Associations between psychosocial work environment factors and first-time and recurrent treatment for depression: a prospective cohort study of 24,226 employees.

AIMS: Adverse factors in the psychosocial work environment are associated with the onset of depression among those without a personal history of depression. However, the evidence is sparse regarding whether adverse work factors can also play a role in depression recurrence. This study aimed to prospectively examine whether factors in the psychosocial work environment are associated with first-time and recurrent treatment for depression. METHODS: The study included 24,226 participants from the Danish Well-being in Hospital Employees study. We measured ten individual psychosocial work factors and three theoretical constructs (effort-reward imbalance, job strain and workplace social capital). We ascertained treatment for depression through registrations of hospital contacts for depression (International Statistical Classification of Diseases and Related Health Problems version 10 [ICD-10]: F32 and F33) and redeemed prescriptions of antidepressant medication (Anatomical Therapeutic Chemical [ATC]: N06A) in Danish national registries. We estimated the associations between work factors and treatment for depression for up to 2 years after baseline among those without (first-time treatment) and with (recurrent treatment) a personal history of treatment for depression before baseline. We excluded participants registered with treatment within 6 months before baseline. In supplementary analyses, we extended this washout period to up to 2 years. We applied logistic regression analyses with adjustment for confounding. RESULTS: Among 21,156 (87%) participants without a history of treatment for depression, 350 (1.7%) had first-time treatment during follow-up. Among the 3070 (13%) participants with treatment history, 353 (11%) had recurrent treatment during follow-up. Those with a history of depression generally reported a more adverse work environment than those without such a history. Baseline exposure to bullying (odds ratio [OR] = 1.72, 95% confidence interval [95% CI]: 1.30-2.32), and to some extent also low influence on work schedule (OR = 1.27, 95% CI: 0.97-1.66) and job strain (OR = 1.24, 95% CI: 0.97-1.57), was associated with first-time treatment for depression during follow-up. Baseline exposure to bullying (OR = 1.40, 95% CI: 1.04-1.88), lack of collaboration (OR = 1.31, 95% CI: 1.03-1.67) and low job control (OR = 1.27, 95% CI: 1.00-1.62) were associated with recurrent treatment for depression during follow-up. However, most work factors were not associated with treatment for depression. Using a 2-year washout period resulted in similar or stronger associations. CONCLUSIONS: Depression constitutes a substantial morbidity burden in the working-age population. Specific adverse working conditions were associated with first-time and recurrent treatment for depression and improving these may contribute to reducing the onset and recurrence of depression.

Efficacy of dexmedetomidine compared with midazolam for sedation in adult intensive care patients: a systematic review.

Patients in Intensive Care Unit (ICU) often require sedatives which commonly include midazolam and the more recently developed α2-receptor agonist, dexmedetomidine. It was our aim to compare the sedative and clinical effectiveness of dexmedetomidine vs midazolam in adults admitted to ICU, using an objective appraisal of randomized control trials. Medline, Embase, SCOPUS, Web of Knowledge, Cinhal, the United States National Library of Medicine, and the Cochrane Database of Systematic Reviews were searched using keywords: 'dexmedetomidine', 'midazolam', and 'intensive care'. These were limited to human studies and adults (>18 yr old). Six randomized controlled trials were found and were critically appraised using a standardized appraisal method. Two papers described the time spent by each intervention group within a specified target sedation range and both found no statistically significant difference between midazolam and dexmedetomidine (P=0.18 and P=0.15). A third paper found no statistically significant difference in the length of time that patients were sedated within a target zone (P=0.445). Two additional pilot studies did not report P values as they were insufficiently statistically powered. A final paper found that, of the eight occasions measured, patients on dexmedetomidine were more often within the target sedation range than patients on midazolam. The sedative benefits of dexmedetomidine vs midazolam remain inconclusive. While some secondary outcomes showed clinical effectiveness of dexmedetomidine, more research is needed to validate the findings of these studies.

N-methyl-D-aspartate receptor subunit dysfunction at hippocampal glutamatergic synapses in an animal model of attention-deficit/hyperactivity disorder.

