Neurotransmitters increase cyclic nucleotides in postganglionic neurons: immunocytochemical demonstration

Deep insights: intravital imaging with two-photon microscopy

Intravital multiphoton microscopy is widely used to assess the structure and function of organs in live animals. Although different tissues vary in their accessibility for intravital multiphoton imaging, considerable progress has been made in the imaging quality of all tissues due to substantial technical improvements in the relevant imaging components, such as optics, excitation laser, detectors, and signal analysis software. In this review, we provide an overview of the technical background of intravital multiphoton microscopy. Then, we note a few seminal findings that were made through the use of multiphoton microscopy. Finally, we address the technical limitations of the method and provide an outlook for how these limitations may be overcome through future technical developments.

Cytochemical Localization of Adenylate Cyclase in Broken Cell Preparations of the Cerebral Cortex

Broken cell preparations derived from rat cerebral cortical grey matter were studied cytochemically to localize adenylate cyclase (AC) activity in subcellular organelle membranes. AC activity was localized by visualizing reaction product in brain particulate fractions by electron microscopy. Activity was found in the endoplasmic reticulum, on the inside of the inner mitochondrial membrane and on both leaflets of the nuclear membrane. Reaction product was found in the postsynaptic density area of most synapses. The reaction product tended to be more prominent in the presence of flouride. A synaptosome-rich fraction was shown to have NE stimulated AC activity which was blocked in vitro by both a α-and an β-blocker and in vivo by propranolol.

Acute two-photon imaging of the neurovascular unit in the cortex of active mice

In vivo two-photon scanning fluorescence imaging is a powerful technique to observe physiological processes from the millimeter to the micron scale in the intact animal. In neuroscience research, a common approach is to install an acute cranial window and head bar to explore neocortical function under anesthesia before inflammation peaks from the surgery. However, there are few detailed acute protocols for head-restrained and fully awake animal imaging of the neurovascular unit during activity. This is because acutely performed awake experiments are typically untenable when the animal is naïve to the imaging apparatus. Here we detail a method that achieves acute, deep-tissue two-photon imaging of neocortical astrocytes and microvasculature in behaving mice. A week prior to experimentation, implantation of the head bar alone allows mice to train for head-immobilization on an easy-to-learn air-supported ball treadmill. Following just two brief familiarization sessions to the treadmill on separate days, an acute cranial window can subsequently be installed for immediate imaging. We demonstrate how running and whisking data can be captured simultaneously with two-photon fluorescence signals with acceptable movement artifacts during active motion. We also show possible applications of this technique by (1) monitoring dynamic changes to microvascular diameter and red blood cells in response to vibrissa sensory stimulation, (2) examining responses of the cerebral microcirculation to the systemic delivery of pharmacological agents using a tail artery cannula during awake imaging, and (3) measuring Ca(2+) signals from synthetic and genetically encoded Ca(2+) indicators in astrocytes. This method will facilitate acute two-photon fluorescence imaging in awake, active mice and help link cellular events within the neurovascular unit to behavior.

Suppression of excitatory cholinergic synaptic transmission by Drosophila dopamine D1-like receptors

The physiological function of dopamine is mediated through its G-protein-coupled receptor family. In Drosophila, four dopamine receptors have been molecularly characterized so far. However, due largely to the absence of a suitable preparation, the role of Drosophila dopamine receptors in modulating central synaptic transmission has not been examined. The present study investigated mechanisms by which dopamine modulates excitatory cholinergic synaptic transmission in Drosophila using primary neuronal cultures. Whole-cell recordings demonstrated that cholinergic excitatory postsynaptic currents (EPSCs) were down-regulated by focally applied dopamine (10-500 microm). The vertebrate D1 specific agonists SKF38393 and 6-chloro-APB (10 microm) mimicked dopamine-mediated suppression of cholinergic synaptic transmission with higher potency. In contrast, the D2 agonists quinpirole and bromocriptine did not alter cholinergic EPSCs, demonstrating that dopamine-mediated suppression of cholinergic synaptic transmission is specifically through activation of Drosophila D1-like receptors. Biophysical analysis of miniature EPSCs indicated that cholinergic suppression by activation of D1-like receptors is presynaptic in origin. Dopamine modulation of cholinergic transmission is not mediated through the cAMP/protein kinase A signaling pathway as cholinergic suppression by dopamine occurred in the presence of the protein kinase A inhibitor H-89. In addition, an adenylate cyclase activator, forskolin, led to an increase, not a decrease, of cholinergic EPSC frequency. Finally, we showed that activation of D1-like receptors decreased the frequency of action potentials in cultured Drosophila neurons by inhibiting excitatory cholinergic transmission. All our data demonstrated that activation of D1-like receptors in Drosophila neurons negatively modulates excitatory cholinergic synaptic transmission and thus inhibits neuronal excitability.

