain of the zebra finch were investigated electrophysiologically and with anterograde and retrograde tracing methods to determine their functional organization, the sources of their pontine afferents, and the targets of their telencephalic efferents. The nucleus was found to be partitioned into three major components, a rostral lingual part that received a hypoglossal projection via a lateral subnucleus of the principal sensory trigeminal nucleus (PrV), a middle beak part that received a trigeminal projection via a medial subnucleus of PrV, and a caudal auditory part that received a short latency auditory projection via the intermediate nucleus of the lateral lemniscus. Beak NB also received a projection from a paralateral lemniscal nucleus, and the dorsocaudal part of auditory NB and the medially adjacent neostriatum also received a projection from a lateral subnucleus of the superior vestibular nucleus (VS). The efferent projections of each of the three major parts of NB were mainly to the adjacent neostriatum frontale (NF), which then provided projections to the lobus parolfactorius (exclusive of area X), the lateral archistriatum intermedium (Ail), and the lateral neostriatum caudale (NCl). Ail received a projection from NCl and provided terminal fields to the contralateral NCl and the NF. The major projections of Ail, however, descended bilaterally through the brainstem via the occipitomesencephalic tracts, with dense terminations in the medial spiriform nucleus and with extensive bilateral terminations throughout the lateral reticular formation of the pons and medulla. For the most part, jaw, tongue, and tracheosyringeal motor nuclei did not receive terminations. The results suggest that NB in zebra finch, like NB in pigeon and duck, is likely to be a major component of trigeminal sensorimotor circuitry involved in feeding and in other oral-manipulative behaviors. Results also show that the auditory component of NB is not directly linked to the vocal control system at telencephalic levels, but the possibility remains that the lingual, beak, and auditory parts of NB play a role in vocalization by multisynaptic influences on cranial nerve motor nuclei innervating various parts of the vocal tract.