Neurotransmitter plasticity at the molecular level

Large-Scale Analysis of the Diversity and Complexity of the Adult Spinal Cord Neurotransmitter Typology

The development of nervous system atlases is a fundamental pursuit in neuroscience, since they constitute a fundamental tool to improve our understanding of the nervous system and behavior. As such, neurotransmitter maps are valuable resources to decipher the nervous system organization and functionality. We present here the first comprehensive quantitative map of neurons found in the adult zebrafish spinal cord. Our study overlays detailed information regarding the anatomical positions, sizes, neurotransmitter phenotypes, and the projection patterns of the spinal neurons. We also show that neurotransmitter co-expression is much more extensive than previously assumed, suggesting that spinal networks are more complex than first recognized. As a first direct application, we investigated the neurotransmitter diversity in the putative glutamatergic spinal V2a-interneuron assembly. These studies shed new light on the diverse and complex functions of this important interneuron class in the neuronal interplay governing the precise operation of the central pattern generators.

Adult spinal motoneurons change their neurotransmitter phenotype to control locomotion

An intriguing feature of the nervous system is its plasticity—the remarkable lifelong capacity to change and adapt in light of intrinsic and extrinsic stimuli. Among the many different adaptive mechanisms that occur within the nervous system, changes in neurotransmission form an important plasticity-bestowing mechanism in the reconfiguration of neuronal circuits. Here, we reveal that physical activity and spinal cord injury can switch the neurotransmitter phenotype of the fast axial motoneurons to coexpress glutamate. Furthermore, our study shows that the adult vertebrate spinal motoneurons corelease glutamate alongside ACh in neuromuscular junctions to regulate motor behaviors. Thus, our findings suggest that fast motoneuron glutamatergic respecification enables a motor function-enhancing mechanism in vertebrates.

A particularly essential determinant of a neuron’s functionality is its neurotransmitter phenotype. While the prevailing view is that neurotransmitter phenotypes are fixed and determined early during development, a growing body of evidence suggests that neurons retain the ability to switch between different neurotransmitters. However, such changes are considered unlikely in motoneurons due to their crucial functional role in animals’ behavior. Here we describe the expression and dynamics of glutamatergic neurotransmission in the adult zebrafish spinal motoneuron circuit assembly. We demonstrate that part of the fast motoneurons retain the ability to switch their neurotransmitter phenotype under physiological (exercise/training) and pathophysiological (spinal cord injury) conditions to corelease glutamate in the neuromuscular junctions to enhance animals’ motor output. Our findings suggest that motoneuron neurotransmitter switching is an important plasticity-bestowing mechanism in the reconfiguration of spinal circuits that control movements.

Localization and neurochemical characteristics of the extrinsic sympathetic neurons projecting to the pylorus in the domestic pig

The pylorus, an important part of the digestive tract controlling the flow of chyme between the stomach and the duodenum, is widely innervated by intrinsic and extrinsic nerves. To determine the locations of postganglionic sympathetic perikarya that innervate the pylorus of the domestic pig, a retrograde tracing method with application of Fast Blue tracer was used. All positive neuronal cell bodies (ca. 1750) were found in the celiac-cranial mesenteric ganglion complex (CSMG), however, the coeliac poles of this complex provided the major input to the pylorus. Afterwards, the immunohistochemical staining procedure was applied to determine biologically active substances expressed in the FB-labeled perikarya. Approximately 77% of the FB-positive cell bodies contained tyrosine hydroxylase (TH), 87% dopamine β-hydroxylase (DβH), 40% neuropeptide Y (NPY), 12% somatostatin (SOM) and 7% galanin (GAL). The presence of all these substances in the ganglion tissue was confirmed by RT-PCR technique. Double immunocytochemistry revealed that all of the TH-positive perikarya contained DβH, about 40% NPY, 12% SOM and 8% GAL. Additionally, all above-cited immunohistochemical markers as well as VIP, PACAP, ChAT, LEU, MET, SP and nNOS were observed within nerve fibers associated with the FB-positive perikarya. Immunocytochemical labeling of the pyloric wall tissue disclosed that TH+, DβH+ and NPY+ nerve fibers innervated ganglia of the myenteric and submucosal plexuses, blood vessels, both muscular layers and the muscularis mucosae; nerve fibers immunoreactive to GAL mostly innervated both muscular layers, while SOM+ nerve fibers were observed within the myenteric plexus. Presented study revealed sources of origin and immunohistochemical characteristics of the sympathetic postganglionic perikarya innervating the porcine pylorus.

Transcriptional profiles reveal similarities and differences in the effects of developmental neurotoxicants on differentiation into neurotransmitter phenotypes in PC12 cells

Unrelated developmental neurotoxicants nevertheless converge on common functional and behavioral outcomes. We used PC12 cells, a model of neuronal development, to explore similarities and differences for organophosphate pesticides (chlorpyrifos, diazinon), an organochlorine pesticide (dieldrin) and a metal (Ni(2+)), focusing on transcriptional profiles related to differentiation into acetylcholine, dopamine and norepinephrine phenotypes. Agents were introduced at 30 microM for 24 or 72 h, treatments devoid of cytotoxicity. Using microarrays, we examined the mRNAs encoding the proteins involved in neurotransmitter biosynthesis, storage, and degradation, along with the complete panoply of receptors for each transmitter. All three pesticides evoked concordant patterns of effects on genes involved in neural growth and neurite extension, with a distinctly different pattern for Ni(2+). All four toxicants promoted differentiation into the dopamine phenotype at the expense of the acetylcholine phenotype, involving separable effects of each agent on the various gene families; however, there were major differences in the ability of each to promote or repress the norepinephrine phenotype. Chlorpyrifos and diazinon, although displaying many similarities in their transcriptional profiles, also showed major disparities in keeping with their known differences in synaptic and behavioral outcomes after neonatal exposures to these agents in vivo. Surprisingly, there were closer similarities among diazinon, dieldrin and Ni(2+) than for each agent to chlorpyrifos. Our results illustrate how cell culture systems, combined with microarray technology, can screen for developmental neurotoxicants, serving as a model for alternative approaches to the detection and characterization of the impact of exogenous chemicals on brain development.

Human embryonic stem cells for brain repair?

Cell therapy has been perceived as the main or ultimate goal of human embryonic stem (ES) cell research. Where are we now and how are we going to get there? There has been rapid success in devising in vitro protocols for differentiating human ES cells to neuroepithelial cells. Progress has also been made to guide these neural precursors further to more specialized neural cells such as spinal motor neurons and dopamine-producing neurons. However, some of the in vitro produced neuronal types such as dopamine neurons do not possess all the phenotypes of their in vivo counterparts, which may contribute to the limited success of these cells in repairing injured or diseased brain and spinal cord in animal models. Hence, efficient generation of neural subtypes with correct phenotypes remains a challenge, although major hurdles still lie ahead in applying the human ES cell-derived neural cells clinically. We propose that careful studies on neural differentiation from human ES cells may provide more immediate answers to clinically relevant problems, such as drug discovery, mechanisms of disease and stimulation of endogenous stem cells.

Full-length and truncated neurokinin-1 receptor expression and function during monocyte/macrophage differentiation

The substance P (SP)-preferring receptor neurokinin-1 receptor (NK-1R) has two forms: a full-length receptor consisting of 407 aa and a truncated receptor consisting of 311 aa. These two receptors differ in the length of the C terminus of NK-1R. We studied the undifferentiated and phorbol myristate acetate (PMA)-differentiated human monocyte/macrophage cell line THP-1 to investigate the expression and function of NK-1R. The expression of full-length and truncated NK-1R in this cell line was determined by using real-time PCR and immunofluorescence staining. Undifferentiated THP-1 cells expressed only truncated NK-1R. The differentiation of THP-1 cells with PMA to a macrophage-like phenotype resulted in the expression of full-length NK-1R, which was functionally accompanied by an SP (10(-6) M)-induced Ca2+ increase. In contrast, the addition of SP (10(-6) M) did not trigger Ca2+ response in undifferentiated THP-1 cells; however, SP did enhance the CCR5-preferring ligand RANTES (CCL5)-mediated Ca2+ increase. When a plasmid containing the full-length NK-1R was introduced into undifferentiated THP-1 cells, exposure to SP triggered Ca2+ increase, demonstrating that the full-length NK-1R is required for SP-induced Ca2+ increase. The NK-1R antagonist aprepitant (Emend, Merck) inhibited both the SP-induced Ca2+ increase in PMA-differentiated THP-1 cells and the SP priming effect on the CCL5-mediated Ca2+ increase, indicating that these effects are mediated through the full-length and truncated NK-1R, respectively. Taken together, these observations demonstrate that there are unique characteristics of NK-1R expression and NK-1R-mediated signaling between undifferentiated THP-1 cells and THP-1 cells differentiated to the macrophage phenotype.

