Development of vagal afferent projections circumflex to the obex in the embryonic chick brainstem visualized with voltage-sensitive dye recording

Using voltage-sensitive dye recording, we surveyed neural responses related to the vagus nerve in the embryonic chick brainstem. In our previous studies, we identified four vagus nerve-related response areas in the brainstem. On the stimulated side, they included (1) the nucleus of the tractus solitarius (NTS: the primary sensory nucleus) and (2) the dorsal motor nucleus of the vagus nerve (DMNV), whereas on the contralateral side, they corresponded to (3) the parabrachial nucleus (PBN: the second/higher-ordered nucleus) and (4) the medullary non-NTS region. In the present study, in addition to these areas, we identified another response area circumflex to the obex. The intensity of the optical signal in the response area was much smaller than that in the NTS/DMNV, and the spatio-temporal pattern could be discerned after signal averaging. The conduction rate to the response area was slower than that to the other four areas. Ontogenetically, the response area was distributed on the stimulated side at the 6-day embryonic stage, and it spread into the contralateral side in 7- and 8-day embryonic stages. These distribution patterns were consistent with projection patterns of vagal afferent fibers stained with a fluorescent tracer, suggesting that the response area included a primary sensory nucleus. In comparison with the functional development of the other four response areas, we traced the functional organization of vagus nerve-related nuclei in the embryonic brainstem.

The development of descending projections from the brainstem to the spinal cord in the fetal sheep

Background

Although the fetal sheep is a favoured model for studying the ontogeny of physiological control systems, there are no descriptions of the timing of arrival of the projections of supraspinal origin that regulate somatic and visceral function. In the early development of birds and mammals, spontaneous motor activity is generated within spinal circuits, but as development proceeds, a distinct change occurs in spontaneous motor patterns that is dependent on the presence of intact, descending inputs to the spinal cord. In the fetal sheep, this change occurs at approximately 65 days gestation (G65), so we therefore hypothesised that spinally-projecting axons from the neurons responsible for transforming fetal behaviour must arrive at the spinal cord level shortly before G65. Accordingly we aimed to identify the brainstem neurons that send projections to the spinal cord in the mature sheep fetus at G140 (term = G147) with retrograde tracing, and thus to establish whether any projections from the brainstem were absent from the spinal cord at G55, an age prior to the marked change in fetal motor activity has occurred.

Results

At G140, CTB labelled cells were found within and around nuclei in the reticular formation of the medulla and pons, within the vestibular nucleus, raphe complex, red nucleus, and the nucleus of the solitary tract. This pattern of labelling is similar to that previously reported in other species. The distribution of CTB labelled neurons in the G55 fetus was similar to that of the G140 fetus.

Conclusion

The brainstem nuclei that contain neurons which project axons to the spinal cord in the fetal sheep are the same as in other mammalian species. All projections present in the mature fetus at G140 have already arrived at the spinal cord by approximately one third of the way through gestation. The demonstration that the neurons responsible for transforming fetal behaviour in early ontogeny have already reached the spinal cord by G55, an age well before the change in motor behaviour occurs, suggests that the projections do not become fully functional until well after their arrival at the spinal cord.

Extensive reorganization of primary afferent projections into the gustatory brainstem induced by feeding a sodium-restricted diet during development: less is more

Neural development is especially vulnerable to environmental influences during periods of neurogenesis and rapid maturation. In fact, short periods of environmental manipulations confined to embryonic development lead to significant changes in morphology and function. A guiding principal emerging from studies of sensory systems is that experimentally induced effects are most dramatic in higher neural levels (e.g., cortex) and primarily involve postnatal synaptic refinements. In contrast to other sensory systems, the gustatory system is particularly susceptible to the effects of deprivation much earlier and with profound changes evident in the brainstem. Here we show that feeding pregnant rats a custom diet featuring a low-sodium content for 9 d before the tongue appears in the fetus produces extensive restructuring of the gustatory brainstem. Rats born to mothers fed the custom diet from embryonic day 3 (E3) to E12 have terminal field volumes of the greater superficial petrosal, chorda tympani, and glossopharyngeal nerves at adulthood that are expanded as much as 10 times beyond that found in rats fed a standard rat chow. The widespread alterations are not attributable to increased numbers of nerve cells, increased target size, or obvious changes in peripheral taste function. Moreover, we show that the limited period of feeding the custom diet has much larger effects than if rats were fed the diet to postweaning ages. Our results suggest that early periods of altered experience, especially during nucleus of the solitary tract neurogenesis, leads to a restructuring of the gustatory brainstem, which in turn may impact the control of sensory and homeostatic processes.

