Anatomy of the antennal motoneurons in the brain of the honeybee (Apis mellifera)

This paper describes the morphology and location of the cerebral motoneurons that control the movement of the antennae in the honeybee. The position of each antenna is controlled by two muscle systems; the basal segment (scape) is moved by four muscles within the head capsule, and two muscles within the scape control the distal segments (flagellum) of the antenna. The motor system of the scape is controlled by nine motoneurons, and that of the flagellum by six motoneurons. All of these motoneurons share the dorsal lobe as a common projection area where their dendritic fields overlap extensively. These motoneurons do not have contralateral projections. The cell bodies of the antennal motoneurons are located in the soma layer lateral to the dorsal lobe. The somata for each muscle system are arranged in three clusters; two clusters are located in a region of the cortex dorsal to the dorsal lobe and one cluster is located in the cortex ventral to the dorsal lobe. In the cortex dorsal to the dorsal lobe, one cluster of each muscle system shares the same region. Altogether five groups of cell bodies can be distinguished. Double labeling of the motoneurons and presumptive mechanosensory primary antennal afferents with fluorescent dyes has shown that there is an extensive overlap of axonal projection of antennal mechanosensory afferents with dendritic fields of antennal motoneurons. © 1995 Wiley-Liss, Inc.     

Central distribution of trigeminal and upper cervical primary afferents in the rat studied by anterograde transport of horseradish peroxidase conjugated to wheat germ agglutinin

Injections of WGA-HRP were made in the rat trigeminal ganglion and C1-3 dorsal root ganglia (DRGs) to study the central projection patterns and their relations to each other. Trigeminal ganglion injections resulted in heavy terminal labeling in all trigeminal sensory nuclei. Prominent labeling was also observed in the solitary tract nucleus and in the medial parts of the dorsal horn at C1-3 levels, but labeling could be followed caudally to the C7 segment. Contralateral trigeminal projections were found in the nucleus caudalis and in the dorsal horn at C1-3 levels. The C1 DRG was found to be inconstant in the rat. When it was present, small amounts of terminal labeling were found in the external cuneate nucleus (ECN) and the central cervical nucleus (CCN). No dorsal horn projections were seen from the C1 DRG. Injections in the C2 DRG resulted in heavy labeling in the ECN, nucleus X, CCN, and dorsal horn, where it was mainly located in lateral areas. Labeling could be followed caudally to the Th 7 segment. C2 DRG projections also appeared in the cuneate nucleus (Cun), in all the trigeminal sensory nuclei, and in the spinal, medial, and lateral vestibular nuclei. A small C2 DRG projection was observed in the ventral cochlear nucleus. C3 DRG injections resulted in heavy labeling in both medial middle and lateral parts of the dorsal horn, in the ECN, and in nucleus X, whereas the labeling in the CCN was somewhat weaker. Smaller projections were seen to trigeminal nuclei, Cun, and the column of Clarke. Comparisons of the central projection fields of trigeminal and upper cervical primary afferents indicated a somatotopic organization but with a certain degree of overlap.     

Serotonin depolarizes type A and C primary afferents: an intracellular study in bullfrog dorsal root ganglion

Intracellular recordings were obtained from the somata of type A and C primary afferents in the isolated bullfrog dorsal root ganglion (DRG) preparation. Bath application of serotonin (5-HT) in concentrations of 0.25-1.0 mM led to slow and fast depolarizing responses. Slow, maintained 5-HT depolarizations were observed in 47% of type A and 70% of type C neurons. These slow depolarizations were associated with an underlying increase in input resistance (Rin). In some type A neurons, the Rin increase was masked by a decrease in Rin due to depolarization-induced rectification. The slow 5-HT depolarization of type A, but not type C neurons showed pronounced tachyphylaxis to repeated 5-HT applications. In type C afferents, serotonin's slow action was often accompanied by spontaneous firing. Manganese decreased slow 5-HT depolarizations of both cell types. A slow depolarization and excitation of type C afferents by methysergide and cinanserin was also observed. Fast transient 5-HT depolarizations accompanied by a rapid decrease in Rin were observed in 7% of type A and 24% of type C neurons. In some DRG cells the fast and slow depolarizations combined to form a biphasic response. The actions of 5-HT reported here resemble in some ways 5-HT responses recorded extracellularly from the spinal terminations of primary afferents.     

