The action of norepinephrine in the rat hippocampus. I. Iontophoretic studies

Gating of neuronal transmission in the hippocampus: efficacy of transmission varies with behavioral state

Electrical stimuli were applied to the angular bundle of the freely moving rat, and the neuronal responses were recorded ipsilaterally in the dentate gyrus and the CA1 field of the hippocampus. The number of neurons responding monosynaptically in the dentate gyrus was relatively small when the animal was alert and not moving but was much greater both during slow-wave sleep and during rapid eye movement sleep. In Ca1, however, the trisynaptic population response was considerably smaller during rapid eye movement sleep and when the animal was alert than during slow-wave sleep. These findings are interpreted in terms of a set of behaviorally dependent "neural gates". Measurement of the synaptic current at the dentate gyrus induced monosynaptically by stimulation of the angular bundle further suggests that the mechanism by which gating occurs at this level is either a tonic inhibitory synaptic influence exerted upon the granule cells during the alert state, a tonic excitatory influence during slow-wave sleep, or both.

Electrophysiological concomitants of eating induced from neocortex and hippocampus by electrical stimulation and injection of KC1 or norepinephrine

EEG and DC activity were recorded from the hippocampus and neocortex in freely moving rats during consummatory behavior elicited by electrical stimulation and application of KC1 or norepinephrine to these structures. Eating induced by KC1 application or electrical stimulation of the neocortex or hippocampus was accompanied by single or multiple waves of spreading depression (SD), i.e., by traveling slow potential change. An analysis of single vs. multiple cortical SD waves indicated that when multiple waves occurred, feeding was elicited by the first wave. Injection of norepinephrine into the hippocampus resulted in a significantly larger and qualitatively different feeding response compared to KC1 injections. No apparent changes in the EEG or DC activity occurred upon norepinephrine injections.

Electrophysiology and cytology of hippocampal formation transplants in the anterior chamber of the eye. I. Intrinsic organization

Pieces of the immature hippocampal formation were transplanted to the anterior chamber of adult rat eyes. The transplants survived, became vascularized from the host irides, and proliferated extensively in proportion to the age of the donor fetus. These transplants mature and develop an adult organization in oculo. This maturation proceeds unimpaired in the absence of gyrus dentatus or after superior cervical ganglionectomy.

Modulation in the sensitivity of noradrenergic receptors in the CNS studied by the responsiveness of the cyclic AMP system

Various characteristics of the altered responsiveness to noradrenaline (NA) of the cyclic Amp (cAMP) generating system of cortical brain slices have been studied in rat after chronic reserpine treatment and in mice after chronic D-amphetamine treatment. Supersensitivity of the cAMP system to NA following reserpine treatment and subsensitivity after D-amphetamine treatment exhibit many common features. Firstly, in both cases the modified responsiveness to NA occurs rapidly after the beginning of the treatment (one day for reserpine and 5 h after amphetamine) and recovers slowly after the end of the treatment. Additionally, the altered states of sensitivity of the cAMP system to NA are the result of a modification of the maximal response rather than of an altered affinity of the system to NA. Since, following D-amphetamine treatment the change of sensitivity is still apparent in the presence of a potent phosphodiesterase inhibitor, the involvement of a gross alteration of phosphodiesterase activity is unlikely. In this case too, while the response to adenosine is slightly decreased, the responses to dopamine and serotonin of the cAMP system observed in brain slices following D-amphetamine treatment is not detected in a cell-free preparation. Thus, it appears that drug treatments, modifying synaptic transmission in opposite directions, lead also to changes in opposite directions of the responsiveness of the cAMP system to NA. The hypothesis that the mechanisms underlying such phenomena are related to a modified number of functional noradrenergic receptors is discussed.

Interactions of nigrostriate synaptic transmission, iontophoretic O-methylated phenethylamines, dopamine, apomorphine and acetylcholine

Recordings were made from, and drugs applied to, neurons in the caudate nucleus of unanesthetized cats, using multibarrel micropipette electrodes. The substantia nigra was stimulated by sterotactically placed electrodes. Three O-methylated derivatives of dopamine, meta-methoxyphenethylamine (m-MPEA), para-methosy-phenethylamine (p-MPEA) and 3,4-demethoxyphenethylamine (DIMPEA), inhibited most, excited a few, and had no detectable effect on a substantial number of the cells upon which they were tested. A statistically significant correlation was found between the effects of dopamine (DA) and the three O-methylated derivatives on the same populations of cells. Iontophoretic release of the O-methylated derivatives could not prevent the actions of DA, nor could it block synaptically mediated effects of the nigrostriate pathway. It is concluded that the three O-methylated products are partial agonists of DA. The findings are difficult to reconcile with the suggestion that the experimental parkinsonian-like symptoms caused by O-methylated phenethylamines are the consequence of blockade of dopaminergic synapses. No correlation, negative or positive, was found between the effects of DA and of acetylcholine (ACh). The findings do not support the theory that balanced sets of antagonistic synapses, one dopaminergic, the other cholinervic, operate upon individual neurons in the caudate nucleus. Apomorphine and dopamine were shown to have similar effects on a substantial number of neurons, even though the onset and offset of the effect of apomorphine were slower than those of DA. This observation agrees with the suggestion that some of the central effects of apomorphine are due to an action at dopaminoceptive receptor sites.