Single-cell RT-PCR, in situ hybridization histochemical, and immunohistochemical studies of substance P and enkephalin co-occurrence in striatal projection neurons in rats

Single-cell RT-PCR studies in 3-4-week-old rats have raised the possibility that as many as 20% of striatal projection neurons may be a unique type that contains both substance P (SP) and enkephalin (ENK). We used single-cell RT-PCR, retrograde labeling, in situ hybridization histochemistry, and immunolabeling to characterize the abundance of this cell type, its projection target(s), and any developmental changes in its frequency. We found by RT-PCR that 11% of neurons containing either SP or ENK contained both in 4-week-old rats, while in 4-month-old rats SP/ENK colocalization was only 3%. SP-only neurons tended to co-contain dynorphin and ENK-only neurons neurotensin, while SP/ENK neurons tended to contain dynorphin. Single-cell RT-PCR showed SP/ENK co-occurrence in 4-week-old rats to be no more common among striatal neurons retrogradely labeled from the substantia nigra than among those retrogradely labeled from globus pallidus. Double-label in situ hybridization showed SP/ENK perikarya to be scattered throughout striatum, making up 8% of neurons containing either SP or ENK at 4 weeks, but only 4% at 4 months. Immunolabeling showed that presumptive striatal terminals in globus pallidus externus, globus pallidus internus and substantia nigra pars reticulata that colocalized SP and ENK were scarce. Terminals colocalizing SP and ENK were, however, abundant in the substantia nigra pars compacta. Thus, SP-only and ENK-only neurons make up the vast majority of striatal projection neurons in rats, the frequency of SP/ENK colocalizing striatal neurons is low in adult rats (3-4%), and SP/ENK colocalizing neurons primarily project to SNc but do not appear to be confined to striosomes.

Butyrate, a gut-derived environmental signal, regulates tyrosine hydroxylase gene expression via a novel promoter element

Butyrate is a diet-derived, gut fermentation product with an array of effects on cultured mammalian cells including inhibition of proliferation, induction of differentiation and regulation of gene expression. We showed that physiological concentrations of butyrate can regulate transcription of tyrosine hydroxylase (TH) and preproenkephalin (ppEnk) gene in PC12 cells. In promoter deletion studies, electrophoretic mobility shift assays and by site-directed mutagenesis, we identified a novel butyrate response element (BRE) in the 5' upstream region of the rat TH gene, homologous to the previously mapped motif in the ppEnk promoter. No such enhancers were found in DBH or PNMT promoters, and both catecholamine system-related gene promoters were unaffected by butyrate. The BRE motif interacts with nuclear proteins in a sequence-specific manner, shows binding potentiation in butyrate-differentiated PC12 cells and bound protein(s) are competed away with TH-CRE oligonucleotides or by the addition of CREB-specific antibodies, suggesting involvement of CREB or CREB-related transcription factors. Moreover, single point mutation in the distal BRE abolished binding of transcription factors and reduced the response to butyrate in transient transfection studies. The canonical CRE motif of the TH promoter was also found necessary for transcriptional activation of the TH gene by butyrate. Our data identified a novel functional element in the promoter of both the TH and ppEnk genes mediating transcriptional responses to butyrate. Dietary butyrate may have an extended role in the control of catecholamine and endogenous opioid production at the level of TH and ppEnk gene transcription neuronal plasticity, cardiovascular functions, stress adaptation and behavior.

Human neuronal cells (NT2-N) express functional substance P and neurokinin-1 receptor coupled to MIP-1 beta expression

Substance P (SP), the most extensively studied and potent member of the tachykinin family, is a major modulator of inflammation and immunomodulatory activities within the central and peripheral nervous systems. We have examined the gene expression of SP and its receptor in a human neuronal cell line (NT2-N). Using reverse transcribed polymerase chain reaction (RT-PCR), the four isoforms of preprotachykinin-A gene transcripts (alpha, beta, gamma, and delta) were detected in the NT2-N. We also identified the presence of mRNA for neurokinin-1 receptor (NK-1R), a primary receptor for SP, in the NT2-N cells. Concomitant with NT2 cell differentiation into neurons, SP and NK-1R mRNA expression increased consistently. Intracellular SP and cell membrane NK-1R immunoreactivity were all observed in NT2-N cells. Most importantly, we demonstrated that SP and NK-1R presented in NT2-N cells are functionally involved in the regulation of macrophage inflammatory protein 1 beta (MIP-1beta), an important beta-chemokine participating in the activation and directional migration of immune cells to sites of central nervous systems (CNS) inflammation. Thus, SP and its receptor may play an important role in modulation of neuronal functions related to regulation of immune activities within the CNS. The NT2-N cell line is well suited for in vitro investigations of the SP-NK-1R pathway in immune responses and inflammation in the CNS.

The hypothalamus and hypertension

Most forms of hypertension are associated with a wide variety of functional changes in the hypothalamus. Alterations in the following substances are discussed: catecholamines, acetylcholine, angiotensin II, natriuretic peptides, vasopressin, nitric oxide, serotonin, GABA, ouabain, neuropeptide Y, opioids, bradykinin, thyrotropin-releasing factor, vasoactive intestinal polypeptide, tachykinins, histamine, and corticotropin-releasing factor. Functional changes in these substances occur throughout the hypothalamus but are particularly prominent rostrally; most lead to an increase in sympathetic nervous activity which is responsible for the rise in arterial pressure. A few appear to be depressor compensatory changes. The majority of the hypothalamic changes begin as the pressure rises and are particularly prominent in the young rat; subsequently they tend to fluctuate and overall to diminish with age. It is proposed that, with the possible exception of the Dahl salt-sensitive rat, the hypothalamic changes associated with hypertension are caused by renal and intrathoracic cardiopulmonary afferent stimulation. Renal afferent stimulation occurs as a result of renal ischemia and trauma as in the reduced renal mass rat. It is suggested that afferents from the chest arise, at least in part, from the observed increase in left auricular pressure which, it is submitted, is due to the associated documented impaired ability to excrete sodium. It is proposed, therefore, that the hypothalamic changes in hypertension are a link in an integrated compensatory natriuretic response to the kidney's impaired ability to excrete sodium.

Neurotrophins, but not depolarization, regulate substance P expression in the developing optic tectum

Neurotransmitter expression can be regulated by both activity and neurotrophins in a number of in vitro systems. We examined whether either of these factors was likely to play a role in the in vivo optic nerve-dependent regulation of a substance P-like immunoreactive (SP-ir) population of cells in the developing optic tectum of the frog. In contrast to our previous results with the adult system, blocking tectal cell responses to glutamate release by retinal ganglion cells with 6-cyano-7-nitroquinoxaline-2,3 dione (CNQX) did not affect the percent of SP-ir cells in the developing tectum. Treatment with d-(-)-2-amino-5-phosphonovaleric acid (d-AP-5) was also ineffective in this regard, although both it and CNQX treatment disrupted visual map topography. Chronic treatment with brain-derived neurotrophic factor (BDNF) and neurotrophin-4/5 (NT-4/5) produced increases in SP-ir cells in the treated lobes of normal animals, which were significant in the case of NT-4/5. Both substances also prevented the decrease of SP cells that would otherwise occur in the deafferented lobe of unilaterally optic nerve-transected tadpoles. These changes in the percent of SP-ir cells occurred without any detectable changes in the overall number of tectal cells. NGF had no effect on SP expression. Nor did it affect topographic map formation, which was disrupted by treatment with either BDNF or NT-4/5. Our results demonstrate that different mechanisms regulate SP expression in the developing and adult tectum. They indicate that neurotrophin levels in the developing optic tectum may selectively regulate a specific neuropeptide-expressing population of cells.