Central processing of sex pheromone,host odour,and oviposition deterrent information by interneurons in the antennal lobe of female Spodoptera littoralis (Lepidoptera: Noctuidae)

Physiological and anatomical characteristics of antennal lobe interneurons in female Spodoptera littoralis (Boisd.) were investigated using intracellular recording and staining techniques. Responses of local interneurons and projection neurons to female sex pheromone components, host plant odours, and behaviourally active oviposition deterrents were recorded. We found local interneurons and projection neurons that responded specifically to only one or two of the tested odours, but we also found less specific cells, and neurons that responded to most of the tested odourants. These findings show that there are not only specific olfactory pathways in female moths up to the protocerebral level, but also that integration can begin in the antennal lobe. No correlation was found between the degree of specificity of either local interneurons or projection neurons and their respective morphological characteristics. Specialized and unspecialized local interneurons arborized throughout the antennal lobe. Specialized and unspecialized projection neurons had uniglomerular arborizations in the antennal lobe and sent their axons to the calyces of the mushroom body, and to the lateral horn of the protocerebrum. One specific projection neuron had multiglomerular arborizations and projected only to the lateral horn of the protocerebrum. Projection neurons arborizing in the glomeruli closest to the entrance of the antennal nerve always responded to pheromone components. No other correlations were found between the arborization pattern of projection neurons in the antennal lobe or in the protocerebrum and their response characteristics. The sensitivity of local interneurons and projection neurons was in the same range as that of receptor neurons in olfactory sensilla on the antennae, suggesting a much lower convergence in the central nervous system in females than in the pheromone-processing pathway in males. © 1994 Wiley-Liss, Inc.     

Specific expression of ezrin, a cytoskeletal-membrane linker protein, in a subset of chick retinotectal and sensory projections

Lamina-specific neuronal connections are a fundamental feature in many parts of the vertebrate central nervous system. In the chick, the optic tectum is the primary visual centre, and it has a multilaminated structure consisting of 15 laminae, of which only three or four receive retinal projections. Each of the retinorecipient laminae establishes synaptic connections selectively from one of a few subsets of retinal ganglion cells (RGCs). We have generated a series of monoclonal antibodies that appear to stain only one of the retinorecipient laminae. One of these, TB4, stained lamina F which receives inputs from a subpopulation of approximately 10-20% of RGCs which express the presynaptic acetylcholine receptor beta2-subunit. TB4 recognized a single 79-kDa protein on immunoblotting. cDNA cloning and immunochemical analysis revealed that the TB4 antigen molecule was ezrin, a cytoskeletal-membrane linker molecule belonging to the ezrin-radixin-moesin family. Unilateral enucleation of the eye, both prior to and after the establishment of retinotectal projections, attenuated the lamina-selective staining with TB4 in the contralateral tectum, suggesting that ezrin is anterogradely transported from RGCs to lamina F. Ezrin was thus expressed in a subset of RGCs that project to lamina F. Similar subset-selective expression and resultant lamina-selective distribution of ezrin were also observed in the lamina-specific central projections from the dorsal root ganglia. The staining pattern with TB4 in the dorsal root ganglia and spinal cord indicated that high expression of ezrin was restricted in cutaneous sensory neurons, but not in muscle sensory neurons. Since ezrin modulates cell morphology and cell adhesion profiles by linking membrane proteins with the cytoskeleton, it was suggested that ezrin is involved in the formation and/or maintenance of lamina-specific connections for neuronal subpopulations in the visual and somatosensory systems.     

