Central and systemic effects of a vasopressin V1 antagonist on MAP recovery after haemorrhage in rats

The present study examined the effects of central and peripheral administration of a vascular (V1) vasopressin (AVP) receptor antagonist on blood pressure, heart rate, and AVP levels in conscious rats. Rats subjected to rapid arterial haemorrhage were administered the AVP V1 antagonist [d(CH2)5Tyr(Me)AVP] either 5 min pre- or 20 min posthaemorrhage. Mean arterial blood pressure (MAP) was monitored for 45 min, after which the animals were killed and selected brain regions and plasma taken for AVP measurement. Intravenous (i.v.) administration of d(CH2)5Tyr(Me)AVP at 10 micrograms kg-1, but not 100 ng kg-1, significantly reduced MAP between 20 and 45 min posthaemorrhage compared with saline-treated controls. In contrast, administration of d(CH2)5Tyr(Me)AVP at 100 ng kg-1 intracerebroventricularly caused an attenuated MAP recovery to haemorrhage comparable with the effect of the antagonist at 10 micrograms kg-1 i.v. Haemorrhage caused a marked increase in circulating AVP levels, which was further enhanced in rats treated with the V1 antagonist at 10 micrograms kg-1 i.v., but no change in AVP levels of selected brain regions. The results indicate a role for AVP in MAP recovery following haemorrhage which may be centrally mediated.

Effect of intrathecal proctolin administration on the behaviour evoked by the thyrotrophin-releasing hormone (TRH) analogue (RX 77368) and the indoleamine, TRH, substance P and calcitonin gene-related peptide levels and choline acetyltransferase activity in the rat spinal cord

The behavioral effects and the biochemical changes produced following either a single or repeated intrathecal injection respectively, of the insect peptide proctolin (Arg-Tyr-Leu-Pro-Thr-OH) have been compared with the effects of a stable analogue of thyrotrophin-releasing hormone (TRH) in rats. Intrathecal proctolin (1-100 micrograms) did not produce any marked behavioural effects on its own, while intrathecal TRH analogue (RX 77368, 0.5 microgram) administration produced wet-dog shakes and forepaw-licking behaviours. Proctolin (10 micrograms) significantly attenuated the wet-dog shake and forepaw-licking behaviours evoked by intrathecal RX 77368 administration when it was given 30 min before, but not when given in combination with RX 77368. Repeated intrathecal proctolin administration (10 micrograms twice daily for 5 days) significantly reduced the 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid and TRH levels in the ventral, but not in the dorsal, horn of the spinal cord nor in the brainstem, and elevated hypothalamic TRH without affecting plasma free thyroxine levels when compared with values in saline-treated controls. Repeated proctolin injection did not alter substance P levels in any brain region examined, nor did it affect the choline acetyltransferase activity or the calcitonin gene-related peptide-like immunoreactive levels in the ventral horn of the spinal cord, both of which are principally located in motoneurones in this cord region.(ABSTRACT TRUNCATED AT 250 WORDS)

Spinal effects of chronic intrathecal administration of the thyrotrophin-releasing hormone analogue (CG 3509) in rats

The effect of repeated intrathecal administration of a thyrotrophin-releasing hormone (TRH) analogue (CG 3509; 2 micrograms twice daily for 5 days) on wet-dog shake (WDS) and forepaw-licking (FPL) behaviours and spinal cord TRH and indoleamine levels and choline acetyltransferase (ChAT) activity was examined in adult rats. A rapid behavioural tolerance developed to repeated intrathecal injections of CG 3509; WDS and FPL behaviours were reduced by 57% and 34%, respectively, following the fifth injection and remained reduced at the ninth injection. Repeated CG 3509 administration selectively elevated ChAT activity and the level of 5-hydroxytryptamine (5-HT) in the ventral but not in the dorsal horn of the spinal cord, while 5-hydroxyindoleacetic acid (5-HIAA) and TRH levels were unaltered in either region. As ventral horn ChAT activity is principally located within motoneurones this data implies that TRH exerts a trophic-like influence on mature rat motoneurones in vivo. The results also suggest that long-term intrathecal TRH administration may decrease the release of 5-HT from bulbospinal raphe neurones.