Attention-deficit/hyperactivity disorder (ADHD) is the most common neurobehavioural disorder among children. ADHD children are hyperactive, impulsive and have problems with sustained attention. These cardinal features are also present in the best validated animal model of ADHD, the spontaneously hypertensive rat (SHR), which is derived from the Wistar Kyoto rat (WKY). Current theories of ADHD relate symptom development to factors that alter learning. N-methyl-D-aspartate receptor (NMDAR) dependent long term changes in synaptic efficacy in the mammalian CNS are thought to represent underlying cellular mechanisms for some forms of learning. We therefore hypothesized that synaptic abnormality in excitatory, glutamatergic synaptic transmission might contribute to the altered behavior in SHRs. We studied physiological and anatomical aspects of hippocampal CA3-to-CA1 synapses in age-matched SHR and WKY (controls). Electrophysiological analysis of these synapses showed reduced synaptic transmission (reduced field excitatory postsynaptic potential for a defined fiber volley size) in SHR, whereas short-term forms of synaptic plasticity, like paired-pulse facilitation, frequency facilitation, and delayed response enhancement were comparable in the two genotypes, and long-term potentiation (LTP) of synaptic transmission was of similar magnitude. However, LTP in SHR was significantly reduced (by 50%) by the NR2B specific blocker CP-101,606 (10 microM), whereas the blocker had no effect on LTP magnitude in the control rats. This indicates that the SHR has a functional predominance of NR2B, a feature characteristic of early developmental stages in these synapses. Quantitative immunofluorescence and electron microscopic postembedding immunogold cytochemistry of the three major NMDAR subunits (NR1, NR2A; and NR2B) in stratum radiatum spine synapses revealed no differences between SHR and WKY. The results indicate that functional impairments in glutamatergic synaptic transmission may be one of the underlying mechanisms leading to the abnormal behavior in SHR, and possibly in human ADHD.

Glutamate transporters in glial plasma membranes: highly differentiated localizations revealed by quantitative ultrastructural immunocytochemistry.

The glutamate transporters GLT-1 and GLAST were studied by immunogold labeling on ultrathin sections of rat brain tissue embedded in acrylic resins at low temperature after freeze substitution. Both proteins were selective markers of astrocytic plasma membranes. GLT-1 was much higher in hippocampal astrocytes than in cerebellar astrocytes. Astroglial membrane GLAST densities ranked as follows: Bergmann > cerebellar granular layer approximately hippocampus > cerebellar white matter. No astrocyte appeared unlabeled. Astrocytic membranes facing capillaries, pia, or stem dendrites were lower in glutamate transporters than those facing nerve terminals, axons, and spines. Parallel fiber boutons (glutamatergic) synapsin on interneuron dendritic shafts were surrounded by lower transporter densities than those synapsing on Purkinje cell spines. Our findings suggest the localizations of glutamate transporters are carefully regulated.

The expression of vesicular glutamate transporters defines two classes of excitatory synapse.

The quantal release of glutamate depends on its transport into synaptic vesicles. Recent work has shown that a protein previously implicated in the uptake of inorganic phosphate across the plasma membrane catalyzes glutamate uptake by synaptic vesicles. However, only a subset of glutamate neurons expresses this vesicular glutamate transporter (VGLUT1). We now report that excitatory neurons lacking VGLUT1 express a closely related protein that has also been implicated in phosphate transport. Like VGLUT1, this protein localizes to synaptic vesicles and functions as a vesicular glutamate transporter (VGLUT2). The complementary expression of VGLUT1 and 2 defines two distinct classes of excitatory synapse.

An unending challenge: how official decisions have influenced the teaching of nursing in Norway.