Development of the human nucleus of the solitary tract: a cyto- and chemoarchitectural study

The present study investigated the prenatal development of the cyto- and chemoarchitecture of the human nucleus of the solitary tract from 9 to 35 weeks, by using Nissl staining and immunoreactivity to calbindin, calretinin, tyrosine hydroxylase and GAP-43. The nucleus began to gain heterogeneity and show different subnuclei as early as 13 weeks, and approached cytoarchitectural maturation from 21 to 25 weeks. The subnuclear division pattern observed in the fetal nucleus of the solitary tract at 25 weeks was very similar to that of the adult. Neurons immunoreactive to calbindin first appeared in the medial gastrointestinal area of the nucleus at 13 weeks, particularly within a putative gelatinosus subnucleus, while calretinin immunoreactivity during fetal life suggested the possible presence of a central subnucleus. Tyrosine hydroxylase immunoreactive neurons were seen in the medial subdivisions of the nucleus of the solitary tract as early as 13 weeks, but the population continued to increase until 25 weeks. Strong GAP-43 immunoreactivity was also present in the nucleus of the solitary tract at 13 weeks, especially in the dorsolateral and commissural subnuclei, while at 21 weeks there was a significant decline of GAP-43 expression. Results from the chemoarchitectural study showed that the human nucleus of the solitary tract expressed various neurochemical substances at an early developmental age (13 weeks), even before cellular and neuropil maturation was fully attained. Expression of these factors may play an important role in establishment and integration of viscerosensory function in the nucleus.

Glutamatergic synapses in the rat nucleus tractus solitarii develop by direct insertion of calcium-impermeable AMPA receptors and without activation of NMDA receptors

Calcium influxes through ionotropic glutamate receptors (AMPA and NMDA receptors, AMPARs and NMDARs) are considered to be critical for the shaping and refinement of neural circuits during synaptogenesis. Using a combined morphological and electrophysiological approach, we evaluated this hypothesis at the level of the nucleus tractus solitarii (NTS), a brainstem structure that is a gateway for many visceral sensory afferent fibres. We confirmed that in the NTS, the first excitatory synapses appeared at embryonic day 18. We next characterized the biophysical properties of NTS AMPARs. Throughout perinatal development, both evoked and miniature EPSCs recorded in the presence of an NMDAR blocker were insensitive to polyamines and had linear current-voltage relationships. This demonstrated that AMPARs at NTS excitatory synapses were calcium-impermeable receptors composed of a majority of GluR2 subunits. We then investigated the influence of calcium influxes through NMDARs on the development of NTS synaptic transmission. We found that NMDAR expression at synaptic sites did not precede AMPAR expression. Moreover, NMDAR blockade in utero did not prevent the development of AMPAR synaptic currents and the synaptic clustering of GluR2 subunits. Thus, our data support an alternative model of synaptogenesis that does not depend on calcium influxes through either AMPARs or NMDARs. This model may be particularly relevant to the formation of neural networks devoted to basic behaviours required at birth for survival.

Delays in neuronal differentiation in Mash1/Ascl1 mutants

The inactivation of a developmental transcription factor may lead to the complete absence of a specific cell type. More commonly, though, it only partially impairs its generation. The modalities of this partial effect have rarely been documented in any detail. Here, we report a novel function for the bHLH transcription factor Ascl1/Mash1 in the generation of the nucleus of the solitary tract (nTS). In Mash1(-/-) late embryos, the nTS is markedly atrophic. Tracing back the origin of this atrophy, we show that nTS precursors appear in the mutants 1 day later than in the wild type and then accumulate at a slower pace. We also show that the previously reported atrophy of the sympathetic chain in Mash1 mutants is similarly preceded by a delay of 1 to 2 days in the appearance of differentiated ganglionic cells. Finally, we provide evidence that the acceleration imposed by Mash1, regardless of the production of post-mitotic cells, affects differentiation itself, both generic and type-specific.

