Distribution of androgen and estrogen receptor mRNA-containing cells in the rat brain: an in situ hybridization study

The distribution of cells that express mRNA encoding the androgen (AR) and estrogen (ER) receptors was examined in adult male and female rats by using in situ hybridization. Specific labeling appeared to be largely, if not entirely, localized to neurons. AR and ER mRNA-containing neurons were widely distributed in the rat brain, with the greatest densities of cells in the hypothalamus, and in regions of the telencephalon that provide strong inputs in the medial preoptic and ventromedial nuclei, each of which is thought to play a key role in mediating the hormonal control of copulatory behavior, as well as in the lateral septal nucleus, the medial and cortical nuclei of the amygdala, the amygdalohippocampal area, and the bed nucleus of the stria terminalis. Heavily labeled ER mRNA-containing cells were found in regions known to be involved in the neural control of gonadotropin release, such as the anteroventral periventricular and the arcuate nuclei, but only a moderate density of labeling for AR mRNA was found over these nuclei. In addition, clearly labeled cells were found in regions with widespread connections throughout the brain, including the lateral hypothalamus, intralaminar thalamic nuclei, and deep layers of the cerebral cortex, suggesting that AR and ER may modulate a wide variety of neural functions. Each part of Ammon's horn contained AR mRNA-containing cells, as did both parts of the subiculum, but ER mRNA appeared to be less abundant in the hippocampal formation. Moreover, AR and ER mRNA-containing cells were also found in olfactory regions of the cortex and in both the main and accessory olfactory bulbs. AR and ER may modulate nonolfactory sensory information as well since labeled cells were found in regions involved in the central relay of somatosensory information, including the mesencephalic nucleus of the trigeminal nerve, the ventral thalamic nuclear group, and the dorsal horn of the spinal cord. Furthermore, heavily labeled AR mRNA-containing cells were found in the vestibular nuclei, the cochlear nuclei, the medial geniculate nucleus, and the nucleus of the lateral lemniscus, which suggests that androgens may alter the central relay of vestibular and auditory information as well. However, of all the regions involved in sensory processing, the heaviest labeling for AR and ER mRNA was found in areas that relay visceral sensory information such as the nucleus of the solitary tract, the area postrema, and the subfornical organ. We did not detect ER mRNA in brainstem somatic motoneurons, but clearly labeled AR mRNA-containing cells were found in motor nuclei associated with the fifth, seventh, tenth, and twelfth cranial nerves. Similarly, spinal motoneurons contained AR but not ER mRNA.(ABSTRACT TRUNCATED AT 400 WORDS)     

Connections of the auditory midbrain in a teleost fish, Cyprinus carpio

Central auditory pathways were traced in Japanese carp, Cyprinus carpio, using electrophysiological mapping and HRP tract-tracing methods. Multiunit recordings made from the carp torus semicircularis, the major midbrain area for processing octavolateralis information, revealed a mediolateral segregation of auditory and lateral line sensory modalities. Iontophoretic injections of HRP were made into the medial torus to trace afferent and efferent projections of the carp auditory midbrain. Following unilateral HRP injections into the medial torus, retrogradely labeled neurons were observed within six nuclei of the carp medulla. Two octaval nuclei, the anterior octavus nucleus and descending octavus nucleus, contained HRP-filled neurons. Labeled neurons were also observed within the ipsilateral superior olive, scattered among fibers of both lateral lemnisci, and bilaterally within the medullary reticular formation. In addition, bilateral retrograde cell labeling was found within a group of Purkinje-like cells located adjacent to the IVth ventricle, just rostral to the level of the VIIIth nerve. Few labeled neurons were found within the nucleus medialis, a principal target for lateral line afferents within the medulla. At midbrain levels, retrogradely labeled neurons were observed within the contralateral torus semicircularis and the ipsilateral optic tectum. Three forebrain nuclei project to the carp auditory midbrain. Within the diencephalon, descending projections originate from the anterior tuberal nucleus, bilaterally, and from the ipsilateral central posterior thalamic nucleus. The ipsilateral caudal telencephalon also projects to the carp auditory midbrain via large multipolar neurons within area dorsalis pars centralis. Anterograde labeling of fibers and terminals revealed efferent projections of the carp auditory midbrain to the following targets: the ipsilateral superior olive, the ipsilateral medullary reticular formation, the deep layers of the optic tectum, the contralateral torus semicircularis, the anterior tuberal nucleus, and the central posterior thalamic nucleus. These results, together with recent studies of lateral line pathways in teleosts (Finger, '80, '82a), demonstrate that central auditory and lateral line pathways are anatomically distinct in the carp, at least from medullary to diencephalic levels. Furthermore, there are striking similarities in the organization of the central auditory pathways of the carp and those of amphibians and land vertebrates.     