BACKGROUND: Over a period of more than 50 years, there have been huge changes in nursing education in Norway owing to large numbers of political and other official resolutions. AIM: To evaluate how these decisions have had influence upon the role of the nurse teacher. METHODS: The contents of political documents, government-sponsored curricula and articles in The Norwegian Nurse Organization's journal Sykepleien were analysed. FINDINGS: The main findings are structured into two periods. During the period from 1950 to 1979, nurse education was strongly bound by official detailed terms for the curriculum, and the role of the teacher was ruled by these regulations. In the next period, from 1980 to the present, the situation in nursing education changed. From now on, the teachers had to develop the curricula based on more general plans and regulations. During these years, the numbers of students increased dramatically, and there also was tremendous pressure on nurse teachers to undertake further qualifications and to do scientific work. At the same time, the teachers had to fulfil their duties in teaching and supervising the students, and support their supervisors in clinical practice. CONCLUSION: The role of the nurse teachers in Norway has, in many ways, been driven by many different interests and they are still struggling to meet the different demands made upon them.

Subcellular localization of the glutamate transporters GLAST and GLT at the neuromuscular junction in rodents.

The vertebrate neuromuscular junction (NMJ) is known to be a cholinergic synapse at which acetylcholine (ACh) is released from the presynaptic terminal to act on postsynaptic nicotinic ACh receptors. There is now growing evidence that glutamate, which is the main excitatory transmitter in the CNS and at invertebrate NMJs, may have a signaling function together with ACh also at the vertebrate NMJ. In the CNS, the extracellular concentration of glutamate is kept at a subtoxic level by Na(+)-driven high-affinity glutamate transporters located in plasma membranes of astrocytes and neurons. The glutamate transporters are also pivotal for shaping glutamate receptor responses at synapses. In order to throw further light on the potential role of glutamate as a cotransmitter at the NMJ we used high-resolution immunocytochemical methods to investigate the localization of the plasma membrane glutamate transporters GLAST (glutamate aspartate transporter) and GLT (glutamate transporter 1) in rat and mice NMJ regions. Confocal laser-scanning immunocytochemistry showed that GLT is restricted to the NMJ in rat and mouse skeletal muscle. Lack of labeling signal in knock-out mice confirmed that the immunoreactivity observed at the NMJ was specific for GLT. GLAST was also localized at the NMJ in rat but not detected in mouse NMJ (while abundant in mouse brain). Post-embedding electron microscopic immunocytochemistry and quantitative analyses in rat showed that GLAST and GLT are enriched in the junctional folds of the postsynaptic membrane at the NMJ. GLT was relatively higher in the slow-twitch muscle soleus than in the fast-twitch muscle extensor digitorum longus, whereas GLAST was relatively higher in extensor digitorum longus than in soleus. The findings show--together with previous demonstration of vesicular glutamate, a vesicular glutamate transporter and glutamate receptors--that mammalian NMJs contain the machinery required for synaptic release and action of glutamate. This indicates a signaling role for glutamate at the normal NMJ and provides a basis for the ability of denervated muscle to be reinnervated by glutamatergic axons from the CNS.

Protein phosphatase-1 regulation in the induction of long-term potentiation: heterogeneous molecular mechanisms.

Protein phosphatase inhibitor-1 (I-1) has been proposed as a regulatory element in the signal transduction cascade that couples postsynaptic calcium influx to long-term changes in synaptic strength. We have evaluated this model using mice lacking I-1. Recordings made in slices prepared from mutant animals and also in anesthetized mutant animals indicated that long-term potentiation (LTP) is deficient at perforant path-dentate granule cell synapses. In vitro, this deficit was restricted to synapses of the lateral perforant path. LTP at Schaffer collateral-CA1 pyramidal cell synapses remained normal. Thus, protein phosphatase-1-mediated regulation of NMDA receptor-dependent synaptic plasticity involves heterogeneous molecular mechanisms, in both different dendritic subregions and different neuronal subtypes. Examination of the performance of I-1 mutants in spatial learning tests indicated that intact LTP at lateral perforant path-granule cell synapses is either redundant or is not involved in this form of learning.

Ultrastructural quantification of glutamate receptors at excitatory synapses in hippocampus of synapsin I+II double knock-out mice.