Characteristicas and response differences to iontophoretically applied norepinephrine, D-amphetamine and acetylcholine on neurons in the medial and lateral vestibular nuclei of the cat

Midcollicular decerebrate cats, with their cerebellum removes, were tested with controlled acceleratory motion in order to identify neurons in the medial vestibular nucleus (MVN) and lateral vestibular nucleus (LVN) which responded to a motion stimulus. Five-barredled micropipettes were used to record single neuron activity and to apply norepinephrine (NE), d-amphetamine and acetylcholine (ACh). These agents were studied on spontaneously firing cells which responded to a motion stimulus and others which were in the MVN were inhibited by NE and d-amphetamine but were unaffected by iontophoresis of the alpha-adrenergic blocking agent phentolamine or the beta-antagonists, MJ-1999 or propranolol. In the LVN a majority of the cells tested were excited by NE and d-amphetamine. NE excitation in the LVN was antagonized by phentolamine but not by MJ-1999 or propranolo. Cats pretreated with reserpine to deplete brain catechlamines showed typical responses to NE BUT IONTOPHORESIS OF D-AMPHETAMINE WAS WITHOUT EFFECT. Unlike the differential sensitivity observed for NE, ACh excited most cells in both the MVN and LVN. NE and ACh produced similar responsed on vestibular neurons modulated by motion and those not responsive to motion. These observations suggest that NE-containing terminals are in close proximity to the vestibular neurons which were tested and further implicate both NE and ACh as neurotransmitters in afferent pathways to the vestibular nuclei.

The action of norepinephrine in the rat hippocampus. III. Hippocampal cellular responses to locus coeruleus stimulation in the awake rat

The behavioral and physiological effects of electrical stimulation of the nucleus locus coeruleus (LC) were studied in the awake rat. LC electrodes consistently supported high rates of self-stimulation (SS). LC stimulation also inhibited spontaneous cellular discharges in the hippocampus (HPC). Both the LC-induced inhibition of HPC units and the LC-evoked SS behavior were antagonized by alpha-methyltyrosine and 6-hydroxydopamine. In addition, chlorpromazine and diethyldithiocarbamate antagonized LC-induced inhibition of HPC units. D-Amphetamine facilitated SS behavior and reduced spontaneous HPC unit activity. The reinforcing properties of LC stimulation correlate closely with inhibition of cellular activity in the hippocampus; both actions appear to be mediated by norepinephrine.

The action of norepinephrine in the rat hippocampus. IV. The effects of locus coeruleus stimulation on evoked hippocampal unit activity

Activity of neurons in the hippocampus (HPC) was recorded in awake, freely moving rats. Most cells were inhibited by either a loud auditory stimulus (tone) or by electrical stimulation of the nucleus locus coeruleus (LC). The inhibitory responses to the tone were antagonized by drugs that interfere with central noradrenergic transmission. When LC stimulation was used as the unconditioned stimulus in a classical conditioning paradigm, previously inhibitory responses to the tone were reinstituted. When behaviorally subthreshold LC stimulation preceded a tone which was correlated with food, the existing conditioned response to the tone was potentiated. These data suggest that the generalized inhibitory response of HPC neurons to a tone is modulated by the noradrenergic pathway and that experimental activation of LC can potentiate HPC responses to behaviorally significant conditioned stimuli.

Cyclic AMP and central noradrenaline receptors: failure to activate diencephalic adrenergic feeding pathways

Intracranial injection of graded doses of dibutyryl 3',5'-cyclic adenosine monophosphoric acid (cAMP) at sites in the accumbens/stria terminalis nuclei of satiated rats elicited behavioural arousal and occasional convulsive episodes at higher doses, but failed to affect food consumption even in sites where injection of noradrenaline (65 nmol) consistently elicited increased feeding. Intracranial aminophylline (550 nmol) or dopamine (65 nmol) were also without effect on food consumption. This result does not support recent suggestions that cAMP serves as the second messenger in central noradrenergic motivational pathways.

