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L W Swanson

Publications and source records attributed to L W Swanson.

At least 19 recordsLinked to original sources
PubMed1992

The dorsal premammillary nucleus: an unusual component of the mammillary body.

The results of anterograde and retrograde axonal transport experiments in the rat indicate that the dorsal premammillary nucleus (PMd) gives rise to a branched pathway ending in the anterior thalamic group and brainstem, like the medial and lateral mammillary nuclei. However, unlike these nuclei, the ascending PMd projection courses through and to the anterior hypothalamic nucleus, and the descending PMd projection ends in the periaqueductal gray, superior colliculus, and adjacent parts of the reticular formation. Also unlike the traditional mammillary nuclei, the PMd does not receive a direct input from the columns of the fornix; instead, it receives a bilateral input from the anterior hypothalamic nucleus, which in turn receives inputs from areas related to the prefrontal cortex, amygdala, and hippocampus. The results provide interesting perspectives on the organization of medial hypothalamic circuits underlying the goal-oriented behaviors associated with hunger, thirst, and reproduction.

Animals↗
PubMed1992

Connections of the posterior nucleus of the amygdala.

The connections of a relatively homogeneous band of neurons in the caudal amygdala have been examined with anterograde and retrograde axonal tracing methods in the rat. This region, called here the posterior nucleus of the amygdala (PA), corresponds in part to an area that has been referred to as the cortico-amygdaloid transition area, posterior part of the medial nucleus of the amygdala, amygdalo-hippocampal transition area, and posteromedial basal nucleus. Experiments with fluorogold and phaseolus vulgaris leucoagglutinin (PHAL) indicate that the major neuronal input to the PA arises in the ventral premammillary nucleus, and that substantial projections also arise in olfactory-related areas such as the medial nucleus of the amygdala, bed nucleus of the accessory olfactory tract, and posterior cortical nucleus of the amygdala, as well as in the ventral subiculum and adjacent parts of hippocampal field CA1. Other seemingly minor inputs, including cholinergic fibers from the substantia innominata, dopaminergic fibers from the ventral tegmental area, and serotoninergic fibers from the dorsal nucleus of the raphe, were also identified. The efferent projections of the PA as determined with the PHAL method appear to follow five major routes: 1) a relatively small group of laterally directed fibers innervates the dorsal endopiriform nucleus, and a few of these fibers reach cortical area TR and the lateral entorhinal area; 2) another small group of fibers courses medially to innervate the ventral subiculum and adjacent parts of field CA1; 3) many fibers course ventrally to innervate the outer molecular layer of the medial part of the posterior cortical nucleus of the amygdala; 4) a moderate group of fibers courses rostrally to innervate primarily the posterodorsal part of the medial nucleus of the amygdala, although some fibers continue on to end less densely in rostral parts of the medial nucleus of the amygdala before leaving the amygdala through the ansa peduncularis; and 5) the major output of the PA courses through the stria terminalis. One branch of this pathway massively innervates the principal nucleus of the bed nuclei of the stria terminalis before entering the medial hypothalamus, where it ends massively in the anteroventral periventricular and medial preoptic nuclei, ventrolateral part of the ventromedial nucleus and adjacent parts of the basal lateral hypothalamic area, and ventral premammillary nucleus. The other branch sends fibers to the ventral lateral septal nucleus, nucleus accumbens, olfactory tubercle, and infralimbic area of the prefrontal cortex.(ABSTRACT TRUNCATED AT 400 WORDS)

Amygdala↗
PubMed1992

Projections of the ventral subiculum to the amygdala, septum, and hypothalamus: a PHAL anterograde tract-tracing study in the rat.

The projections of the ventral subiculum are organized differentially along the dorsoventral (or septotemporal) axis of this cortical field, with more ventral regions playing a particularly important role in hippocampal communication with the amygdala, bed nuclei of the stria terminalis (BST), and rostral hypothalamus. In the present study we re-examined the projection of the ventral subiculum to these regions with the Phaseolus vulgaris leucoagglutinin (PHAL) method in the rat. The results confirm and extend earlier conclusions based primarily on the autoradiographic method. Projections from the ventral subiculum course either obliquely through the angular bundle to innervate the amygdala and adjacent parts of the temporal lobe, or follow the alveus and fimbria to the precommissural fornix and medial corticohypothalamic tract. The major amygdalar terminal field is centered in the posterior basomedial nucleus, while other structures that appear to be innervated include the piriformamygdaloid area, the posterior basolateral, posterior cortical, posterior, central, medial, and intercalated nuclei, and the nucleus of the lateral olfactory tract. Projections from the ventral subiculum reach the BST mainly by way of the precommissural fornix, and provide rather dense inputs to the anterodorsal area as well as the transverse and interfascicular nuclei. The medial corticohypothalamic tract is the main route taken by fibers from the ventral subiculum to the hypothalamus, where they innervate the medial preoptic area, "shell" of the ventromedial nucleus, dorsomedial nucleus, ventral premammillary nucleus, and cell-poor zone around the medial mammillary nucleus. We also observed a rather dense terminal field just dorsal to the suprachiasmatic nucleus that extends dorsally and caudally to fill the subparaventricular zone along the medial border of the anterior hypothalamic nucleus and ventrolateral border of the paraventricular nucleus. The general pattern of outputs to the hypothalamus and septum is strikingly similar for the ventral subiculum and suprachiasmatic nucleus, the endogenous circadian rhythm generator.