First localization and biochemical identification of chromogranin B- and secretoneurin-like immunoreactivity in the fetal human vagal/nucleus solitary complex

The human vagal/nucleus solitary complex is a primary visceral relay station and an integrative brain stem area which displays a high density of chromogranin B- and secretoneurin-like immunoreactivity. In this study, we localized and biochemically identified these proteins during prenatal development. At prenatal week 11, 15, 20 and 37, we performed a chromatographic analysis to identify the molecular forms of PE-11, a peptide within the chromogranin B sequence, and secretoneurin, a peptide within secretogranin II. Their localization was studied with immunocytochemistry, and was compared to that of substance P which is well established as a functional neuropeptide in the vagal/nucleus solitary complex. At prenatal week 11, chromogranin B-, secretoneurin- and substance P-like immunoreactivities were detected consisting of varicosities, varicose fibers and single cells. At the same time, PE-11 and secretoneurin appeared as a single peak in chromatographic analysis. Prohormone convertases PC1- and PC2-like immunoreactivities were also present at week 11. In general, the density for each peptide increased during later fetal stages with the highest density at week 37. These results demonstrate that each chromogranin peptide is expressed during human fetal life in neurons of the vagal/nucleus solitary complex indicating that these peptides could be important during prenatal development.

Optical detection of convergent projections in the embryonic chick NTS

Multiple-site optical recording of neural activity was performed in the nucleus of the tractus solitarius (NTS) of the chick embryo with stimulation of the glossopharyngeal nerve (N. IX) and vagus nerve (N. X). We measured the amplitudes of the optical signals related to glutamate-mediated excitatory postsynaptic responses, and calculated the ratio of the signal evoked by simultaneous N. IX/N. X stimulation to the signal obtained after mathematical summation of the individual N. IX and N. X responses. The ratio was significantly lower than 100% in the rostral region of the NTS, in which postsynaptic responses were elicited by both N. IX and N. X stimulations. This result means that there is a convergence of visceral inputs via the N. IX and N. X in the embryonic chick NTS. The existence of the convergence suggests that the NTS performs complex integration of information from multiple sensory inputs from the early stages of embryogenesis.

Optical Mapping Reveals Developmental Dynamics of Mg2+-/APV-Sensitive Components of Glossopharyngeal Glutamatergic EPSPs in the Embryonic Chick NTS

To examine whether there are any differences in functional organization between the glossopharyngeal nerve (N. IX)– and vagus nerve (N. X)–projecting areas in the nucleus of the tractus solitarius (NTS), we performed optical recording of neural responses evoked by N. IX stimulation in 5- to 9-day-old embryonic chick brain stem preparations and compared the results with those in our previous studies concerning the N. X-related NTS. First, we investigated dl-2-amino-5-phosphonovaleric acid (APV)/Mg2+sensitivity of the glutamatergic excitatory postsynaptic potentials (EPSPs) in the N. IX-related NTS. In 7- to 9-day-old preparations, we found regional differences in the degree of both the APV-induced reduction and Mg2+-free–induced enhancement of the EPSPs. We constructed developmental maps of spatial patterns of the APV- and Mg2+-sensitive components and showed that functional expression of the N-methyl-d-aspartate (NMDA) receptor dynamically changed during development. Second, we studied initial expression of synaptic functions in the N. IX-related NTS. In 6-day-old preparations, although action potentials alone were usually detected in normal Ringer solution, small EPSPs were elicited in a Mg2+-free solution. This result suggests that the NMDA receptor–mediated synaptic function is latently generated in the N. IX-related NTS at the 6-day-old embryonic stage and that external Mg2+regulates the onset of synaptic functions. Developmental patterns of APV/Mg2+sensitivity and the stage of initial expression of the glossopharyngeal EPSP were similar to those of the N. X, suggesting that the developmental sequence of the synaptic function in the NTS is the same for the N. IX- and N. X-related NTS.