Hippocampal innervation by serotonin neurons of the midbrain raphe in the rat

The organization of the brainstem serotonin neuron projection to the hippocampal formation was analyzed in the rat. This projection arises in the raphe nuclei of the midbrain. Following destruction of the midbrain raphe nuclei, chiefly nucleus centralis superior, there is a 72% decrease in hippocampal serotonin content. Injection of tritiated amino acid into the midbrain raphe nuclei results in transport of tritiated protein to the hippocampal formation and this transport is blocked in animals pretreated by intraventricular administration of 5,6-dihydroxytryptamine (5,6-DHT). Autoradiographic analysis indicates that the transport reaches the hippocampal formation primarily via two major pathways, the cingulum and the fornix. Cingulum fibers terminate predominantly in the dorsal hippocampus whereas the fornix distributes throughout the entire hippocampal formation. Some fibers reach the ventral hippocampus from the entorhinal area. Within the hippocampus there is dense labeling in a restricted lamina of the CA1 stratum lacunosum-moleculare with moderate labeling in stratum radiatum. Stratum oriens is sparsely labeled in CA1 and moderately so in CA2 and CA3. Stratum radiatum and stratum lacunosum-moleculare are moderately densely labeled in CA2 and Ca3. The area dentata is sparsely to moderately labeled in the molecular layer and heavily labeled in a thin lamina of the hilar zone immediately beneath the granule cell layer. The remaining hilar zone is moderately labeled. All of the discrete labeling of the hippocampus and area dentata described above is absent in animals pretreated with 5,6-DHT. These observations indicate that serotonin neurons of the midbrain raphe provide a highly organized innervation of the hippocampal formation in the rat.

The central adrenergic system. An immunofluorescence study of the location of cell bodies and their efferent connections in the rat utilizing dopamine-beta-hydroxylase as a marker

A sensitive immunofluorescence technique was used to describe systematically the distrubution of dopamine-beta-hydroxylase (DBH)-containing cell bodies, non-terminal fiber pathways, and terminal fields in the brain of the male albino rat. DBH is the enzyme that catalyzes the conversion of dopamine to noradrenaline, and as such is useful as an anatomical marker for noradrenaline and possibly adrenaline neurons. The enzyme is not present in dopamine- or indolamine-containing neurons. Ten micron frozen sections (1-in 20 series) were prepared in the frontal, sagittal, and horizontal planes from the olfactory bulb to the upper cervical segments of the spinal cord; adjacent sections in each plane were stained for DBH and for cells (toluidine blue=azure II). An atlas consisting of 40 projection drawings of selected frontal sections illustrates the results of the investigation. DBH perikarya are confined to three groups in the pons and medulla: the well defined locus coeruleus, a more diffuse but continuous subcoeruleus group that arches through the pons and ventral medulla, and a third dorsal medullary group centered in the dorsal motor nucleus of the vagus. A single principal adrenergic fiber system distributes a great many of the axons from these neuron groups to a majority of nuclear areas in the brain. In the pons and medulla two components of the fiber system may be distinguished. A medullary branch may be followed from the posterior aspect of the subcoeruleus group dorsally and then anteriorly through the lateral tegmental field and ventral aspect of the vestibular complex to a position subjacent to the locus coeruleus, where it is joined by a subcoeruleus branch consisting of a large number of fibers coursing among cells along the length of the subcoeruleus group, and by fibers arising from the locus coeruleus. Anterior to the locus coeruleus the principal adrenergic bundle courses as a single fiber tract immediately ventrolateral to the central gray in the mesencephalon and in the zona incerta and substantia innominata in the diencephalon. At the level of the septal area separate bundles reach the cortex dorsally over the genu of the corpus calosum via the medial septal-diagonal band nuclei and the lateral septum and ventrally between the olfactory tubercle and caudate-putamen. In the medulla and pons adrenergic fibers undoubtedly course in both directions. Anterior to the most rostral pontine cell bodies, however, all fibers presumably ascend. Along the course of the bundle distinct branches emerge to innervate circumscribed terminal fields. In addition, certain regions of the brain such as the reticular formation and pontine gray receive diffuse DBH innervation derived from less clearly defined pathways. A small number of areas in the brain contain little or no detectable DBH. These include the caudate-putamen, nucleus accumbens, globus pallidus, olfactory tubercle, subthalamic nucleus, substantia nigra, pretectal area, third, fourth and sixth cranial verve nuclei, and the trapezoid body nucleus.

