Ontogeny of somatostatin-like immunoreactivity in the human fetus and infant spinal cord

Morphology and distribution of hypothalamic peptidergic systems

Neuropeptides participate in the regulation of numerous hypothalamic functions that are aimed for sustaining the homeostasis of the organism. These neuropeptides can act in two different levels. They can influence the release of hormones from the adenohypophysis via the portal circulation; in addition, they can act as neurotransmitters/neuromodulators modulating the functioning of numerous hypothalamic neurotransmitter systems. Indeed, most of these peptidergic systems form a complex network in the infundibular and periventricular nuclei of the human hypothalamus, communicating with each other by synaptic connections that may control fundamental physiologic functions. In the present chapter, we provide an overview of the distribution of neuropeptides in the human hypothalamus using immunohistochemistry and high-resolution, three-dimensional mapping.

Human Dorsal Root Ganglia

Sensory neurons with cell bodies situated in dorsal root ganglia convey information from external or internal sites of the body such as actual or potential harm, temperature or muscle length to the central nervous system. In recent years, large investigative efforts have worked toward an understanding of different types of DRG neurons at transcriptional, translational, and functional levels. These studies most commonly rely on data obtained from laboratory animals. Human DRG, however, have received far less investigative focus over the last 30 years. Nevertheless, knowledge about human sensory neurons is critical for a translational research approach and future therapeutic development. This review aims to summarize both historical and emerging information about the size and location of human DRG, and highlight advances in the understanding of the neurochemical characteristics of human DRG neurons, in particular nociceptive neurons.

Somatostatin and its 2A receptor in dorsal root ganglia and dorsal horn of mouse and human: expression, trafficking and possible role in pain

Background

Somatostatin (SST) and some of its receptor subtypes have been implicated in pain signaling at the spinal level. In this study we have investigated the role of SST and its sst2A receptor (sst2A) in dorsal root ganglia (DRGs) and spinal cord.

Results

SST and sst2A protein and sst2 transcript were found in both mouse and human DRGs, sst2A-immunoreactive (IR) cell bodies and processes in lamina II in mouse and human spinal dorsal horn, and sst2A-IR nerve terminals in mouse skin. The receptor protein was associated with the cell membrane. Following peripheral nerve injury sst2A-like immunoreactivity (LI) was decreased, and SST-LI increased in DRGs. sst2A-LI accumulated on the proximal and, more strongly, on the distal side of a sciatic nerve ligation. Fluorescence-labeled SST administered to a hind paw was internalized and retrogradely transported, indicating that a SST-sst2A complex may represent a retrograde signal. Internalization of sst2A was seen in DRG neurons after systemic treatment with the sst2 agonist octreotide (Oct), and in dorsal horn and DRG neurons after intrathecal administration. Some DRG neurons co-expressed sst2A and the neuropeptide Y Y1 receptor on the cell membrane, and systemic Oct caused co-internalization, hypothetically a sign of receptor heterodimerization. Oct treatment attenuated the reduction of pain threshold in a neuropathic pain model, in parallel suppressing the activation of p38 MAPK in the DRGs

Conclusions

The findings highlight a significant and complex role of the SST system in pain signaling. The fact that the sst2A system is found also in human DRGs and spinal cord, suggests that sst2A may represent a potential pharmacologic target for treatment of neuropathic pain.

Developmental changes in the expression of somatostatin receptors (1–5) in the brain, hypothalamus, pituitary and spinal cord of the human fetus

The actions of somatostatin (SST) in the nervous system are mediated by specific high affinity SST receptors (SSTR1-5). However, the role of this hormone and the distribution of its receptor subtypes have not yet been defined in neural structures of the human fetus. We have analyzed four neural tissues (CNS, hypothalamus, pituitary and spinal cord) from early to midgestation for the expression of five human SSTR mRNAs, using a reverse transcription-polymerase chain reaction and Southern blot approach. These fetal neural tissues all express mRNA for multiple SSTR subtypes from as early as 16 weeks of fetal life but the developmental patterns of expression vary considerably. Transcripts for SSTR1 and SSTR2A are the most widely distributed, being expressed in all four neural tissues. SSTR2A is often the earliest transcript to be detected (7.5 weeks in CNS). SSTR3 mRNA is confined to the pituitary, hypothalamus, and spinal cord. SSTR4 is expressed in fetal brain, hypothalamus and spinal cord but not pituitary. SSTR5 mRNA is detectable in the pituitary and spinal cord by 14-16 weeks of fetal life. This mapping of SSTR mRNA expression patterns in human fetal neural tissues is an important first step toward our goal of determining the role of SST in the nervous system during early stages in human development.