Differential expression of catecholamine biosynthetic enzymes in the rat ventrolateral medulla

Adrenergic (C1) neurons located in the rostral ventrolateral medulla are considered a key component in the control of arterial blood pressure. Classically, C1 cells have been identified by their immunoreactivity for the catecholamine biosynthetic enzymes tyrosine hydroxylase (TH) and/or phenylethanolamine N-methyltransferase (PNMT). However, no studies have simultaneously demonstrated the expression of aromatic L-amino acid decarboxylase (AADC) and dopamine beta-hydroxylase (DBH) in these neurons. We examined the expression and colocalization of all four enzymes in the rat ventrolateral medulla using immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR) analysis. Retrograde tracer injected into thoracic spinal segments T2-T4 was used to identify bulbospinal neurons. Using fluorescence and confocal microscopy, most cells of the C1 group were shown to be double or triple labeled with TH, DBH, and PNMT, whereas only 65-78% were immunoreactive for AADC. Cells that lacked detectable immunoreactivity for AADC were located in the rostral C1 region, and approximately 50% were spinally projecting. Some cells in this area lacked DBH immunoreactivity (6.5-8.3%) but were positive for TH and/or PNMT. Small numbers of cells were immunoreactive for only one of the four enzymes. Numerous fibres that were immunoreactive for DBH but not for TH or PNMT were noted in the rostral C1 region. Single-cell RT-PCR analysis conducted on spinally projecting C1 neurons indicated that only 76.5% of cells that contained mRNA for TH, DBH, and PNMT contained detectable message for AADC. These experiments suggest that a proportion of C1 cells may not express all of the enzymes necessary for adrenaline synthesis.

Detection of substance P and its receptor in human fetal microglia

Substance P, the most abundant neurokinin in the CNS, is a major modulator of the immune system. We have examined the gene expression of substance P and its receptor in human fetal brain microglia. Using reverse transcription-polymerase chain reaction and Southern blotting assay, the four isoforms of preprotachykinin-A gene transcripts (alpha, beta, gamma and delta) were detected in the microglia. The human fetal microglia produced significantly higher levels of endogenous substance P protein (640-850 pg/10(6) cells) than did human peripheral blood monocyte-derived macrophages (25-50 pg/10(6) cells), as determined by an enzyme immunoassay. Using immunohistochemical staining with an anti-substance P antibody, cell membrane substance P immunoreactivity was observed. In addition, we identified the presence of messenger RNA for neurokinin-1 receptor, a primary receptor for substance P in human fetal microglia.From these data, we propose that substance P and its receptor are biologically involved in regulating the functions of microglia, and potentially play an important role in host defense of the central nervous system.

GABAergic deafferentation hypothesis of brain aging and Alzheimer's disease revisited

Considering the mechanisms responsible for age- and Alzheimer's disease (AD)-related neuronal degeneration, little attention was paid to the opposing relationships between the energy-rich phosphates, mainly the availability of the adenosine triphosphate (ATP), and the activity of the glutamic acid decarboxylase (GAD), the rate-limiting enzyme synthesizing the gamma-amino butyric acid (GABA). Here, it is postulated that in all neuronal phenotypes the declining ATP-mediated negative control of GABA synthesis gradually declines and results in age- and AD-related increases of GABA synthesis. The Ca2+-independent carrier-mediated GABA release interferes with Ca2+-dependent exocytotic release of all transmitter-modulators, because the interstitial (ambient) GABA acts on axonal preterminal and terminal varicosities endowed with depolarizing GABA(A)-benzodiazepine receptors; this makes GABA the "executor" of virtually all age- and AD-related neurodegenerative processes. Such a role of GABA is diametrically opposite to that in the perinatal phase, when the carrier-mediated GABA release, acting on GABA(A)/chloride ionophore receptors, positively controls chemotactic migration of neuronal precursor cells, has trophic actions and initiates synaptogenesis, thereby enabling retrograde axonal transport of target produced factors that trigger differentiation of neuronal phenotypes. However, with advancing age, and prematurely in AD, the declining mitochondrial ATP synthesis unleashes GABA synthesis, and its carrier-mediated release blocks Ca2+-dependent exocytotic release of all transmitter-modulators, leading to dystrophy of chronically depolarized axon terminals and block of retrograde transport of target-produced trophins, causing "starvation" and death of neuronal somata. The above scenario is consistent with the following observations: 1) a 10-month daily administration to aging rats of the GABA-chloride ionophore antagonist, pentylenetetrazol, or of the BDZ antagonist, flumazenil (FL), each forestalls the age-related decline in cognitive functions and losses of hippocampal neurons; 2) the brains of aging rats, relative to young animals, and the postmortem brains of AD patients, relative to age-matched controls, show up to two-fold increases in GABA synthesis; 3) the aging humans and those showing symptoms of AD, as well as the aging nonhuman primates and rodents--all show in the forebrain dystrophic axonal varicosities, losses of transmitter vesicles, and swollen mitochondria. These markers, currently regarded as the earliest signs of aging and AD, can be reproduced in vitro cell cultures by 1 microM GABA; the development of these markers can be prevented by substituting Cl- with SO4(2-); 4) the extrasynaptic GABA suppresses the membrane Na+, K+-ATPase and ion pumping, while the resulting depolarization of soma-dendrites relieves the "protective" voltage-dependent Mg2+ control of the N-methyl-D-aspartate (NMDA) channels, thereby enabling Ca2+-dependent persistent toxic actions of the excitatory amino acids (EAA); and 5) in whole-cell patch-clamp recording from neurons of aging rats, relative to young rats, the application of 3 microM GABA, causes twofold increases in the whole-cell membrane Cl- conductances and a loss of the physiologically important neuronal ability to desensitize to repeated GABA applications. These age-related alterations in neuronal membrane functions are amplified by 150% in the presence of agonists of BDZ recognition sites located on GABA receptor. The GABA deafferentation hypothesis also accounts for the age- and AD-related degeneration in the forebrain ascending cholinergic, glutamatergic, and the ascending mesencephalic monoaminergic system, despite that the latter, to foster the distribution-utilization of locally produced trophins, evolved syncytium-like connectivities among neuronal somata, axon collaterals, and dendrites, to bidirectionally transport trophins. (ABSTRACT TRUNCATED)

Plasticity in adult and ageing sympathetic neurons

The nature of neural plasticity and the factors that influence it vary throughout life. Adult neurons undergo extensive and continual adaptation in response to demands that are quite different from those of early development. We review the main influences on the survival, growth and neurotransmitter expression in adult and ageing sympathetic neurons, comparing these influences to those at work in early development. This "developmental" approach is proposed because, despite the contrasting needs of different phases of development, each phase has a profound influence on the mechanisms of plasticity available to its successors. Interactions between neurons and their targets, whether effector cells or other neurons, are vital to all of these aspects of neural plasticity. Sympathetic neurons require access to target-derived diffusible neurotrophic factors such as NGF, NT3 and GDNF, as well as to bound elements of the extracellular matrix such as laminin. These factors probably influence plasticity throughout life. In adult life, and even in old age, sympathetic neurons are relatively resistant to cell death. However, they continue to require target-derived diffusible and bound factors for their maintenance, growth and neurotransmitter expression. Failure to maintain appropriate neuronal function in old age, for example in the breakdown of homeostasis, may result partly from a disturbance of the dynamic, trophic relationship between neurons and their targets. However, there is no clear evidence that this is due to a failure of targets to synthesize neurotrophic factors. On the neural side of the equation, altered responsiveness of sympathetic neurons to neurotrophic factors suggests that expression of the trk and p75 neurotrophin receptors contributes to neuronal survival, maintenance and growth in adulthood and old age. Altered receptor expression may therefore underlie the selective vulnerability of some sympathetic neurons in old age. The role of neural connectivity and activity in the regulation of synthesis of target-derived factors, as well as in neurotransmitter dynamics, is reviewed.