A model for pleiotropic muscarinic potentiation of fast synaptic transmission

The predominant form of muscarinic excitation in the forebrain and in sympathetic ganglia arises from m1 receptors coupled to the G(q/11) signal transduction pathway. Functional components of this system have been most completely mapped in frog sympathetic B neurons. Presynaptic stimulation of the B neuron produces a dual-component muscarinic excitatory postsynaptic potential (EPSP) mediated by suppression of voltage-dependent M-type K(+) channels and activation of a voltage-insensitive cation current. Evidence from mammalian systems suggests that the cation current is mediated by cyclic GMP-gated channels. This paper describes the use of a computational model to analyze the consequences of pleiotropic muscarinic signaling for synaptic integration. The results show that the resting potential of B neurons is a logarithmic function of the leak conductance over a broad range of experimentally observable conditions. Small increases (<4 nS) in the muscarinically regulated cation conductance produce potent excitatory effects. Damage introduced by intracellular recording can mask the excitatory effect of the muscarinic leak current. Synaptic activation of the leak conductance combines synergistically with suppression of the M-conductance (40 --> 20 nS) to strengthen fast nicotinic transmission. Overall, this effect can more than double synaptic strength, as measured by the ability of a fast nicotinic EPSP to trigger an action potential. Pleiotropic muscarinic excitation can also double the temporal window of summation between subthreshold nicotinic EPSPs and thereby promote firing. Activation of a chloride leak or suppression of a K(+) leak can substitute for the cation conductance in producing excitatory muscarinic actions. The results are discussed in terms of their implications for synaptic integration in sympathetic ganglia and other circuits.

Nitric oxide release and long term potentiation at synapses in autonomic ganglia

1. Long-term potentiation (LTP) of synaptic transmission in autonomic ganglia is reviewed, together with the possible role of nitric oxide (NO) in this process. 2. Calcium levels in preganglionic nerve terminals are elevated during at least the induction phase of LTP following a tetanus as well as during LTP induced by transmitter substances acting on the nerve terminals. Of the large number of calcium-dependent processes in the nerve terminal that might affect transmitter release, only calcium-calmodulin has been shown to be important in both the induction and maintenance of LTP. 3. The possibility that there is a decrease in the open time of nerve-terminal potassium channels following a tetanus, leading to an increase in duration of the terminal action potential and hence an increase in calcium influx and transmitter release is considered. There is little evidence for such an effect as yet for preganglionic nerve terminals. 4. Phosphorylation of potassium channels by cAMP-dependent protein kinase can lead to their inactivation with consequent action potential broadening in some systems. Exogenous cAMP enhances synaptic efficacy at preganglionic nerve terminals. Whether this occurs through an inactivation of potassium channels is not known. 5. Nitric oxide (NO) synthase is present in both sympathetic ganglia and the ciliary ganglia. NO increases synaptic efficacy in both ganglia. In at least the case of ciliary ganglion this is due to elevation of quantal secretion. 6. NO can in some conditions increase the terminal action potential duration in ciliary ganglia, probably through decrease in the Ic potassium current. There is evidence that this happens through cGMP modulating cAMP phosphodiesterases, thereby affecting cAMP phosphorylation of the Ic channel. 7. Blocking NO synthase markedly decreases LTP following a tetanus in the ciliary ganglion. The possibility is considered that NO is released from the terminal during a tetanus and through altering cAMP phosphorylation of Ic enhances transmitter release.

Distribution of NADPH-diaphorase activity in rat paravertebral, prevertebral and pelvic sympathetic ganglia

Paravertebral (superior cervical and stellate), prevertebral (coeliac-superior mesenteric, inferior mesenteric) and pelvic (hypogastric) sympathetic ganglia of the rat were investigated by enzyme histochemistry to ascertain the distribution of nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-diaphorase) activity. In the paravertebral ganglia the majority of the sympathetic neuronal perikarya contained lightly and homogeneously distributed formazan reaction product but there was a range of staining intensities amongst the neuron population. In contrast, in the prevertebral ganglia, intense NADPH-diaphorase staining was present in certain neurons. Firstly, a population of neurons of the coeliac-superior mesenteric ganglion complex were surrounded by densely NADPH-diaphorase-positive 'baskets' of fibres and other stained fibres were seen in interstitial nerve bundles and in nerve trunks connected to the ganglion complex. Secondly, in both the inferior mesenteric ganglion and hypogastric ganglion there were many very intensely NADPH-diaphorase positive neurons. Stained dendritic and axonal processes emerged from these cell bodies. In both ganglia this population of neurons was smaller in size than the lightly stained ganglionic neurons and commonly had only one long (presumably axonal) process. The similarity of these highly NADPH-diaphorase-positive neurons with previously described postganglionic parasympathetic neurons in the hypogastric ganglion is discussed.