Previous findings, mainly in in vitro systems, have shown that the density of vesicles and the synaptic efficacy at excitatory synapses are reduced in the absence of synapsins, despite the fact that transgenic mice lacking synapsins develop an epileptic phenotype. Here we study glutamate receptors by quantitative immunoblotting and by quantitative electron microscopic postembedding immunocytochemistry in hippocampus of perfusion fixed control wild type and double knock-out mice lacking synapsins I and II. In wild type hippocampus the densities of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor subunits were higher (indicated for glutamate receptor subunit 1, highly significant for glutamate receptor subunits 2/3) in mossy fiber-to-cornu ammonis 3 pyramidal cell synapses than in the Schaffer collateral/commissural-to-cornu ammonis 1 pyramidal cell synapses, the two synapse categories that carry the main excitatory throughput of the hippocampus. The opposite was true for N-methyl-D-aspartate receptors. The difference in localization of glutamate receptor subunit 1 receptor subunits was increased in the double knock-out mice while there was no change in the overall expression of the glutamate receptors in hippocampus as shown by quantitative Western blotting. The increased level of glutamate receptor subunit 1 at the mossy fiber-to-cornu ammonis 3 pyramidal cell synapse may result in alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors with reduced proportions of glutamate receptor subunit 2, and hence increased Ca2+ influx, which could cause increased excitability despite of impaired synaptic function (cf. [Krestel HE, Shimshek DR, Jensen V, Nevian T, Kim J, Geng Y, Bast T, Depaulis A, Schonig K, Schwenk F, Bujard H, Hvalby O, Sprengel R, Seeburg PH (2004) A genetic switch for epilepsy in adult mice. J Neurosci 24:10568-10578]), possibly underlying the seizure proneness in the synapsin double knock-out mice. In addition, the tendency to increased predominance of N-methyl-d-aspartate receptors at the main type of excitatory synapse onto cornu ammonis 1 pyramidal cells might contribute to the seizure susceptibility of the synapsin deficient mice. The results showed no significant changes in the proportion of 'silent' Schaffer collateral/commissural synapses lacking alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors or in the synaptic membrane size, indicating that plasticity involving these parameters is not preferentially triggered due to lack of synapsins.

Venous bypass of complicated stent placement for recurrent extracranial carotid occlusive disease.

Aim of the study was to to demonstrate a useful solution to carotid angioplasty and stent complications. A 67 year old male had uncomplicated left carotid endarterectomies in 1985 and 1986. A left distal common carotid angioplasty and stent in 1999 was complicated by stenosis. In 2000 a left common carotid bypass from the lower common carotid to the distal internal carotid well above the stent was performed, yielding retrograde filling of the external carotid, distal antegrade filling of the internal carotid, and widely patent vessels in subsequent Doppler studies. He is currently doing well clinically with no recurrent stenosis. In conclusion a second redo carotid operation was deferred in favor of angioplasty and stent, which had complications. Despite prior operations the only difficulty with the reoperation was obtaining control of the distal internal carotid above the stent. The strategy demonstrated here will be useful to correct complications of carotid angioplasty and stenting.

Redistribution of neuroactive amino acids in hippocampus and striatum during hypoglycemia: a quantitative immunogold study.

Postembedding immunocytochemistry was used to localize aspartate, glutamate, gamma-aminobutyric acid (GABA), and glutamine in hippocampus and striatum during normo- and hypoglycemia in rat. In both brain regions, hypoglycemia caused aspartatelike immunoreactivity to increase. In hippocampus, this increase was evident particularly in the terminals of known excitatory afferents-in GABA-ergic neurons and myelinated axons. Aspartate was enriched along with glutamate in nerve terminals forming asymmetric synapses on spines and with GABA in terminals forming symmetric synapses on granule and pyramidal cell bodies. In both types of terminal, aspartate was associated with clusters of synaptic vesicles. Glutamate and glutamine immunolabeling were markedly reduced in all tissue elements in both brain regions, but less in the terminals than in the dendrosomatic compartments of excitatory neurons. In glial cells, glutamine labeling showed only slight attenuation. The level of GABA immunolabeling did not change significantly during hypoglycemia. The results support the view that glutamate and glutamine are used as energy substrates in hypoglycemia. Under these conditions both excitatory and inhibitory terminals are enriched with aspartate, which may be released from these nerve endings and thus contribute to the pattern of neuronal death characteristic of hypoglycemia.

