Carole C. Lamotte

Human spinal neurons: Innervation by both substance p and enkephalin

Abstract The distribution of the peptides substance P and methionine-enkephalin in relation to neurons in the human thoracic and lumbar spinal cord has been studied with the unlabeled peroxidase anti-peroxidase method employing antibodies directed against substance P and methionine-enkephalin. The peptides have been localized in varicosities and terminal-like processes in close apposition to the soma and proximal dendrites of neurons in the marginal zone, the intermediolateral nucleus, intermediomedial nucleus, the reticular nucleus of lamina V and the ventral horn; some cells in all these regions are innervated by both peptides. The findings provide morphological evidence of these peptides in the human spinal cord. The demonstration of innervation by both peptides of single neurons in laminae I and V provides some morphological basis to models that postulate the interaction of substance P and enkephalin in pain modulation. The innervation of other neuron types indicates that these neuropeptides may be involved in other spinal functions as well.

El Mouse as a Model of Focal Epilepsy: A Review

Summary: The El mouse is a model of hereditary sensory precipitated temporal lobe epilepsy. All adult El mice given rhythmic vestibular stimulation (e.g. tossing, rocking) during development will experience tonic‐clonic convulsions when given similar stimulation as adults. The seizures have prodromal, convulsive, and postictal stages. EEG and 2‐deoxyglucose studies have localized the seizures to the temporal lobe, with onset in the hippocampus. El mice have a decreased threshold for convulsion by electrical or pharmacologic stimulation. A variety of anticonvulsant medications eliminate El mouse seizures, including phenytoin (PHT), phenobarbital (PB), valproate (VPA), and ethosuximide (ESM). Anatomic studies have shown subtle differences in the thalamus and hippocampus of El mice. Immunohistochemistry of the El mouse hippocampus has revealed changes in peptidergic and gabaergic cell populations. Numerous biochemical differences have been found between El and non‐convulsive mice, including increased acetylcholine (ACh), dopamine (DA), GABA, serotonin (5‐HT), and decreased norepinephrine (NE).

Ultrastructure of chemically defined neuron systems in the dorsal horn of the monkey. II. Methionine-enkephalin immunoreactivity

Enkephalinergic axons and terminals were identified by the PAP immunohistochemical method in lamina I (marginal zone) and lamina IIO (outer substantia gelatinosa) in the dorsal horn of the monkey spinal cord. Synaptic profiles with enkephalin-like immunoreactivity (MELI) contained clear, round, vesicles, sometimes a few large granular vesicles, and usually formed asymmetrical contacts. MELI terminals forming synaptic contacts with various sizes of dendrites and with dendritic spines were the most common type of relationship found; axosomatic contacts were few. Additionally, two types of complexes were observed in which an MELI terminal formed a specialized apposition with an unlabelled terminal. The contact often resembled a synapse and in most cases the MELI terminal was suspected to be presynaptic. One complex consisted of a MELI terminal apposing the LGV type terminal (containing large granular vesicles), which in turn was presynaptic to a dendrite. (The identity of the LGV terminal could not be determined, but it had some characteristics similar to those described for substance P terminals and for a class of primary afferents in the monkey dorsal horn). The other type of complex consisted of a MELI terminal apposing an R-type terminal (containing small, round, clear vesicles) which was in turn presynaptic to a dendrite. Often, the MELI terminal also formed a synapse onto the same dendrite. The axodendritic, axospinous and axosomatic contacts of MELI terminals in the superficial dorsal horn may produce some of the depressive postsynaptic-like effects of enkephalin iontophoresis onto dorsal horn neurons. In these cases the responses of dorsal horn neurons to both low threshold and nociceptive primary afferents is suppressed. However, the opiate receptor-dependent PAD of C-fibers observed in the dorsal horn may be mediated by the MELI complexes formed with LGV and R terminals found in lamina I.

Immunocytochemical and electron microscopic study of serotonin neuronal organization in the dorsal raphe nucleus of the monkey

Serotonin neurons in the dorsal raphe nucleus were identified using an antibody to a serotonin-bovine serum albumin conjugate and the peroxidase anti-peroxidase method. Nerve cell bodies showing serotonin-like immunoreactivity ranged in size from 15 to 22 micron in diameter; their dendrites were also immunoreactive. Immunostaining was present in the cytoplasmic matrix, outer membranes of mitochondria, rough endoplasmic reticulum, multivesicular bodies and dense-cored vesicles. Heavily immunoreactive axonal varicosities contained small round vesicles (18-35 nm) and larger dense-cored vesicles (50-90 nm). Both unmyelinated (0.2-0.5 micron) and myelinated (0.8-1.1 micron) serotonin-like immunoreactive axons were found, often interspersed within bundles of similar caliber unlabeled axons. Serotonin-like immunoreactive somata and dendrites were postsynaptic to numerous unlabeled terminals that contained either (a) clear round vesicles (18-25 nm) with many small dense-cored vesicles (30-50 nm), (b) clear round vesicles (18-25 nm) with large dense-cored vesicles (90-110 nm) or (c) clear round vesicles (18-25 nm) with or without flat vesicles. In addition pairs of unlabeled terminals formed crest synapses onto serotonin-like immunoreactive dendritic spines. This variety of unlabeled terminals making contact with serotonin-like immunoreactive elements suggests that several neuronal systems with possibly different transmitters may regulate serotonin raphe neurons. We occasionally observed serotonin-like immunoreactive dendrites and terminals in apposition to other serotonin-like immunoreactive dendrites with membrane specializations at the site of contact. This might represent a possible site for the self inhibition of serotoninergic neurons reported in physiological studies of the serotonin system in the dorsal raphe nucleus.

