[Catecholamines in regulation of development of GnRH neurons of rat fetuses].

The contents of dopamine, serotonin, and noradrenaline in rat fetuses developing under the conditions of their deficiency induced by administration of alpha-methyl-para-tyrosine to females during 11th to 16th or 20th day of pregnancy and in fetuses, whose mothers were given saline at the same time, were determined using HPLC with subsequent electrochemical detection. Administration of alpha-methyl-para-tyrosine led to decreased levels of dopamine and noradrenaline in the areas of migration of GnRH-neurons in fetuses on days 17 and 21 of prenatal development. The concentration of serotonin remained unchanged, except in the head nasal area in males on day 21. The areas of interaction between the brain catecholaminergic systems and migrating and differentiating GnRH-neurons were determined by double immunohistochemical labeling. Close topographical location of GnRH-immunoreactive neurons and tyrosine hydroxylase-immunoreactive in the area of nucleus accumbens on days 17 and 20, as well as in the median eminence on day 20. The GnRH concentration in the caudal areas of migration of GnRH-neurons under the normal conditions and in the case of catecholamine deficiency was determined using radioimmunoassay. After administration of alpha-methyl-para-tyrosine the GnRH concentration in the anterior hypothalamus decreased in females. The data obtained suggest the involvement of catecholamines in the regulation of development of GnRH-Neurons during prenatal development. In addition, the adequacy and efficiency of the used model of catecholamine deficiency for studying the development of such neurons was confirmed.

[A population of neurons expressing tyrosine hydroxylase and migrating from olfactory placode into forebrain during ontogenesis in rats]. / Populiatsiia neironov, ékspressiruiushchikh tirozingidroksilazu, migriruiushchikh iz oboniatel'nykh plakod v perednii mozg, v ontogeneze u krys.

Olfactory placodes, that give rise to the olfactory and respiratory epithelia during ontogenesis, are a source of many neurons migrating into forebrain in the direction of growth of the olfactory nerves. The neurons expressing gonadotropin releasing hormone (GnRH) are among the best studied in the population in question. This hormone is responsible for the central regulation of reproduction in adult animals. It was already shown that, in addition to the GnRH-immunoreactive neurons, a small amount of neurons expressing tyrosine hydroxylase (TH), the first enzyme of catecholamine synthesis, migrates into the forebrain. Such a transient population of TH-immunoreactive neurons was shown by means of single and double immmunohistochemical labeling. The TH neurons were first found on branches of the olfactory, terminal, and vomeronasal nerves, along the trajectory of migration of GnRH-immunoreactive neurons on day 15 of embryogenesis, which preceded the appearance of GnRH-immunoreactive neurons. On days 17-21 of embryogenesis, both populations of neurons were found in almost the same areas and on day 21 single neurons contained both GnRH and TH. There were no neurons expressing decarboxylase of aromatic acids (DAA), the second enzyme of catecholamine synthesis, among TH-immunoreactive neurons, thus suggesting noncatecholaminergic nature of these neurons. However, single nonenzymatic DAA-immunoreactive neurons were found in the area of anterior olfactory nuclei in the forebrain, which suggests their involvement in local cooperative synthesis of catecholamines in the area where GnRH-immunoreactive neurons penetrate in the forebrain. Thus, the neurons expressing TH, TH and GnRH, and DAA were found in rats during prenatal period in the nasal part of the head along the nerves projecting into the forebrain and in the rostral part of forebrain. The origin and functional significance of these neurons are discussed.

[Effect of catecholamines on migration and differentiation of gonadotropin releasing hormone-neurons in rats]. / Vliianie kateholaminov na migratsiiu i differentsirovku gonadotropin-relizing gormon-neironov u krys.

The GnRH producing neurons are the key link of neuroendocrine regulation of the adult reproductive system. Synthesis and secretion of GnRH are, in turn, under the afferent catecholaminergic control. Taking into account that catecholamines exert morphogenetic effects on target cells during ontogenesis, this study was aimed at investigation of the effects of catecholamines on development of GnRH neurons in rats during ontogenesis. We carried out comparative quantitative and semiquantitative analyses of differentiation and migration of GnRH neurons in fetuses of both sexes under the conditions of normal metabolism of catecholamines (administration of saline) or their pharmacologically induced deficiency (administration of alpha-methylparatyrosine). The inhibition of catecholamine synthesis from day 11 of embryogenesis led to an increasing number of GnRH neurons in rostral regions of the trajectory of their migration over the brain: in the area of olfactory tubercles on day 17 and in the area of olfactory bulb on days 18 and 21. In addition, the optical density of GnRH neurons located in the rostral regions of migration was higher in the fetuses after administration of alpha-methylparatyrosine during embryogenesis, as compared to the control. It has been concluded that catecholamines stimulate the migration of GnRH neurons and affect their differentiation.

Estimation of neocortical serotonin-2 receptor binding potential by single-dose fluorine-18-setoperone kinetic PET data analysis.

