Noradrenergic nuclei that receive sensory input during mating and project to the ventromedial hypothalamus play a role in mating-induced pseudopregnancy in the female rat

In female rats, vaginal-cervical stimulation (VCS) received during mating induces bicircadian prolactin surges that are required for the maintenance of pregnancy or pseudopregnancy (PSP). The neural circuits that transmit VCS inputs to the brain have not been fully described, although mating stimulation is known to activate medullary noradrenergic cell groups that project to the forebrain. In response to VCS, these neurones release noradrenaline within the ventrolateral division of the ventromedial hypothalamus (VMHvl) and the posterodorsal medial amygdala (MePD), two forebrain sites that are implicated in the initiation of PSP. Noradrenaline receptor activation within the VMHvl is both necessary and sufficient for PSP induction, suggesting that noradrenaline acting within the VMHvl is particularly important in mediating the effects of VCS towards the establishment of PSP. We therefore investigated whether or not endogenous, VCS-induced noradrenaline release within the VMHvl is involved in PSP induction in the rat. Before the receipt of sufficient mating stimulation to induce PSP, a retrograde neurotoxin, dopamine-β-hydroxylase-saporin (DBH-SAP), was infused bilaterally into the either the VMHvl or the MePD to selectively destroy afferent noradrenergic nuclei in the brainstem. DBH-SAP infusions into the VMHvl lesioned mating-responsive noradrenergic neurones in A1 and A2 medullary nuclei and reduced the incidence of PSP by 50%. Infusions of DBH-SAP into the MePD had no effect on the subsequent induction of PSP. These results suggest that VCS is conveyed to mating-responsive forebrain areas by brainstem noradrenergic neurones, and that the activity of noradrenergic cells projecting to the VMHvl is involved in the induction of PSP.

Presynaptic α7 and non-α7 nicotinic acetylcholine receptors modulate [3H]d-aspartate release from rat frontal cortex in vitro

The presynaptic nicotinic modulation of glutamatergic transmission in the CNS has been associated with activation of the alpha7 subtype of nicotinic acetylcholine receptor (nAChR) in sub-cortical regions, whereas in the frontal cortex, non-alpha7 nAChRs have been implicated. The aim of this investigation was to directly characterise nAChR-evoked release of excitatory amino acids from rat frontal cortex, by monitoring the release of [3H]D-aspartate from superfused synaptosomes or minces. Co-administration of a nAChR agonist with a depolarising stimulus enhanced [3H]D-aspartate release above the effect of depolarising agent alone. This enhancement was blocked by the nicotinic antagonist mecamylamine. Other experiments revealed that in the absence of a depolarising stimulus, the nAChR agonists nicotine, epibatidine and anatoxin-a could evoke the release of [3H]D-aspartate in a Ca2+- and concentration-dependant manner. Differential sensitivity to the alpha7- and beta2*-selective nAChR antagonists alpha-bungarotoxin (alpha-Bgt) and dihydro-beta-erythroidine (DHbetaE) implicated two nAChR subtypes (alpha7 and beta2*), and this was supported by using the subtype-selective agonists choline (10 mM; alpha7 selective, blocked by alpha-Bgt but not by DHbetaE) and 5-Iodo-A-85380 (10 nM; beta2*-selective, blocked by DHbetaE but not by alpha-Bgt). Immunocytochemistry showed that alpha-Bgt labelling was associated with structures immunopositive for vesicular glutamate transporters, in both frontal cortex sections and synaptosome preparations, supporting the presence of alpha7 nAChR on glutamatergic terminals in rat frontal cortex.

Spinal noradrenergic activation mediates allodynia reduction from an allosteric adenosine modulator in a rat model of neuropathic pain

Activation of adenosine A1 receptors by endogenous adenosine or synthetic agonists produces anti-nociception in animal models of acute pain and also reduces hypersensitivity in models of inflammatory and nerve-injury pain. Allosteric adenosine modulators facilitate adenosine agonist binding to the A1 receptor. The purpose of the current study was to examine the effect, mechanisms of action, and interaction with noradrenergic systems of intrathecal (i.t.) or oral administration of the allosteric adenosine modulator T62 in a rat model of neuropathic pain. A spinal nerve ligation rat model (SNL; ligation of left L5 and L6 spinal nerve roots) was used. One week after SNL surgery, an i.t. catheter was inserted. Withdrawal threshold to mechanical stimulation of the left hind paw was determined before and after surgery, confirming mechanical hypersensitivity. Oral or i.t. T62 reduced hypersensitivity induced by SNL. The effects of i.t. T62 were inhibited by i.t. injection of an A1 receptor antagonist and by an 2-adrenergic antagonist but not by an A2 adenosine receptor antagonist. Anti-dopamine hydroxylase (DH)-saporin treatment reduce spinal norepinephrine content by 97%, accompanied by an almost complete loss of DH immunoreactive axons in the spinal dorsal horn and neurons in the locus coeruleus. The effect of T62 was completely lost in animals treated with anti-DH-saporin. These data support the hypothesis that activation of the A1 receptor by the allosteric modulator, T62, produces anti-nociception via spinal noradrenergic activation.