Immunoreactivity against choline acetyltransferase,gamma-aminobutyric acid,histamine, octopamine,and serotonin in the larval chemosensory system of Dosophila melanogaster

We have studied the distribution of choline acetyltransferase (ChAT), gamma-aminobutyric acid (GABA), histamine, octopamine and serotonin in the larval chemosensory system of Drosophila melanogaster. Colocalization at the confocal level with green fluorescent protein (GFP) or Tau-GFP reporters, expressed in selected P[GAL4] enhancer trap lines, was used to identify the cells making up these neurotransmitters. As in the adult fly, larval olfactory afferents project into the (larval) antennal lobe (LAL), where they synapse onto local interneurons and projection neurons, whereas gustatory afferents terminate essentially in the tritocerebral-subesophageal (TR-SOG) region. We demonstrate that the neuropils of the LAL and the TR-SOG are immunoreactive to ChAT and GABA. In addition, serotonin- and octopamine-immunoreactive fibers are present in the LAL. ChAT immunostaining is localized in subsets of olfactory and gustatory afferents and in many of the projection neurons. In contrast, GABA is expressed in most, and perhaps all, of the local interneurons. Serotonin immunoreactivity in the LAL derives from a single neuron that is situated close to the LAL and projects to additional neuropil regions. Taken together, these findings resemble the situation in the adult fly. Hence, given the highly reduced numbers of odorant receptor neurons in the larva, as shown in a previous study (Python and Stocker [2002] J. Comp. Neurol. 445:374-387), the larval system may become an attractive model system for studying the roles of neurotransmitters in olfactory processing.     

The effects of convulsant doses of penicillin on primary afferents, dorsal root ganglion cells, and on ‘presynaptic’ inhibition in the spinal cord

Intracellular recordings were made from neurons in dorsal root ganglia (DRG) of rats, isolated in vitro. The depolarization of DRG cells caused by the application of gamma-aminobutyric acid (GABA) diminished reversibly when penicillin (0.08–2.0 mM) was added to the bathing fluid. The decrease of the input resistance of DRG cells measured during GABA perfusion was also depressed in the presence of penicillin, but no evidence of a shift of the reversal potential of the GABA-induced depolarization was found. Nor did penicillin (up to 10 mM) cause a change in the voltage-current function, in electrical excitability, in the inclination to repetitive firing, bursting discharge, or after discharge. In decapitate cat preparation the amplitude of the negative dorsal root potential (DRP or DR V) diminished by 0–50% after the i.v. administration of 0.5–1.0 × 10⁶I.U./kg (the convulsant dose) of penicillin. Post-tetanic depression of the DRP was aggravated by penicillin. The degree of depression of the DRP bore no relationship to the promptness of the eruption, and to the intensity, of the seizure activity induced by penicillin. The rates of rise and fall of the negative DRP (DR V) were consistently slowed, the positive DRP (DR V) reduced, and the dorsal root reflex (DRR) blocked by penicillin. Inhibitory reflex effects presumed to be presynaptic were either enhanced or unchanged, never depressed by penicillin. This was seen when inhibitory function was gauged by monosynaptic reflex amplitude, and also from the inhibition of ventral root electronic excitatory postsynaptic potentials (VR EPSPs). Possible explanations of these seemingly paradoxical findings are discussed, with arguments in favor and against each.     

Brainstem afferents to the magnocellular basal forebrain studied by axonal transport, immunohistochemistry, and electrophysiology in the rat