Potentiation of nicotinic transmission in the rat superior cervical sympathetic ganglion: effects of cyclic GMP and nitric oxide generators

The efficacy of nicotinic transmission in the rat superior cervical ganglion in vitro (24-26 degrees C) was estimated by extracellular recording of the postganglionic compound action potential response to stimulation of the preganglionic nerve at a slow rate (one shock every 60 s). Atropine (2 microM) was included to block muscarinic transmission, and hexamethonium (200-250 microM) was used to produce a submaximal response sensitive to potentiation and inhibition of nicotinic transmission. Upon exposure to 1-100 microM 8-bromo-guanosine 3',5'-cyclic monophosphate (8-Br-cGMP), nicotinic transmission was potentiated by 6 +/- 1% (n = 4) to 89 +/- 5% (n = 5) in a dose-dependent manner. 8-Bromo-adenosine 3',5'-cyclic monophosphate (8-Br-cAMP, 10-100 microM) also potentiated nicotinic transmission (3.8 +/- 0.3% (n = 3) to 43 +/- 4% (n = 3)). However, 8-Br-cGMP was at least 2-fold more effective than 8-Br-cAMP. Sodium nitroprusside (0.1 microM to 1 mM) and sodium azide (0.1-100 microM) were used to stimulate the formation of endogenous cGMP52. Nicotinic transmission was potentiated by these substances also. The response was increased by 3.4 +/- 0.7% (n = 4) to 32 +/- 2% (n = 5) upon exposure to 0.1-100 microM sodium nitroprusside, and by 5.5 +/- 0.9% (n = 3) to 18 +/- 4% (n = 4) upon exposure to 0.1-100 microM sodium azide. Ferricyanide ion (10-100 microM) appeared to be ineffective, as would be expected if the effect of nitroprusside was due to the nitric oxide rather than the cyanide or ferric moieties.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulation by acetylcholine and inhibition by norepinephrine of transglutaminase activity in superior cervical ganglia excised from adult rats

Very rapid changes in activity of transglutaminase (TG), a calcium-dependent enzyme contributing to cross-linkage formation of intracellular polypeptide chains, were observed in vitro in rat superior cervical ganglion (SCG) and nodose ganglion (NG) following application of cholinergic or adrenergic agonists and antagonists. In SCG, a tissue rich in synapses, the depolarizing agent acetylcholine (ACh, 0.1 mM) produced an 8.7-fold increase in TG activity within 5 min that lasted for 30 min and returned to control levels by 2 h. In contrast, the ACh-induced increase in TG activity in NG, a tissue containing neuronal cell bodies with few synapses, was more gradual and of smaller magnitude, reaching a peak of approximately 2.4 times control by 30 min that was maintained for at least 2 h. In both tissues the ACh-stimulation was effectively blocked by the nicotinic antagonist, hexamethonium (0.1 mM), whereas the muscarinic antagonist, atropine (0.1 mM), partially blocked the ACh effect in SCG and was without effect in NG. Addition of the hyperpolarizing adrenergic agonists norepinephrine (NE, 50 microM), isoproterenol (0.2 mM) or dopamine (0.1 mM) produced an inhibition of TG activity in SCG but had no effect in NG. The inhibitory effects of the adrenergic agonists in SCG were blocked by the beta-adrenergic antagonist, propranolol (10 microM) and alpha 2-adrenergic antagonist, yohimbine (10 microM). A kinetic study revealed that the ACh-induced stimulation of TG activity in SCG and NG was a result of decrease in apparent Km and an increase in Vmax value, whereas the NE-induced inhibition of SCG enzyme activity was a result of an increased Km and decreased Vmax. 45Ca2+ influx into excised SCG or NG was significantly reduced by the application of either ACh or NE. The ACh inhibition was effectively blocked by either hexamethonium or atropine. The NE inhibition was more effectively blocked by yohimbine than by propranolol. These results suggest that the rapid alterations of TG activity in SCG produced by cholinergic and adrenergic neurotransmitters are attributable to the processes of receptor-mediated depolarization and hyperpolarization, respectively, via modulation of nerve-impulse-induced Ca2+ fluxes during synaptic activity.