Aspartate- and Glutamate-like Immunoreactivities in Rat Hippocampal Slices: Depolarization-induced Redistribution and Effects of Precursors.

The light microscopic localization of aspartate-like immunoreactivity (Asp-LI) was compared to that of glutamate-like immunoreactivity (Glu-LI) in hippocampal slices by means of specific polyclonal antibodies recognizing the amino acids fixed by glutaraldehyde. After incubation in Krebs' solution with normal (5 mM) or depolarizing concentrations of K+, and various additives, the slices were fixed with glutaraldehyde, resectioned and processed according to the peroxidase - antiperoxidase procedure. At 5 mM K+, Glu-LI was localized in nerve-terminal like dots with a conspicuous laminar distribution, the highest Glu-LI concentrations coinciding with the terminal fields of major excitatory pathways thought to use glutamate or aspartate as transmitters. The localization of Asp-LI showed some similarity to that of Glu-LI, but the laminar distribution was less differentiated and the immunoreactivity was much weaker. At 40 and 55 mM K+ the nerve terminal localizations of Glu-LI and Asp-LI were strongly reduced. Concomitantly, both immunoreactivities appeared in astroglial cells. These changes were Ca2+-dependent. The nerve ending staining patterns of Asp-LI and Glu-LI could be sustained during depolarization if the medium was supplemented with glutamine (0.5 mM). Under these conditions Asp-LI became more intense and its distribution approached that of Glu-LI. This suggests that, when stimulated, some nerve endings can increase their reservoir of releasable aspartate. The presence of glutamine during depolarization strongly reduced glial Asp-LI and Glu-LI, possibly due to its providing nitrogen for conversion of glutamate to glutamine. alpha-Ketoglutarate, another glia-derived precursor of neuronal glutamate, was virtually ineffective in supporting Glu-LI and Asp-LI in nerve endings, and did not suppress Glu-LI or Asp-LI in glia. Our findings provide morphological support for the view that excitatory nerve endings under certain conditions can contain high levels of both aspartate and glutamate (possibly in the same terminals), and that aspartate as well as glutamate can be released synaptically. Further, they underline the importance of the glial supply of the nerve endings with precursor glutamine, which allows them to build up and sustain high concentrations of transmitter amino acids during release.

Glutamate- and GABA-containing neurons in the mouse and rat brain, as demonstrated with a new immunocytochemical technique.

Antisera were raised against gamma-aminobutyric acid (GABA) or glutamate (Glu) conjugated to bovine serum albumin with glutaraldehyde. After purification, these antisera reacted strongly with fixed GABA or Glu, but not significantly with other amino acids fixed with glutaraldehyde to brain macromolecules. The antisera were used to demonstrate the distributions of Glu-like and GABA-like immunoreactivities (Glu-LI and GABA-LI) in parts of the perfusion-fixed mouse and rat brain, including the olfactory bulb, cerebral neocortex, thalamus, basal ganglia, lower brain stem, and cerebellum. The level of GABA-LI varied widely among brain regions, thus it was very high in the globus pallidus and substantia nigra and low in the bulk of the thalamus. The GABA antisera labeled nonpyramidal neurons of the neocortex, most cells of the reticular nucleus of the thalamus, medium-sized cells of the caudatoputamen, and stellate, basket, Golgi, and Purkinje cells of the cerebellum. The distribution of GABA-LI closely matched that of the GABA-synthesizing enzyme, glutamic acid decarboxylase (GAD), as revealed in immunocytochemical studies by others. However, the GABA antisera seem to be better suited than GAD antisera for demonstrating putative GABA-ergic axons. The results suggest that GABA-LI, as displayed by the present method, is a good marker of neurons thought to use GABA as a transmitter. Glutamate-like immunoreactivity was much more evenly distributed among regions than GABA-LI, but was particularly low in globus pallidus and substantia nigra and high in the cerebral cortex. Mitral cells of the olfactory bulb, pyramidal neocortical cells, and other cells assumed to use Glu or aspartate as transmitter were stained for Glu-LI, but so also were neurons that are thought to use other transmitters, such as cells in the substantia nigra pars compacta, in the dorsal raphe nucleus, and in the brain stem motor nuclei. The Glu antisera seem to reveal the "transmitter pool" as well as the "metabolic pool" of Glu in perfusion-fixed material. This report shows that it is possible by means of immunocytochemistry to display reliably the tissue contents of GABA and Glu in material that has been fixed by perfusion with glutaraldehyde.