UNLABELLED: Because it satisfies most of the characteristics required to quantify in vivo neocortical serotonin-2 (5HT2) receptors, 18F-setoperone was selected for use in PET estimation of the neocortical 5HT2 binding parameters in baboons according to a single-dose paradigm. METHODS: The neocortical binding potential (i.e., Bmax/KD or the k3/k4 ratio) was assessed by three different methods, with the cerebellum taken as the reference structure in all instances. Method 1 was based on a Logan-Patlak graphical analysis of both cerebellar and neocortical data, which allows estimation of the neocortical k3'/k4 ratio; it required a separate estimation of k5 and k6 from classical nonlinear least-squares (NLSQ) three-compartment modeling of cerebellar data. Method 2 was an original combination of a four-compartment Logan-Patlak procedure for neocortical data and an NLSQ three-compartment procedure for cerebellar data, allowing the neocortical k3/k4 ratio to be obtained directly. In Method 3, an NLSQ three-compartment procedure was applied to cerebellar data and an NLSQ four-compartment procedure to neocortical data, allowing separate determinations of k3 and k4 for the neocortex and, in turn, the k3/k4 ratio. RESULTS: In all three methods, the arterial plasma input function was corrected for the presence of 18F-metabolites, and the vascular fraction was either fitted or fixed. Statistical analysis showed no significant difference among the k3/k4 values obtained from the three methods. Method 3 was the least stable because of an occasional poor NLSQ four-compartment fit on neocortical data. Method 2 provided the least cumbersome estimate of the k3/k4 ratio and was found easy and accurate for generating parametric maps of the 5HT2 binding potential. CONCLUSION: This method might be useful in clinical investigations to provide quantitative assessment of receptor binding potential. In semiquantitative investigations, the neocortical-to-cerebellum pseudoequilibrium ratio may be adequate, as suggested by the significant correlations with measured k3/k4 ratios found here.

In vivo mapping of brain benzodiazepine receptor changes by positron emission tomography after focal ischemia in the anesthetized baboon.

BACKGROUND AND PURPOSE: Recent reports have shown an increase in specific binding (in vitro) of [3H]PK 11195 to peripheral-type benzodiazepine receptors in both experimental animals and humans, reflecting a glial/macrophagic reaction within and around focal ischemic insults. We have evaluated by positron emission tomography the time course of changes in brain uptake in vivo of 11C-labeled PK 11195 and flumazenil (an antagonist of central benzodiazepine receptors) as indirect and direct markers of neuronal loss, respectively, after focal cerebral ischemia. METHODS: Ten anesthetized baboons were submitted to sequential positron emission tomography studies between day 1 and day 91 after unilateral middle cerebral artery occlusion. The studies consisted of successive assessments, in the same positron emission tomography session, of [11C]PK 11195, [11C]flumazenil, cerebral blood flow, and oxygen consumption; late computed tomographic scans were obtained to map the approximate contours of infarction and to define a concentric peri-infarct area. RESULTS: We found a significant time-dependent increase in [11C]PK 11195 uptake in the peri-infarcted area, maximum at 20 to 40 days after occlusion. In contrast, there was a time- and perfusion-independent significant decrease in [11C]flumazenil uptake in the infarcted area, stable from day 2 onward, and already present in one baboon at day 1. Challenge studies with saturating doses of cold ligands confirmed that these changes represented alterations in specific binding. [11C]Flumazenil uptake was not affected in hypometabolic (but apparently noninfarcted, ie, deafferented) cortical areas. CONCLUSIONS: The delayed and apparently transient increases in [11C]PK 11195 specific uptake in vivo presumably represent glial/macrophage reaction; the marked depression in [11C]flumazenil specific binding, which appears selective for synaptic damage, is both precocious and sustained and thus may be better suited for the early assessment of ischemic damage in humans.

Determination of 18F-fluoro-2-deoxy-D-glucose rate constants in the anesthetized baboon brain with dynamic positron tomography.

We have determined the rate constants (ki*) of 18F-fluorodeoxyglucose (FDG) in the unlesioned baboon brain, for use in positron emission tomography (PET) measurements of glucose utilization. In contrast to earlier reports, we used a radiosynthesis which guarantees production of FDG essentially uncontaminated by fluorodeoxymannose, and an improved determination of ki* by (1) direct measurement of the time-shift between bolus arrival in femoral arterial plasma and brain, (2) rapid initial PET frames, and (3) extended data acquisition (up to 180 min). Young adult baboons were studied under anesthesia with either phencyclidine or etomidate. The FDG time-activity curves obtained from temporal grey matter showed a consistent decline after about 80 min, indicating true product loss. Three-compartment modelling was performed for increasing fitting intervals (20-120 min) with both a 5-parameter (K1*-k4*, and vascular volume (Vo)) and a 4-parameter (K1*-k3*,Vo) model. With the latter, both the calculated FDG net clearance ((K* = K1*.k3*/(k2* + k3*)) and the fitted kinetic constants were dependent on fitting interval, i.e., they showed sustained unstability. With the former, the constant k4*, which presumably represents dephosphorylation, was overestimated and unstable for short fitting times (presumably due to heterogeneous brain compartments in the sample tissue), but stabilized at approximately 0.01 min-1 for fitting times > or = 80 min; K1*-k3* and K* were also stable after this time. These findings were identical for both anesthetic regimen. Thus, in the anesthetized baboon, the FDG ki* values can be reliably determined based on an adequate PET acquisition paradigm and with a model that incorporates k4* and > or = 80 min time-activity data.