Isoflurane and nociception: spinal alpha2A adrenoceptors mediate antinociception while supraspinal alpha1 adrenoceptors mediate pronociception

BACKGROUND

The authors recently established that the analgesic actions of the inhalation anesthetic nitrous oxide were mediated by noradrenergic bulbospinal neurons and spinal alpha2B adrenoceptors. They now determined whether noradrenergic brainstem nuclei and descending spinal pathways are responsible for the antinociceptive actions of the inhalation anesthetic isoflurane, and which alpha adrenoceptors mediate this effect.

METHODS

After selective lesioning of noradrenergic nuclei by intracerebroventricular application of the mitochondrial toxin saporin coupled to the antibody directed against dopamine beta hydroxylase (DbetaH-saporin), the antinociceptive action of isoflurane was determined. Antagonists for the alpha1 and alpha2 adrenoceptors were injected at spinal and supraspinal sites in intact and spinally transected rats to identify the noradrenergic pathways mediating isoflurane antinociception. Null mice for each of the three alpha2-adrenoceptor subtypes (alpha2A, alpha2B, and alpha2C) and their wild-type cohorts were tested for their antinociceptive response to isoflurane.

RESULTS

Both DbetaH-saporin treatment and chronic spinal transection enhanced the antinociceptive effects of isoflurane. The alpha1-adrenoceptor antagonist prazosin also enhanced isoflurane antinociception at a supraspinal site of action. The alpha2-adrenoceptor antagonist yohimbine inhibited isoflurane antinociception, and this effect was mediated by spinal alpha2 adrenoceptors. Null mice for the alpha2A-adrenoceptor subtype showed a reduced antinociceptive response to isoflurane.

CONCLUSIONS

The authors suggest that, at clinically effective concentrations, isoflurane can modulate nociception via three different mechanisms: (1) a pronociceptive effect requiring descending spinal pathways, brainstem noradrenergic nuclei, and supraspinal alpha1 adrenoceptors; (2) an antinociceptive effect requiring descending noradrenergic neurons and spinal alpha2A adrenoceptors; and (3) an antinociceptive effect mediated within the spinal cord for which no role for adrenergic mechanism has been found.

Central noradrenergic lesioning using anti-DBH-saporin: anatomical findings

The ability to create lesions of discrete neuronal populations is an important strategy for clarifying the function of these populations. The power of this approach is critically dependent upon the selectivity of the experimental lesioning technique. Anti-neuronal immunotoxins offer an efficient way to produce highly specific neural lesions. Two previous immunotoxins have been shown to be effective in both the CNS and PNS. They are OX7-saporin, which is targeted at Thy1, and 192-saporin, which is targeted at the low affinity neurotrophin receptor, p75NTR. In the present study, we sought to determine if an immunotoxin targeted at the neurotransmitter synthesizing enzyme, dopamine beta-hydroxylase (DBH), could selectively destroy central noradrenergic neurons after intraventricular administration. This immunotoxin, which consists of a monoclonal antibody to DBH coupled by a disulfide bond to saporin (a ribosome inactivating protein), has been shown to be selectively toxic to peripheral noradrenergic sympathetic neurons in rats after systemic injection. In the present study, immunohistochemical and Cresyl violet staining showed that the noradrenergic neurons of the locus coeruleus are destroyed bilaterally after intraventricular (i.c.v.) injection of 5, 10, and 20 micrograms of anti-DBH-saporin (alpha-DBH-sap) into rats. Complete bilateral lesioning of the A5 and A7 cell groups occurred at the two higher doses. Lesions of the A1/C1 and A2/C2/C3 cell groups were incomplete at all three doses. Dopaminergic neurons of the substantia nigra and ventral tegmental area and serotonergic neurons of the raphé, all monoaminergic neurons that do not express DBH, survived all alpha-DBH-sap doses. The cholinergic neurons of the basal forebrain, which are selectively killed by i.c.v. injection of 192-saporin, and cerebellar Purkinje cells which are killed by OX7-saporin, were not killed by alpha-DBH-sap. These results show that alpha-DBH-sap efficiently and selectively destroys CNS noradrenergic neurons after i.c.v. injection. The preferential destruction of locus coeruleus, A5, and A7 over A1/C1 and A2/C2/C3 may be due to more efficient access of the immunotoxin to these neurons and their terminals after i.c.v. injection.