Calcium‐binding protein immunoreactivity characterizes the auditory system of Gekko gecko

Geckos use vocalizations for intraspecific communication, but little is known about the organization of their central auditory system. We therefore used antibodies against the calcium‐binding proteins calretinin (CR), parvalbumin (PV), and calbindin‐D28k (CB) to characterize the gecko auditory system. We also examined expression of both glutamic acid decarboxlase (GAD) and synaptic vesicle protein (SV2). Western blots showed that these antibodies are specific to gecko brain. All three calcium‐binding proteins were expressed in the auditory nerve, and CR immunoreactivity labeled the first‐order nuclei and delineated the terminal fields associated with the ascending projections from the first‐order auditory nuclei. PV expression characterized the superior olivary nuclei, whereas GAD immunoreactivity characterized many neurons in the nucleus of the lateral lemniscus and some neurons in the torus semicircularis. In the auditory midbrain, the distribution of CR, PV, and CB characterized divisions within the central nucleus of the torus semicircularis. All three calcium‐binding proteins were expressed in nucleus medialis of the thalamus. These expression patterns are similar to those described for other vertebrates. J. Comp. Neurol. 518:3409–3426, 2010. © 2010 Wiley‐Liss, Inc.     

Distribution of androgen and estrogen receptor mRNA in the brain and reproductive tissues of the leopard gecko, Eublepharis macularius

Incubation temperature during embryonic development determines gonadal sex in the leopard gecko, Eublepharis macularius. In addition, both incubation temperature and gonadal sex influence behavioral responses to androgen and estrogen treatments in adulthood. Although these findings suggest that temperature and sex steroids act upon a common neural substrate to influence behavior, it is unclear where temperature and hormone effects are integrated. To begin to address this question, we identified areas of the leopard gecko brain that express androgen receptor (AR) and estrogen receptor (ER) mRNA. We gonadectomized adult female and male geckos from an incubation temperature that produces a female-biased sex ratio and another temperature that produces a male-biased sex ratio. Females and males from both temperatures were then treated with equivalent levels of various sex steroids. Region-specific patterns of AR mRNA expression and ER mRNA expression were observed upon hybridization of radiolabeled (35S) cRNA probes to thin sections of reproductive tissues (male hemipenes and female oviduct) and brain. Labeling for AR mRNA was very intense in the epithelium, but not within the body, of the male hemipenes. In contrast, expression of ER mRNA was prominent in most of the oviduct but not in the luminal epithelium. Within the brain, labeling for AR mRNA was conspicuous in the anterior olfactory nucleus, the lateral septum, the medial preoptic area, the periventricular preoptic area, the external nucleus of the amygdala, the anterior hypothalamus, the ventromedial hypothalamus, the premammillary nucleus, and the caudal portion of the periventricular nucleus of the hypothalamus. Expression of ER mRNA was sparse in the septum and was prominent in the ventromedial hypothalamus, the caudal portion of the periventricular nucleus of the hypothalamus, and a group of cells near the torus semicircularis. Many of these brain regions have been implicated in the regulation of hormone-dependent, sex-typical reproductive and agonistic behaviors in other vertebrates. Consequently, these nuclei are likely to control such behaviors in the leopard gecko and also are candidate neural substrates for mediating temperature effects on behavior.     