Phox2bcontrols the development of peripheral chemoreceptors and afferent visceral pathways

We report that the afferent relays of visceral (cardiovascular, digestive and respiratory) reflexes, differentiate under the control of the paired-like homeobox gene Phox2b: the neural crest-derived carotid body, a chemosensor organ, degenerates in homozygous mutants, as do the three epibranchial placode-derived visceral sensory ganglia (geniculate, petrosal and nodose), while their central target, the nucleus of the solitary tract,which integrates all visceral information, never forms. These data establish Phox2b as an unusual `circuit-specific' transcription factor devoted to the formation of autonomic reflex pathways. We also show that Phox2b heterozygous mutants have an altered response to hypoxia and hypercapnia at birth and a decreased tyrosine hydroxylase expression in the petrosal chemosensory neurons, thus providing mechanistic insight into congenital central hypoventilation syndrome, which is associated with heterozygous mutations in PHOX2B.

Cardiovascular regulation and expressions of NO synthase-tyrosine hydroxylase in nucleus tractus solitarius of ovine fetus

The purpose of this study was to examine cardiovascular responses to fourth cerebral ventricle (4V) administration of nitroglycerin (NTG) or an inhibitor of nitric oxide (NO) synthase (NOS) in the near-term ovine and to determine whether, during birth, neuronal NOS (nNOS) is induced in noradrenergic A1 neurons in the medial nucleus tractus solitarius (mNTS). In chronically instrumented fetal sheep, 4V injection of NTG (1.2 nmol), an NO donor, produced an arterial blood depressor and a moderate decrease in heart rate. Arterial blood pressure is increased by 4V administration of NG-nitro-L-arginine methyl ester (10 nmnol), an inhibitor of NOS, in fetuses. Sections of the medulla from fetuses and newborn lambs were examined by using immunolabeling with tyrosine hydroxylase (TH) antibody combined with NADPH diaphorase (NADPHd) histochemistry, a marker of nNOS activity. The NADPHd-positive cells and TH-positive cells containing NADPHd reactivity were significantly increased in the mNTS of newborns compared with the fetuses. The results suggest that during birth, there is upregulation of NADPHd/nNOS in the noradrenergic neurons of mNTS resulting in a centrally mediated reduction of fetal arterial blood pressure.

Expression of neuropeptide FF, prolactin-releasing peptide, and the receptor UHR1/GPR10 genes during embryogenesis in the rat

Recently, several RF-amide peptides have been identified in mammals. These peptides have a similar C-terminal RF-motif and share some G-protein coupled receptors. Neuropeptide FF (NPFF) and prolactin-releasing peptide (PrRP) are expressed in the same brain areas in the adult rat and act both in prolactin release and cardiovascular regulation. Here, we characterized the embryonal expression from embryonal day 14 to postnatal day 0 of both peptide mRNAs and the mRNA distribution of UHR1/GPR10-like receptor by using in situ hybridization (ISH) and quantitative reverse transcriptase-polymerase chain reaction. NPFF mRNA was found in the spinal cord, caudal solitary tract nucleus, and surprisingly, in the medullary reticular formation. The only peripheral organs displaying NPFF mRNA expression were the lungs and the spleen. PrRP gene expression was seen in the caudal solitary tract nucleus, medullary reticular formation, pontine isthmus and liver, kidney, and testis. The receptor UHR1/GPR10 gene was expressed consistently in the medullary reticular formation and the adrenal gland but also transiently in several locations. All three genes showed weak but even ISH signal in the pituitary. These findings suggest different roles for the peptides during development and indicate that UHR1/GPR10-like receptor could also bind other ligands in addition to PrRP.