Measurement of catecholamines, indoleamines, thyrotrophin releasing hormone and substance P in rat and human spinal cord using a common extraction method

An extraction method is described that allows the measurement of 5-hydroxyindoleacetic acid, dopamine, noradrenaline, substance P and thyrotrophin releasing hormone in the same sample of rat or human spinal cord. The substances were extracted using a mixture of 45% ethanol/0.1 M acetic acid and 0.02% sodium metabisulphite. The amines were then measured using high performance liquid chromatography with electrochemical detection and the peptides by radioimmunoassay. The common extraction method makes maximum use of limited postmortem material, reduces assay time and allows study of the interrelationships between the amines and peptides in rat or human spinal cord.

Involvement of catecholaminergic neurones and alpha-adrenoceptors in the wet-dog shake and forepaw licking behaviour produced by the intrathecal injection of an analogue of thyrotrophin-releasing hormone (CG 3509)

Intrathecal injection of the analogue of TRH, CG 3509, into conscious rats produced dose-related wet-dog shakes and forepaw licking, which showed a bell-shaped relationship of intensity to dose. Pretreatment with alpha-MPT intraperitoneally, markedly reduced levels of noradrenaline and dopamine in the spinal cord and brainstem and attenuated both CG 3509-induced responses, while intrathecal treatment with DSP4 selectively reduced noradrenaline in the spinal cord without affecting either behaviour. Since denervation supersensitivity may develop following treatment with DSP4, these results are not inconsistent with a proposal that bulbospinal noradrenergic neurones modulate the behaviour induced by CG 3509. Wet-dog shakes and forepaw licking induced by CG 3509 were reduced by pretreatment with phenoxybenzamine or prazosin, suggesting that a tonic noradrenergic pathway may facilitate both behavioural responses through alpha 1-adrenoceptors. Methoxamine, combined with CG 3509 partially attenuated the wet dog shake behaviour, but methoxamine produced marked hindlimb jerking which might physiologically antagonise wet-dog shakes. Concomitant administration of clonidine and CG 3509 potently reduced wet-dog shakes in a dose-related manner but did not significantly affect forepaw licking, while idazoxan did not significantly affect either response. The latter findings imply that alpha 2-adrenoceptors play different roles in modulating the two behavioural responses and the possible synaptic location of the receptors is discussed. Taken together these results suggest that CG 3509 may release noradrenaline from bulbospinal neurones regulating motor function.

Measurement of lung volume with 81Krm in a dynamic scintigram

The meaning of 81Krm counts obtained in a dynamic series of gated lung ventilation scans was evaluated in terms of flow rate, lung volume, or the flow/volume ratio. Flow and volume signals were recorded together with scintigraphic events in 29 subjects breathing 81Krm and after its decay, 127Xe as a tracer of lung volume. Gated ventilation scans and respiratory signals were reconstructed. Statistical analyses were carried out for linear regressions between total normalized counts detected by the gamma camera and (1) flow rate, (2) lung volume and (3) flow/volume ratio. Inspiration and expiration were analysed separately. For both isotopes, the best correlation was obtained between counts and lung volume (r greater than 0.93). No correlation was obtained between counts and flow rate or flow/volume ratio. Thus, we conclude that 81Krm count variations in gated scans correlate well with tidal volume.

Regional distribution of substance P- and thyrotrophin-releasing hormone-like immunoreactivity and indoleamines in the rabbit spinal cord

The distribution of thyrotrophin-releasing hormone (TRH), substance P, and the indoleamines [5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA)] has been examined in selected regions of the thoracic and lumbar spinal cord of the rabbit using sensitive radioimmunoassays for the first two and HPLC with electrochemical detection for the indoleamines. The levels of TRH- and substance P-like immunoreactivity (TRH-I and SP-I, respectively) were greatest in the ventral and dorsal grey matter, respectively. The level of TRH-I in most thoracic regions was greater than that in equivalent lumbar regions, but the only segmental difference in SP-I was in the ventral grey matter, where the lumbar segment contained more immunoreactivity. 5-HT and 5-HIAA were more evenly distributed than either peptide and showed no segmental variation in levels in equivalent regions, but the ventral grey matter contained significantly higher levels of 5-HT and had a greater 5-HT/5-HIAA ratio than all other regions. The absolute levels and the overall distribution of SP-I, TRH-I, and indoleamines in the thoracolumbar cord of the rabbit was very similar to that previously reported in both rats and humans, and the possible functional role of the peptides and indoleamines in spinal neurones is discussed.