Amygdala↗
PubMed1992

Projections of the ventral premammillary nucleus.

The projections of the ventral premammillary nucleus (PMv) have been examined with the Phaseolus vulgaris leucoagglutinin (PHAL) method in adult male rats. The results indicate that the nucleus gives rise to two major ascending pathways and a smaller descending pathway. One large ascending pathway terminates densely in most regions of the periventricular zone of the hypothalamus, with the notable exception of the suprachiasmatic, suprachiasmatic preoptic, and median preoptic nuclei. This pathway is in a position to influence directly many cell groups known to regulate anterior pituitary function. The second large pathway ascends through the medial zone of the hypothalamus and densely innervates the ventrolateral part of the ventromedial nucleus and adjacent basal parts of the lateral hypothalamic area, medial preoptic nucleus, principal nucleus of the bed nuclei of the stria terminalis, ventral lateral septal nucleus, posterodorsal part of the medial nucleus of the amygdala, posterior nucleus, and immediately adjacent regions of the posterior cortical nucleus of the amygdala. It is already known that these regions are major components of the sexually dimorphic circuit, and, interestingly, that they provide the major neural inputs to the PMv. The smaller descending projection from the PMv seems to innervate preferentially the posterior hypothalamic nucleus, although a small number of fibers appear to end in the tuberomammillary nucleus, supramammillary nucleus, specific regions of the medial mammillary nucleus, interfascicular nucleus, interpeduncular nucleus, periaqueductal gray, dorsal nucleus of the raphe, laterodorsal tegmental nucleus, Barrington's nucleus, and locus coeruleus. Relatively sparse terminal fields associated with ascending fibers were also observed in the dorsomedial nucleus of the hypothalamus; in the nucleus reuniens, parataenial nucleus, paraventricular nucleus of the thalamus, and mediodorsal nucleus; in the central nucleus of the amygdala, anterodorsal part of the medial nucleus of the amygdala, posterior part of the basomedial nucleus of the amygdala; and in the ventral subiculum and adjacent parts of hippocampal field CA1, and the infralimbic and prelimbic areas of the medial prefrontal cortex. Taken as a whole, the evidence suggests that the PMv receives two major inputs--one from the sexually dimorphic circuit, and the other from the blood in the form of gonadal steroid hormones--and gives rise to two major outputs: one (perhaps feed-forward) to the neuroendocrine (periventricular) zone of the hypothalamus, and the other (perhaps feed-back) to the sexually dimorphic circuit.

Animals↗
PubMed1992

Brain 4: a novel mammalian POU domain transcription factor exhibiting restricted brain-specific expression.

The POU domain gene family of transcription factors share a conserved bipartite DNA binding domain, and exhibit distinct temporal and spatial patterns of expression during development, particularly in the forebrain. A cDNA encoding a new member of the POU-III class of the POU domain gene family, referred to as Brn-4, was isolated from a rat hypothalamic cDNA library. Like other mammalian POU-III genes previously characterized (Brn-1, Brn-2, Tst-1), Brn-4 transcripts are initially widely expressed at all levels of the developing neural tube, but in contrast to other previously described POU-III genes, are subsequently restricted to only a few regions of the adult forebrain, including the supraoptic and paraventricular nuclei of the hypothalamus. Brn-4 was shown to bind to DNA sequences containing the octamer motif and to trans-activate promoters containing this DNA binding motif, based on the actions of a unique N-terminal information. This ontogenic pattern of Brn-4 expression in concert with that of Oct-2 and Pit-1, indicates that certain POU domain genes potentially exert their primary functions widely during early neural development, and in a very limited set of neurons in the mature brain.