GABA- and glycine-immunoreactive neurons in the spinal cord of the carp, Cyprinus carpio.

gamma-Aminobutyric acid (GABA) and glycine are the two main inhibitory transmitter amino acids in the central nervous system of vertebrates. The distribution of cells containing GABA and glycine in the carp spinal cord was examined by using specific antisera raised against the two amino acids conjugated to bovine serum albumin. The immunoreaction on serial paraffin sections was visualized by a streptavidin-biotin method. Both antisera gave highly specific labelings of cells. At least three types of GABA-immunoreactive cells were found. They were small cells in the dorsal grey matter, various sized cells in the central and ventral grey, and some ependymal cells contacting the central canal. In addition, very small cells and neuropil structures in the dorsal horn were strongly immunoreactive to the GABA serum. Certain cells in the ventral horn have moderate numbers of labelled synaptic boutons on the perikarya, but very few GABA-labelled terminals were found on putative motoneurons. The immunoreactive ependymal cells appeared to have a ventrolaterally directed axon. The glycine antiserum labelled small and intermediate cells in the dorsal grey, large, elongated cells in the median region, and varying sized cells in the ventral grey. The numbers and density of immunoreactive cells and neuropil structures in the ventral horn were fewer and lower than in GABA-stained sections. The median large cells had a thick ventrolateral process. The ventral intermediate cells were often found near putative motoneurons. Labelled synaptic boutons were present on most ventral cells including putative motoneurons and interneurons. Abundant distribution of cells immunoreactive to both antisera suggest important roles of both GABA and glycine as neurotransmitters for controlling swimming movements in teleosts.

Glutamate, GABA, and glycine in the human retina: an immunocytochemical investigation.

The distribution of the neuroactive amino acids glutamate, GABA, and glycine in the human retina was examined in consecutive semithin sections treated with antisera specific for fixed glutamate, GABA, and glycine, respectively. Glutamate immunoreactivity was conspicuous in all photoreceptor cells (rods more strongly labelled than cones), and in a majority (85-89%) of the cells in the inner nuclear layer (INL). Rod spherules and cone pedicles showed a greater enrichment of glutamate immunoreactivity than the parent cell bodies and inner segments. Also, structures of the inner plexiform layer (IPL) were labelled. A large majority (83-91%) of cells in the ganglion cell layer (GCL) was strongly stained, as were most axons in the nerve fibre layer. Müller cell processes appeared unstained. GABA immunoreactivity was present in presumed amacrine but not in bipolar-like cells. The stained cells were restricted to the inner 1/3 of the INL and were more frequent in central than in peripheral retina (40% and 26% of all cells in the inner 1/2 of INL, respectively). GABA positive cell processes, probably originating from interplexiform cells, appeared to traverse the INL and end in the outer plexiform layer. Dense immunolabeling was found in the IPL. GABA immunoreactive cells (some also stained for glutamate) comprised 23% of all GCL cells in the peripheral retina, but only 5% in the central retina. Most of them were localized adjacent to the IPL. A few GABA positive (possibly ganglion) cells extended a single fibre toward the nerve fibre layer. Solitary GABA positive fibres were seen in this layer and in the optic nerve. Glycine immunoreactivity was observed in cells with the location typical of amacrine and bipolar (peripheral retina) cells, as well as in punctate structures of the IPL. In contrast to the GABA positive cells, the glycine positive cells were more frequent in the peripheral than in the central retina (42% and 23% of all cells in inner 1/3 of INL, respectively). A few cells in the GCL (0.5-1.5%) were glycine positive. Glutamate colocalized with GABA or glycine in a majority of the cells stained for either of these inhibitory transmitters (90-95% of the GABA positive cells, and 80-86% of the glycine positive cells, in the INL). Some bipolar cells were stained for both glutamate and glycine. Colocalization of GABA and glycine occurred in a subpopulation (3-4%) of presumed amacrine cells, about half of which was also glutamate positive.