Anatomic relationships between aromatase and androgen receptor mRNA expression in the hypothalamus and amygdala of adult male cynomolgus monkeys

This study mapped the regional locations of cells expressing cytochrome P450 aromatase (P450AROM) and androgen receptor (AR) mRNAs in the adult male macaque hypothalamus and amygdala by in situ hybridization histochemistry using monkey-specific cRNA probes. High densities of P450AROM and AR mRNA-containing neurons were observed in discrete hypothalamic areas involved in the regulation of gonadotropin secretion and reproductive behavior. P450AROM mRNA-containing neurons were most abundant in the medial preoptic nucleus, bed nucleus of the stria terminalis, and anterior hypothalamic area, whereas AR mRNA-containing neurons were most numerous in the ventromedial nucleus, arcuate nucleus, and tuberomamillary nucleus. Moderate to heavily labeled P450AROM mRNA-containing cells were present in the cortical and medial amygdaloid nuclei, which are known to have strong reciprocal inputs with the hypothalamus. Heavily labeled P450AROM mRNA-containing cells were found in the accessory basal amygdala nucleus, which projects to the cingulate cortex and hippocampus, areas that are important in the expression of emotional behaviors and memory processing. In contrast to P450AROM, the highest density of AR mRNA labeling in the temporal lobe was associated with the cortical amygdaloid nucleus and the pyramidal cells of the hippocampus. All areas that contained P450AROM mRNA-expressing cells also contained AR mRNA-expressing cells, but there were areas in which AR mRNA was expressed but not P450AROM mRNA. The apparent relative differences in the expression of P450AROM and AR mRNA-containing neurons within the monkey brain suggests that T acts through different signaling pathways in specific brain areas or within different cells from the same region.     

Distribution of androgen receptor mRNA expression in vocal,auditory, and neuroendocrine circuits in a teleost fish

Across all major vertebrate groups, androgen receptors (ARs) have been identified in neural circuits that shape reproductive‐related behaviors, including vocalization. The vocal control network of teleost fishes presents an archetypal example of how a vertebrate nervous system produces social, context‐dependent sounds. We cloned a partial cDNA of AR that was used to generate specific probes to localize AR expression throughout the central nervous system of the vocal plainfin midshipman fish (Porichthys notatus). In the forebrain, AR mRNA is abundant in proposed homologs of the mammalian striatum and amygdala, and in anterior and posterior parvocellular and magnocellular nuclei of the preoptic area, nucleus preglomerulosus, and posterior, ventral and anterior tuberal nuclei of the hypothalamus. Many of these nuclei are part of the known vocal and auditory circuitry in midshipman. The midbrain periaqueductal gray, an essential link between forebrain and hindbrain vocal circuitry, and the lateral line recipient nucleus medialis in the rostral hindbrain also express abundant AR mRNA. In the caudal hindbrain‐spinal vocal circuit, high AR mRNA is found in the vocal prepacemaker nucleus and along the dorsal periphery of the vocal motor nucleus congruent with the known pattern of expression of aromatase‐containing glial cells. Additionally, abundant AR mRNA expression is shown for the first time in the inner ear of a vertebrate. The distribution of AR mRNA strongly supports the role of androgens as modulators of behaviorally defined vocal, auditory, and neuroendocrine circuits in teleost fish and vertebrates in general. J. Comp. Neurol. 518:493–512, 2010. © 2009 Wiley‐Liss, Inc.     