Physiological and pharmacological evidence for a serotonergic projection to the hippocampus

Rat hippocampal pyramidal cells were studied for their response to serotonin applied iontophoretically and to stimulation of the midbrain raphe nuclei. Ninety-two percent of the cells studied were inhibited by serotonin. Fourty-eight percent of the cells responded by inhibition to dorsal and median raphe stimulation. The inhibitory response to raphe stimulation was absent when the rats were pretreated with p-chlorophenylalanine (PCPA), a serotonin synthesis inhibitor; PCPA effects were alleviated by 5-HTP or 5-HT administration. The response to raphe stimulation was blocked by emthysergide and cyproheptadine. The responses to raphe stimulation were potentiated by chlorimipramine, a serotonin reuptake blocker. These data satisfy several of the criteria required to identify serotonin as the inhibitory neurotransmitter for the raphe-hippocampal pathway

Analogs of cyclic adenosine monophosphate: correlation of inhibition of Purkinje Neurons with Protein Kinase Activation

Cyclic adenosine monophosphate (cyclic AMP) and 11 derivatives were applied to rat cerebellar Purkinje cells by iontophoresis. Cyclic AMP inhibited 63 percent of the cells, while the 8-parachlorophenylthio- and 8-benzylthio- analogs of cyclin AMP inhibited the spontaneous firing of 92 and 89 percent of cells, respectively. The ability of the 11 analogs to inhibit neuronal firing correlated ( r= + .78) with their reported potency in activating cyclic AMP-dependent protein kinase. These results extend previous studies, pointing to the mediation by cyclic AMP of the noradrenergic inhibition of Purkinje neurons, and provide new physiological evidence that protein phosphorylation is a major step in the action of cyclic AMP.

Supersensitivity of central neurons--a brief review of an emerging concept

The concept that "denervation" or "pharmacological disuse" supersensitivity develops in central neuronal systems subsequent to sustained attenuation of normal neurohumoral mechanisms is reviewed. Particular emphasis is placed on biochemical and electrophysiological parameters of supersensitivity in dopaminergic (striatal) neuronal systems. The possible applicability of theories invoking changes in receptor sensitivity to the phenomenon of narcotic tolerance and physical dependence and to psychoactive drug therapy is discussed.

Neuronal excitability modulation over the sleep cycle: a structural and mathematical model

A model for control of the desynchronized phase of the sleep cycle postulates reciprocal interaction between cells in the pontine gigantocellular tegmental field (FTG cells) and cells in the nucleus locus coeruleus and nucleus subcoeruleus (LC cells). This physiological model leads to equations of the Lotka-Volterra type; the time course of activity predicted by the model is in good agreement with actual long-term recordings of FTG cells and single-cycle data for LC cells.

Sleep cycle oscillation: reciprocal discharge by two brainstem neuronal groups

During the sleep cycle in cats, neurons localized to the posterolateral pole of the nucleus locus coeruleus and the nucleus subcoeruleus undergo discharge rate changes that are the opposite of those of the pontine reticular giant cells. The inverse rate ratios and activity curves of these two interconnected populations are compatible with reciprocal interaction as a physiological basis of sleep cycle oscillation.

Characterization of an inhibitory receptor in rat hippocampus: a microiontophoretic study using conformationally restricted amino acid analogues

1 Pyramidal cells in rat hippocampus were used to study the molecular dimensions of a receptor for inhibitory amino acids in the central nervous system. The inhibitory potencies of gamma-aminobutyrate (GABA), beta-alanine and glycine were compared by standard microiontophoretic techniques. Subsequently, rigid cyclopentane and cyclohexane amino acid analogues were applied by iontophoresis and their relative efficacies were compared with those of the naturally occurring amino acids.2 GABA was the most effective of the small aliphatic amino acids in producing inhibition of the firing of hippocampal pyramidal neurones. beta-Alanine was less effective and glycine was the least effective. GABA-induced inhibition was antagonized by concurrent iontophoresis of picrotoxin or bicuculline, whereas strychnine did not antagonize GABA inhibition.3 The ability of the series of substituted aminocyclopentane and aminocyclohexane carboxylic acids to produce inhibition of pyramidal cells was a direct function of the separation of amino and carboxylic acid groups. In both series of the cyclic amino acids the most potent inhibition was demonstrated when the spatial separation was similar to that of the extended GABA molecule (4.74 A). Additionally, the inhibition of hippocampal pyramidal cells by (+/--cis-3-amino-cyclopentanecarboxylic acid, like that produced by GABA, could be blocked by simultaneous application of picrotoxin or bicuculline, but not by strychnine.4 The present results suggest that the physiologically active conformation of GABA is the fully extended molecule, and additionally indicate that one dimension of the postsynaptic receptor site is within the range of 4.2 to 4.8 ångströms.

Cyclic AMP and cyclic GMP may mediate opposite neuronal responses in the rat cerebral cortex

Electrophysiologically identified pyramidal tract neurons in the rat cerebral cortex were tested with norepinephrine, acetylcholine, adenosine 3',5'-monophosphate (cyclic AMP), and guanosine 3',5'-monophosphate (cyclic GMP) applied by microiontophoresis. The neurons were usually inhibited by norepinephrine and cyclic AMP, but excited by acetylcholine and cyclic GMP. These opposing responses of pyramidal tract neurons to cyclic AMP and cyclic GMP suggests that these two nucleotides could function as reciprocal intracellular second messengers for norepinephrine and acetylcholine, respectively.