The effect of p-chloroamphetamine and p-chlorophenylalanine on the level of thyrotropin-releasing hormone and its receptors in some brain structures and lumbar spinal cord of the rat

Defects in breathing and thermoregulation in mice with near-complete absence of central serotonin neurons

Serotonergic neurons project widely throughout the CNS and modulate many different brain functions. Particularly important, but controversial, are the contributions of serotonin (5-HT) neurons to respiratory and thermoregulatory control. To better define the roles of 5-HT neurons in breathing and thermoregulation, we took advantage of a unique conditional knock-out mouse in which Lmx1b is genetically deleted in Pet1-expressing cells (Lmx1b(f/f/p)), resulting in near-complete absence of central 5-HT neurons. Here, we show that the hypercapnic ventilatory response in adult Lmx1b(f/f/p) mice was decreased by 50% compared with wild-type mice, whereas baseline ventilation and the hypoxic ventilatory response were normal. In addition, Lmx1b(f/f/p) mice rapidly became hypothermic when exposed to an ambient temperature of 4 degrees C, decreasing core temperature to 30 degrees C within 120 min. This failure of thermoregulation was caused by impaired shivering and nonshivering thermogenesis, whereas thermosensory perception and heat conservation were normal. Finally, intracerebroventricular infusion of 5-HT stimulated baseline ventilation, and rescued the blunted hypercapnic ventilatory response. These data identify a previously unrecognized role of 5-HT neurons in the CO(2) chemoreflex, whereby they enhance the response of the rest of the respiratory network to CO(2). We conclude that the proper function of the 5-HT system is particularly important under conditions of environmental stress and contributes significantly to the hypercapnic ventilatory response and thermoregulatory cold defense.

Inhibition of pudendal reflexes in spinal rats. Reassessing the role of serotonin

The effects of serotonin (5-HT) and thyrotropin-releasing hormone (TRH) on penile reflexes were investigated in intact and spinally transected male rats. Doses of intrathecal 5-HT (0.0, 1.13, 2.26, 11.3, 22.6, and 113.0 nmol), in a range previously shown to inhibit pudendal reflexes in anesthetized spinal preparations, prolonged the latency to the first penile erection in awake intact rats. However, these doses also provoked hyperreactivity and vocalization. Doses of intrathecal TRH (100 and 500 pmol) that effectively inhibited penile erection in intact animals were less effective in spinalized animals. Finally, a combination of subthreshold doses of TRH (100 pmol) and 5-HT (4.0 nmol) at a ratio known to affect other TRH/5-HT-mediated circuits significantly extended erection latency in animals with spinal transections. These data suggest that 5-HT and TRH are both involved in the inhibitory circuits regulating penile erection, either through corelease onto the same population of cells or through independent release onto different populations of neurons.

Role of serotonin in nephrotoxic serum nephritis in WKY rats

Our objective was to determine whether serotonin is involved in inducing nephrotoxic serum nephritis in WKY rats. After injection of antiglomerular basement membrane antiserum, urinary protein excretion was significantly decreased in rats treated with the serotonin receptor antagonist, MCI-9042, and in rats treated with p-chlorophenylalanine. Similarly, severe necrotizing lesions and crescent formation were inhibited in a dose-dependent manner by treatment with MCI-9042 and p-chlorophenylalanine. The number of intraglomerular ED-1-positive cells was increased on day 3 and thereafter in the placebo group. A significant increase in the number of crescent lesions was observed in the placebo group on day 7 and thereafter. Neither adenosine diphosphate- nor collagen-induced platelet aggregations were inhibited in platelet-rich plasma from rats treated with MCI-9042. No significant differences were observed in the production of circulating antibody and antibody deposition in rat glomeruli among the study groups. These results indicate that pathologic changes and urinary protein excretion are closely related to the presence of serotonin in nephrotoxic serum nephritis of WKY rats. Thus serotonin may play a key role in the glomerular injury in this model. Studies on the mode of action of MCI-9042 on platelet aggregation in vivo indicate that the antiplatelet effect of this drug did not contribute to the inhibition of renal injury in this experimental model. This study suggests that serotonin participates in macrophage-mediated immune injury in nephrotoxic serum nephritis of WKY rats.

Light and electron microscopic studies of the effects of p-chloroamphetamine on the monoaminergic innervation of the rat spinal cord

A previous report has shown that small diameter serotoninergic (5-HT) axons innervating the forebrain are selectively eliminated by treatment with an amphetamine derivative, (+/-)p-chloroamphetamine (PCA; Mamounas et al., [1991] J. Comp. Neurol. 314:558-586). It is well known that the spinal cord is the target of numerous monoaminergic fibers of different types. We have previously shown that the dorsal and ventral horns and the intermediolateral cell column are innervated by numerous serotonin-, noradrenaline- and dopamine-containing axons, including both thin axons with small varicosities and beaded axons with large varicosities. In all these regions, the large majority of fine indolaminergic fibers do not establish synaptic contacts, contrasting with the beaded axons which mostly exhibit synapses. The present work was conducted to study the effect of PCA on the monoaminergic innervation of the adult rat spinal cord. Animals received two subcutaneous doses of PCA 24 hours apart and were perfused 3 weeks later. Immunocytochemistry was performed to detect 5-HT, noradrenergic and dopaminergic fibers by using light and electron microscopy. Light microscopy revealed that PCA treatment caused a marked and selective elimination of the fine 5-HT-immunoreactive fibers, mainly found in the dorsal horn, but spared all other larger axons. This selective effect on the dorsal horn innervating thin 5-HT fibers was confirmed with the electron microscope by calculating the synaptic incidence(s) of monoaminergic innervation. These results suggest that fine and beaded 5-HT axons correspond to two anatomically, biochemically and pharmacologically different types of fibers, which could arise from two subpopulations of brainstem neurons. In addition, this drug could be used to provide an experimental animal, devoid of 5-HT nonsynaptic fibers, thereby facilitating a study on the role of dorsal horn nonsynaptic system in pain modulation.

The role of dopamine receptors in the release of thyrotropin-releasing hormone from the rat striatum and nucleus accumbens: an in vitro study

In the present study we examined the influence of dopamine (DA) stimulants: amphetamine (an agent releasing DA), apomorphine (a non-selective agonist of DA receptors), quinpirole (a selective agonist of D2 receptors) and SKF-38393 (a selective agonist of D1 receptors) on the in vitro release of thyrotropin-releasing hormone (TRH) from the rat striatal slices and nucleus accumbens fragments. It was shown that amphetamine, apomorphine and quinpirole (all those drugs added in concentrations of 10(-8)-10(-5) M), concentration-dependently increased the release of TRH, a more potent effect being observed in striatal slices. On the other hand, SKF-38393 (10(-6)-10(-5) M) was ineffective. Furthermore, the increases in the TRH release from the striatal slices, induced by 10(-5) M of amphetamine, apomorphine or quinpirole, were completely blocked by the selective D2 receptor antagonist sulpiride (10(-5) M), but not by the selective D1 receptors antagonist SCH-23390 (10(-5) M). These results indicate that stimulation of D2 receptors is responsible for the TRH release from the striatum and nucleus accumbens in vitro, and that this effect may be involved in the decrease in the peptide content in the striatum following DA stimulants, observed earlier in in vivo studies.