Hexokinase I Messenger RNA in the Rat Central Nervous System

Hexokinase I (ATP: -hexose 6-phosphotransferase, EC 2.7.1.1) is the first enzyme required in the metabolism of glucose in the central nervous system and plays a major role in regulation of the cerebral glycolytic rate. The distribution of hexokinase I mRNA was examined throughout the central nervous system of the rat by use of oligonucleotide probes and in situ hybridization histochemistry. In the rhinencephalon, strong hexokinase I mRNA labeling was demonstrated in the glomerular, mitral, internal granular, and internal plexiform layers, whereas the olfactory nerve, external plexiform, and subependymal layers and ependyma were devoid of labeling. Within the telencephalon, strong labeling was present in all layers (with the exception of the molecular layer) of the cerebral cortex, in the septum, in CA1-4 and dentate gyrus of the hippocampus, and in several amygdaloid nuclei. There was only weak labeling in the nucleus accumbens and caudate putamen. In the diencephalon, there was in general a strong labeling in the epithalamus, in several thalamic nuclei, including the anteriodorsal, anterioventral, anteriomedial, reticular, paravetricular, intermediodorsal, anteriomedial, interanteriomedial, rhomboid, reuniens, and parafascicular thalamic nuclei. Several hypothalamic regions, including the subfornical organ, the medial preoptic area, the suprachiasmatic, supraoptic, paraventricular, dorsomedial, ventromedial nuclei, and the zona incerta, were strongly labeled. In the mesencephalon, there was particularly strong labeling in the pars compacta and reticulata of the substantia nigra, central gray, and red nucleus, in the Darkschewitsch nucleus, and in the medial accessory oculomotor nucleus. In the rhombencephalon, there was strong hybridization in all raphe nuclei, pontine, tegmental, lateral parabrachial, olivary nuclei, and several cranial motor nuclei. All neurons of the locus ceruleus were heavily labeled. Very strong labeling was present in Purkinje and granular cells of the cerebellar cortex. Neurons of the medulla oblongata area postrema, nucleus tractus solitarius, reticular nucleus, nucleus cuneatus and several motor nuclei were strongly labeled. In the spinal cord, labeled cells were present in all laminae, and also neurons of the dorsal root ganglion were heavily labeled. Hexokinase I mRNA was also demonstrated in the epithelium lining the choroid plexus. In the E15 fetus, very strong labeling was seen in the liver, heart, and trigeminal ganglion, with less intense labeling in the brain and other tissues having more moderate labeling. Administration of 2% saline as drinking water resulted in a marked increase in hexokinase I mRNA in the magnocellular neurons of the supraoptic and paraventricular nuclei. In summary, the results show extensive neuronal distribution of hexokinase I mRNA with regional differences in the expression pattern.     

In situ mRNA hybridization study of the distribution of choline acetyltransferase in the human brain

We examined the distribution of choline acetyltransferase (ChAT) mRNA in the brain of six autopsied individuals by in situ hybridization with -labeled human ChAT riboprobes. Neurons containing hybridization signal for ChAT mRNA were observed in the nucleus of the diagonal band of Broca, the basal nucleus of Meynert, the caudate nucleus, the putamen, the pedunculopontine tegmental nucleus, the laterodorsal tegmental nucleus, the parabigeminal nucleus, the oculomotor nucleus and the trochlear nucleus. These findings were in good agreement with previous ChAT-immunohistochemical data. In contrast, labeled neurons were not observed in the medial septal and medial habenular nuclei, in which previously ChAT-immunoreactive neurons have been identified in many mammalian species, including the human. An unexpected result of the present study was the demonstration of neurons with ChAT mRNA signal in restricted areas of the human cerebral cortex.     

Distribution of vesicular glutamate transporter 2 in auditory and song control brain regions in the adult zebra finch (Taeniopygia guttata)

The songbird brain has a system of interconnected nuclei that are specialized for singing and song learning. Wada et al. (2004; J. Comp. Neurol. 476:44–64) found a unique distribution of the mRNAs for glutamate receptor subunits in the song control brain areas of songbirds. In conjunction with data from electrophysiological studies, these finding indicate a role for the glutamatergic neurons and circuits in the song system. This study examines vesicular glutamate transporter 2 (VGLUT2) mRNA and protein expression in the zebra finch brain, particularly in auditory areas and song nuclei. In situ hybridization assays for VGLUT2 mRNA revealed high levels of expression in the ascending auditory nuclei (magnocellular, angular, and laminar nuclei; dorsal part of the lateral mesencephalic nucleus; ovoidal nucleus), high or moderate levels of expression in the telencephalic auditory areas (cudomedial mesopallium, field L, caudomedial nidopallium), and expression in the song nuclei (HVC, lateral magnocellular nucleus of the anterior nidopallium, robust nucleus of the arcopallium), where levels of expression were greater than in the surrounding brain subdivisions. Area X did not show expression of VGLUT2 mRNA. Nuclei in the descending motor pathway (dorsomedial nucleus of the intercollicular complex, retroambigual nucleus, tracheosyringeal motor nucleus of the hypoglossal nerve) expressed VGLUT2 mRNA. The target nuclei of VGLUT2 mRNA‐expressing nuclei showed immunoreactivity for VGLUT2 as well as hybridization signals for the mRNA of glutamate receptor subunits. The present findings demonstrate the origins and targets of glutamatergic neurons and indicate a central role for glutamatergic circuits in the auditory and song systems in songbirds. J. Comp. Neurol. 522:2129–2151, 2014. © 2013 Wiley Periodicals, Inc.     