Comparison of dopamine binding sites in the rat superior cervical ganglion and caudate nucleus

A comparison of morphological and biochemical characteristics of the D1-type dopamine receptor has been assessed in two experimental tissues, the superior cervical ganglion (SCG) and caudate nucleus of the rat. Correlation of the distribution of this dopaminergic binding site using in vitro autoradiographic localization of [3H]SCH 23390, a selective D1-binding antagonist, demonstrated no specific association of this receptor subtype with cyclic AMP immunoreactive structures in the superior cervical ganglion. In contrast, the caudate nucleus demonstrated specific D1-binding sites associated with cyclic AMP immunoreactive elements. Biochemical analyses of the D1-dopamine binding sites showed only 20% of the amount of radioligand bound in SCG homogenates as compared to the quantity bound in homogenates of the caudate nucleus. The non-cyclase linked dopaminergic receptor, assessed using D2-type radioligand binding, was much less prevalent than the binding of the D1-subtype in either experimental tissue. Only a small amount of [3H]sulpiride binding, indicative of the D2-receptor subtype, could be measured in the SCG as compared to the caudate nucleus. This work has demonstrated differences in the amount, and the cellular association of dopamine binding sites in peripheral versus central nervous system areas with dopamine sensitive adenylate cyclase mechanisms.

A new approach to immunocytochemistry of 3',5'-cyclic guanosine monophosphate: preparation, specificity, and initial application of a new antiserum against formaldehyde-fixed 3',5'-cyclic guanosine monophosphate

The development of a new 3',5'-cyclic guanosine monophosphate (cGMP) antiserum was initiated starting from the following considerations: (a) adequate fixation of cGMP is a prerequisite for a reliable demonstration of soluble cGMP, and (b) fixation might influence the specificity of the immunocytochemical demonstration of cGMP. Therefore, cGMP-protein conjugate was prepared in a way which equals tissue fixation. cGMP was coupled to bovine thyroglobulin using formaldehyde. Antibodies against this conjugate were raised in rabbits. The specificity of the antisera was evaluated in a gelatin model system. No immunoreactivity was observed with nucleotides other than cGMP or with rabbit preimmune sera. Immunoinhibition experiments showed that only the cGMP-formaldehyde-thyroglobulin conjugate and, to a lesser extent free cGMP, absorbed onto the antiserum. In rat brain an extensive localization of cGMP-immunostaining was found. Examples are hippocampus CAI and CAII, and cortical layers II and V. No cGMP-immunostaining was found in the cerebellum. In vitro incubated superior cervical ganglia showed cGMP-immunostaining in the large postganglionic neuronal cell bodies; this cGMP-immunostaining increased upon incubation of the ganglia in iso-osmolar 100 mM K+. In conclusion, we prepared a new-type highly specific antiserum against cGMP, suitable to demonstrate cGMP-immunoreactivity in tissue material.

Single cell quantitative immunocytochemistry of cyclic GMP in the superior cervical ganglion of the rat

In the superior cervical ganglion of the rat, using a newly developed antiserum against formaldehyde-fixed 3',5'-cyclic guanosine monophosphate (cGMP), cGMP immunoreactivity was observed in the large postganglionic neuronal cell bodies; no cGMP-immunofluorescence was found in nuclei or in satellite cells, glia or fibroblasts. In vitro incubation of ganglia in media with high K+ (up to 100 mM) or carbachol (10(-8)-10(-5) M) showed an increase only in cGMP-immunofluorescence in the large postganglionic cell bodies. The intensity of the immunofluorescence was taken as a measure for cGMP-immunoreactivity and was quantitated using a Leitz MPV-II system. Dose-response curves were constructed for the increase in cGMP-immunofluorescence intensity for K+ and carbachol. The carbachol stimulated cGMP-immunofluorescence intensity was antagonized competitively by atropine, whereas the high K+ stimulated cGMP-immunofluorescence intensity was not. Hexamethonium (10(-6) M) was without effect on the carbachol stimulated cGMP-immunofluorescence intensity. The morphological and pharmacological data indicate that we developed a very specific procedure for quantitative immunocytochemistry of cGMP in tissue sections. This technique makes it possible to use cGMP-immunofluorescence intensity as a postsynaptic parameter in individual cell bodies in heterogeneous tissue.