Taurine-like immunoreactivity in the brain of the honeybee.

Taurine (2-aminoethanesulfonic acid) is one of the most abundant free amino acids in the insect central nervous system. We have investigated the distribution of taurine-like immunoreactivity in the brain of the honeybee with an antiserum recognizing fixed taurine. Taurine-like immunoreactivity appeared within neuronal perikarya, neurites, and terminals, whereas glial cells were unlabelled. All photoreceptor cells of the compound eyes and the ocelli were stained. So were the fibers of the anterior superior optic tract, which connects the optic lobes to the mushroom bodies in the median protocerebrum. In the mushroom bodies the majority of intrinsic Kenyon cells showed high levels of taurine-like immunoreactivity. The lateral antennoglomerular tract, which interconnects the mushroom bodies with the antennal lobes, was also intensely stained. In the antennal lobes, strong labelling was observed within a few fibers that invade a set of posterior glomeruli from the posterior margin. Sensory projections from the antennal nerve into the antennal lobes showed only intermediate levels of staining. Sensory projections into the dorsal lobe were devoid of taurine-like immunoreactivity. Labral, mandibular, maxillary, and labial nerves, which innervate the various parts of the feeding apparatus, contain a set of five to eight heavily stained fibers. A comparison of taurine-like immunoreactivity with glutamate- and GABA-like immunoreactivities in the brain of the honeybee indicates that the three amino acids are enriched in distinct neuronal populations.

Projections to the pontine nuclei from choline acetyltransferase-like immunoreactive neurons in the brainstem of the cat.

By use of retrograde transport of horseradish peroxidase-wheat germ agglutinin (HRP-WGA) in combination with monoclonal antibodies against choline acetyltransferase (ChAT), we show that putative cholinergic inputs to the feline pontine nuclei originate from cells in the dorsolateral pontine tegmentum. These cells form a loosely arranged continuum that nevertheless may be subdivided into two groups on the basis of differences in cell morphology. One group consists of double-labeled cells in the periventricular gray substance medial to, and partly merging with, the nucleus locus coeruleus. The other group consists of double-labeled cells surrounding the brachium conjunctivum. In two cats with tracer injections in the pontine nuclei, 81% and 84%, respectively, of the retrogradely labeled cells in the dorsolateral pontine tegmentum are ChAT-like immunoreactive (ChAT-LI). In the same experiments, many ChAT-LI cells, but no retrogradely labeled cells, are seen in the basal telencephalon. The pontine nuclei contain a plexus of thin ChAT-LI fibers with varicosities resembling en passant as well as terminal boutons. These ChAT-LI fibers appear to branch extensively and cover all parts of the pontine nuclei. Following injections of rhodamine-B-isothiocyanate (RITC) in the thalamus and Fluoro-Gold in the pontine nuclei and surrounding regions in the same animal, all retrogradely labeled cells in the dorsolateral pontine tegmentum are labeled with both tracers, whereas most cells in the paramedian pontine reticular formation are labeled either with RITC or Fluoro-Gold. Thus it appears that all cells in the dorsolateral pontine tegmentum that project to the pontine nuclei also project to the thalamus. In analogy with findings by others in the dorsal lateral geniculate nucleus, we suggest that the putative cholinergic projections to the pontine nuclei may serve to modulate transmission of cerebellar afferent information in accordance with the behavioral state of the animal.

The early development of neurons with GABA immunoreactivity in the CNS of Xenopus laevis embryos.