Organization of the auditory brainstem in a lizard, Gekko gecko. I. Auditory nerve, cochlear nuclei, and superior olivary nuclei

We used tract tracing to reveal the connections of the auditory brainstem in the Tokay gecko (Gekko gecko). The auditory nerve has two divisions, a rostroventrally directed projection of mid- to high best-frequency fibers to the nucleus angularis (NA) and a more dorsal and caudal projection of low to middle best-frequency fibers that bifurcate to project to both the NA and the nucleus magnocellularis (NM). The projection to NM formed large somatic terminals and bouton terminals. NM projected bilaterally to the second-order nucleus laminaris (NL), such that the ipsilateral projection innervated the dorsal NL neuropil, whereas the contralateral projection crossed the midline and innervated the ventral dendrites of NL neurons. Neurons in NL were generally bitufted, with dorsoventrally oriented dendrites. NL projected to the contralateral torus semicircularis and to the contralateral ventral superior olive (SOv). NA projected to ipsilateral dorsal superior olive (SOd), sent a major projection to the contralateral SOv, and projected to torus semicircularis. The SOd projected to the contralateral SOv, which projected back to the ipsilateral NM, NL, and NA. These results suggest homologous patterns of auditory connections in lizards and archosaurs but also different processing of low- and high-frequency information in the brainstem.     

In situ hybridization localization of choline acetyltransferase mRNA in adult rat brain and spinal cord

The cellular distribution of choline acetyltransferase (ChAT) mRNA within the adult rat central nervous system was evaluated using in situ hybridization. In forebrain, hybridization of a ³⁵S-labeled rat ChAT cRNA densely labeled neurons in the well-characterized basal forebrain cholinergic system including the medial septal nucleus, diagonal bands of Broca, nucleus basalis of Meynert and substantia innominata, as well as in the striatum, ventral pallidum, and olfactory tubercle. A small number of lightly labeled neurons were distributed throughout neocortex, primarily in superficial layers. No cellular labeling was detected in hippocampus. In the diencephalon, dense hybridization labeled neurons in the ventral aspect of the medial habenular nucleus whereas cells in the lateral hypothalamic area and supramammillary region were more lightly labeled. Hybridization was most dense in neurons of the motor and autonomic cranial nerve nuclei including the oculomotor, Edinger-Westphal, and trochlear nuclei of the midbrain, the abducens, superior salivatory, trigeminal, facial and accessory facial nuclei of the pons, and the hypoglossal, vagus, and solitary nuclei and nucleus ambiguus of the medulla. In addition, numerous cells in the pedunculopontine and laterodorsal tegmental nuclei, the ventral nucleus of the lateral lemniscus, the medial and lateral divisions of the parabrachial nucleus, and the medial and lateral superior olive were labeled. Occasional labeled neurons were distributed in the giantocellular, intermediate, and parvocellular reticular nuclei, and the raphe magnus nucleus. In the medulla, light to moderately densely labeled cells were scattered in the nucleus of Probst's bundle, the medial vestibular nucleus, the lateral reticular nucleus, and the raphe obscurus nucleus. In spinal cord, the cRNA densely labeled motor neurons of the ventral horn, and cells in the intermediolateral column, surrounding the central canal, and in the spinal accessory nucleus. These results are in good agreement with reports of the immunohistochemical localization of ChAT and provide further evidence that cholinergic neurons are present within neocortex but not hippocampus.     