Brainstem afferents to the magnocellular basal forebrain were studied by using tract tracing, immunohistochemistry and extracellular recordings in the rat. WGA-HRP injections into the horizontal limb of the diagonal band (HDB) and the magnocellular preoptic area (MgPA) retrogradely labelled many neurons in the pedunculopontine and laterodorsal tegmental nuclei, dorsal raphe nucleus, and ventral tegmental area. Areas with moderate numbers of retrogradely labelled neurons included the median raphe nucleus, and area lateral to the medial longitudinal fasciculus in the pons, the locus ceruleus, and the medial parabrachial nucleus. A few labelled neurons were seen in the substantia nigra pars compacta, mesencephalic and pontine reticular formation, a midline area in the pontine central gray, lateral parabrachial nucleus, raphe magnus, prepositus hypoglossal nucleus, nucleus of the solitary tract, and ventrolateral medulla. A similar but not identical distribution of labelled neurons was seen following WGA-HRP injections into the nucleus basalis magnocellularis. The possible neurotransmitter content of some of these afferents to the HDB/MgPA was examined by combining retrograde Fluoro-Gold labelling and immunofluorescence. In the mesopontine tegmentum, many retrogradely labelled neurons were immunoreactive for choline acetyltransferase. In the dorsal raphe nucleus, some retrogradely labelled neurons were positive for serotonin and some for tyrosine hydroxylase (TH); however, the majority of retrogradely labelled neurons in this region were not immunoreactive for either marker. The ventral tegmental area, substantia nigra pars compacta, and locus ceruleus contained retrogradely labelled neurons which were also immunoreactive for TH. Of the retrogradely labelled neurons occasionally observed in the nucleus of the solitary tract, prepositus hypoglossal nucleus, and ventrolateral medulla, some were immunoreactive for either TH or phenylethanolamine-N-methyltransferase. To characterize functionally some of these brainstem afferents, extracellular recordings were made from antidromically identified cortically projecting neurons, mostly located in the HDB and MgPA. In agreement with most previous studies, about half (48%) of these neurons were spontaneously active. Electrical stimulation in the vicinity of the pedunculopontine tegmental and dorsal raphe nuclei elicited either excitatory or inhibitory responses in 21% (13/62) of the cortically projecting neurons.(ABSTRACT TRUNCATED AT 400 WORDS)     

Molecular characterization and comparative localization of the mRNAs encoding two glutamic acid decarboxylases (GAD65 and GAD67) in the brain of the African lungfish, Protopterus annectens

The existence of two distinct genes encoding two isoforms of glutamic acid decarboxylase (GAD65 and GAD67) has been demonstrated in most vertebrate classes, yet little is known about their differential distributions and functions in the central nervous system in nonmammalian vertebrates. In the present study, we have partially sequenced the cDNAs encoding GAD65 and GAD67 in the lungfish Protopterus annectens and determined their relative distributions in the adult brain by in situ hybridization histochemistry. The expression patterns of the GAD65 and GAD67 mRNAs were globally similar; the highest expression levels being observed in the granular layer of the olfactory bulb, the pallium, the subpallium, the anterior preoptic area, the thalamus, the hindbrain central gray, and the rhombencephalic visceral areas. However, striking differential expression was noticed in several structures. Very high to high concentrations of GAD67 mRNA were seen in the dorsal and ventral aspects of the anterior olfactory nucleus, which is in marked contrast to the very low expression of GAD65 in this region. Similarly, high levels of GAD67 mRNA were observed in the intermediate and ventral parts of the medial pallium that were virtually devoid of GAD65 mRNA. In contrast, GAD65 mRNA was found in the periaqueductal gray that did not express GAD67 mRNA. The differential expression of GAD65 and GAD67 mRNAs in these regions of the lungfish CNS indicates that the two GAD isoforms can be differentially regulated and that they may have distinct physiological roles.     

Peptidergic neurons in the snail Helix pomatia: Distribution of neurons in the central and peripheral nervous systems that react with an Antibody raised to the insect neuropeptide,leucokinin I

In this study, antiserum raised against an insect myotropic peptide, leucokinin I (DPAFNSWGamide), was: used for mapping leucokinin-like immunoreactive (LK-LI) neurons in the gastropod mollusc, Helix pomatia. Immunocytochemistry performed on both whole-mounts and cryostat sections demonstrated LK-LI neurons in all ganglia of the central nervous system (CNS), except the visceral ganglion. Altogether about 700 immunolabelled neurons have been found, with nearly one-half (46%) in the cerebral ganglia. A large proportion of the LK-LI neurons have small cell bodies and are likely to be interneurons. The most prominent LK-LI cell group is represented by the entire neuron population of the mesocerebri, which is the major source of a thick fiber bundle system, encircling and innervating the whole CNS. One single LK-LI giant neuron was found, which is located in the left pedal ganglion and is termed GLPdLKC (giant left pedal leucokinin immunoreactive cell). This cell has not been identified previously. The ganglion neuropils are heavily innervated by varicose LK-LI fiber arborizations. Some integrative centers, such as the medullary neuropil of the procerebri, reveal an extreme density of LK-LI innervation. All major peripheral nerves contain a large number of LK-LI axons, and LK-LI innervation is found in the musculature of different peripheral organs (buccal mass, lip, tentacles, oviduct, intestine). Among the peripheral organs investigated, the intestine contains a rich varicose LK-LI network, composed of both intrinsic and extrinsic elements. Radioimmunoassay (RIA) demonstrates a very high content of LK-LI material in Helix ganglion extracts (about 50 pmol/CNS). This is the first report on the occurrence of a substance resembling the myotropic neuropeptide leucokinin I in a phylum outside arthropods. Based on our immunocytochemical observations, a role for leucokinin-like peptides in both central and peripheral regulatory processes in Helix is suggested. According to double-labelling experiments, only a small number of the LK-LI neurons are labelled with an antibody to the vertebrate tachykinin substance P.     

