Immunohistochemical localization of enkephalin and substance P in the nucleus caudalis of the spinal trigeminal V in the medulla oblongata of the human fetus

Appearance of fetal pain could be associated with maturation of the mesodiencephalic structures

Fetal pain remains a controversial subject both in terms of recognizing its existence and the time-frame within which it appears. This article investigates the hypothesis that pain perception during development is not related to any determined structures of the central nervous system (CNS), on the contrary, the process of perception could be made with any structure satisfying conditions that the perception of pain is the organization, identification, and interpretation of sensory information in order to represent and understand the environment. According to this definition, chronic decerebrate and decorticate experimental animals, anencephalic, and hydranencephalic patients demonstrate that the basic, most general, appropriate interaction with the environment can be achieved with a functional mesodiencephalon (brain stem, and diencephalon) as the hierarchically highest structure of the CNS during development. In intact fetuses, this structure shows signs of sufficient maturation starting from the 15th week of gestation. Bearing in mind the dominant role of the reticular formation of the brain stem, which is marked by a wide divergence of afferent information, a sense of pain transmitted through it is diffuse and can dominate the overall perception of the fetus. The threshold for tactile stimuli is lower at earlier stages of gestation. The pain inhibition mechanisms are not sufficiently developed during intrauterine development, which is another factor that leads to increased intensity of pain in the fetus. As a conclusion it could be proposed that the fetus is exposed to rudimentary painful stimuli starting from the 15^th gestation week and that it is extremely sensitive to painful stimuli.

Localization of 5-HT1A and 5-HT2A positive cells in the brainstems of control age-matched and Alzheimer individuals

Serotonin receptor 1A and 2A positive cells in postmortem brainstems were demonstrated via immunohistochemistry in eight control age-matched elderly individuals and eight Alzheimer patients. The 5-HT1A positive cells were found in substantia nigra, pontile nucleus, and vagal as well as dorsal raphe nucleus, while 5-HT2A receptor positive cells were found in motor, sensory and spinal trigeminal nuclei, pontile nucleus, substantia nigra, and nucleus solitarius. A comparison in density of positive cells per unit area was made between control age-matched and Alzheimer individuals. Statistically significant differences (p ≤ 0.01) in density were observed in 5-HT1A cells in pontile, dorsal raphe, and vagal nuclei between control age-matched and Alzheimer, and in 5-HT2A positive cells in the sensory trigeminal nucleus, between control and Alzheimer. This de novo study indicated the presence of 5-HT1A and 5-HT2A receptor positive cells in the above nuclei of human brainstem and revealed differences in density between control age-matched and Alzheimer, indicating possible functional derangements in Alzheimer patients in these areas. In addition, colocalization studies indicated that 5-HT1A receptors were in cholinergic cells and gamma-aminobutyric acid positive fibers were linked to 5-HT2A receptor positive cells. It is hoped that understanding these two important 5-HT receptors and their localization might lead to advances in future therapeutic development.

Acute and chronic craniofacial pain: brainstem mechanisms of nociceptive transmission and neuroplasticity, and their clinical correlates

This paper reviews the recent advances in knowledge of brainstem mechanisms related to craniofacial pain. It also draws attention to their clinical implications, and concludes with a brief overview and suggestions for future research directions. It first describes the general organizational features of the trigeminal brainstem sensory nuclear complex (VBSNC), including its input and output properties and intrinsic characteristics that are commensurate with its strategic role as the major brainstem relay of many types of somatosensory information derived from the face and mouth. The VBSNC plays a crucial role in craniofacial nociceptive transmission, as evidenced by clinical, behavioral, morphological, and electrophysiological data that have been especially derived from studies of the relay of cutaneous nociceptive afferent inputs through the subnucleus caudalis of the VBSNC. The recent literature, however, indicates that some fundamental differences exist in the processing of cutaneous vs. other craniofacial nociceptive inputs to the VBSNC, and that rostral components of the VBSNC may also play important roles in some of these processes. Modulatory mechanisms are also highlighted, including the neurochemical substrate by which nociceptive transmission in the VBSNC can be modulated. In addition, the long-term consequences of peripheral injury and inflammation and, in particular, the neuroplastic changes that can be induced in the VBSNC are emphasized in view of the likely role that central sensitization, as well as peripheral sensitization, can play in acute and chronic pain. The recent findings also provide new insights into craniofacial pain behavior and are particularly relevant to many approaches currently in use for the management of pain and to the development of new diagnostic and therapeutic procedures aimed at manipulating peripheral inputs and central processes underlying nociceptive transmission and its control within the VBSNC.