Metabolic and neurochemical plasticity of gamma-aminobutyric acid-immunoreactive neurons in the adult macaque striate cortex following monocular impulse blockade: quantitative electron microscopic analysis

The purpose of the present study was to examine the effects of retinal impulse blockade on gamma-aminobutyric acid (GABA)-immunoreactive (GABA-IR) neurons in cytochrome oxidase (CO)-rich puffs of the adult monkey striate cortex. Specifically, we wished to know if changes occurred in their CO activity, GABA immunoreactivity, and synaptic organization. A double-labeling technique, which combined CO histochemistry and postembedding GABA immunocytochemistry on the same ultrathin sections, was used to reveal simultaneously the distribution of the two markers. We quantitatively compared changes in GABA-IR neurons of deprived puffs (DPs) with respect to non-deprived puffs (NPs) 2 weeks after monocular tetrodotoxin treatment. We found that the proportion of darkly CO reactive mitochondria in GABA-IR neurons of DPs drastically decreased to about half of those in NPs. There was a greater reduction of CO levels in GABA-IR axon terminals than in their cell bodies and dendrites. In contrast, most non-GABA-IR neurons displayed no significant change in their CO levels. Morphologically, GABA-IR neurons and axon terminals in DPs showed a significant shrinkage in their mean size. GABA immunoreactivity, as indicated by the density of immunogold particles in GABA-IR neurons, declined in DPs, and a greater decrease was also found in axon terminals than in cell bodies or dendrites. Moreover, the numerical density of GABA-IR axon terminals and synapses in DPs was significantly reduced without changes in that of asymmetric and symmetric synapses. Thus, the present results support the following conclusions: 1) Oxidative metabolism and neurotransmitter expression in GABA-IR neurons are tightly regulated by neuronal activity in adult monkey striate cortex; 2) GABA-IR neurons are much more vulnerable to functional deprivation than non-GABA-IR ones, suggesting that these inhibitory neurons have stringent requirement for sustained excitatory input to maintain their heightened oxidative capacity; and 3) intracortical inhibition mediated by GABA transmission following afferent deprivation may be decreased in deprived puffs, because the oxidative capacity and transmitter level in GABAergic neurons, especially in their axon terminals, are dramatically reduced.

Deafferentation leads to a down-regulation of nitric oxide synthase in the rat visual system

To test the hypothesis that monocular enucleation can cause a decrease in nitric oxide synthase (NOS) in subcortical visual centers, serial sections of superior colliculi and lateral geniculate nuclei from normal and enucleated rats were processed for NOS immunohistochemistry and NADPH-diaphorase histochemistry. Adjacent sections were also reacted for cytochrome oxidase, a metabolic marker, to demonstrate the change in energy demands. We found that both visual centers normally contained moderate levels of NOS, and eye removal caused a consistent down-regulation of NOS, NADPH-diaphorase and cytochrome oxidase on the deprived contralateral side. Optical densitometric values supported these findings (P < 0.01). Thus, the level and the activity of NOS are regulated by neuronal activity in the rat subcortical visual centers.

Optic nerve-dependent changes in adult frog tectal cell phenotypes

Optic nerve activity helps determine the placement of retinal ganglion cell terminals in the optic tectum of the frog. We investigated whether the presence of this nerve might also influence a characteristic of its target structure, neurotransmitter biosynthesis. We performed unilateral optic nerve transections on adult animals and assayed the percent and intensity of substance P- and serotoninlike immunoreactive (SP-ir and 5-HT-ir, respectively) cells in the deafferented and afferented tectal lobes. Regeneration of the optic nerve was prevented. The percent of SP-ir cells in the afferented tectal lobes was significantly less than that in the deafferented ones either 6 weeks or 5 months following optic nerve lesion. Comparison to normal animals indicated that the change in SP-ir expression was due to a decrease in the percent of immunoreactive cells in the afferented tecta ipsilateral to the optic nerve lesion. The serotoninlike immunoreactivity of tectal cells was also significantly different in the two lobes following optic nerve lesions. This difference resulted from an increase in the percent of 5-HT-ir cells in the deafferented tectum. In addition, the intensity of 5-HT-ir cells in the deafferented lobe was significantly greater than in the afferented one. The staining intensity of SP-ir cells underwent only a transient, relative decrease in the deafferented tectum. We conclude that the optic nerve does regulate substance P and serotonin expression in the tectum, but that this regulation likely occurs through different pathways.

Effects of early captopril treatment and its removal on plasma angiotensin converting enzyme (ACE) activity and arginine vasopressin in hypertensive rats (SHR) and normotensive rats (WKY)

The purpose of this study was to evaluate the effects of early administration and removal of the ACE inhibitor, captopril (CAP) on the plasma ACE activity, AVP levels, and mean arterial pressure (MAP) in groups of rats, control and CAP treated SHR and WKY (SHR, WKY SHRCAP, WKYCAP, respectively and in SHR taken off CAP (OFFCAP) and their progeny (2nd generation, 2ndG). Plasma ACE activity in SHRCAP (54.8 +/- 2.1 mU/ml/min) was significantly greater than in SHR (25.96 +/- 0.34 mU/ml/min) and their offspring (OFFCAP, 26.32 +/- 2.71 and 2ndG, 17.62 +/- 2.47 mU/ml/min, P < 0.001, respectively). Plasma level of AVP in SHR (14.18 +/- 0.98 pg/ml) were greater than in SHRCAP (9.1 +/- 1.01 pg/ml, P < 0.01). A decrease in plasma AVP levels were also noted in OFFCAP (10.48 +/- 0.51 pg/ml) and their offspring 2ndG (10.34 +/- 0.46 pg/ml). Our results did not show a relationship between plasma ACE activity and blood pressure reduction. However, treatment of SHR with captopril produced a decrease in plasma AVP levels which may participate in its antihypertensive mechanism of action.

Development of serotonergic innervation of the chick embryo tectum opticum

This paper describes the development of the serotonergic innervation of the chick tectum opticum as revealed by an immunohistochemical methodology. The development of this innervation was previously described simply as the formation of an irregular network of serotonergic fibers that gradually invades the organ and increases in density. Our results show that the developmental pattern of serotonergic innervation differs significantly through the distinct tectal layers and that it progresses through a characteristic temporospatial pattern related to the lamination process. These findings support the idea that the concept of laminar segregation can be applied to describe the development of the serotonergic innervation. On the other hand, it is clear that the existence of a typical ordered developmental pattern of innervation makes it possible to detect embryonic or post-hatching alterations. Thus, the tectal serotonergic innervation could be used as a suitable model to investigate possible plastic changes in experimental conditions.

Dopamine in the lobster Homarus gammarus: II. Dopamine-immunoreactive neurons and development of the nervous system

Dopamine-immunoreactive neurons were revealed in lobster embryos, larvae, and postlarvae, and staining patterns were compared to neuronal labeling in the juvenile lobster nervous system (Cournil et al. [1994] J. Comp. Neurol. 344:455-469). Dopamine immunoreactivity is first detected by midembryonic life in 35-40 neuronal somata located anteriorly in brain and subesophageal ganglion. When the lobsters assume a benthic life during the first postlarval stage, an average of 58 cell bodies are labeled. The acquisition of dopamine in lobster neurons is a protracted event spanning embryonic, larval, and postlarval life and finally reaching the full complement of roughly 100 neurons in juvenile stages. Some of the dopaminergic neurons previously identified in the mature nervous system, such as the paired Br cells, L cells, and mandibular cells, are labeled in embryos and persist throughout development. In contrast, other neurons stain transiently for dopamine during the developmental period, but, by the adult stage, these neurons are no longer immunoreactive. Such transiently labeled neurons project to the foregut, the thoracic dorsal muscles, the neurohormonal pericardial plexus, and the pericardial pouches. It is proposed that these neurons are alive and functioning in adult lobster but that dopamine levels have been abolished, providing that neurotransmitter status is a dynamic, changing process.