Behavioural and biochemical evidence for the release of noradrenaline in mouse brain by TRH and some of its biologically stable analogues

Small doses of clonidine probably induce hypoactivity (a distinct form of sedation) by stimulating presynaptic alpha 2-adrenoceptors. This was attenuated by injection of 0.1-10 mg/kg of thyrotropin releasing hormone (TRH) or its biologically stable analogues, CG3509, CG3703 and RX77368, when these were given 10 min before clonidine. This effect was dose-dependent in all cases, but the analogues were more potent than TRH. The TRH metabolites, TRH acid and histidyl-proline diketopiperazine (10 mg/kg) were without effect. This response was still attenuated by the analogues, but not TRH, when these were given 1 hr before clonidine. The results, therefore, suggested that it was the basic tripeptide structure which was active and TRH was less potent than its analogues because of rapid metabolism. Attenuation of hypoactivity by TRH and analogues was not due to increased dopaminergic function because apomorphine (5 mg/kg) was ineffective. Thyrotropin releasing hormone (20 mg/kg), CG3509 (10 mg/kg) and CG3703 (1 mg/kg) also induced locomotor activity and produced various other behavioural changes. This was inhibited by prazosin (3 mg/kg) and haloperidol (0.5 mg/kg) but not by yohimbine (1 mg/kg). Apomorphine (5 mg/kg)-induced activity was inhibited by haloperidol and yohimbine but not by prazosin. This indicated that the activity produced by the TRH compounds, but not apomorphine, was partly mediated by alpha 1-adrenoceptors. Both CG3509 (10(-5) and 10(-4) M) and RX77368 (10(-4) M) evoked the release of endogenous noradrenaline from slices of hypothalamus in vitro. The TRH analogues, however, had no affinity for alpha 1- or alpha 2-adrenoceptors in ligand-receptor binding experiments. Viewed overall, the data showed that TRH and its analogues induced the release of noradrenaline in the brain. In addition, a comparison of the behavioural effects of TRH compounds with dopamine and alpha 1-adrenoceptor agonists suggested that in mice these behavioural responses resulted from stimulation of both noradrenergic and dopaminergic function.

Automatic Contour Detection Using a "Fixed-Point Hachimura-Kuwahara Filter" for SPECT Attenuation Correction

Attenuation correction for single-photon emission computed tomography (SPECT) usually assumes a uniform attenuation distribution within the body surface contour. Previous methods to estimate this contour have used thresholding of a reconstructed section image. This method is often very sensitive to the selection of a threshold value, especially for nonuniform activity distributions within the body. We have proposed the "fixed-point Hachimura-Kuwahara filter" to extract contour primitives from SPECT images. The Hachimura-Kuwahara filter, which preserves edges but smoothes nonedge regions, is applied repeatedly to identify the invariant set-the fixed-point image-which is unchanged by this nonlinear, two-dimensional filtering operation. This image usually becomes a piecewise constant array. In order to detect the contour, the tracing algorithm based on the minimum distance connection criterion is applied to the extracted contour primitives. This procedure does not require choice of a threshold value in determining the contour. SPECT data from a water-filled elliptical phantom containing three sources was obtained and scattered projections were reconstructed. The automatic edge detection procedure was applied to the scattered window reconstruction, resulting in a reasonable outline of the phantom.

Thyrotrophin releasing hormone--5-hydroxytryptamine interactions in the brain studied using chronic immunization and chemical lesioning techniques

This study investigates the effects of chemically lesioning 5-hydroxytryptamine (5HT) neurones and chronic passive immunization of central thyrotrophin releasing hormone (TRH) on 5HT and TRH mediated behavioural responses. 5HT lesions produced by 5,7-dihydroxytryptamine (5,7-DHT) enhanced the behavioural response produced by the 5HT receptor agonist 5-methoxy-N,N-dimethyltryptamine (5-MEODMT) while decreasing the locomotor hyperactivity observed following administration of the TRH analogue CG 3509 but having no effect on the reversal of pentobarbitone sleep-time produced by CG 3509. Chronic intracerebroventricular infusion of the purified TRH antibody markedly increased the length of pentobarbitone-induced sleep-time while enhancing the effects of CG 3509 both on locomotor activity and pentobarbitone-induced sleep. TRH antibody infusion also increased the response produced by 5-MEODMT. The results indicate that chronic passive immunization of central TRH induces changes in TRH receptor responsiveness and that there is a functional interaction between TRH and 5HT neuronal systems.