The development of cranial nerve and visceral afferents to the nucleus of the solitary tract in the rat

We have used carbocyanine dye tracing techniques to examine the distribution of afferents from the facial, trigeminal and vagal nerves to the nucleus of the solitary tract (NST) in the developing rat (E13 to P13). Crystals of DiI (1, 1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate) were placed (unilaterally) into the facial or trigeminal ganglia, or into the cervical vagus nerve, and the sections examined with a laser scanning confocal microscope. Inputs from some peripheral structures (tongue, aortic arch, right atrium and lung) to the NST were also analyzed to provide information on the distribution of organ-specific afferents. No afferents were labeled following DiI placement in the above sites at E13. At E14, a few axons from the geniculate ganglion of the facial nerve were present in the NST anlage, but these were restricted to the area adjacent to the solitary tract. These axons began to invade the medial NST at E15. By E17, facial afferent axons had become widespread throughout rostral NST and from E19 the distribution of DiI labeling displayed a morphologically mature pattern. DiI-labeled afferent axons from the trigeminal nerve first emerged into the NST anlage at E14, initially coursing medially to penetrate the ventricular zone. Between E15 and E17, axonal density increased markedly but after E17 became progressively confined to the lateral NST. Axons from the vagus nerve first appeared in the caudal NST as early as E14 and coursed directly into the proliferative zone of the alar plate at all rostrocaudal levels by E15. From E19 through postnatal life, the distribution of vagal afferent axons was essentially stable with particularly dense label in the caudal NST. Cranial nerve afferents to the NST appear to be distributed to appropriate sites from the beginning of ingrowth, with the exception of trigeminal afferents, where some small initial exuberance was found. The terminal fields derived from selected peripheral organs such as lung, right atrium, aortic arch and tongue were also predominantly distributed to appropriate subnuclei from the beginning of ingrowth into the NST, although organ-specific afferent fields appeared to develop dense arbors somewhat later than did individual cranial nerves. Electron microscopy was used to examine regional synapse development in the rat NST. There was some delay between the ingrowth of afferents to the NST (E15) and the first appearance of synaptic thickenings. The earliest synapses were simple (usually) symmetrical membrane thickenings (from E17) and vesicles did not appear until E19. High synaptic density within the C subnucleus appeared during early postnatal life. Synaptic glomeruli, which are a characteristic feature of afferent input to the adult NST, had not developed by birth, indicating that the pre- and perinatal function of the NST must be mediated through simpler, single, axodendritic inputs to NST neurons.

Developmental expression of prolactin releasing peptide in the rat brain: localization of messenger ribonucleic acid and immunoreactive neurons

Prolactin releasing peptide (PrRP) was recently identified as the stimulator of prolactin release from the anterior pituitary. PrRP mRNA is expressed in the medulla oblongata and the hypothalamus in the rat brain. The fibers containing PrRP are widely distributed in the brain, therefore, it was postulated that PrRP may act as a neurotransmitter or neuromodulator as well as an endocrine substance. To clarify the developmental changes in the expression of PrRP during brain development, we examined PrRP in rat fetuses and neonates using in situ hybridization and immunohistochemistry. The PrRP mRNA was expressed in the nucleus of the solitary tract (NTS) at embryonic day 18 (E18) and in the ventral and lateral reticular nucleus (VLRN) of the caudal medulla oblongata at E20. The PrRP mRNA in the hypothalamus was first expressed at postnatal day 13 (P13). Reverse transcription-polymerase chain reaction analysis (RT-PCR) for PrRP revealed that PCR product, a 268 bp band, was detected from either E18 in the medulla or P13 in the hypothalamus. Immunodetection with monoclonal antibody against prepro-PrRP revealed intensive staining of cells in the NTS at E18, in the VLRN at E20 or in the dorsomedial hypothalamus at P13. Immunohistochemistry using monoclonal antibody against mature PrRP at P6 showed PrRP fibers to be distributed in the paraventricular hypothalamic nucleus, periventricular hypothalamic nucleus, medial preoptic area, basolateral amygdaloid nucleus, dorsomedial hypothalamus, ventromedial hypothalamus, periventricular nucleus of the thalamus and bed nucleus of the stria terminalis as previously shown in the adult rat. PrRP fibers were also found in the optic chiasm, dorsal endopiriform nucleus, cingulum, intermediate reticular nucleus, and caudal ventrolateral reticular nucleus at P6 and P9. However, PrRP fibers were never found in the above regions in the adult animal. These findings suggest that PrRP fibers originating in the medulla oblongata have been widely distributed in the rat brain during the early postnatal day and PrRP may play various roles in the brain development.