Localization of two high-threshold potassium channel subunits in the rat central auditory system

The firing pattern of auditory neurons is determined in part by the type of voltage-sensitive potassium channels expressed. The expression patterns for two high-threshold potassium channels, Kv3.1 and Kv3.3, that differ in inactivation properties were examined in the rat auditory system. The positive activation voltage and rapid deactivation kinetics of these channels provide rapid repolarization of action potentials with little effect on action potential threshold. In situ hybridization experiments showed that Kv3.3 mRNA was highly expressed in most auditory neurons in the rat brainstem, whereas Kv3.1 was expressed in a more limited population of auditory neurons. Notably, Kv3.1 mRNA was not expressed in neurons of the medial and lateral superior olive and a subpopulation of neurons in the ventral nucleus of the lateral lemniscus. These results suggest that Kv3.3 channels may be the dominant Kv3 subfamily member expressed in brainstem auditory neurons and that, in some auditory neurons, Kv3.1 and Kv3.3 may coassemble to form functional channels. The localization of Kv3.1 protein was examined immunohistochemically. The distribution of stained somata and neuropil varied across auditory nuclei and correlated with the distribution of Kv3.1 mRNA-expressing neurons and their terminal arborizations, respectively. The intensity of Kv3.1 immunoreactivity varied across the tonotopic map in the medial nucleus of the trapezoid body with neurons responding best to high-frequency tones most intensely labeled. Thus, auditory neurons may vary the types and amount of K(+) channel expression in response to synaptic input to subtly tune their firing properties.     

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.     

Different subthreshold mechanisms underlie song selectivity in identified HVc neurons of the zebra finch.

Songbirds learn and maintain their songs via auditory experience. Neurons in many telencephalic nuclei important to song production and development are song selective, firing more to forward auditory playback of the bird's own song (BOS) than to reverse BOS or conspecific songs. Elucidating circuits that generate these responses can localize where auditory experience influences vocalization, bridging cellular and systems analyses of song learning. Song-selective responses in many song nuclei, including the vocal premotor nucleus robustus archistriatalis (RA) and the basal ganglia homolog area X, are thought to originate in nucleus HVc (used as a proper name), which contains interneurons and relay cells that innervate either RA or area X. Previous studies indicated that only X-projecting neurons have auditory responses, leaving open the source of RA's auditory input and the degree to which song selectivity may be refined in HVc. Here, in vivo intracellular recordings from morphologically and electrophysiologically identified HVc neurons revealed that both relay cell types fire song-selectively. However, their firing arises via markedly different subthreshold processes, and only X-projecting neurons appear to be sites for auditory refinement. RA-projecting neurons exhibited purely depolarizing subthreshold responses that were highly song selective and that were excitatory. In contrast, subthreshold responses of X-projecting neurons included less-selective depolarizing and highly selective hyperpolarizing components. Within individual birds, these BOS-evoked hyperpolarizations closely matched interneuronal firing, suggesting that HVc interneurons make restricted inputs onto X-projecting neurons. Because of the two relay cell types' subthreshold differences, factors affecting their resting membrane potentials could enable them to transmit distinct song representations to their targets.     

Calcitonin gene-related peptide immunoreactive cells and fibers in forebrain vocal and auditory nuclei of the budgerigar (Melopsittacus undulatus).

The distributions of calcitonin gene-related peptide (CGRP) immunoreactive neurons and fibers were mapped within forebrain vocal control and auditory nuclei of a vocal learning psittacine species, the budgerigar (Melopsittacus undulatus). Immunoreactivity was exhibited by telencephalic nuclei previously associated with vocal control pathways on the basis of both tract tracing studies and gene mapping: the central nucleus of the anterior archistriatum (AAc), central nucleus of the lateral neostriatum (NLc), magnocellular nucleus the lobus parolfactorius (LPOm), the oval nucleus of the ventral hyperstiratum (HVo) and the medial division of the oval nucleus of the anterior neostriatum (NAom). The main body of NAo also contained an exceptionally high density of immunoreactive fibers. In contrast to the condition in oscine songbirds, CGRP-positive neuronal somata were not present in any telencephalic vocal control nucleus. CGRP-positive somata were present, however, in diencephalic cell groups that included the shell region of the nucleus ovoidalis (Ov), the nucleus dorsolateralis posterior (DLP) and a region of the ventral thalamus that was retrogradely labeled by tracer deposits into HVo and AAc. CGRP immunoreactive fibers were observed within auditory areas of the telencephalon including Field L and the neostriatum intermedium pars dorsolateralis. The likely sources of these fibers are CGRP-positive neurons within the Ov shell and DLP.     

