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Notes: The modulation of the central cardiovascular effects of α2-adrenoceptor activation by oxytocin in the nucleus tractus solitarii has been evaluated by cardiovascular analysis and by quantitative receptor autoradiography. Microinjections in the nucleus tractus solitarii of a threshold dose of oxytocin effectively and significantly counteracted the vasodepressor and bradycardic actions of an ED50 dose of the α2−adrenoceptor agonist clonidine. The coinjection of a threshold dose of oxytocin with a threshold dose of clonidine did not produce any changes in the mean arterial pressure but a tachycardic response was observed. Receptor autoradiographical experiments showed that oxytocin (3 nM) significantly increased the Kd and Bmax values of [3H]p-aminoclonidine binding sites in the nucleus tractus solitarii compatible with a possible antagonistic interaction with the α2-adrenoceptors, and this effect was blocked by the presence of the specific oxytocin receptor antagonist 1-deamino-2-D-Tyr-(OEt)-4-Thr-8-Orn-oxytocin. These findings suggest the existence of an antagonistic oxytocin/α2-adrenoceptor interaction in nucleus tractus solitarii that may be of relevance for the demonstrated modulation of α2−adrenoceptor induced cardiovascular responses by oxytocin.

Notes: Male and female Sprague-Dawley rats were treated with nicotine during the prenatal period and the first three postnatal weeks (the pregnant and lactating rats were given nicotine hydrogen (+) tartrate (165 mg/l) in the tap water). Catecholamine fluorescence was evaluated using quantitative histofluorometry on brain sections treated according to Falck-Hillarp methodology. In order to evaluate catecholamine utilization in discrete hypothalamic catecholamine nerve terminal networks, the αMT- (α-methyl-(±)-p-tyrosine methyl ester) induced catecholamine disappearance was studied 2 h following the tyrosine hydroxylase inhibition. The body weight was reduced in both the male and female rats from 3 weeks of age until 9 weeks of age following pre- and postnatal treatment with nicotine.Following one week of withdrawal from pre- and postnatal treatment with nicotine, an increased catecholamine utilization was observed in the medial and lateral palisade zones of the median eminence mainly in the female rat. In the female rat, reduced prolactin serum levels were found both in the presence and absence of αMT treatment as well as reduced luteinizing hormone concentration in the presence of αMT treatment.At 6 months of age indications of a maintained, weak activation of the catecholamine nerve terminal systems in the medial palisade zones of the median eminence were observed in male rats pre- and postnatally treated with nicotine. Furthermore, increased noradrenaline levels were found in the paraventricular hypothalamic nucleus. An increase in serum luteinizing hormone levels was also found in these rats. In the 7-month old diestrous rat, maintained marked increases in catecholamine utilization in the medial and lateral palisade zones of the median eminence were found following treatment with nicotine during the pre- and postnatal period. A significant reduction of nigral dopamine stores was also demonstrated. The serum levels of thyroid stimulating hormone, prolactin and luteinizing hormone were unchanged in these rats both in the presence and absence of tyrosine hydroxylase inhibition. Finally, pre- and postnatal treatment with nicotine did not alter [3H]nicotine binding (quantitative receptor autoradiography) in cortical, striatal and thalamic areas of the adult diestrous rat.The results demonstrate that pre- and postnatal treatment with nicotine in the drinking water produces permanent activations of the catecholamine nerve terminal networks of the external layer of the median eminence mainly in the female rat. These changes appear to be associated with reduced serum prolactin levels in the 4-week old female rat. Sex-specific changes occur in discrete noradrenaline nerve terminal systems. The observed changes may have functional consequences for neuroendocrine regulation and for the regulation of food and water intake as well as sex-specific responses to stress in the male versus the female rat. Nicotine-induced disturbances in brain cell replication and differentiation may underlie the permanent alteration found in discrete catecholamine neuron systems after pre- and postnatal exposure to this drug.

Notes: The aim of this work was to evaluate whether oxytocin administered in male rats subcutaneously early in life in the absence or presence of food restriction during pregnancy has life-long effects on the α2-agonist binding sites in the nucleus of the solitarii tract (NTS), in the hypothalamus and the amygdala, as evaluated by quantitative receptor autoradiography. Maternal food restriction alone increased the affinity of the α2-agonist [3H]UK14.304 binding sites exclusively in the NTS. In offspring from ad libitum fed dams, oxytocin treatment significantly increased the density of α2-agonist binding sites in the NTS and in the hypothalamus. The Kd value of the α2-agonist binding sites in the hypothalamus of these rats, but not in the other regions studied, was also significantly increased. In offspring from food-restricted dams, oxytocin treatment produced a significant increase of the Bmax values in the hypothalamus and the amygdala and the Kd value of the α2-agonist binding sites in the NTS of these rats also was selectively and significantly increased. These results suggest that a postnatal, oxytocin-induced increase of regional α2-adrenoceptor function can be seen in adulthood by a persistent, regionally selective increase in the density of central α2-adrenoceptor agonist binding sites, in the absence of an affinity change in the NTS. Such a regional increase of α2-adrenoceptor signalling in adulthood may contribute to the anti-stress action of postnatal oxytocin. By contrast, after prenatal stress, the potential increase in α2-adrenoceptor signalling takes place via selective increases of density with no changes of affinity of the α2-agonist binding sites in the hypothalamus and the amygdala.