Pain management in newborns: how far have we progressed in research and practice?

Compelling research supports the newborn infant's capacity for pain. Yet, pain is frequently underestimated and undertreated. This is a result of limited understanding of pain pathway development, immediate and long-term consequences, measurement tools and approaches, and safety and efficacy of pain-relieving interventions. This paper reviews recent research in relation to management of pain in the newborn, and presents implications for practice and future research.

The monoclonal antibody Alz-50, used to reveal cytoskeletal changes in Alzheimer's disease, also reacts with a large subpopulation of somatostatin neurons in the normal human hypothalamus and adjoining areas

The monoclonal antibody Alz-50 is directed against Alzheimer's disease-related modified tau proteins and reveals cytoskeletal changes, i.e. neurofibrillary tangles and dystrophic neurites. The present study shows that, in the hypothalamus of non-demented control subjects, this same antibody gives a distinctive staining pattern of a subpopulation of somatostatin neurons and beaded fibres. Furthermore, Alz-50 occasionally recognizes somatostatin-containing cell bodies and dystrophic neurite-like fibers in the (neuritic) senile plaques of AD patients. These observations have direct consequences for the interpretation of Alz-50 staining in diagnostic usage and for the assessment of Alzheimer's disease-like changes induced by beta-amyloid in experimental animal brains. On dot spotting, Alz-50 was found to bind to a number of fragments from the somatostatin precursor, of which somatostatin 15-28 stained best. Preadsorption of Alz-50 by somatostatin 15-28, as well as other specificity tests, failed, however, to provide any clue to the nature of the unknown compound(s) stained in the control hypothalamus.

Transient expression of neuropeptide Y and its C-flanking peptide immunoreactivities in the spinal cord and ganglia of human embryos and fetuses

An immunohistochemical study of spinal cord, dorsal root and sympathetic ganglia of human embryos and fetuses demonstrated that neuropeptide Y and its C-flanking peptide could be detected in seven-week-old embryos but were absent or difficult to demonstrate after the 17th week of gestation. The peptides were found in several structures of the spinal cord, e.g. fibres in the dorsal portion of the lateral funiculus, cell bodies and fibres in the dorsal horn, and motoneurons, and also in numerous primary sensory neurons of dorsal root ganglia. They were also present in sympathetic neurons and since these are the only structures expressing neuropeptide Y and its C-flanking peptide in the adult, it must be concluded that their presence in other neurons is a transient developmental feature. To assist in understanding the relationship of these transient structures with other spinal and sensory neurons, a comparison was made with other neuronal structures showing immunoreactivity for two general neuronal markers, neurofilaments and protein gene product 9.5, and two neuropeptides present in primary sensory afferents, somatostatin and substance P. In the dorsal root ganglia, numerous neuropeptide Y- and C-flanking peptide-immunoreactive neurons were observed before substance P- or somatostatin-immunoreactive cells could be detected. Therefore, neuropeptide Y and its C-flanking peptide could represent a primitive peptidergic system appearing before primary sensory neurons express their characteristic adult phenotype. The fibres of the lateral funiculus showing immunoreactivity for neuropeptide Y and its C-flanking peptide were longitudinally orientated and could be detected at all cephalocaudal levels of the spinal cord. Comparison with the other immunohistochemical markers indicated that they were not primary sensory afferents. At least some of them probably originated from neuropeptide Y- and C-flanking peptide-immunoreactive neurons of the dorsal horn, that may be considered to be a subset of early-appearing interneurons.

Immunocytochemical study of peptidergic structures in Brunner's glands

Nervous and endocrine peptidergic structures in human Brunner's glands were studied by immunofluorescence. Endocrine cells storing immunoreactive components respectively similar to somatostatin 14, the amino-terminal portion (1-14) of somatostatin 28, gastrin-cholecystokinin, and peptide YY were distributed throughout the acini. Peptidergic nerve structures contained materials immunologically related to vasoactive intestinal peptide, peptide histidine methionine, substance P, neuropeptide Y, and gastrin-releasing peptide. The latter peptide was detected in discrete fibers running into the acini but within no cell body in the submucosa. All other neuropeptides were stored in fibers, isolated or grouped in bundles, and in perikarya of submucosal ganglia close to the acini. No immunoreactive structures were detected using antisera directed against pancreatic polypeptide, secretin, motilin, neurotensin, or calcitonin gene-related peptide. The results suggest that several regulatory peptides may be involved in the control of Brunner's glands in humans.