Chronic immunization of endogenous thyrotrophin-releasing hormone (TRH) in brain alters the behavioural response to pentobarbital and a TRH analogue

Rats were infused with purified thyrotrophin-releasing hormone (TRH) anti-serum i.c.v. for two weeks and the reversal of pentobarbital-induced anaesthesia, hypothermia and respiratory depression by central administration of a TRH analogue (CG 3509) was measured. After antibody infusion the anaesthesia time was more than doubled but the responses to CG 3509 were increased, suggesting a role for endogenous TRH in arousal mechanisms which is sensitized following chronic immunological blockade.

Regional distribution of immunoreactive-thyrotrophin-releasing hormone and substance P, and indoleamines in human spinal cord

The regional distributions of thyrotrophin-releasing hormone (TRH) and substance P in postmortem human spinal cord were determined by radioimmunoassay in fresh tissue taken from 22 patients who died without known neurological disease. Dorsal, ventral, and intermediolateral spinal cord regions were obtained from different segmental levels (lumbar L1, 2, 3, and 4; thoracic groups T1-3, T4-6, T7-9, and T10-12) together with selective regions of grey matter of lumbar spinal cord. The effects on peptide levels of the age of the patient, the postmortem time interval, and freezing the tissue samples prior to assay were assessed. Levels of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were determined in regional lumbar and thoracic tissue using HPLC with electrochemical detection. Substance P was found in the highest concentration in the dorsal spinal cord, with no significant segmental differences. In contrast, TRH was present in higher levels in the ventral rather than the dorsal spinal cord, with segmental differences. There was a significant difference in the 5-HT/5-HIAA ratio between dorsal and ventral spinal cord, with the highest ratio in the ventral spinal cord. There were no significant differences in substance P, TRH, or 5-HT levels in spinal cords between 5 and 20 h postmortem or from patients aged between 65 and 90 years. Freezing the tissue (-80 degrees C for 24 h) prior to assay significantly reduced TRH and substance P levels compared to samples assayed immediately without prior freezing.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in the behavioural response to a TRH analogue following chronic amitriptyline treatment and repeated electroconvulsive shock in the rat

The arousal elicited in rats by injection into the nucleus accumbens of the thyrotrophin-releasing hormone analogue CG 3509 (orotyl-histidyl-prolineamide) was used to assess the responsiveness to thyrotrophin-releasing hormone following repeated treatment with amitriptyline or electroconvulsive shock. Fourteen day administration of amitriptyline (15 mg kg-1 i.p. twice daily) reduced the behavioural response to bilateral intra-accumbens injection of CG 3509 (2 X 2.5 micrograms). CG 3509-induced hyperactivity, recovery from pentobarbitone-induced anaesthesia and the reversal of both pentobarbitone-induced hypothermia and decreased respiration, were all significantly reduced compared to either the response of the animals prior to amitriptyline administration or that observed in rats following chronic saline administration. Repeated administration of electroconvulsive shock (5 shocks over 10 days) significantly increased CG 3509-induced hyperactivity and the degree of reversal of pentobarbitone-induced hypothermia and respiratory depression following CG 3509 administration. The results demonstrate that chronic antidepressant treatments alter the central functional responsiveness to thyrotrophin-releasing hormone. These changes are discussed with respect to the effects of antidepressant treatments on 5-hydroxytryptamine receptors and possible thyrotrophin-releasing hormone--aminergic interactions.

Effect of respiratory motion on pulmonary activity determinations by positron tomography in dogs

The effect of respiratory motion on pulmonary activity determinations by positron emission tomography (PET) was studied in dogs with experimentally created pulmonary emboli (PE). The location of the PE was evaluated by planar 99mTc lung imaging to determine the appropriate sites for transaxial PET scans. PET scans of the lung then were obtained after i.v. injection of 68Ga-labeled microspheres. PET scans were acquired during slow (15 breaths/min) and fast (30 breaths/min) breathing with the same minute ventilation and then postmortem. Lung perfusion patterns were documented by i.v. injection of India ink before sacrifice. Cross sections of the excised lungs were made at the same levels as the PET scans, and eight sections containing 14 perfusion defects were analyzed. The scans obtained during slow breathing consistently showed edge blurring and demonstrated defects less well than scans obtained during fast breathing or postmortem. The normal-to-defect activity ratios during fast breathing and on the postmortem studies were similar and approximately 17% higher (P less than .01) than in scans obtained in the same animals during slow breathing. The results demonstrate the need for motion correction during quantitative analysis of regional lung activity by positron tomography, and suggest that high-frequency respiration at small tidal volumes may be one means for obtaining this correction.