Enhanced fidelity of diffusive nitric oxide signalling by the spatial segregation of source and target neurones in the memory centre of an insect brain

The messenger molecule nitric oxide (NO) is a key mediator of memory formation that can diffuse in the brain over tens of micrometres. It would seem therefore that NO derived from many individual neurones may merge into a volume signal that is inevitably ambiguous, relatively unspecific and thus unreliable. Here we report on the neuronal architecture that supports the NO-cyclic GMP signalling pathway in the mushroom body of an insect brain, the key centre for associative learning. We show that, in the locust (Schistocerca gregaria), parallel axons of intrinsic neurones (Kenyon cells) form tubular NO-producing zones surrounding central cores of NO-receptive Kenyon cell axons, which do not produce NO. This segregated architecture requires NO to spread at physiological concentrations up to 60 microm from the tube walls into the central NO-receptive cores. By modelling NO diffusion we show that a segregated architecture, which requires NO to act at a distance, affords significant advantages over a system where the same sources and targets intermingle. Segregation enhances the precision of NO volume signals by reducing noise and ambiguity, achieving a reliable integration of the activity of thousands of NO-source neurones. In a neural structure that forms NO-dependent associations, these properties of the segregated architecture may reduce the likelihood of forming spurious memories.     

Behavioral depression produced by an uncontrollable stressor: Relationship to norepinephrine, dopamine, and serotonin levels in various regions of rat brain

This paper presents two experiments that continue efforts to determine the neurochemical changes responsible for stress-induced behavioral depression. These expriments measured active motor behavior in a swim tank as well as levels of norepinephrine (NE), dopamine (DA), and serotonin (5-HT) in various brain regions of rats after the animals had (a) been exposed to electric shocks they could control (Avoidance-escape condition), or (b) received the same shocks with no control over them (Yoked condition), or (c) received no shock (No-shock condition). In the first experiment, measures were taken 90 min after the shock session ended. In the swim test, Yoked animals showed a depression of active behavior relative to the other groups. From measures of monoamine levels, the change found to be most closely related to this post-stress behavioral depression was in NE in the locus coeruleus (LC), where Yoked animals showed a considerable depletion of NE. In the second study, the same measures were taken 48 h and 72–96 h after the stress session. Yoked animals tested at 48 h post-stress showed motor depression, but those tested after 72–96 h did not. NE in the LC was significantly depleted in Yoked animals tested at 48 h post-stress but showed only slight (and non-significant) depletion in those tested 72–96 h post-stress. These results, together with others, suggest that large stress-induced depletion of NE in the LC is involved in mediating behavioral depression brought about by severe stress. It is further suggested that the time course for behavioral recovery and for the disappearance of NE depletion in the LC that was seen in Yoked animals after stress parallels the time course previously reported by other investigators for induction of catecholamine-synthesizing enzymes — tyrosine hydroxylase (TH) and dopamine-β-hydroxylase (DBH) — in the LC, so that induction of TH and DBH activity may be a neurochemical mechanism to bring about recovery from poststress behavioral depression.     