High potassium promotes differentiation of retinal neurons but does not favor rod differentiation

Neural retinal cells of newborn rats were cultured under dissociated culture conditions. Differentiation of several types of retinal cells was confirmed by immunohistochemical detection of type-specific neural phenotypes. We used Thy-1.1 antigen as a ganglion cell marker, HPC-1 or GABA as an amacrine cell marker and rhodopsin as a rod cell marker. With a high concentration of potassium (38 mM), expression of the respective neural phenotypes were differentially affected. High K+ increased the number of Thy-1.1 positive cells 6 to 8 fold, and drastically promoted their neurite extension. The same culture conditions, however, reduced considerably the number of rhodopsin positive cells, possibly due to the unique membrane properties of photoreceptors. A high K+ concentration also promoted differentiation of HPC-1 positive and GABA positive cells, but to a lesser extent than the Thy-1.1 positive cells. Several possibilities were examined to understand the effect of a high K+ concentration on retinal neural cells. The total cell number in cultures with a high K+ concentration was approximately half of that in control cultures at day 3 and slightly smaller at day 11, suggesting that high K+ did not have a positive general effect on the proliferation or survival of retinal cells. Naturally occurring neuronal death (apoptosis) is a well-known phenomenon during retinal development. A histochemical method for detecting DNA fragmentation, a step preceding apoptosis, showed that high K+ had no preventive effect. BrdU (bromodeoxyuridine) immunohistochemistry showed that high K+ did not seem to enhance proliferation of neural precursor cells. These results indicate that a high K+ concentration promotes the expression of neuronal phenotypes but is not a favorable condition for rod differentiation. Since a high K+ concentration is considered to induce depolarization of nerve cells, the present results suggest an anterograde influence from surrounding neuronal cells, through chronic depolarization by elevated K+, is essential for the differentiation and maturation of retinal cells.

Areal differences of NPY mRNA-expressing neurons are established in the late postnatal rat visual cortex in vivo, but not in organotypic cultures

In order to learn about the factors regulating the postnatal development of neocortical peptidergic neuron populations, we have analysed neurons expressing neuropeptide Y (NPY) by immunohistochemistry and in situ hybridization in developing and adult rat visual cortical areas 17 and 18a in vivo, and in organotypic slice cultures of rat visual cortex. For quantitative analysis, the percentage of NPY mRNA-expressing neurons was determined in supragranular layers I-IV, in infragranular layers V and VI and in the white matter. In vivo, this percentage increased in visual areas 17 and 18a until postnatal day 21 in supra- and infragranular layers. Initially, in both areas the neurons were about equally distributed in supra- and infragranular layers (a ratio of 1:1). During the second postnatal month, the percentage of NPY mRNA-expressing neurons in area 18a declined by approximately 50% in both supra- and infragranular layers, so that the ratio of 1:1 remained constant. In contrast, in area 17 the percentage of neurons in supragranular layers remained fairly constant, but it declined to 50% in infragranular layers, so that by postnatal day 70 the ratio was gradually shifted to 2:1. Throughout development, area 18a contained significantly more NPY mRNA-expressing neurons than area 17. In organotypic slice cultures, a high density of NPY mRNA-expressing neurons had appeared by 10 days in vitro. A much higher percentage of neurons expressed NPY mRNA. The ratio of labelled neurons in supra- versus infragranular layers was 1:1. Both ratio and percentage remained constant from 10-85 days in vitro. The decline in vivo was not caused by an elimination of transient cell types. All cell types persisted into adulthood. Four NPY peptide-immunoreactive neuronal types were classified by axonal morphology in organotypic slice cultures and in vivo; they include (i) cells in layer VI/white matter with horizontal axons and ascending collaterals, (ii) cells in layers V/VI with descending axon and horizontal collaterals, (iii) Martinotti cells in layers V/VI with ascending axons, and (iv) cells in layers III-V with columnar axons. Two further types, bipolar cells with axons descending from dendrites and small basket cells with short horizontal axons, both found in vivo in layers II/III, could not be unequivocally identified in organotypic slice cultures. The NPY-immunoreactive neuron types had already formed a dense innervation of the cultures by 10 days in vitro, which remained stable for up to 85 days in vitro, and resembled the innervation observed in vivo. NPY peptide-immunoreactive neurons in organotypic slice cultures and in vivo were distributed in cortical layers II/III, V and VI and the white matter, but rarely in layers I and IV, which corresponded to the distribution of NPY mRNA-expressing neurons. However, with in situ hybridization more neurons were detectable, especially in layers II/III. A majority of NPY mRNA-expressing neurons co-localized NPY peptide, somatostatin and calbindin. We conclude that intrinsic cues were sufficient to drive the molecular expression of the NPY phenotype, the morphological differentiation and the stabilization of an organotypic NPY innervation in organotypic slice cultures. However, the area- and lamina-specific changes observed in vivo were not observed under monoculture conditions.

Circadian change of VIP mRNA in the rat suprachiasmatic nucleus following p-chlorophenylalanine (PCPA) treatment in constant darkness

Neuronal activity of the suprachiasmatic nucleus (SCN) is known to be regulated by two major extrinsic factors conveyed by three anatomically distinct pathways to the SCN: photic stimulus by the direct retinohypothalamic tract (RHT) and the indirect geniculohypothalamic tract (GHT), and information from the brainstem by ascending forebrain serotonergic (5-hydroxytryptamine: 5-HT) tract. It has been shown that VIP mRNA level in neurons of the SCN is altered by external light, but remains stable in constant darkness. In the present study, by using the in situ hybridization technique combined with computer-assisted image analysis, we examined VIP mRNA expression in the SCN of rats in which the two major factors were eliminated, i.e. photic stimulus by exposing animals in total darkness and 5-HT transmission by three-day successive administration of p-chlorophenyl-alanine methylester (an inhibitor of tryptophan hydroxylase, 200 mg/kg, daily). In saline-treated controls, VIP mRNA levels remained almost constant throughout the day. In contrast, in PCPA-treated rats, a significant rhythm of VIP mRNA was observed with a peak at CT 4 and a trough at CT 20. These observations suggest that the removal of photic and 5-HT influence induces VIP mRNA rhythm in the SCN, indicating that VIP mRNA is controlled not only by photic information but also by the circadian clock.

Developmental expression of heterotrimeric G proteins in the nervous system of Manduca sexta

The heterotrimeric G proteins are a conserved family of guanyl nucleotide-binding proteins that appear in all eukaryotic cells but whose developmental functions are largely unknown. We have examined the developmental expression of representative G proteins in the developing nervous system of the moth Manduca sexta. Using affinity-purified antisera against different G alpha subunits, we found that each of the G proteins exhibited distinctive patterns of expression within the developing central nervous system (CNS), and that these patterns underwent progressive phases of spatial and temporal regulation that corresponded to specific aspects of neuronal differentiation. Several of the G proteins examined (including Gs alpha and G(o) alpha) were expressed in an apparently ubiquitous manner in all neurons, but other proteins (including Gi alpha) were ultimately confined to a more restricted subset of cells in the mature CNS. Although most of the G proteins examined could be detected within the central ganglia, only G(o) alpha-related proteins were seen in the developing peripheral nerves; manipulations of G protein activity in cultured embryos suggested that this class of G protein may contribute to the regulation of neuronal motility during axonal outgrowth. G(o) alpha-related proteins were also localized to the developing axons and terminals of the developing adult limb during metamorphosis. These intracellular signaling molecules may, therefore, play similar developmental roles in both the embryonic and postembryonic nervous system.

Neuronal differentiation in cultures of murine neural crest. II. Development of capsaicin-sensitive neurons

A subset of neurons differentiating in cultures of mammalian neural crest cells express a sensitivity to the excitotoxin, capsaicin. The properties of the capsaicin-sensitive neurons in the neural crest cultures are similar to those reported for authentic sensory neurons. For example, the application of capsaicin results in a large, rapid depolarization of capsaicin-sensitive neurons. Capsaicin-sensitive neurons were also detected by the influx of cobalt ions. The development of capsaicin sensitivity in neural crest cultures was dependent on time in culture and on the presence of NGF. A major difference between the crest-derived capsaicin-sensitive neurons and authentic sensory neurons was the simultaneous expression of immunoreactivity for ChAT/TH/CGRP by the former neurons. These experiments indicate that a specific physiological property of authentic sensory neurons is expressed by neurons differentiating from the neural crest in vitro.