Long-term cultivation of cryopreserved human fetal brain cells in a chemically defined medium

Conditions for long-term cultivation of human fetal brain cells in a chemically defined medium were established using cryopreserved brain fragments obtained from legal abortions. Tissue of the same gestational age was pooled and the cells cultured in a fully defined medium containing insulin-like growth factors (IGF I and II). Primary cultures were kept for 2-4 weeks and secondary or tertiary cultures could be maintained for 3 months. The cultures were characterized by morphological, electrophysiological and biochemical methods. Glial cells were predominant during the first two weeks of culture. In later stages of cultivation, glial cells diminished in number and most cells were neuronal. Voltage-dependent Na+ channels were recorded from neurons. Biochemical studies indicated that the fetal brain cells contained and secreted immunoreactive somatostatin as well as the tachykinins, substance P and neurokinin A. Cultures grown in IGF II- or nerve growth factor-containing medium expressed increased choline acetyltransferase activity.

The neuroanatomy, neurophysiology, and neurochemistry of pain, stress, and analgesia in newborns and children

Beginning with a brief description of mature anatomic pathways and neurotransmitters in the "pain system," this article details their development in the human fetus, neonate, and child. Special emphasis is given to the basic mechanisms and physiologic effects of opioid analgesia. The clinical implications of these data are described, particularly with regard to the maintenance of cardiovascular stability and hormonal-metabolic homeostasis in newborns and children undergoing surgery or other forms of stress.

Immunohistochemical distribution of somatostatin in the infant hypothalamus

Somatostatin (SS)-containing neurons were mapped in the normal infant hypothalamus with immunohistochemistry, using the peroxidase anti-peroxidase technique. Neurons displaying SS immunoreactivity show a widespread distribution throughout the hypothalamic region. Principal SS-immunoreactive like (SS-IL) perikarya are located in the paraventricular, infundibular and posterior nuclei and in the preoptic region. High SS innervation is also found in the ventromedial and in the lateral mammillary nuclei, and in the median eminence. In general this distribution of SS-IL agrees well with that reported for rat. Compared to the immunohistochemical distribution of SS in human adult hypothalamus, this mapping in the infant hypothalamus is grossly similar. However some differences may be underlined: the presence of a moderately dense group of SS-IL perikarya in the tuberal and posterior nuclei, and a dense innervation of the ventromedial nucleus and in the median eminence. This first detailed distribution of SS immunoreactivity in infant hypothalamus can provide basic knowledge for further studies of infant neuropathology.

Anatomical distribution of somatostatin immunoreactivity in the infant brainstem

The distribution of somatostatin-immunoreactive structures in the infant brainstem was investigated using the peroxidase-antiperoxidase technique. A wide distribution of somatostatin-immunoreactive cell bodies and fibers was observed throughout the brainstem. Numerous somatostatin-immunoreactive cell bodies and fibers were present in several areas of the brainstem including the substantia grisea centralis and the reticular formation. Some immunoreactive cell bodies were seen in cranial nerve nuclei such as the nucleus praepositus, the nucleus nervi hypoglossi and the vestibular nuclei. Immunoreactive fibers were seen in the nucleus cuneatus, the locus coeruleus, the nucleus tractus solitarius, the nucleus ambiguus, the nucleus tractus spinalis nervi trigemini and the dorsal horn of the spinal cord. These data were in agreement with previous works on the human adult. However, a high density of somatostatin-immunoreactive cell bodies and fibers in the interpeduncular nucleus and in the nucleus centralis superior, and a dense network of somatostatin-immunoreactive fibers in the dorsal part of the nucleus inferior olivarius, were also observed. The role of somatostatin in some brainstem nuclei and its probable implication in some specific neuropathological diseases of the infant brainstem is discussed.

Displaceable somatostatin binding sites in the gray matter and pyramidal paths of the human developing spinal cord

The binding of the somatostatin analogue, 125I-iodo-Tyr-[Tyr0,D-Trp8]S14, to the foetal (18- and 24-week-old) and infant (newborn and 17-month-old) spinal cord was examined using in vitro autoradiography. Somatostatin binding sites were detected at cervical, thoracic and lumbosacral levels in foetal as well as in infant spinal cord. The radiolabelling was localized over the grey especially in the superficial layers of the dorsal horn including the substantia gelatinosa and the marginal zone. In foetal and newborn spinal cord, the direct and crossed pyramidal paths exhibited a substantial binding of the ligand. A similar labelling was not observed in the pyramidal paths of a 17-month-old child or in anencephalic newborn spinal cord or previously described in adult. These results emphasize the early presence of somatostatin binding sites during the ontogeny of the human spinal cord. Further, the transient appearance of somatostatin binding sites in the pyramidal paths, prior the myelination, raises the question whether somatostatin receptors could be involved in the maturation of certain normal paths.