Cyclic nucleotide potentiation of muscarinic responses in neuroblastoma cells

The role of cyclic nucleotides in modulating acetylcholine-induced and dopamine-induced responses was examined with cultured neuroblastoma N1E-115 cells by means of intracellular recording techniques. Acetylcholine-induced muscarinic hyperpolarization and muscarinic depolarization were potentiated by bath application of a dibutyryl analog of adenosine 3',5'-phosphate (cyclic AMP) or phosphodiesterase inhibitors, 3-isobutyl-1-methylxanthine and 4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone. Dibutyryl cyclic AMP did not affect the resting membrane potential and membrane resistance. Acetylcholine-induced nicotinic depolarization was unaffected by dibutyryl cyclic AMP or phosphodiesterase inhibitors. Intracellular pressure injection of cyclic AMP caused a potentiation of muscarinic hyperpolarization and muscarinic depolarization without marked change in the resting membrane potential. Nicotinic depolarization and dopamine depolarization were not affected by cyclic AMP injection. Among the possible metabolites of cyclic AMP, injection of adenosine potentiated muscarinic hyperpolarization, but did not change nicotinic depolarization and dopamine depolarization. Injection of guanosine 3',5'-phosphate (cyclic GMP) potentiated muscarinic hyperpolarization and muscarinic depolarization without effect on nicotinic depolarization and dopamine depolarization. We conclude that cyclic AMP and cyclic GMP enhance muscarinic responses in neuroblastoma cells. It is suggested that synaptic transmission in the nervous system may be modulated postsynaptically by changes in intracellular cyclic nucleotide levels.

Muscarinic acetylcholine receptors are localized on striatal cyclic GMP-containing neurons

The localization of muscarinic acetylcholine receptors has been determined using in vitro binding of radiolabeled quinuclidinyl benzilate ([3H]QNB), a specific reversible muscarinic receptor antagonist. All cyclic GMP-immunoreactive neurons in the rat striatum show clustering of [3H]QNB silver grains overlying their somata following autoradiographic analysis. The autoradiography of total binding of silver grains over the cyclic GMP-containing neurons was approximately 800 times as dense as the surrounding neuropil localization of radioligand binding sites. Incubation of striatal tissue slices in the presence of micromolar atropine, to determine non-specific binding of [3H]QNB, decreased the autoradiographic silver grain density of the neuropil about 2.5 times, and lessened the number of receptor sites detectable on cyclic GMP-positive neurons at least 5-fold. Biochemical examination of [3H]QNB binding on tissue sections demonstrated that the ligand binding is saturable and dependent on section thickness for the muscarine receptor subtype of acetylcholine.

Basal ganglia and Parkinson's disease: neurobiological and pharmacological aspects in animals and man

In this article, the neuroanatomy, neurochemistry and neurobiology of the nigrostriatal and mesolimbic circuitries of animals and man will be reviewed in order to gain insight into the pathognomy and etiology of cognitive and motor disorders in patients with Parkinson's disease, to increase insight into the mechanism of action of present-day antiparkinson agents, and to open perspectives for the design and development of new antiparkinson agents on a rational basis.

Adenylate cyclase activity in the superior cervical ganglion of the rat

Adenylate cyclase activity in cell-free homogenates of the rat superior cervical ganglion (SCG) was assayed under a variety of experimental conditions. Adenylate cyclase activity was decreased by approximately one-half when 1 mM EGTA was included in the homogenization buffer and assay mixture, indicating the presence of a Ca2+-sensitive adenylate cyclase in the ganglion. In the presence of EGTA, basal adenylate cyclase activity in homogenates of the SCG was 12.9 +/- 0.6 pmol cyclic AMP/ganglion/10 min. Enzyme activity was stimulated three- to fourfold by 10 mM NaF or 10 mM MnCl2. Both GTP and its nonhydrolyzable analog guanylylimidodiphosphate (GppNHp) stimulated adenylate cyclase in a concentration-dependent manner over the range of 0.1-10.0 microM. Stimulation by GppNHp was five to six times greater than that produced by GTP at all concentrations tested. Decentralization of the ganglion had no effect on basal or stimulated adenylate cyclase activity. Receptor-linked stimulation of adenylate cyclase was not obtained with any of the following: isoproterenol, epinephrine, histamine, dopamine, prostaglandin E2, or vasoactive intestinal peptide. Thus the receptor-linked regulation of adenylate cyclase activity appears to be lost in homogenates of the ganglion.