Amino Acid Sequence↗
PubMed1991

Enkephalin immunoreactivity and messenger RNA in a discrete projection from the nucleus of the solitary tract to the nucleus ambiguous in the rat.

Previous work described in the rat a circumscribed, partly somatostatinergic, interneuronal projection from the esophageal afferent part of the nucleus of the solitary tract (NTSc) to esophageal motor neurons in the compact formation of the nucleus ambiguous (NAcf: Cunningham and Sawchenko, J Neurosci 9:1668, 1989). In the present study, axonal transport, immunohistochemical and in situ hybridization histochemical techniques were used to determine whether enkephalin (ENK), a peptide known to be expressed in a number of somatostatin-containing medullary cell groups, is also expressed in the projection from the NTSc to the NAcf. The results may be summarized as follows: 1) cells immunoreactive (IR) for prepro-enkephalin (ppENK)-derived peptides were found in the NTSc in colchicine-pretreated animals; in untreated animals, a dense ENK-IR terminal field was observed in the NAcf: sections stained with antisera against dynorphin-related peptides showed sparse staining in both regions; 2) signal indicating the presence of ppENK messenger RNA (mRNA) was found over the NTSc, including over a majority of cells identified using a retrograde tracing technique as projecting to the region of the NAcf; the signal for ppENK mRNA signal was greater than that for prepro-somatostatin (ppSS) in the NTSc; 3) a combined anterograde tracing-immunohistochemical technique demonstrated a strong correspondence between the distribution of inputs from the NTS to the NAcf, and the distribution of endogenous ENK-IR varicosities; in addition, leucine (L)-ENK-IR was found in an appreciable number of varicosities in the NAcf that had been anterogradely labeled from the NTSc; 4) unilateral electrolytic lesions of the rostromedial NTS, which included the central subnucleus, virtually eliminated ENK-IR in the ipsilateral NAcf, while staining on the contralateral side was unaffected. Taken together, these studies provide evidence that ppENK- and ppSS-derived peptides are expressed in the pathway from the NTSc to the NAcf, a pathway thought to play a role in the reflex control of esophageal peristalsis.

Animals↗
PubMed1991

Enkephalin mRNA production by cochlear and vestibular efferent neurons in the gerbil brainstem.

Preproenkephalin mRNA production by efferent neurons projecting to the gerbil inner ear was assessed using combined in situ hybridization and retrograde labeling with fluorescent tracers. Virtually all vestibular efferent neurons were positive for preproenkephalin mRNA. Of the cochlear efferents, one-half of the medial olivocochlear neurons were positive for enkephalin. All lateral olivocochlear neurons were negative for enkephalin. The results suggest that there are two, biochemically distinct subpopulations of medial olivocochlear efferents in the gerbil.

Animals↗
PubMed1991

TEF, a transcription factor expressed specifically in the anterior pituitary during embryogenesis, defines a new class of leucine zipper proteins.

We have identified and characterized a new member of the leucine zipper (bZIP) gene family of transcription factors, thyrotroph embryonic factor (TEF). Analysis of the ontogeny of TEF gene expression reveals the presence of TEF transcripts, beginning on embryonic day 14, only in the region of the rat anterior pituitary gland in which thyrotrophs arise. This pattern of gene expression corresponds temporally and spatially to the onset of thyroid-stimulating hormone (TSH beta) gene expression, which defines the thyrotroph phenotype. Coupled with this observation, we find that TEF can bind to and trans-activate the TSH beta promoter. In contrast to this restricted pattern of expression during embryogenesis, TEF transcripts appear in several tissues in the mature organism. We propose that TEF belongs to a new class of bZIP proteins on the basis of the unique homology between TEF and another member of the bZIP gene family, the albumin D box-binding protein (DBP). TEF and DBP transcripts are coexpressed in a pituitary cell line, and these two proteins can readily form heterodimers. The DNA-binding and dimerization domains of TEF correspond to those found in other bZIP proteins. We have however, identified a cluster of basic amino acids, found only in TEF and DBP, that is necessary for the proper DNA-binding site specificity of TEF. A major trans-activation domain of TEF resides outside the region of homology to other bZIP proteins. These data are consistent with a role for a member of a new class of bZIP transcription factors in activating gene expression in the developing thyrotroph.

Amino Acid Sequence↗
PubMed1991

Tst-1, a member of the POU domain gene family, binds the promoter of the gene encoding the cell surface adhesion molecule P0.