Modulation of cardiac beta-adrenergic receptors by dopamine beta-hydroxylase

Incubation of cardiac sarcolemma in the presence of dopamine beta-hydroxylase (DBH), a catecholamine biosynthetic enzyme, increased beta-adrenergic receptor density by 68% as measured by [3H]dihydroalprenolol (DHA) binding. The addition of DBH to plasma membranes isolated from brain, kidney, skeletal muscle, liver and intestine did not alter [3H]DHA binding. Cardiac alpha-receptors were unaffected under similar conditions. Since DBH is coreleased with norepinephrine, these results indicate that a functional coupling of the putative beta-adrenergic receptor with DBH may exist in cardiac muscle.

Ethacrynic acid-induced convulsions and brain noradrenaline in mice

The intracerebroventricular injection of ethacrynic acid (a 50% convulsive dose; 50 micrograms/mouse) accelerated brain noradrenaline turnover and decreased noradrenaline contents. The decrease in noradrenaline contents was antagonized by 2-amino-5-phosphonovalerate but not by diazepam. Both 2-amino-5-phosphonovalerate and diazepam suppressed the incidence of ethacrynic acid-induced convulsions while reserpine, alpha-methyl-para-tyrosine or FLA-63 augmented it. The results suggest that stimulation by ethacrynic acid of excitatory amino acid neurons enhances-noradrenergic neuronal anticonvulsive activity.

[Relationship between arsenic-induced hypothermia and brain monoamines. (2). The roles of noradrenaline and dopamine]

It has been reported that hypothermia induced by intravenous administration of As2O3 3 mg/kg in rabbits is due to a decrease of noradrenaline (NA) in the hypothalamus. In this paper, the role of NA or dopamine (DA) on As2O3-induced hypothermia in rabbits were investigated. As2O3-induced hypothermia was not inhibited by pretreatment with FLA-63, a potent dopamine-beta-hydroxylase inhibitor, which produces an increase of DA and a decrease of NA in rabbit brain; and it was also inhibited by pretreatment with haloperidol or pimozide, potent DA-receptor blocking agents. On the contrary, pretreatment with phenoxybenzamine or dibenamine, alpha-receptor blocking agents, completely inhibited these hypothermia. These findings indicated that NA took an important part in thermoregulation in rabbits and certified that DA or DA-receptors were not involved As2O3-induced hypothermia.

Accumulation of a tetrahydroisoquinoline in phenylketonuria

3',4'-Deoxynorlaudanosolinecarboxylic acid (DNLCA), a tetrahydroisoquinoline derived from dopamine and phenylpyruvic acid, has been detected by computerized mass fragmentography in urine of phenylketonuric children and in urine and brain of rats with experimentally induced hyperphenylalaninemia. Levels of DNLCA in brain of treated animals were more than tenfold higher than controls, and the excess tetrahydroisoquinoline appeared to accumulate in the cerebellum and cortex. DNLCA is a noncompetitive inhibitor of dopamine beta-hydroxylase (inhibition constant, Ki, = 0.42 mM) and is taken up by the brain.

Effects of catecholamine manipulations on three different self-stimulation behaviors

Rats with self-stimulation electrodes in the medial part of lateral hypothalamus (LH) or in the lateral part of LH were trained to bar press, to run in a continuous, square-shaped runway, and to move their tails from side to side while otherwise restrained, all using LH stimulation on an FI 2 sec schedule as the reinforcement. At low doses of pimozide (a dopaminergic blocker) or of FLA-57 (a dopamine beta-hydroxylase inhibitor) different effects on rates of responding were observed on each of the 3 tasks at the 2 electrode placements, indicating that the rate reductions were not the results of specific performance effects of the drugs. The patterns of rate changes suggested that the effects of LH stimulation on behavior in the runway were primarily, but not exclusively mediated by a dopaminergic system; that the effects of LH stimulation on tail movement were primarily, but not exclusively mediated by a noradrenergic system; and that the effect of LH stimulation on bar pressing was mediated by both, or either of these substrates. These results suggest that the reinforcement of behavior by LH stimulation is flexibly mediated by at least 2 different neural systems.

[Labile arterial hypertension and sympathetic tonus. Hemodynamic study]

Cardiac output, cardiopulmonary (CPBV) and total (TBV) blood volumes, vascular reactivity to norepinephrine and dopamine B hydroxylase (DBH) were determined in 41 borderline hypertensives patients in comparison with 28 normal subjects. Cardiac output (P less than 0.001) and CPBV/TBV ratio (P less than 0.01) were significantly increased. The ratio was directly correlated to the pressor-response to norepinephrine (P less than 0.01) and the DBH level (P less than 0.005). The results suggest that sympathetic overactivity plays a dominant role in the cardiac output elevation of borderline hypertensive patients.