Light and electron microscopic demonstration of guanylate cyclase in rat brain

Guanylate cyclase (GTP pyrophosphate-lyase (cyclizing), EC4.6.1.2.) was histochemically demonstrated in rat brain with light and electron microscopes by using a specific monoclonal antibody to soluble guanylate cyclase from rat brain. Under a light microscope, intense reactions were seen in caudate-putamen complex, neocortex and cerebellar cortex. Immunoreactive cells were mainly some types of neurons such as small neurons in caudate-putamen complex, Purkinje cells in cerebellar cortex and pyramidal cells in neocortex. Some astroglial cells were also stained. Not all neurons or glial cells exhibited the positive guanylate cyclase reactivity. Electron microscopic examination revealed that guanylate cyclase was localized within postsynaptic components (perikaryon and dendrites) in neurons and in the cytoplasm and plasma membrane of astroglia. Presynaptic terminals were free of reaction. The observation supports a possibility that cyclic GMP is involved in the postsynaptic events of neuronal transmission and the regulation of intracellular processes.

Cyclic adenosine 3',5'-monophosphate and beta-effects in rat isolated superior cervical ganglia

Isoprenaline (0.01-1 microM) increased the amount of cyclic adenosine 3',5'-monophosphate (cyclic AMP) in rat isolated superior cervical ganglia by up to 10 times after 10 min application. Cyclic AMP levels returned to control values after 20 min washing. Salbutamol, in concentrations (1-100 microM) that depolarized the ganglion and facilitated submaximal transmission, did not significantly raise ganglionic cyclic AMP levels. The action of isoprenaline was antagonized by butoxamine (apparent KI approximately equal to 0.14 microM) and weakly by practolol (apparent KI approximately equal to 9.1 microM). The effect of 0.1 microM isoprenaline was also inhibited 94% by 100 microM of the adenylate cyclase inhibitor, 9-(tetrahydro-2-furyl)adenine (SQ 22,536). Exogenous dibutyryl cyclic AMP did not replicate the effects of isoprenaline on ganglionic d.c. potentials or submaximal transmission. The phosphodiesterase inhibitors theophylline, isobutylmethylxanthine or 4-(3,4-dibutoxybenzyl)-2-imidazolidinone (Ro 20-1724) did not potentiate these electrical responses to isoprenaline. The adenylate cyclase inhibitor, SQ 22,536, did not inhibit the electrical responses to isoprenaline. It is concluded that available evidence does not support the view that the ganglion depolarization or facilitation of submaximal transmission in rat isolated ganglia produced by isoprenaline are likely to be mediated by cyclic AMP.

Cyclic AMP and cyclic GMP response to stress in brain and pituitary: stress elevates pituitary cyclic AMP

Male rats were exposed to six stressors (saline injection, cold, forced running, Formalin injection, immobilization, electric footshock) for 15, 30, or 60 min. Following sacrifice by microwave irradiation, cyclic AMP and cyclic GMP levels were measured in pituitary, pineal and 8 regions of rat brain. All stressors except saline increased plasma corticosterone, plasma prolactin and pituitary cyclic AMP levels compared to control animals. The magnitude of the pituitary cyclic AMP response was highly correlated with the intensity of the stress as determined by the levels of plasma prolactin. Electric footshock increased pituitary cyclic AMP levels over 10 fold and plasma prolactin over 60 fold. Cyclic AMP levels in other brain regions were not altered. Cerebellar cyclic GMP was increased only by stressors that involved increased motor activity.

The regulation of cyclic nucleotides in a sympathetic ganglion

Preganglionic nerve terminal stimulation in rat superior cervical ganglia causes marked increases in the levels of cyclic nucleotides. Results are similar when preganglionic nerve stimulation is compared with elevated [K+]0 or 4-aminopyridine. Although intact nerve terminals and Ca2+ are required for the response to occur, pharmacological studies indicate that acetylcholine and adrenergic transmitters are not involved in the cyclic nucleotide response. It is suggested that cyclic nucleotide accumulation occurs in the nerve terminals or an unknown transmitter or substance participates in the postsynaptic accumulation of the cyclic nucleotides. Polypeptides tested thus far do not seem to be implicated. Interrelationships among phospholipid turnover, Ca2+-exchange and cyclic nucleotide accumulation in rat sympathetic ganglia are considered, but are difficult to establish.

Effects of dopamine and dibutyryl cyclic adenosine monophosphate on delayed release of transmitter at the rat neuromuscular junction

The effects of dopamine and dibutyryl cyclic adenosine monophosphate (db-cAMP) on delayed release of transmitter were studied in vitro in the phrenic nerve-diaphragm muscle preparation in the rat using intracellular recording techniques. Dopamine at 1 X 10(-4) mol 1(-1) prevented the initial facilitation of delayed release of transmitter. This inhibitory phase was transformed into a transient facilitation of delayed release. We observed that dopamine hyperpolarized muscle fibres by about 9%. Thus motor nerve terminals may also have been hyperpolarized by dopamine; however, it is unlikely that this hyperpolarization explains the observed effects on delayed release of transmitter. Db-cAMP at 1 X 10(-3) mol 1(-1) predominantly augmented delayed release of acetylcholine. These effects of dopamine and db-cAMP on delayed release of transmitter are discussed in terms of a modulation of calcium fluxes in the presynaptic nerve terminal.