Tst-1, a member of the POU domain gene family, is expressed in specific neurons and in myelinating glia in the mammalian nervous system. Bacterially expressed Tst-1 binds specifically to the promoter of the gene encoding myelin protein P0, a Schwann cell surface adhesion molecule. In cotransfection assays, Tst-1 can specifically repress the P0 promoter. The N-terminal part of Tst-1 protein is highly glycine- and alanine-rich, a structural feature shared by the helix-loop-helix protein TFEB.

Amino Acid Sequence↗
PubMed1990

Dwarf locus mutants lacking three pituitary cell types result from mutations in the POU-domain gene pit-1.

Mutations at the mouse dwarf locus (dw) interrupt the normal development of the anterior pituitary gland, resulting in the loss of expression of growth hormone, prolactin and thyroid-stimulating hormone, and hypoplasia of their respective cell types. Disruptions in the gene encoding the POU-domain transcription factor, Pit-1, occur in both characterized alleles of the dwarf locus. The data indicate that Pit-1 is necessary for the specification of the phenotype of three cell types in the anterior pituitary, and directly link a transcription factor to commitment and progression events in mammalian organogenesis.

Amino Acid Sequence↗
PubMed1990

The distribution of mRNA encoded by a new member of the neuronal nicotinic acetylcholine receptor gene family (alpha 5) in the rat central nervous system.

The cellular localization of transcripts for a new putative agonist-binding subunit of the neuronal nicotinic acetylcholine receptor (nAChR), alpha 5, was examined using in situ hybridization in the rat central nervous system (CNS), alpha 5 subunit mRNA was localized to a small number of regions when compared with two of the other known agonist-binding subunits, alpha 3 and alpha 4, alpha 5 mRNA is expressed at relatively high levels in neurons of the subiculum (pyramidal layer), presubiculum and parasubiculum (layers IV and VI), which are components of the hippocampal formation, in the substantia nigra pars compacta and ventral tegmental area, in the interpeduncular nucleus, and in the dorsal motor nucleus of the vagus nerve. Moderate hybridization signals were detected in neurons of the isocortex (layer VIb), anterior olfactory nucleus, trigeminal ganglion, superior olivary complex, nucleus of the solitary tract, and area postrema. No hybridization above background levels was seen in the amygdala, septum, thalamus, hypothalamus, or cerebellum. These results suggest that the alpha 5 subunit differs from other known agonist-binding subunits in its distribution.

Animals↗
PubMed1990

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)

Animals↗
PubMed1990

RNA levels of neuronal nicotinic acetylcholine receptor subunits are differentially regulated in axotomized facial motoneurons: an in situ hybridization study.

In situ hybridization histochemistry using complementary RNA probes revealed that alpha 3 and beta 2 neuronal nicotinic acetylcholine receptor subunit mRNAs were expressed in 12% and 40% of facial motoneurons of the rat, respectively. The alpha 3 subunit mRNA signals disappeared in response to axotomy, whereas the beta 2 subunit mRNA signal was remarkably enhanced, suggesting that mRNA levels of receptor subunits are differentially regulated in axotomized motoneurons.

Animals↗
PubMed1990

Localization of neuropeptide precursor-synthesizing neurons in the rat olfactory bulb: a hybridization histochemical study.

The distribution of seven kinds of neuropeptide precursor mRNA-containing neurons was investigated in the rat main and accessory olfactory bulbs, where various peptides have previously been identified immunohistochemically, by means of in situ hybridization using [35S]cRNA probes. In the glomerular layer, numerous preprothyrotropin-releasing hormone mRNA-expressing neurons, moderate numbers of preprosomatostatin and preproenkephalin A neurons, and a small number of preprocholecystokinin neurons were detected. In the external plexiform layer, numerous medium sized preprocholecystokinin and preprocorticotropin-releasing hormone neurons, and a small number of beta-preprotachykinin A neurons were observed. In addition, small preprovasoactive intestinal polypeptide and preprothyrotropin-releasing hormone neurons were evenly distributed in the external plexiform layer. Medium to large sized beta-preprotachykinin A neurons formed a thin layer in the mitral cell layer. In the granule cell layer, in addition to numerous small preproenkephalin A neurons, moderate numbers of small beta-preprotachykinin A and preprocorticotropin-releasing hormone neurons, and a small number of preprothyrotropin-releasing hormone neurons, were identified. Large sized preprosomatostatin neurons were located in the deep layer of the granule cell layer. The distribution patterns of these neurons, as a whole, confirmed previous studies based on immunohistochemistry, although peptide precursor mRNA-expressing neurons were far more numerous than those immunoreactive to the respective neuropeptides. Moreover, mRNA-expressing neurons were observed in areas where no immunoreactive neurons had been observed (e.g. preprovasoactive intestinal polypeptide and preprosomatostatin neurons in the mitral cell layer of the assessory olfactory bulb). The distribution patterns were generally similar in the main and accessory olfactory bulbs.