Increase in levels and ex vivo release of thyrotrophin-releasing hormone (TRH) in specific regions of the CNS of the rat by chronic treatment with antidepressants

This study has investigated the effects of chronic treatment with amitriptyline, chlorimipramine, mianserin and metergoline on levels and ex vivo release of thyrotrophin-releasing hormone (TRH), 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in specific regions of the brain and lumbar spinal cord of the rat. All four treatments caused a significant increase in levels of TRH in the lumbar spinal cord with amitriptyline producing the most marked effect. Amitriptyline alone caused a similar marked increase in levels of TRH in the nucleus accumbens and suprachiasmatic nucleus but none of the treatments had a significant effect on the TRH content of the median eminence or septal nuclei. Potassium-induced release of TRH and 5-HT ex vivo was measured from tissue slices of the nucleus accumbens, septal nuclei and lumbar spinal cord after treatment with amitriptyline and mianserin. An increase in release of TRH was observed only from tissue slices of areas where increased levels of the peptide had occurred; namely nucleus accumbens and lumbar spinal cord after administration of amitriptyline and lumbar spinal cord after mianserin. None of the drugs significantly altered the ex vivo release of 5-HT or 5-HIAA. The results are discussed in relation to a possible interaction between TRH and 5-HT receptors in the antidepressant action of these drugs.

A comparison of the locomotor effects induced by centrally injected TRH and TRH analogues

Thyrotrophin-releasing hormone (TRH) and its stable analogues CG3509 and RX77368 were injected directly into the nucleus accumbens, septum and striatum of the rat and locomotor activity was recorded. TRH (5-20 micrograms) caused a dose-dependent increase in locomotor activity when injected into the nucleus accumbens. TRH (20 micrograms) also increased locomotor activity after administration into the septum but not when put into the striatum. Both the TRH analogues (0.1 and 1.0 microgram) produced closely related increases in activity when injected into either the nucleus accumbens or septum but CG3509 was more potent with a longer lasting effect. Also, in contrast with TRH (20 micrograms), both TRH analogues stimulated locomotor activity when injected into the striatum at a dose of 1 microgram but the effect was less marked and delayed in onset compared to the nucleus accumbens and septum response. Dopamine (100 micrograms) injected into the accumbens or septum also produced significant increases in locomotor activity. The locomotor effects of the peptides are discussed in relation to a possible dopamine-mediated mechanism which contrasts with the actions of TRH and the analogues on barbiturate anaesthesia.

Changes in monoamine metabolites measured by simultaneous in vivo differential pulse voltammetry and intracerebral dialysis

A direct comparison has been made of the drug-induced changes in extracellular levels of 3,4-dihydroxyphenylacetic acid and 5-hydroxyindoleacetic acid measured using intracerebral dialysis and differential pulse voltammetry with carbon fibre electrodes. The comparison was carried out in chloral hydrate anaesthetized rats with a pretreated carbon fibre electrode implanted in one striatum and an intracerebral dialysis loop in the contralateral striatum. 3,4-Dihydroxyphenylacetic acid and 5-hydroxyindoleacetic acid in the dialysis perfusates were assayed by high pressure liquid chromatography with electrochemical detection. d-Amphetamine (2 mg/kg) decreased extracellular 3,4-dihydroxyphenylacetic acid and the height of the 3,4-dihydroxyphenylacetic acid oxidation peak, while haloperidol (0.5 mg/kg) increased 3,4-dihydroxyphenylacetic acid levels measured in the perfusates and the height of the 3,4-dihydroxyphenylacetic acid oxidation peak. In these experiments there were parallel changes in 3,4-dihydroxyphenylacetic acid levels and peak height and a close correlation between these changes. Tranylcypromine (10 mg/kg) produced an almost parallel decrease in extracellular 5-hydroxyindoleacetic acid (dialysis) and the height of the 5-hydroxyindoleacetic acid oxidation peak, with similar percentage changes and good correlation values being obtained. However, while 5-hydroxy-L-tryptophan (25 mg/kg) increased both the 5-hydroxyindoleacetic acid levels and the height of the 5-hydroxyindoleacetic acid oxidation peak, 5-hydroxyindoleacetic acid in the dialysis perfusates showed a greater increase than the oxidation peak. The results show a close correlation between changes in extracellular 3,4-dihydroxyphenylacetic acid and its respective voltammetric peak and strongly support the use of in vivo differential pulse voltammetry for monitoring dopamine metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)

Decrease in levels of thyrotrophin-releasing hormone (TRH) in the n. accumbens and lumbar spinal cord following repeated electroconvulsive shock