Changes in GABA and parvalbumin immunoreactivities in the cerebral cortex of lizards after narine occlusion

Olfactory deprivation produced by narine occlusion has been suggested to reduce the activity in the cerebral cortex of lizards. Here we analyzed the short-term changes in GABA and parvalbumin (PV) immunoreactivities in the cerebral cortex of lizards after narine occlusion. The number and distribution of GABA- and parvalbumin-immunoreactive (IR) cells have been studied by immunocytochemistry in the cerebral cortex of control and olfactory-deprived lizards. The distribution of GABA-IR cells as well as that of PV-IR cells was similar in control and deprived animals, and PV-IR cells were GABA-IR in all cases. However, significant changes were observed in the absolute number of GABA- and PV-IR cells. GABA-IR cells were more abundant in deprived animals than in control ones. In contrast, the number of PV-IR cells decreased significantly and PV immunoreactivity in dendrites and boutons was lower in deprived animals. These results suggest that the reduction in the number of PV-IR cells in olfactory-deprived lizards occurs without loss of GABA cells, and that PV expression is under the control of olfactory activity and remains plastic in the cerebral cortex of adult lizards.

Developmental expression of G proteins in a migratory population of embryonic neurons

Directed neuronal migration contributes to the formation of many developing systems, but the molecular mechanisms that control the migratory process are still poorly understood. We have examined the role of heterotrimeric G proteins (guanyl nucleotide binding proteins) in regulating the migratory behavior of embryonic neurons in the enteric nervous system of the moth, Manduca sexta. During the formation of the enteric nervous system, a group of approx. 300 enteric neurons (the EP cells) participate in a precise migratory sequence, during which the undifferentiated cells populate a branching nerve plexus that lies superficially on the visceral musculature. Once migration is complete, the cells then acquire a variety of position-specific neuronal phenotypes. Using affinity-purified antisera against different G protein subtypes, we found no apparent staining for any G protein in the EP cells prior to their migration. Coincident with the onset of migration, however, the EP cells commenced the expression of one particular G protein, Go alpha. The intensity of immunostaining continued to increase as migration progressed, with Go alpha immunoreactivity being detectable in the leading processes of the neurons as well as their somata. The identity of the Go alpha-related proteins was confirmed by protein immunoblot analysis and by comparison with previously described forms of Go alpha from Drosophila. When cultured embryos were treated briefly with aluminium fluoride, a compound known to stimulate the activity of heterotrimeric G proteins, both EP cell migration and process outgrowth were inhibited. The effects of aluminium fluoride were potentiated by alpha toxin, a pore-forming compound that by itself caused no significant perturbations of migration. In preliminary experiments, intracellular injections of the non-hydrolyzable nucleotide GTP gamma-S also inhibited the migration of individual EP cells, supporting the hypothesis that G proteins play a key role in the control of neuronal motility in this system. In addition, once migration was complete, the expression of Go alpha-related proteins in the EP cells underwent a subsequent phase of regulation, so that only certain phenotypic classes among the differentiated EP cells retained detectable levels of Go alpha immunoreactivity. Thus Go may perform multiple functions within the same population of migratory neurons in the course of embryonic development.

Ontogeny of the distribution of tachykinins in rat cerebral cortex: immunocytochemistry and in situ hybridization histochemistry

Tachykinins in the mammalian brain are derived from two genes: preprotachykinin A, encoding substance P and neurokinin A, and preprotachykinin B, encoding neurokinin B. Using immunocytochemistry and in situ hybridization histochemistry, we have investigated the ontogeny and distribution of substance P and neurokinin B in various cortical areas of rat cerebrum at different prenatal and postnatal ages. Preprotachykinin A mRNA-positive and -immunoreactive cells were first detected at birth and were abundant in layer VIb and the adjacent white matter in the cingulate and frontal cortices. By postnatal day 5, the numbers of substance P-expressing cells were diminished dramatically in those layers. However, their number gradually increased and spread out laterally to cover parietal and temporal cortices from P5 to P15 in layer V. At these stages, cells were also observed in layer II, although fewer in number. The number of substance P mRNA-positive neurons and substance P-immunoreactive cells decreased gradually from P10 and P15 onward, respectively. On the other hand, expression of neurokinin B, as detected by in situ hybridization histochemistry or immunocytochemistry, was not evident until P10. Neurons expressing this tachykinin were concentrated in layer II, and to a lesser extent in layers V and VI. This pattern of distribution was retained through P45. The present data show a marked difference between these two tachykinins in onset and trends of development, suggesting functional independence of these two tachykinins in the cerebral cortex.

Chicken tyrosine hydroxylase gene: isolation and functional characterization of the 5' flanking region

Tyrosine hydroxylase (TH) is the rate-limiting enzyme in the biosynthesis of catecholamines. We describe here the isolation of the chicken TH gene and the analysis of 3 kb of its 5' flanking region. The chicken TH transcription unit spans 19 kb. The 60-bp proximal promoter contains a TATA box and a cyclic AMP response element (CRE) sequence. The 5' flanking region contains several AP1-, AP2-, and octamer-like sequences as well as a glucocorticoid response element at position -1.4 kb. A construct containing the 3-kb 5' flanking DNA fused to the chloramphenicol acetyltransferase (CAT) gene was transiently transfected into PC12 cells, and the effect of various effectors was tested. Only forskolin increased the CAT activity, likely owing to the presence of the CRE sequence. Constructs prepared by progressively deleting the 5' flanking DNA were transfected into PC12 and QT6 (quail transformed fibroblasts) cells. In both cell types, the transcriptional activity increased with deletion of the 5' flanking region. These results show that the 60-bp region containing the TATA box and the CRE is sufficient to act as a constitutive promoter for the chicken TH gene and that this region appears to be negatively controlled by upstream sequences.

Glutamic acid decarboxylase gene expression in thalamic reticular neurons transplanted as a cell suspension in the adult thalamus

The goal of the present study was to determine whether alterations in neuronal morphology and connections in thalamic grafts were accompanied by changes in the expression of mRNA encoding glutamic acid decarboxylase (GAD), the key enzyme in the synthesis of GABA, the normal neurotransmitter of neurons of the thalamic reticular nucleus. Cell suspensions of rat fetal tissue containing both thalamic reticular nucleus and ventrobasal primordia were transplanted into the excitotoxically lesioned somatosensory thalamus of adult rats. Levels of messenger RNA (mRNA) encoding GAD (Mr 67,000; GAD67) were measured 7 days to 4 months following transplantation via quantitative in situ hybridization with 35S-radiolabeled antisense RNAs. Expression of GAD67 mRNA in the thalamic reticular nucleus was analyzed in parallel in rat pups between 0 and 30 days postnatally, and in adult animals. As already observed with immunohistochemistry, transplanted neurons of the thalamic reticular nucleus did not group in specific clusters but rather mingled with unlabeled (putatively ventrobasal) neurons. Levels of labelling for GAD67 mRNA per neuron increased over time and reached adult levels during the third week post-grafting, i.e. 2 weeks after the theoretical birthdate of the neurons (grafted at embryonic days 15-16). Similar values were observed and a plateau was reached at similar time points during normal ontogeny. The results suggest that, in contrast to morphology and size of the neuronal cell bodies, gene expression of GAD67 develops normally despite the ectopic location of neurons of the thalamic reticular nucleus in the somatosensory thalamus, the abnormal connectivity and the lack of segregation from non-GABAergic neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Pretreatment of rat brain slices with ouabain decreases chloride-dependent L-glutamate transport in synaptic membrane

Possible roles of (Na(+)-K+)-ATPase on regulation of Cl(-)-dependent L-glutamate (L-Glu) transport in rat synaptic membrane were examined. Pretreatment of rat cerebral slices with 20 micrograms/ml veratrine, 56 mM K+ and 20 microM monensin increased Cl(-)-dependent L-[3H]-Glu uptake into membrane vesicles prepared from the slices. Pretreatment with (Na(+)-K+)-ATPase inhibitors, 100 microM ouabain, 100 microM strophanthidin, 100 microM vanadate and K(+)-free medium, decreased the uptake by 25-30%, while 5 microM A23187 and 10 microM ruthenium red had no effect. Ouabain (100 microM) caused the maximal effect in 10-20 min of incubation. The effect of (Na(+)-K+)-ATPase inhibitors was reversible and characterized by a decrease in Vmax of the uptake. Addition of 5 microM ouabain abolished the increases in the uptake induced by either veratrine, 56 mM K+ or monensin. Dose-inhibition curve of ouabain on the increased Cl(-)-dependent L-[3H]-Glu uptake was bi-phasic; ouabain at 0.5-5 microM selectively diminished the stimulatory effect of veratrine and inhibited the basal uptake at higher concentrations. Veratrine had no effect on L-[3H]-Glu uptake in 5 microM strophanthidin containing or K(+)-free medium. These results suggest the involvement of (Na(+)-K+)-ATPase in the veratrine-induced increase in Cl(-)-dependent L-Glu transport in rat brain synaptic membranes.