Development of the cyto- and chemoarchitectural organization of the rat nucleus of the solitary tract

The nucleus of the solitary tract (NST) is the major visceral sensory nucleus in the brainstem. The development of the rat nucleus of the solitary tract was followed during late prenatal and early postnatal life in order to determine when subnuclear organization and chemoarchitectural features develop. In Nissl-stained sections, the nucleus of the solitary tract becomes visible as a distinct cluster of cells by about E17. Between E17 and E19, a profound change in the Nissl-stained appearance of the nucleus occurred, so that by E19 all the subnuclei were discernible. Acetylcholinesterase activity in the developing NST showed an early period of rapid differentiation (E15 to E17), while by E19 the basic adult pattern of distribution of this enzyme had already been achieved. The subnuclei of the NST began to show clear differential staining for nicotinamide adenine dinucleotide phosphate diaphorase at about the same time as reactivity for that enzyme first appeared (E19). With respect to calbindin- and calretinin-immunoreactive neurons within the nucleus, many of the chemoarchitectural features associated with these two markers were obvious even by late fetal life. For example, in the central subnucleus, a strongly labelled, dense population of calbindin-immunoreactive neurons was present from E17; while in calretinin-immunoreacted material, this subnucleus was prominent because of its immunonegativity also from E17. Nevertheless, the total number of calbindin- and calretinin-immunoreactive neurons in the NST did not peak until late postnatal life. Tyrosine hydroxylase immunoreactive neurons were visible from E15, began differentiation by E17 and were distributed in a similar pattern to the adult from E19. Substance P immunoreactivity in the NST was also very similar to the adult pattern by E19. Many of these immunochemical and histochemical markers indicate a similar pattern of development, i.e. a rapid period of differentiation until E19, by which time a relatively stable adult-like pattern has been attained. The present findings indicate that many of the cyto- and chemoarchitectural features of this nucleus are present well before birth, by which time the nucleus must serve vitally important functions such as relaying information for control of respiration and the circulation.

Developmental changes of (3)H-labelled mu-opioid receptors in brainstems of intra-uterine growth-restricted rats

The opioid mu-system is involved in brainstem-mediated respiratory control. Infants with intra-uterine growth restriction (IUGR) have more respiratory disorders in the early postnatal period. Using [(3)H]DAGO, a mu-selective ligand, and a computer-based image analysis of autoradiography, we compared the ontogeny and distribution of mu-opioid binding sites in the brainstem of IUGR and control rats in utero (E21), at birth (P0) and on postnatal days 1 (P1), P7, P10, P14 and P21. The ontogeny pattern was found to be similar in both groups. The density of the binding sites, which was low in E21, increased at P0, slightly declined at P1 and remained relatively constant thereafter. The distribution of DAGO-binding sites, also similar in both groups, was heterogeneous and was much denser in the dorsal areas of medulla and pons. In particular, binding sites were highly concentrated in nuclei involved in the cardio-respiratory function. However, DAGO-binding density was higher at all ages (except for P0 and P1) in IUGR than in control rats. Taken together, these results give at least a partial explanation for the effects of IUGR which lowers the Apgar score at birth and raises the incidence of respiratory disorders in infants.

Optical approaches to embryonic development of neural functions in the brainstem

The ontogenetic approach to physiological events is a useful strategy for understanding the functional organization/architecture of the vertebrate brainstem. However, conventional electrophysiological techniques are difficult or impossible to employ in the early embryonic central nervous system. Optical techniques using voltage-sensitive dyes have made it possible to monitor neural activities from multiple regions of living systems, and have proven to be a useful tool for analyzing the embryogenetic expression of brainstem neural function. This review describes recent progress in optical studies made on embryonic chick and rat brainstems. Several technical issues concerning optical recording from the embryonic brainstem preparations are discussed, and characteristics of the optical signals evoked by cranial nerve stimulation or occurring spontaneously are described. Special attention is paid to the chronological analyses of embryogenetic expression of brainstem function and to the spatial patterning of the functional organization/architecture of the brainstem nuclei. In addition, optical analyses of glutamate, GABA, and glycine receptor functions during embryogenesis are described in detail for the chick nucleus tractus solitarius. This review also discusses intrinsic optical signals associated with neuronal depolarization. Some emphases are also placed on the physiological properties of embryonic brainstem neurons, which may be of interest from the viewpoint of developmental neurobiology.