The study investigated the effects of single and repeated electroconvulsive shock on levels and release of TRH in specific brain regions and thoracic and lumbar spinal cord. Whilst single electroconvulsive shock had no effect on TRH in any of the regions of the brain and spinal cord studied, repeated electroshock (5 shocks over 10 days and the rats killed 24 hr after the last shock) caused a significant decrease (-42 and -40% respectively) in levels of TRH in the nucleus accumbens and lumbar spinal cord. In the thoracic cord the level of TRH was also decreased after repeated electroshock but this did not reach significance. In contrast repeated electroshock had no significant effect on the content of TRH of the septal nuclei, hypothalamus, suprachiasmatic nucleus, or dorsal and medial raphe nuclei. Release of TRH was measured from slices prepared from nucleus accumbens and septal nuclei after repeated electroshock. A decrease in release was observed in nucleus accumbens with no effect in the septal nuclei. the results are discussed in relation to the possible interaction between dopaminergic and serotoninergic neurones and TRH in the antidepressant effects of electroconvulsive therapy.

The TRH analogue CG3509 increases in vivo catechol/ascorbate oxidation in the N. accumbens but not in the striatum of the rat

The effects of injection of the thyrotrophin-releasing hormone (TRH) analogue, orotyl-histidyl-proline amide (CG3509) into the accumbens and striatum, was studied on dopamine metabolism by means of in vivo voltammetry. Forty minutes after infusion of CG3509 (1-5 micrograms) into the n. accumbens there was a significant dose-related increase in the oxidation peak, corresponding to the oxidation of the dopamine metabolite, dihydroxyphenylacetic acid (DOPAC) and ascorbic acid. The size of this peak returned to normal by 80 min after the infusion. There was no change in the indole oxidation peak. Infusion of CG3509 (5 micrograms) had no effect on the size of either the catechol or the indole oxidation peaks recorded in the striatum. Intraventricular injection of CG3509 (10 micrograms) also increased DOPAC/ascorbic acid oxidation peak recorded in the n. accumbens, without altering the indole peak. While the voltammetric technique used in the present experiments is not able fully to separate ascorbic acid and DOPAC in vivo, the results support the view that TRH and its analogues selectively increase dopaminergic activity in the mesolimbic region.

Quantification of morphologic, cytologic, and kinetic parameters of unirradiated swine skin: a histologic model

The gross changes of erythema and desquamation produced by irradiation indicate population and functional variations occurring in the epidermis, microvasculature, and dermis. However, the parameters do not distinguish the individual population kinetics. This study determines multiple histologic and cell kinetic parameters of unirradiated swine skin. The prickle cell layer exists as a shell three to six cells thick. The proliferative basal layer exists as a confluent monolayer with 2031 +/- 48 cells/cm; it has a growth fraction of 1, an average cell generation time of 12.3 +/- 2.4 days, a TS of 9.4 +/- 2.9 hr, and a TS + T1/2M of 17 to 19 hr. The labeling index is 3.9 +/- 0.1% with a diurnal variation having a 5% peak at 1800 hr and a 2.5% nadir at 0900-1100 hr. The mitotic index varies from 1.7 to 3.2% and has no clear-cut diurnal variation. These values are similar to those available for man. These data and those published previously are utilized to define a histologic model of the irradiated epidermal cell renewal system. These measured values are compared with those derived from analysis of available time-dose isoeffect data using a single-hit multitarget and a linear-quadratic model. The derived dose-survival curve is steeper with a D0 between 97 and 255 rad compared to the measured value of 337 rad.

Analeptic effects of centrally injected TRH and analogues of TRH in the pentobarbitone-anaesthetized rat