Developmentally regulated secreted factors control expression of muscarinic receptor subtypes in embryonic chick retina

Two molecular mass subtypes of muscarinic receptor are expressed by the chick retina (72 and 86 kDa). During development, the ratio of subtypes changes, with the 72-kDa form becoming predominant. We have found that subtypes switch can occur in retina cell culture, and have investigated factors that influence this in vitro increase in the 72-kDa receptor. Increases similar to those in vivo occurred when cells were cultured at 10(5) cells/cm2, but not at 10-fold lower density. High-density cultures, maintained on coverslips, showed no receptor development when transferred to large volumes of fresh medium, indicating that cell-cell contact alone was not responsible for induction. However, replacement of fresh medium with conditioned medium (from high-density cultures) resulted in normal induction. There were no morphological differences between cultures with high and low levels of the 72-kDa receptor. Conditioned medium also induced 72-kDa receptors in low-density cultures, consistent with a minimal role for cell-cell contact. Efficacy of conditioned medium was markedly dependent on age. Media from cells cultured 1-4 days had no effect, but media from cells cultured 5-8 and 1-8 days elicited 1.6-fold and fourfold increases in the 72-kDa subtype, respectively. The data indicate that maturing retina cells secrete developmentally regulated factors that are necessary for abundant expression of the 72-kDa muscarinic receptor subtype.

Ageing in the autonomic nervous system: a result of nerve-target interactions? A review

There are few generalisations that can be made regarding the changes that occur in autonomic nerves during ageing. Old age has different effects, including loss of neurones, loss of axon branches and alterations in neurotransmitters and other intracellular features. However, these age-related events are associated with particular and often small groups of neurones and are frequently species specific. Changes occur at different periods during development and maturity without any obvious age-stage at which neurodegenerative changes come to predominate. Some of the observations regarding neuronal changes in old age can be interpreted as the result of altered interactions between neurones and their peripheral target tissues. Recent studies in my laboratory support this contention. The neurotrophic theory has been used to explain such interactions during early development and it seems possible that, for example, alterations in the access of neurones to target-derived growth factors may underlie some of the changes that have been observed in old age. Plasticity in the mature autonomic nervous system may also be governed by similar relationships between nerves and their target tissues.

Coexistence of cholinergic, catecholaminergic, serotonergic, and glutamatergic neurotransmitter markers in mouse clonal hybrid neurons derived from the septal region

Two clonal immortalized neurons designated SN6.1b and SN6.2a were isolated by limiting dilution from a mouse embryonic septal cholinergic neuronal hybrid cell line SN6 (Hammond et al., 1986). In the serum-containing medium without extra differentiating agents, one-third of SN6.1b cells stably exhibited a morphology of differentiated neurons with extensive elaborate neurites, while a majority of SN6.2a cells, along with the parent cell line SN6, were round in shape with poorly branched short processes. Neurochemical studies showed that both clones synthesized choline acetyltransferase (ChAT), dopamine, norepinephrine, serotonin, and glutamate. Immunocytochemically, they expressed a number of neuronal antigens, such as 200-kDa neurofilament protein, neuron-specific enolase, microtubule-associated protein 2, tau protein, tubulin, neural cell adhesion molecule, Thy-1.2, saxitoxin-binding sodium channel protein, ChAT, tyrosine hydroxylase, serotonin, and glutamate. The coexistence of cholinergic, catecholaminergic, serotonergic, and glutamatergic neurotransmitter markers in the clonal hybrid septal neurons that express a variety of immunocytochemical properties of differentiated neurons suggests that embryonic septal cholinergic neurons are potentially multiphenotypic with respect to neurotransmitter synthesis.

Guanethidine sympathectomy increases substance P concentration in the superior sympathetic ganglion of adult rats

Adult rats received intraperitoneal injections of guanethidine or saline for 5 weeks. Six to 8 weeks following completion of treatment, concentrations of substance P and neuropeptide Y (NPY) were measured by radioimmunoassay in the superior cervical ganglion (SCG) and thoracic spinal cord. The SCG was also immunostained for NPY and substance P. No differences were observed in thoracic spinal cord content of either NPY or substance P. We observed depletion of NPY immunoreactive neurons and NPY levels in the SCG, and pharmacologic evidence of postganglionic denervation in guanethidine-treated rats. In guanethidine-treated rats, there was a marked increase of substance P levels in the SCG, where substance P was localized in fibers, but not cell bodies. Thus, sprouting of substance P-containing sensory fibers in the sympathetic ganglia occurs following postganglionic sympathectomy in adult rats.

AP-1 complex and c-fos transcription are involved in TPA provoked and trans-synaptic inductions of the tyrosine hydroxylase gene: insights into long-term regulatory mechanisms

We have previously shown that the phorbol ester, TPA, which activates protein kinase C, causes, in PC12 cells, a transcriptional activation of tyrosine hydroxylase (TH), the key enzyme in catecholamine synthesis. The study has now been extended to examine the processes that underlie this transcriptional stimulation and, in addition, to seek whether similar mechanisms are involved in long-term trans-synaptic induction of the TH gene in adrenal medullae of rats that have been given a single injection of reserpine. In both systems, it was found that the induction of c-fos gene transcription was associated with that of the TH gene but with different kinetics. The promoter of the TH gene contains (at position -207/-200) a sequence (TGATTCA) which differs from the consensus TRE or AP-1 site (TGACTCA) by one nucleotide. Experiments were carried out to investigate whether the AP-1 protein complex which is known to contain Fos and Jun binds to the putative TRE region of the TH promoter. In the gel shift assays, the nuclear protein extracts derived from TPA-treated PC12 cells and from AM of reserpine injected rats displayed a higher magnitude of binding to a 25-mer TRE-TH oligonucleotide as compared to controls. The results showed that the behaviour of TRE-TH was atypical in that two retarded complexes (A and B) were observed, which were displaced by specific competitors. Trans-activation experiments with plasmids TRE-TH/TK/CAT and -754/-19 TH/pUC18-CAT in PC12 cells showed an increase in CAT activity in response to TPA that correlates with the previously observed increase in TH transcriptional activity by TPA.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic deafferentation in monkeys differentially affects nociceptive and nonnociceptive pathways distinguished by specific calcium-binding proteins and down-regulates gamma-aminobutyric acid type A receptors at thalamic levels

Chronic deafferentation of skin and peripheral tissues is associated with plasticity of representational maps in cerebral cortex and with perturbations of sensory experience that include severe "central" pain. This study shows that in normal monkeys the nonnociceptive, lemniscal component of the somatosensory pathways at spinal, brainstem, and thalamic levels is distinguished by cells and fibers immunoreactive for the calcium-binding protein parvalbumin, whereas cells of the nociceptive component at these levels are distinguished by immunoreactivity for 28-kDa calbindin. Long-term dorsal rhizotomies in monkeys lead to transneuronal degeneration of parvalbumin cells at brainstem and thalamic sites accompanied in the thalamus by a down-regulation of gamma-aminobutyric acid type A receptors and an apparent increase in activity of calbindin cells preferentially innervated by central pain pathways. Release from inhibition and imbalance in patterns of somatosensory inputs from thalamus to cerebral cortex may constitute subcortical mechanisms for inducing changes in representational maps and perturbations of sensory perception, including central pain.