Immunohistochemical localization of guanylate cyclase within neurons of rat brain

The immunohistochemical localization of guanylate cyclase [GTP pyrophosphate-lyase (cyclizing), EC 4.6.1.2] has been examined in rat neocortex, caudate-putamen, and cerebellum by using specific monoclonal antibodies. Immunofluorescence could be seen within somata and proximal dendrites of neurons in the these regions. A nuclear immunofluorescence reaction to guanylate cyclase was characteristically absent. The staining pattern for guanylate cyclase was coincident with previously described localizations of cyclic GMP immunofluorescence within medium spiny neurons of the caudate-putamen and pyramidal cells of the neocortex. Cerebellar guanylate cyclase immunoreactivity was primarily confined to Purkinje cells and their primary dendrites, similar to the pattern reported for cyclic GMP-dependent protein kinase localization. Guanylate cyclase immunofluorescence was abolished when the monoclonal antibodies were exposed to purified enzyme prior to incubation of the tissue slices or when control antibody was substituted for the primary antibody. Immunohistochemical localization of cyclic AMP in these same tissues was readily distinguished from that of guanylate cyclase or cyclic GMP, showing uniform fluorescence throughout the cell bodies of neurons and glial elements.

Dissimilar effects on body temperature in the cat produced by guanosine 3',5'-monophosphate, acetylcholine and bacterial endotoxin

1 Guanosine 3',5'-monophosphate (cyclic GMP) and N2-2'-O-dibutyryl guanosine 3',5'-monophosphate (db cyclic GMP) have been injected into the third cerebral ventricle (i.c.v.) of the unanaesthetized cat and the effects of rectal temperature and on behavioural and autonomic activities observed and compared with those of acetylcholine and physostigmine. 2 Acetylcholine (100 nmol) and physostigmine (100 nmol) injected together i.c.v. produced a rise in body temperature in cats at an environmental temperature of 20-24 degrees C, which was abolished by pretreatment i.c.v. with atropine (200 nmol). 3 Cyclic GMP and db cyclic GMP (10--1250 nmol) had no effect on body temperature in cats at an environmental temperature of 20--24 degrees C but produced hypothermia (1250 nmol) in cats at an environmental temperature of 9--11 degrees C. 4 The O-somatic antigen of Shigella dysenteriae (20 microgram/kg i.v.) produced fever in cats which was not potentiated by caffeine (25 mg/kg i.p.). Levels of endogenous cyclic GMP in c.s.f. taken from the cisterna magna during fever induced by bacterial endotoxin in the presence or absence of paracetamol (50 mg/kg i.p.) and/or caffeine were similar to values for afebrile cats. 5 It is concluded that exogenous cyclic GMP and db cyclic GMP can inhibit central events mediating autonomic and behavioural thermoregulation stimulated in cats by exposure to cold environments.

Ultrastructural localization of cyclic GMP and cyclic AMP in rat striatum

The subcellular localization of cyclic GMP and cyclic AMP in the rat caudate-putamen has been studied using horseradish peroxidase immunocytochemistry. Both of the putative neurotransmitter second messengers were visualized in neurons and glial cells at light microscopic resolutions, but not all cells of either category gave detectable staining. This was confirmed at the ultrastructural level where both stained and unstained elements of the same cell type were found within the same field. A striking variation was seen in cyclic nucleotide staining intensity within individual neural and glial cells. Both of the cyclic nucleotides were detected within postsynaptic terminal boutons and within astroglial processes. Cyclic GMP postsynaptic staining was stronger than glial staining, whereas the localization pattern was reversed for cyclic AMP. The synaptic localization of cyclic AMP and cyclic GMP immunoreactivity adds support to the idea that these compounds have an influential role in synaptic function within the striatum.

Mechanisms of slow postsynaptic potentials

Classical views of synaptic transmission have to be modified to take account of slow postsynaptic potentials (p.s.ps), which are often mediated by novel ionic and molecular mechanisms and which are sometimes evoked by neuropeptides. Understanding slow p.s.ps will provide insights into the mechanisms of biological signal transduction and long-term signalling in the nervous system.