Animals↗
PubMed1990

Pituitary cell phenotypes involve cell-specific Pit-1 mRNA translation and synergistic interactions with other classes of transcription factors.

Development of the anterior pituitary gland involves proliferation and differentiation of ectodermal cells in Rathke's pouch to generate five distinct cell types that are defined by the trophic hormones they produce. A detailed ontogenetic analysis of specific gene expression has revealed novel aspects of organogenesis in this model system. The expression of transcripts encoding the alpha-subunit common to three pituitary glycoprotein hormones in the single layer of somatic ectoderm on embryonic day 11 established that primordial pituitary cell commitment occurs prior to formation of a definitive Rathke's pouch. Activation of Pit-1 gene expression occurs as an organ-specific event, with Pit-1 transcripts initially detected in anterior pituitary cells on embryonic day 15. Levels of Pit-1 protein closely parallel those of Pit-1 transcripts without a significant lag. Unexpectedly, Pit-1 transcripts remain highly expressed in all five cell types of the mature pituitary gland, but the Pit-1 protein is detected in only three cell types--lactotrophs, somatotrophs, and thyrotrophs and not in gonadotrophs or corticotrophs. The presence of Pit-1 protein in thyrotrophs suggests that combinatorial actions of specific activating and restricting factors act to confine prolactin and growth hormone gene expression to lactotrophs and somatotrophs, respectively. A linkage between the initial appearance of Pit-1 protein and the surprising coactivation of prolactin and growth hormone gene expression is consistent with the model that Pit-1 is responsible for the initial transcriptional activation of both genes. The estrogen receptor, which has been reported to be activated in a stereotypic fashion subsequent to the appearance of Pit-1, appears to be capable, in part, of mediating the progressive increase in prolactin gene expression characteristic of the mature lactotroph phenotype. This is a consequence of synergistic transcriptional effects with Pit-1, on the basis of binding of the estrogen receptor to a response element in the prolactin gene distal enhancer. These data imply that both transcriptional and post-transcriptional regulation of Pit-1 gene expression and combinatorial actions with other classes of transcription factors activated in distinct temporal patterns, are required for the mature physiological patterns of gene expression that define distinct cell types within the anterior pituitary gland.

Animals↗
PubMed1990

A family of POU-domain and Pit-1 tissue-specific transcription factors in pituitary and neuroendocrine development.

The anterior pituitary gland provides a model for investigating the molecular basis for the appearance of phenotypically distinct cell types, within an organ, a central question in development. The rat prolactin and growth hormone genes are selectively expressed in distinct cell types (lactotrophs and somatotrophs) of the anterior pituitary gland, which reflect differential mechanisms of gene activation or restriction because of interactions of multiple factors binding to these genes. We find that the pituitary-specific 33,000 dalton transcription factor, Pit-1, normally expressed in somatotrophs, lactotrophs, and thyrotrophs, can bind to and activate both growth hormone and prolactin promoters in vitro at levels even tenfold lower than those normally present in pituitary cells. In the case of the prolactin gene, high levels of expression in transgenic animals required two cis-active regions; a distal enhancer (-1.8 to -1.5 kb) and a proximal region (-422 to +33 bp). Each of these regions alone can direct low levels of fusion gene expression to prolactin-producing cell types in transgenic mice, but a synergistic interaction between these regions is necessary for high levels of expression. The initial appearance of the prolactin transgene expression closely follows the appearance of high levels of Pit-1, but later increases in expression coincident with appearance of mature lactotrophs suggest the operation of additional, critical positive factor(s). Unexpectedly, transgenes containing the distal enhancer removed from its normal context are expressed in both the prolactin-producing lactotrophs and the TSH-producing thyrotrophs, thereby suggesting that sequences flanking this enhancer are necessary to restrict expression to the correct cell type within the pituitary. These data indicate that distinct processes of gene activation and restriction are necessary for the fidelity of cell-type specific expression within an organ. Consistent with this model, we find that lactotroph cell lines that cannot express the growth hormone gene contain high levels of functional Pit-1. We suggest a large, highly related POU-domain gene family, potentially exceeding 100 members, has been conserved and expanded in evolution to meet the increasing requirements for more intricate patterns of cell phenotypes. The POU-domain subgroup of the homeodomain gene family, in concert with other homeodomain proteins and with other classes of transcription factors, is likely to contribute to the establishment of the mammalian neuroendocrine system.

Animals↗