The effect of intracerebral injection of TRH and several biologically stable TRH analogues in the pentobarbitone anaesthetized rat was examined. Bilateral injection of TRH (5.0 micrograms total dose) and the analogues RX 77368 (0.01-1.0 microgram), CG 3509 (0.1-1.0 microgram), DN-1417 (1.0 microgram) and MK-771 (1.0 microgram) into the nucleus accumbens reduced the pentobarbitone-induced sleeping time. The TRH metabolite DKP (5 micrograms) had no effect on the sleeping time following intra-accumbens injection. Intra-septal injection of TRH (1.0-5.0 micrograms), RX 77368 (0.1-1.0 microgram) and CG 3509 (0.1-1.0 microgram) also reversed the pentobarbitone-induced sleeping time. In contrast, TRH (5 micrograms) injected into the striatum had no effect on the pentobarbitone-induced sleeping time, and CG 3509 (0.1 microgram) and RX 77368 (0.1 microgram) had weaker effects following intrastriatal injection compared to injection of these analogues into the nucleus accumbens and septum. Measurements of core temperature and respiration rate in rats following intra-accumbens or septal injection of TRH, CG 3509 and RX 77368 showed these peptides to reverse pentobarbitone-induced hypothermia and stimulate respiration rate. However, while intrastriatal injections of CG 3509 and RX 77368 caused an increase in respiration rate they had no effect on core temperature. These results suggest a close association between peptide-induced respiratory stimulation and reversal of pentobarbitone-induced anaesthesia. Since intra-accumbens and septal injection of dopamine (20-100 micrograms) failed to reverse anaesthesia, it is unlikely that the peptide-induced responses are mediated via dopamine release.

Observations of the dynamics of ionic potassium-38 in brain

Short time course potassium dynamics in brain were investigated in the cat. 38K (T1/2 = 7.6m) was prepared on the BNL 60" cyclotron by the 40Ar(p, 3n)38K reaction. Positron decay in brain was measured by the limited angle of view positron camera (LAPC). Radioactivity corrected for physical decay following intravenous bolus injection of 38K showed an initial peak followed by a washout phase with a subsequent monotonic increase. The slope of the washout phase was linearly related to PaCO2 and the subsequent monotonic increase paralleled the arterial concentration of the tracer. No significant changes in 38K radioactivity were determined following coma producing levels of phenobarbital or seizure producing doses of potassium penicillin as compared to control.

The effects of 5,7-dihydroxytryptamine and p-chlorophenylalanine on thyrotrophin-releasing hormone in regions of the brain and spinal cord of the rat

The distribution of thyrotrophin-releasing hormone (TRH) and 5-hydroxytryptamine (5-HT) were compared in ten regions of the rat brain and in lumbar spinal cord. After dissection, using a cutting box and tissue punches, TRH was measured by radioimmunoassay and 5-HT by HPLC with electrochemical detection. Within the brain the highest levels of TRH were found in the median eminence and the remaining hypothalamus. There were also relatively high levels in the suprachiasmatic nucleus, septal nuclei and nucleus accumbens. Highest levels of 5-HT were found in the raphe nuclei, hypothalamic nuclei, nucleus accumbens, stria terminalis, septal nuclei and hippocampus. 5,7-Dihydroxytryptamine (5,7-DHT; 200 micrograms, i.c.v.) markedly reduced levels of 5-HT in brain and spinal cord. In the ventral lumbar cord there was a comparable decrease of TRH and 5-HT (-80%) and a smaller but significant decrease in the nucleus accumbens (-55%) and septal nuclei (-38%). p-Chlorophenylalanine (PCPA; 250 mg/kg X 2) reduced levels of 5-HT (-80%), without significantly altering those of noradrenaline. p-Chlorophenylalanine also significantly reduced levels of TRH in the nucleus accumbens (-72%) but not in the other regions of brain or spinal cord taken. The results are discussed in relation to the previously described co-existence of TRH and 5-HT in the spinal cord and the possible alternative forms of interactions between amine and peptide in the nucleus accumbens.

The ramp injection of radiotracers for blood flow measurement by emission tomography

A prototype instrument based on the coincidence detection of annihilation radiation was built to control the arterial concentration of a radionuclide as a uniformly increasing ramp function over a preset injection interval (ranging from 1.6 min to 13.6 h). The device was designed to accommodate radionuclides of different physical and biological half-life, and the physiological characteristics of the system being studied. A kinetic model based on the Kety-Schmidt integral was developed to permit the determination of cerebral blood flow (CBF). Both the kinetic model and the ramp injector were tested in cats studied with the PETT III positron emission tomograph and 4-(18F)-fluoroantipyrine as the CBF tracer. The ratio lambda/f of the brain-to-blood partition coefficient (lambda) and blood flow (f) were determined simultaneously by serial measurements with positron emission tomography.