Aminergic neurons: state control and plasticity in three model systems

Aminergic neurons have particular functions in many systems, and in this review their role is discussed and compared in three systems: those parts of the central nervous system controlling sleep and waking in the cut; the superior cervical ganglion: and the isolated nervous system of Aplysia. In the cat the aminergic neurons are most important in a waking state during which time external information is received, processed, and can be retrieved, and during which time habituation and sensitization occur. Aminergic neurons appear to have similar roles in state control in plasticity in both the Aplysia nervous system and the superior cervical ganglion. The striking similarities in the role of aminergic neurons in these three systems support the speculation that aminergic neurons have uniquely important roles in regulation of the plastic properties of neurons.

Cyclic nucleotides and aggressive behavior

Cyclic nucleotides, particularly cyclic AMP, have been implicated as second messengers in neuronal activity. Attempts to demonstrate an association between endogenous cAMP or cGMP levels and rodent aggressive behavior have been only partially successful. Low levels of cAMP in rodent brain appear associated with lower levels of affective aggression. Consistent with this possible relationship is our finding that the infusion of dibutyryl cAMP into rodent cerebroventricles decreases aggressive behavior. The infusion of dibutyryl cyclic GMP, conversely, facilitates shock-induced fighting in the rat.

Correlated effects of acetylcholine and cyclic guanosine monophosphate on membrane properties of mammalian neocortical neurons

The effects of successive extracellular iontophoresis of acetylcholine (ACh) and atropine, and intracellular hyperpolarizing iontophoresis of cyclic GMP (cGMP) were studied in single neurons of the coronal-pericruciate cortex of awake cats. (a) Fifty-seven percent of the neurons that were tested responded to ACh with an increase in neuronal input resistance (Rm) and 50% responded to ACh with an increase in firing rate; 65% responded to cGMP with an increase in Rm and 60% responded to cGMP with an increase in firing rate. (b) After application of atropine, increases in Rm and firing rate associated with iontophoresis of ACh failed to recur. (c) Persistent increases in Rm following application of ACh accompanied by current-induced neuronal discharge were not diminished by subsequent application of atropine. (d) Atropine did not prevent increases in Rm and firing rate associated with intracellular iontophoresis of cGMP. (e) All cells tested with both ACh and cGMP that were shown initially to respond to extracellular ACh with increases in Rm were later shown to have comparable responses to cGMP.

A cytochemical and ultrastructural study of the "S.I.F." cells in cat sympathetic ganglia

According to the hypothesis of Eccles and Libet, the small intensely fluorescent cells (S.I.F. cells) in the sympathetic ganglion would represent an essential element in the inhibition of the principal neuron. As a contribution to the study of this important problem, we have investigated serial sections in superior cervical (S.C.G.) and celiac (C.G.) ganglia of the cat, a species that has not been extensively studied up to now, both by fluorescence and electron microscopy. We have shown that the "S.I.F." cells are three times fewer in the cat S.C.G. than in the rat S.C.G. There are five times more "S.I.F." cells in the C.G. of the cat than in the S.C.G. of the same species. Moreover we have described two types of "S.I.F." cells. Type I is composed of cells characterized by highly polymorphous large dense-cored vesicles. These cells lack processes and are grouped in clusters centered on fenestrated capillaries. They could be endocrine function cells. Type II is formed of isolated cells which exibit long processes and establish synaptic junctions with the dendrites of the principal neurons. In this case, the dense-cored vesicles are very regular and much smaller. These cells could be equivalent to interneurons. Type I very strongly predominates in the S.C.G. and C.G. of the cat where it represents more than 90% of the "S.I.F." cell total observed by fluorescence microscopy. A priori such a quantitative and qualitative heterogeneity hardly consistent with Eccles and Libet's hypothesis based on the existence of dopaminergic interneurons only, allows the question to be raised as to the functional significance of the "S.I.F." cells in ganglion physiology. The notion of modulation of ganglionic transmission does not seem to be quiered by these new data but could be founded on different forms of action embodied in the broader conception of the neuromodulation phenomenon.

Cerebrospinal fluid cyclic AMP and acid monoamine metabolites following probenecid: studies in psychiatric patients

At probenecid levels greater than 10 microgram/ml, CSF cAMP was independent of CSF probenecid concentration. At these levels of probenecid, cAMP transport out of CSF is probably maximally blocked and cAMP levels reflect cAMP release into CSF. CSF cAMP was significantly higher in RDC-diagnosed schizophrenics than in other psychotics or depressives. A significant decrease in CSF cAMP was found in psychotic patients treated with chlorpromazine, No changes in CSF cAMP were observed in patients treated with tricyclic antidepressants or lithium.