Expression of AMPA receptor subunit flip/flop splice variants in the rat auditory brainstem and inferior colliculus

The expression of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor subunit mRNAs and their flip/flop splice variants was evaluated in the rat auditory brainstem and inferior colliculus employing in situ hybridization with radiolabeled oligonucleotide probes. A differential expression of AMPA receptor subunits in auditory nuclei was observed. In general, neurons in all nuclei of the auditory brainstem express high levels of GluR-C flop and GluR-D flop mRNA, but low to very low levels of GluR-A and GluR-B mRNA. The strongest GluR-C and -D flop expression is found in the ventral and medial part of the anteroventral cochlear nucleus, the posteroventral cochlear nucleus, and the medial and the lateral superior olive. These nuclei are part of the binaural auditory pathway which is important for sound localization in space. In contrast, neurons in the central nucleus of the inferior colliculus express high levels of GluR-B flip but only low levels of the other AMPA receptor subunits. From our data, we conclude that neurons of nuclei involved in binaural processing exhibit a specific "auditory AMPA receptor" which consists primarily of GluR-C flop and -D flop and often lacks GluR-B subunits; this indicates fast kinetics and high Ca(2+) permeability of AMPA receptor currents. In contrast, neurons in the central nucleus of the inferior colliculus contain large amounts of GluR-B flip subunits resulting in Ca(2+) impermeable AMPA receptors with slow kinetics.     

Expression of androgen receptor mRNA in zebra finch song system: developmental regulation by estrogen

By using improved methods for in situ hybridization to detect expression of androgen receptor (AR) mRNA, the distribution of expression was mapped in the adult male zebra finch brain. In the neural song circuit, robust expression was found in area X of the lobus parolfactorius (LPO) as well as in other song regions previously reported. Expression was also found in many areas of the hypothalamus and dorsal thalamic nuclei, nucleus intercollicularis and ventricular areas of the midbrain, cerebellar Purkinje and granule cells, the hyperstriatum, medial neostriatum, medial LPO, and archistriatum. In juvenile males, AR mRNA expression was first detected in nucleus high vocal center (HVC) at posthatch day 9 (P9), in area X at P9-P11, and in the region of the robust nucleus (RA) in the medial archistriatum by P7. Estrogen treatment of hatchling females caused an increase in the expression of AR mRNA in HVC and area X by P11, whereas treatment of hatchling males with the aromatase inhibitor fadrozole decreased the expression of AR mRNA at P11. The present results indicate that masculine development of AR expression begins in area X and HVC before they are thought to be synaptically connected, suggesting that different song nuclei initiate sexual differentiation independently of transsynaptic masculinizing influences. The present results suggest that estrogen is necessary for full masculine AR expression in the song system and that the estrogenic regulation of AR contributes to subsequent differential actions of androgen in male and female song nuclei.     

Midbrain acoustic circuitry in a vocalizing fish

The mapping of auditory circuitry and its interface with vocal motor systems is essential to the investigation of the neural processing of acoustic signals and its relationship to sound production. Here we delineate the circuitry of a midbrain auditory center in a vocal fish, the plainfin midshipman. Biotin injections into physiologically identified auditory sites in nucleus centralis (NC) in the torus semicircularis show a medial column of retrogradely filled neurons in the medulla mainly in a dorsomedial division of a descending octaval nucleus (DO), dorsal and ventral divisions of a secondary octaval nucleus (SO), and the reticular formation (RF) near the lateral lemniscus. Biotin-filled neurons are also located at midbrain-pretectal levels in a medial pretoral nucleus. Terminal fields are identified in the medulla (ventral SO, RF), isthmus (nucleus praeeminentialis), midbrain (nucleus of the lateral lemniscus, medial pretoral nucleus, contralateral NC, tectum), diencephalon (lateral preglomerular, central posterior, and anterior tuber nuclei), and telencephalon (area ventralis). The medial column of toral afferent neurons is adjacent to and overlapping the positions of DO and SO neurons shown previously to be linked to the vocal pacemaker circuitry of the medulla. Midshipman are considered "hearing generalists" because they lack the peripheral adaptations of "specialists" that enhance the detection of the pressure component of acoustic signals. Whereas the results indicate a general pattern of acoustic circuitry similar to that of specialists, they also show central adaptations, namely, a vocal-acoustic interface in DO and SO related to this species' vocal abilities.