Differential development of beta-endorphin and mu opioid binding sites in mouse brain

Mouse brains of various ages from embryonal day 14 (E14) to adult were analyzed for opioid receptor binding using the enkephalin analog Tyr-D-Ala-Gly-NMe-Phe-Gly-ol (DAMGE) and the opiate alkaloid dihydromorphine (DHM) as mu-selective radioligands. Binding parameters were estimated from homologous and heterologous competition binding curves. During the postnatal period, Kd values for [3H]DAMGE did not change but Bmax values (fmol/mg protein) increased 2.7 fold from postnatal day 3 (P3) to P7. Minor receptor density fluctuations were evident from P7 to adult. Similar results were obtained with [3H]DHM. In contrast, estimation of total mu binding sites (fmol/brain) revealed a continuous rise from P3 to the adult. The postnatal developmental profile of total mu binding sites was comparable to the weight gain of mouse brain and the increase in protein content. In contrast, during the same period beta-endorphin immunoreactivity (IR) levels undergo an increase that is inversely proportional to mu opioid receptor Bmax values. [3H]DAMGE binding to E14 membrane preparations was inhibited to a greater extent by Gpp(NH)p than that to P1 or adult. Additional characterization of mu receptors was accomplished by heterologous competition binding assays. IC50 values for beta-endorphin in competition with [3H]DHM and [3H]DAMGE were age dependent and differed for the two radioligands. These results suggest that mu receptor selectivity for mu-specific peptide and alkaloid ligands changes as a function of age.

Organization and plasticity of GABA neurons and receptors in monkey visual cortex

The GABA neurons of monkey area 17 are a morphologically and chemically heterogeneous population of interneurons that are normally distributed most densely within the geniculocortical recipient zones of the visual cortex. In adult monkeys deprived of visual input from one eye, the levels of immunoreactivity for GABA and GAD within neurons of these geniculocortical zones is reduced. Similar changes are seen in the levels of proteins that make up the GABAA receptor sub-type. The effects of monocular deprivation on other substances suggest that specific types of GABA neurons, such as those in which the tachykinin neuropeptide family and parvalbumin coexist with GABA, are greatly influenced by changes in visual input. That some proteins remain normal within deprived-eye neurons and that other proteins are increased indicates the changes in the GABA cells of the cortex are not the result of a general reduction in protein synthesis. Comparisons of what is known about the morphological and synaptic features of GABA cells in area 17 and the characteristics of cells affected by monocular deprivation suggests that certain classes, such as the clutch cell, may be preferential targets of deprivation. Such a selective loss of certain GABA neurons would have broad implications for the possible physiological plasticity of cortical cells, for if ongoing studies determine that specific receptive field properties are affected by monocular deprivation in adults, the correlation of functional properties and classes of GABA cells would be possible.

Intraspinal sprouting of calcitonin gene-related peptide containing primary afferents after deafferentation in the rat

The occurrence of sprouting in the spinal cord in response to denervation has been a subject of debate. To test for sprouting of primary afferent fibers after denervation, rats were unilaterally deafferented for 35 days (chronic side) by dorsal rhizotomies performed from T2 to T8 and T10 to L5, thus isolating or sparing the T9 root. The contralateral T9 root was spared by a similar surgery 5 days (acute side) prior to sacrifice. The survival time on the chronic side presumably allows intraspinal sprouting of T9 primary afferents to occur whereas the time on the acute side does not. To test for sprouting of primary afferents, it is necessary to identify these nerve processes. Calcitonin gene-related peptide (CGRP) immunoreactivity has been localized to a subpopulation of primary afferent nerve processes and their terminals within the dorsal horn. Therefore, immunohistochemical methods were used to determine the distribution of CGRP immunoreactivity in laminae I and II on both sides of the spinal cord. Using image analysis, there was an increase of 153 to 704% in the density of CGRP immunoreaction product on the chronic side compared to the acute side in the spared segment. This difference is statistically significant. Furthermore, the increased density on the chronic side extended two segments cranial and two segments caudal to the spared root segment. No difference was found in the laminar distribution between sides. These data support the hypothesis of primary afferent sprouting following spinal cord denervation.

Transient expression of opioid receptors in defined regions of developing brain: are embryonic receptors selective?

The developmental profile of opioid receptors was studied in rat and guinea pig striatum and hippocampus. The two brain regions show different receptor profiles during development, which are characteristic for each animal. Yet, both tissues and animal species share one common feature; the binding of the universal opioid ligand [3H]diprenorphine per milligram of protein is high at the early embryonic period, it decreases toward birth, and then gradually increases to the adult levels. This apparent transient expression of the receptors during the early developmental stage was manifested in the guinea pig as an actual decrease in the total receptor number. As an attempt to characterize the receptors involved in this process, the binding of the selective mu-opioid ligand [3H]Tyr-D-Ala-Gly-MePhe-NH(CH2)OH [( 3H]DAGO) was studied in striatal membranes of young (P1) and adult (P60) rats. Competition between [3H]DAGO and the delta-selective peptide Tyr-D-Pen-Gly-Phe-D-Pen (DPDPE) shows higher affinity of the delta opioid to P1 membranes than to P60 membranes, though the number of delta receptors in P1 membranes is very small. This observation is in line with a previous study suggesting that opioid receptors in embryonic striatum and hippocampus are less selective to various opioids than those of adult brain. An additional difference between adult and embryonic tissue was observed on Scatchard analysis of [3H]DAGO binding; striatum P60 membranes exhibit one binding site with a KD of 0.8 +/- 0.1 nM and Hill coefficient of 0.96, whereas striatum P1 membranes bind the peptide in an apparent cooperative fashion with an overall Hill coefficient of 1.30.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrical activity in cerebellar cultures determines Purkinje cell dendritic growth patterns

In primary dissociated cultures of mouse cerebellum a number of Purkinje cell-specific marker proteins and characteristic ionic currents appear at the appropriate developmental time. During the first week after plating, Purkinje cell dendrites elongate, but as electrical activity emerges the dendrites stop growing and branch. If endogenous electrical activity is inhibited by chronic tetrodotoxin or high magnesium treatment, dendrites continue to elongate, as if they were still immature. At the time that branching begins, intracellular calcium levels become sensitive to tetrodotoxin, suggesting that this cation may be involved in dendrite growth. Even apparently mature Purkinje cells alter their dendritic growth in response to changes in activity, suggesting long-term plasticity.

Vasoactive intestinal polypeptide in dorsal root terminals of the rat spinal cord is regulated by the axoplasmic transport in the peripheral nerve

Vasoactive intestinal polypeptide (VIP) immunoreactivity in the upper spinal dorsal horn is markedly increased after transection, crush or vinblastine treatment of the ipsilateral, segmentally related peripheral nerve. After regeneration of the peripheral nerve, VIP disappears from the upper dorsal horn. Transection-induced VIP increase is abolished by rhizotomy. It is concluded that the expression of VIP is restricted by factor(s) carried by retrograde axoplasmic transport to dorsal root ganglion cells.

Triggers and substrates of hippocampal synaptic plasticity

It is widely assumed that behavioral learning reflects adaptive properties of the neuronal networks underlying behavior. Adaptive properties of networks in turn arise from the existence of biochemical mechanisms that regulate the efficacy of synaptic transmission. Considerable progress has been made in the elucidation of the mechanisms involved in synaptic plasticity at central synapses and especially those responsible for the phenomenon of long-term potentiation (LTP) of synaptic transmission in hippocampus. While the nature and the timing requirements of the triggering steps are reasonably well known, there is still a lot of uncertainty concerning the mechanisms responsible for the long-term changes. Several biochemical processes have been proposed to play critical roles in promoting long-lasting modifications of synaptic efficacy. This review examines first the triggers that are necessary to produce LTP in the hippocampus and then the different biochemical processes that have been considered to participate in the maintenance of LTP. Finally, we examine the relationships between LTP and behavioral learning.