We have used an antibody to glutaraldehyde fixation complexes of gamma-amino butyric acid (GABA) to stain the developing central nervous system of Xenopus laevis embryos. Neuronal somata, growth cones, axons, and dendrites were found with GABA-like immunoreactivity. Transmission electron microscope (TEM) observations were made of axons and synapses. By observation of the earliest stages of differentiation of neurons, seven classes of putative GABAergic interneurons were discerned. 1) Ascending neurons are first stained in the hindbrain at stage 26 and later extend caudally in the spinal cord. They have ascending ipsilateral axons. 2) Midhindbrain reticulospinal neurons are first stained at stage 25 and develop as a compact group with descending ipsilateral and contralateral axons. 3) Vestibular complex commissural neurons are first stained at stage 29/30 in a dorsal position near the entry of the seventh and eighth cranial nerves. They have ventral commissural axons that descend contralaterally and their somata form a compact mass. 4) Rostral hindbrain commissural neurons are first stained at stage 33/34 just rostral to the entry of the trigeminal nerve. They each have a decussating projection. 5) Rostral midbrain neurons are first stained in the midbrain at stage 29/30 and are later associated with prominent dorsal and ventral commissures. 6) Optic tract and 7) rostral forebrain neurons are found in the forebrain associated with strongly stained axon tracts. The direction of axonal growth from its earliest stages was distinct for each class of hindbrain and spinal cord neuron.

Glutamate is concentrated in and released from parallel fiber terminals in the dorsal cochlear nucleus: a quantitative immunocytochemical analysis in guinea pig.

The present paper addresses the identity of the neurotransmitter(s) of the parallel fibers in the molecular layer of the dorsal cochlear nucleus, a brainstem center in the pathway for sound perception. The distribution of putative neurotransmitter amino acids was studied by using postembedding single- and double-immunolabeling procedures. Perfusion-fixed brains and immersion-fixed slices from in vitro release experiments were evaluated. Quantitative immunogold analyses revealed that the parallel fiber terminals were significantly enriched with glutamate immunoreactivity compared with other terminals, dendrites, and glial processes. Within the parallel fiber terminals, the gold particles signaling the presence of glutamate were concentrated over vesicle clusters relative to the axoplasmic matrix. Furthermore, the parallel fiber terminals, but not the parent granule cell bodies, could be depleted of glutamate immunoreactivity by exposure to depolarizing concentrations of K+ in vitro. This depletion was partly dependent on Ca2+. In double-labeled preparations, the glutamine:glutamate ratio was by far higher in glial processes than in other types of profile. Aspartate immunoreactivity was mainly concentrated in neuronal cell bodies and dendrites and was very low in fiber terminals, particularly in those of the parallel fibers. These data indicate that parallel fiber terminals contain a glutamate pool that is associated with synaptic vesicles and that can be subject to release. The glial processes that are found in proximity to the terminals may provide them with the glutamine required for glutamate replenishment. No evidence was found for a neurotransmitter role of aspartate in the parallel fibers.

Extrasynaptic localization of taurine-like immunoreactivity in the lamprey spinal cord.

Taurine is an endogenous amino acid that can occur in nerve terminals in the central nervous system and that can produce inhibitory neuronal responses. It is unclear, however, whether this amino acid can function as a synaptic transmitter. To examine the distribution of taurine at high anatomical resolution in a vertebrate, light and electron microscopic immunocytochemical postembedding techniques were applied to the lamprey spinal cord (Ichtyomyzon unicuspis and Lampetra fluviatilis), which contains many large, unmyelinated axons. The most intense immunolabeling occurred in a population of liquor-contacting cells (tanycytes), located around the central canal, which extended processes to the dorsal, lateral, and ventral margins of the spinal cord. In addition, a proportion of the taurine-immunoreactive cells contained gamma-aminobutyric acid (GABA)-like immunoreactivity. A moderate level of taurine immunoreactivity was also present in ependymal cells, located around the central canal, as well as in astrocytes throughout all regions of the spinal cord. At the ultrastructural level, the taurine immunoreactivity showed an even distribution in the cytoplasm of the labeled cells. In contrast to the glial labeling, neuronal cell bodies and axons exhibited very low levels of taurine labeling, which were similar to the level of background labeling. The synaptic vesicle clusters within the axons did not show any clear accumulation of taurine immunoreactivity. These results suggest that taurine may have metabolic roles in the lamprey spinal cord, and, as in other systems, it may take part in osmoregulation. However, the lack of immunolabeling in presynaptic elements is not consistent with a role of taurine as a synaptic transmitter.