Lamina x of primate spinal cord: Distribution of five neuropeptides and serotonin

The distribution of substance P, somatostatin, cholecystokinin, vasoactive intestinal polypeptide, enkephalin and serotonin in axons, terminals and neurons was compared in the area surrounding the central canal (lamina X) at five representative levels of the monkey spinal cord, using peroxidase-antiperoxidase immunocytochemistry. Immunoreactive neurons containing each of the neurochemicals were identified. At the cervical, thoracic and lumbar levels the area lateral to the canal had dense terminal fields immunoreactive for each neurochemical. The dorsal commissural region, the pericanal area, and the ventral commissural area were supplied by some but not all of the substances. In the lower thoracic cord innervation extended into the dorsal midline area and into the ventromedial commissural region. In contrast, in the sacral cord, the dorsal commissural region could be subdivided on the basis of innervation, and the lateral region was densely supplied by only cholecystokinin and serotonin, while the sacral ventral commissure and the pericanal area were supplied by all six neurochemicals. The immunocytochemical mappings were compared with published maps of functional classes of neurons and with the distribution of primary afferents and descending fibers in lamina X. The dense peptidergic and serotonergic innervation in the lateral area and the dorsal commissural area corresponded particularly with the location of projection neurons and primary afferents described in other studies.

Organization of Dorsal Horn Neurotransmitter Systems

The spinal cord dorsal horn is endowed with neural structures rich in a variety of neurotransmitters and neuromodulators, including amino acids, peptides, catecholamines, and serotonin. Many are concentrated in the superficial dorsal horn (laminae I, II, and III), with precise subregional accumulations specific for each substance.

VIP-, SS-, and GABA-like immunoreactivity in the mid-hippocampal region of El (epileptic) and C57BL/6 mice

The El (epileptic) mouse is a model of hereditary sensory precipitated temporal lobe epilepsy. We compared vasoactive intestinal polypeptide-like immunoreactivity (VIP-LI), somatostatin-like immunoreactivity (SS-LI), and gamma-aminobutyric acid-like immunoreactivity (GABA-LI) in the mid-hippocampal region of El and C57BL/6 mice. Specific interneuron populations with VIP-LI and GABA-LI were elevated in the El mice, whereas SS-LI populations were unchanged. These neurochemical alterations may be contributing to the epileptic predisposition of El mice.

Deafferentation-induced regulation of AMPA receptors in the spinal cord of the adult rat

Glutamate released from primary afferents is thought to be involved in mediating spinal reflexes, nociception, and the development and consequent maintenance of hyperalgesia. The role of glutamate is dependent on the distribution and regulation of glutamate receptors in the spinal cord. Due to the numerous glutamate receptor subtypes and their differential physiological profiles, the system is quite complex. Understanding the regulation of the various glutamate receptor subunits may aid in the elucidation of the role of glutamate in somatosensory processing. In this study we found a transient reduction in delta-amino-3-hydroxy-5-methyl-isoxazole-4-propionate (AMPA) receptors in the dorsal horn following partial deafferentation. The time course for the alterations of spinal AMPA receptors may correspond to the functional consequence of deafferentation.

Deafferentation-Induced Expression of GAP-43, NCAM, and NILE in the Adult Rat Dorsal Horn Following Pronase Injection of the Sciatic Nerve

The expression of growth-associated protein 43 (GAP-43), neural cell adhesion molecule (NCAM), and nerve-growth-factor-inducible large external glycoprotein (NILE) in the adult rat dorsal horn was examined at several survival times after unilateral pronase injection of the sciatic nerve. Pronase injection produces a permanent major loss of sciatic primary afferents in the dorsal horn, and there is a later sprouting of saphenous afferents into the sciatic territory. Small-diameter myelinated and nonmyelinated saphenous afferents sprout within the superficial dorsal horn, and larger, myelinated afferents sprout within the deep dorsal horn. In the present study, GAP-43 and NCAM immunoreactivity increased in the superficial dorsal horn by 10 days after injection. By 20 days, the increase spread into the deep dorsal horn; NCAM returned to normal after 1-2 months, but GAP-43 persisted up to 4 months. NILE immunoreactivity appeared in laminae I and II by 10 days and increased up to 30 days; by 2 months no NILE remained. NILE never spread into the deeper dorsal horn, regardless of survival time. These data suggest a correlation in the expression of both NCAM and NILE with the sprouting of fine-diameter sprouting afferents in laminae I and II, and of NCAM expression with the sprouting of larger-diameter afferents in the deep dorsal horn.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in substance P and calcitonin gene-related peptide binding in the dorsal horn of rat spinal cord following pronase-induced deafferentation

Quantitative receptor autoradiography was used to evaluate potential alterations in substance P (SP) and calcitonin gene-related peptide (CGRP) binding in the L4 spinal segment of rats following unilateral poisoning of the sciatic nerve with pronase. Ten days after pronase-induced deafferentation there was a significant increase in SP and CGRP binding in the superficial (I-II) and deeper (II-IV) laminae of the dorsal horn ipsilaterally. Densitometric measurements revealed a 50% return towards normal values for SP binding by 90 days postpronase injection in all laminae examined, while the density of CGRP binding showed a partial return towards normal values for laminae III-IV only. These differential responses may be indicative of the mechanisms underlying pronase-induced peripheral neuropathy.