Notes: In the rat the monoamine and neuropeptide innervation of the sympathetic visceral nuclei has been analysed using retrograde tracing and single and double immunolabelling procedures. When combined with tyrosine hydroxylase (TH), 5-hydroxytryptamine (5-HT) and enkephalin (ENK) immunocytochemistry, somata and dendrites of many preganglionic sympathetic neurons projecting to the coeliac ganglion visualized by retrograde tracing are found in close association with strands and plexa of strongly TH, 5-HT or ENK immunoreactive (IR) nerve terminals, while others have only a minor association with strong TH, 5-HT and ENK immunoreactivities, suggesting that a differential control of preganglionic sympathetic neurons is possible. Experiments with double immunolabelling procedures give further support to a direct innervation of preganglionic sympathetic neurons by TH, 5-HT and ENK IR nerve terminals. In conclusion, the present results open up the possibility for differential regulation of the preganglionic sympathetic neurons according to the Sherringtonian concept of spatial occlusion and facilitation in a pool of motoneurons.

Notes: In the rat the monoaminergic and neuropeptidergic innervation of the sympathetic visceral nuclei of the entire thoracic spinal cord has been analysed in serial horizontal sections using immunocytochemistry. Tyrosine hydroxylase (TH), Phenyl-ethanolamine-N-methyl-transferase (PNMT), 5-hydroxytryptamine (5-HT), substance P (SP) and enkephalin (ENK) immunoreactive (IR) nerve terminals form tufts of plexa with strong IR in the principal part of the intermediolateral nucleus (ILp) with the terminals in an extraperikaryal location. High densities of these strongly IR terminals are also found in the principal part of the intercalated nucleus (ICp) and in the paraependymal part of the intercalated nucleus (ICpe). The various types of IR nerve terminals also form rostro-caudally oriented and latero-medially oriented strands of strongly IR nerve terminals at regular intervals within each segment. Outside these sympathetic nuclei the terminals are absent or only weakly to moderately IR. The similar pattern of monoamine and peptide innervation of the putative preganglionic sympathetic neurons along the entire thoracic spinal cord may be related to the general three dimensional architecture of the preganglionic multipolar neurons. Thus, these inputs tend to cover the entire surface area of the preganglionic neurons in a uniform way. Some heterogeneities have been observed for the TH, PNMT and neuropeptide Y (NPY) innervation which may contribute to a differential control of sympathetic preganglionic neurons. It is suggested that the unique features of the descending monoaminergic or peptidergic neurons to sympathetic spinal nuclei are related to a demand for maintained transmission upon prolonged activation in these cardiovascular systems, allowing the maintenance of cardiovascular homeostasis.

Notes: Dual probe microdialysis was employed in freely moving 6-hydroxydopamine (6-OHDA) hemilesioned rats to investigate the effects of blockade of N-methyl-D-aspartate (NMDA) receptors in the dorsolateral striatum on glutamate (Glu) release from the ipsilateral substantia nigra pars reticulata (SNr). Perfusion for 60 min with the NMDA antagonist dizocilpine (0.1 and 1 μm) in the dopamine (DA)-denervated striatum stimulated nigral Glu release (peak effect of 139 ± 7% and 138 ± 9%, respectively). The lower (0.01 μm) and higher (10 μm) concentrations were ineffective. In sham-operated rats, dizocilpine failed to affect nigral Glu release up to 1 μm but induced a prolonged stimulation at 10 μm (153 ± 9% at the end of perfusion). The present results show that DA-deficiency in the striatum of hemiparkinsonian rats is associated with increased responsivity of nigral Glu release to striatal NMDA receptor blockade. This suggests that changes of NMDA receptor mediated control of the striatofugal pathways occur during Parkinson's disease (PD).

Notes: This report characterizes an in vivo intracerebral long-distance diffusion model using dual-probe microdialysis. Two probes 1 mm apart were implanted into the striatum of control and 6-hydroxydopamine (6-OHDA)-lesioned halothane-anaesthetized male rats. Either tritiated dopamine (500 n m3H-DA) or mannitol (1.5 μm3H-mannitol) was infused continuously for 5 h, while samples were collected from the other probe. Samples (10 μl) were counted by liquid scintillation. For the DA-infused rats, another 10 μL was separated with high-pressure liquid chromatography (HPLC)–electrochemical detection into individual fractions containing 3,4-dihydroxy phenylacetic acid (DOPAC) and homovanillinic acid (HVA), and counted for β-decay. The total transfer of 3H-labelled compounds described the overall effect of cellular uptake, metabolism and clearance into the microcirculation, and was compared with that of an extracellular marker, 3H-mannitol. The migration reached steady-state levels, generating an equilibrium between delivery and removal from the extracellular space. The half-time of the steady-state values, t50%, was in all cases lower in 6-OHDA-treated rats compared with control. In addition, the t50% values of 3H-mannitol were lower than those following the 3H-dopamine infusion in both control or 6-OHDA-lesioned rats. However, it was not possible to detect any unmetabolized 3H-dopamine at the 1 mm distance. In conclusion, the dual-probe microdialysis approach proved to be a valid method to study in vivo diffusion and migration in the brain, and the intracerebral spread of compounds highly depends on the nature of the compound infused.