Effect of mating on the metabolic activity of the brain and pituitary gland assessed by [C]2-deoxyglucose in a reflex ovulator, the vole (Microtus agrest s)

The neural pathways involved in reflex ovulation in the vole (Microtus agrestis) have been investigated with the [¹⁴C]2-deoxyglucose (2-DG) method. Female voles were injected i.p. with 2-DG and either not mated, sham-mated (mounted by males but vagina was taped) or mated for a period of 45 min after the injection, after which the animals were decapitated. The brain was processed for autoradiography and the relative metabolic activities (rma) of selected areas of the brain and pituitary gland were determined. The plasma separated from trunk blood was assayed for the concentration of luteinizing hormone (LH). The lordosis quotients (LQ) were (mean ± S.E.M.) 81 ± 8 (n = 5) in mated compared with 47 ± 8 (n = 5) in sham-mated voles. The rma of the midbrain central grey (CG) and reticular formation (RF) were significantly greater in mated and sham-mated voles compared with the values in unmated voles. There were no other between-group differences in the rma of the other 28 areas of the brain or pituitary gland studied in spite of the fact the plasma LH concentration in mated voles was 36.9 ± 9.6 ng NIH-LH-S18/ml compared with undetectable (< 2.5 ng/ml) values in all the sham-mated and unmated animals. These results show that in the vole increased metabolic activity of the CG and RF is associated with lordosis, but that the reflex release of LH is not accompanied by any significant change in the metabolic activity of the brain or the pituitary gland.     

Formation of free radicals in hypoxic ischemic brain damage in the neonatal rat, assessed by an endogenous spin trap and lipid peroxidation

The formation of free radicals and lipid peroxidation in the brain after hypoxic ischemia was investigated. Seven-day-old rats were subjected to unilateral (left) carotid artery ligation followed by 70 min of hypoxia with 8% oxygen at 36°C. The animals were randomized into six groups as follows: control animals (no anesthesia, ligation or hypoxia) and animals decapitated at 0, 15, 30, 60 and 180 min into the reoxygenation period. Lipid peroxidation was quantified in brain homogenates using the thiobarbituric acid assay (TBA). The TBA–malondialdehyde (MDA) complex was measured with HPLC. The semi-dehydroascorbate radical was measured using electron spin resonance (ESR) spectroscopy. The semi-dehydroascorbate radical levels increased more than 3-fold in the left HI hemisphere compared to the left control hemisphere 15 min posthypoxic ischemia. The amount of MDA was significantly increased in the hypoxic ischemic (HI) hemisphere ipsilateral to the carotid ligation compared with contralateral hypoxic hemisphere. The MDA level in the left HI hemisphere was also significantly elevated at 0, 15, 30 and 60 min, but not at 180 min into the reoxygenation period. Reoxygenation after hypoxic ischemia thus induced formation of semi-dehydroascorbate radicals and lipid peroxidation.     

Excitation of locus coeruleus neurons by an adenosine 3',5'-cyclic monophosphate-activated inward current: extracellular and intracellular studies in rat brain slices

The firing rate of locus coeruleus (LC) neurons in rat brain slices was increased reversibly by agents that either elevate intracellular levels of adenosine 3',5'-cyclic monophosphate (cAMP) or mimic its actions (e.g., forskolin, and activator of adenylate cyclase, 8-Br-cAMP, a membrane permeable analog of cAMP, and Ro20-1724, a preferential inhibitor of cAMP-phosphodiesterase). Intracellular recordings showed that 8-Br-cAMP and forskolin induce a depolarization of LC neurons, accompanied by a decrease in input resistance. The 8-Br-cAMP- and forskolin-elicited depolarization persisted in the presence of cobalt, a calcium channel blocker. Steady-state current-voltage curves revealed that in the voltage range of -50 to -120 mV, 8-Br-cAMP and forskolin induced an inward current, which did not reverse at the potassium equilibrium potential and could not be blocked by tetrodotoxin. Partial replacement of sodium with Tris or choline markedly reduced the depolarization elicited by 8-Br-cAMP. We conclude that 8-Br-cAMP and forskolin act through a common mechanism to increase the firing rate of locus coeruleus neurons by inducing a cAMP-activated inward current, carried out at least in part by sodium ions.     