Prenatal X-irradiation increases GFAP- and calbindin D28k-immunoreactivity in the medial subdivision of the nucleus of solitary tract in the rat

Glial fibrillary acidic protein- (GFAP) and calbindin D28k-immunoreactivity (IR) were investigated in the medial subdivision of the nucleus of the solitary tract (mNST) of prenatally X-irradiated rats. Pregnant rats were exposed to a single whole-body X-irradiation on day 11 or 16 of gestation at a dose of 1. 3 Gy. The offspring were killed at 7-14 days of age for the immunohistochemical observations. Rat pups showed strong GFAP-IR at the level rostral to the obex when receiving X-rays on day 11 of gestation, with hypertrophy of astrocyte cell bodies and cytoplasmic processes, but weak GFAP-IR when receiving X-rays on day 16 of gestation. Calbindin D28k-IR was stronger in the animals receiving X-rays on day 11 or 16 of gestation compared to that in the control animals. In the present study, the increase of GFAP- and calbindin D28k-IR cells in the mNST might indicate that adaptative mechanisms are taking place to preserve integrated nervous system function and possibly, to provide neuroprotection.

Ovine fetal estrogen sulfotransferase in brain regions important for hypothalamus-pituitary-adrenal axis control

Ovine parturition is initiated by increases in fetal hypothalamus-pituitary-adrenal (HPA) axis activity which, in turn, increase placental estrogen biosynthesis and ultimately increase uterine contractility. In addition to their action in the uterus, estrogens in fetal plasma augment fetal corticotropin (ACTH) secretion. In late gestation, estrone sulfate is more abundant in fetal plasma than unconjugated estrone and it is possible that there is interconversion of sulfoconjugated and unconjugated steroids within the fetal brain. We studied hypothalamus and brainstem tissue from fetal, neonatal, and adult sheep to test the hypothesis that the ovine brain contains estrogen sulfotransferase. Although no significant ontogenic pattern was revealed, the presence of estrogen sulfotransferase within the hypothalamus and brainstem was detectable. Immunohistochemistry revealed the presence of estrogen sulfotransferase in the paraventricular nucleus of the hypothalamus, the nucleus of the tractus solatarius, and the rostral ventral lateral medulla. We conclude that ovine fetal hypothalamus and brainstem contain estrogen sulfotransferase in brain regions important for HPA axis control.

Responses to glossopharyngeal stimulus in the early embryonic chick brainstem: spatiotemporal patterns in three dimensions from repeated multiple-site optical recording of electrical activity

In an effort to assess the spatial patterning of glossopharyngeal responses in the early embryonic chick brainstem, we used a multiple-site optical recording system with a 12 x 12 element photodiode array and a voltage-sensitive merocyanine-rhodanine dye (NK2761) to monitor neural transmembrane voltage activities. Seven and 8 d old embryonic chick brainstems were sliced into 1400-1600 microns thick sections with the glossopharyngeal and vagal nerves attached, and then stained with the dye. Neural voltage-related optical signals were evoked by a positive brief (depolarizing) square current pulse applied to the glossopharyngeal nerve with a microsuction electrode, and then recorded simultaneously from many loci in the objective two-dimensional image plane of a compound microscope. In addition to the multiple-site optical recording technique, we tried to introduce an optical sectioning method by changing the focal plane of the microscope to obtain three-dimensional information. Thus, we have been able to assess semiquantitatively the three-dimensional profiles of two glossopharyngeal response areas corresponding to the nucleus of the glossopharyngeal nerve (nucleus nervi glossopharyngei) and the nucleus of the tractus solitarius. Furthermore, glutaminergic excitatory postsynaptic potentials were determined within the response area corresponding to the nucleus of the tractus solitarius. In addition, we also compared the glossopharyngeal and vagal response areas and found that the cores of the related nuclei are separated in three dimensions.