Early appearance of acetylcholinergic, serotoninergic, and peptidergic neurons and fibers in the developing human central nervous system

Animal experiments have already shown that neurotransmitters and neuropeptides are not only important for normal functioning of the adult central nervous system (CNS) but are also crucial to its development. However, information on the spatio-temporal distribution of these endogenous substances in the developing human CNS is still scarce. With the use of immunocytochemical staining and a constant supply of properly fixed human abortuses from southern China, an early appearance of acetylcholinesterase, enkephalin, and substance P immunoreactivities was detected first in the spinal cord (weeks 5 to 7 of gestation), then in the brainstem nuclei (weeks 11 to 12). Their overlapping localizations in many regions of the CNS suggest possible interactions among neurons containing these substances, which are in turn important for the proper establishment of the neuronal circuitry. Immunoreactivity for neuropeptide Y appeared initially in the lateral region of upper segments of the spinal cord at week 12 of gestation, then spread latero-medially and cranio-caudally to the sacral region. In the hippocampus, neuropeptide Y neurons appeared from week 15 onwards. Serotoninergic neurons were found in the dorsal raphe nucleus at week 10 and then decreased in number as the fetus grew older. Somatostatin releasing inhibitory factor, vasopressin, and oxytocin were detected in the hypothalamus from weeks 12 to 14 onwards, and monoamine oxidase, succinic dehydrogenase, parvalbumin, calbindin D28K, and vasoactive intestinal peptide were found in the visual cortex at midgestation. The early appearance and the abundance of the neurotransmitters and neuropeptides in the developing CNS indicate that they may play a key role in neuronal differentiation.

Ultrastructural study of NADPH-d positive neurons in laminae I and II of the rat caudal spinal trigeminal nucleus

The present study investigated the ultrastructure of neurons in the caudal spinal trigeminal nucleus. These neurons which are believed to function as interneurons in the transmission of orofacial nonreflexive nociceptive information, measured 20 microns x 11 microns, and were nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) positive. The reaction product, formazan, was localized in the nuclear envelope, mitochondria, rough endoplasmic reticulum, and multivesicular bodies of these neurons. It was also localized in the membrane of the smooth endoplasmic reticulum at the axon terminal. The neurons were contacted by both axosomatic and axodendritic synapses formed by both NADPH-d positive and NADPH-d negative axon terminals. Two types of NADPH-d positive axon terminals could be recognized. The first was a large terminal containing many stained mitochondria and unstained small round agranular vesicles mixed with some slightly flattened ones. It formed asymmetrical axodendritic synapse. The second type of axon terminals contained pleomorphic synaptic vesicles and formed asymmetrical synapses upon both dendrites and soma. The sources of NADPH-d positive axon terminals were discussed. Most of the unstained axon terminals forming axosomatic and axodendritic synapses with stained cell bodies and dendrites contained flattened vesicles. In addition to the above, complicated synaptic configurations showing NADPH-d positive axoaxonic synapses in relation to NADPH-d negative dendritic spines were also seen in which a NADPH-d negative dendritic spine was completely contacted by a NADPH-d positive bouton which was in turn contacted by another NADPH-d positive bouton.

Regional distribution of substance P binding sites in the brainstem of the human newborn

The distribution of [3H]substance P ([3H]SP) binding sites in the brainstem of the human newborn was investigated in eleven cases (aged 1 h to 6 months) by in vitro quantitative receptor autoradiography. The binding of [3H]SP to newborn brainstem tissue was found to be saturable (for the eight cases examined, Kd and Bmax (M +/- S.E.M.) were 0.29 +/- 0.03 nM and 206 +/- 21 fmol/mg tissue, respectively). Competition studies showed unlabeled SP to be the most potent peptide for displacing [3H]SP binding from tissue sections. The desaturating effect of GTP on the specific binding of [3H]SP was also investigated, but was not found to be significant. Autoradiographic analysis showed that the neurokinin-1 (NK-1)/SP binding sites were widely but unevenly distributed, and that they varied with age. The highest densities of (NK-1)/SP binding sites were observed in the locus coeruleus, olivaris inferior nuclei, raphe magnus and obscurus nuclei, while low to moderate densities were observed in other brainstem structures. These findings support the idea that SP is involved in cardiovascular regulation, and that it may interact with the catecholaminergic and/or serotonergic system.

An immunohistochemical study of the c-fos protooncogene in the developing human retina

The localization and distribution of the protooncogene c-fos were studied immunohistochemically in the retina of human fetuses ranging in age from 15 to 40 weeks of gestation. The highest levels of immunoreactivity were observed in the retinae of younger fetuses, decreasing in intensity with increasing age. At 15 weeks of gestation intense immunoreactivity was observed in the inner nuclear layer while the photoreceptor cells exhibited moderate staining. At 26 weeks of gestation, immunoreactivity in the inner nuclear layer was reduced. The ganglion cells, amacrine cells and photoreceptor cells showed moderate immunopositivity throughout the 26-40 weeks period. The role of c-fos in development is discussed in the light of its other known functions.