Expression of endothelial and inducible NOS-isoforms is increased in Alzheimer’s disease, in APP23 transgenic mice and after experimental brain lesion in rat: evidence for an induction by amyloid pathology

The nitric oxide-synthesizing enzyme nitric oxide synthase (NOS) is present in the mammalian brain in three different isoforms, two constitutive enzymes (i.e., neuronal, nNOS, and endothelial eNOS) and one inducible enzyme (iNOS). All three isoforms are aberrantly expressed in Alzheimer’s disease giving rise to elevated levels of nitric oxide apparently involved in the pathogenesis of this disease by various different mechanisms including oxidative stress and activation of intracellular signalling mechanisms. It still is a matter of debate, however, whether the abnormal expression of NOS isoforms has some primary importance in the pathogenetic chain and might thus be a potential therapeutic target or only reflects a secondary effect that occurs at more advanced stages of the disease process. To tackle this question, we analysed the expression of both eNOS and iNOS in patients with sporadic AD, in transgenic mice expressing human amyloid precursor protein (APP) with the Swedish double mutation under control of the Thy1 promotor (APP23 mice), and after electrolytic cortical lesion in rat, an experimental paradigm associated with elevated expression of APP. In all three conditions, an astrocytosis was induced accompanied by a strong increase of both iNOS and eNOS. Both NOS isoforms were frequently though not always colocalized. Thus, based on the expression pattern of NOS isoforms three types of astrocytes, expressing only one of the two isoforms or both together could be distinguished. In both AD and transgenic mice eNOS-expressing astrocytes exceeded iNOS-expressing astrocytes in number. Astrocytes with elevated levels of iNOS or eNOS were constantly seen in direct association with Aβ-deposits in AD and transgenic mice and were found in the vicinity of the lesion site in the rat cortex. The results of the present study show that expression of both iNOS and eNOS is increased in activated astrocytes under experimental conditions associated with elevated expression of APP (electrolytic brain lesion) or Aβ-deposition (APP23 transgenic mice). Therefore, it is suggested that altered expression of these NOS isoforms being part of AD pathology is secondary to the amyloid pathology and might not be primarily involved in the pathogenetic chain though it might contribute to the maintenance, self-perpetuation and progression of the neurodegenerative process.     

Effects induced by cannabinoids on monoaminergic systems in the brain and their implications for psychiatric disorders

The endocannabinoid system and CB(1) receptors participate in the control of emotional behavior and mood through a functional coupling with the classic monoaminergic systems. In general, the acute stimulation of CB(1) receptors increases the activity (spontaneous firing rate) of noradrenergic (NE), serotonergic (5-HT) and dopaminergic (DA) neurons as well as the synthesis and/or release of the corresponding neurotransmitter in specific brain regions. Notably, the antagonist/inverse agonist rimonabant (SR141617A) can decrease the basal activity of NE and 5-HT neurons, suggesting a tonic/constitutive regulation of these neuronal systems by endocannabinoids acting at CB(1) receptors. Monoaminergic systems are modulated via CB(1) receptors by direct or indirect effects depending on the localization of this inhibitory receptor, which can be present on monoaminergic neurons themselves and/or inhibitory (GABAergic) and/or excitatory (glutamatergic) regulatory neurons. The repeated stimulation of CB(1) receptors is not associated with the induction of tolerance (receptor desensitization) on the activity of NE, 5-HT and DA neurons, in contrast to chronic agonist effects on neurotransmitter synthesis and/or release in some brain regions. CB(1) receptor desensitization may alter the direct and/or indirect effects of cannabinoid drugs modulating the functionality of monoaminergic systems. The sustained activation of monoaminergic neurons by cannabinoid drugs can also be related to changes in the function of presynaptic inhibitory α(2)-adrenoceptors or 5-HT(1A) receptors (autoreceptors and heteroreceptors), whose sensitivity is downregulated or upregulated upon chronic CB(1) agonist exposure. The functional interactions between endocannabinoids and monoaminergic systems in the brain indicate a potential role for CB(1) receptor signaling in the neurobiology of various psychiatric disorders, including major depression and schizophrenia as the major syndromes.