Quantitative autoradiography with radiopharmaceuticals, Part 1: Digital film-analysis system by videodensitometry: concise communication

A simple low-cost digital film-analysis system using videodensitometry was developed to quantitate autoradiograms. It is based on a TV-film analysis system coupled to a minicomputer. Digital sampling of transmitted light intensities through the autoradiogram is performed with 8-bit gray levels according to the selected array size (128 X 128 to 1024 X 1024). The performance characteristics of the system provide sufficient stability, uniformity, linearity, and intensity response for use in quantitative analysis. Digital images of the autoradiograms are converted to radioactivity content, pixel by pixel, using step-wedge standards. This type of low-cost system can be installed on conventional mini-computers commonly used in modern nuclear medical facilities. Quantitative digital autoradiography can play an important role, with applications stretching from dosimetry calculations of radiopharmaceuticals to metabolic studies in conjunction with positron-emission tomography.

A manually-operated brain tissue slicer suitable for neurotransmitter release studies

A simple, inexpensive device has been designed to prepare slices or prisms of brain tumor for metabolic and release experiments by means of a hand-operated method. It is particularly suitable for very rapid slicing of small, irregular pieces of brain tissue dissected from animals or specimens available at biopsy. This simple apparatus was produced as an alternative to the more widely used motor-driven tissue choppers. A comparison of the morphological and metabolic integrity of tissue produced by the new slicer and a conventional tissue chopper is presented. The hand tissue slicer has been used to measure the release of monoamine neurotransmitters and specific neuropeptides in vitro.

Thyrotrophin-releasing hormone analogues increase dopamine release from slices of rat brain

Rat brain slices were incubated with a high concentration of K+, thyrotrophin-releasing hormone (TRH), or one of two biologically stable TRH analogues (CG 3509 or RX 77368). Basal release of endogenous dopamine, measured by electrochemical detection, was increased by K+ (30 mM) from slices of hypothalamus, septum, nucleus accumbens, and striatum. CG 3509 (10-(5) -10-(3) M) increased the release of dopamine from slices of nucleus accumbens, septum, and hypothalamus in a dose-dependent fashion, whereas RX 77368 (10-(4) M) increased the release of dopamine from the septum only. Neither analogue increased the release of striatal dopamine. The results provide further evidence for specific regional interactions between TRH and dopamine in rat brain.

The relation of proton activation of brain to cerebral blood flow

The interaction of brain with high energy protons produces positron emitting nuclides. The present study examines the response of the decay events to oxygen-15 induced by such activation in brain to alterations of cerebral blood flow as measured by a limited angle planar positron camera. Decay events correlate directly to the cerebral blood flow. The interaction of brain with high energy protons appears to offer an alternative means for the delivery of a freely diffusible tracer into brain.

A computer linear regression model to determine ventilatory anaerobic threshold

The anaerobic threshold has generally been determined by simple visual inspection of ventilation or other gas-exchange data obtained during incremental exercise. To establish objective criteria for the determination of anaerobic threshold, a computer algorithm has been developed that models the ventilatory response to exercise using multisegment linear regression. The best-fit regression model is chosen by minimizing the pooled residual sum of squares . The anaerobic threshold is reported as the first break point in that model. The computer-determined anaerobic threshold values for 37 subjects were compared with subjectively determined values as chosen by four independent observers. The observers' estimates, when pooled to yield a single a single value for each subject, gave a mean value for the gas-exchange anaerobic threshold of 2.26 +/- 0.69 l/min. The estimates by the computer method averaged 2.21 +/- 0.65 l/min. The correlation coefficient for these two methods was 0.94.

The effects of monoamine neurotoxins on peptides in the rat spinal cord

The coexistence of two neuronally-localised peptides, substance P and thyrotropin-releasing hormone (TRH), in descending serotoninergic nerve fibres to the spinal cord was investigated using immunocytochemical and biochemical methods. Substance P-like material in the spinal cord was shown to be identical to the undecapeptide substance P by the criteria of gel filtration, high performance liquid chromatography and behaviour in substance P specific radioimmunoassays. Immunocytochemical staining for 5-hydroxytryptamine, substance P, and TRH showed that all three substances had a similar distribution in nerve fibres and terminals in the ventral and lateral grey matter of the spinal cord. After treatment with the serotonin neurotoxin 5,7-dihydroxytryptamine, neuronal elements containing 5-hydroxytryptamine, substance P and TRH degenerated and disappeared from these parts of the spinal cord in parallel with one another. Biochemical measurements of 5-hydroxytryptamine, substance P and TRH in the spinal cord after treatment with 5,7-dihydroxytryptamine confirmed that these three substances were all depleted from the ventral horn and, in addition, showed that there was a small depletion of substance P from the dorsal horn. Two other neuropeptides, somatostatin and methionine-enkephalin were not depleted from the spinal cord by treatment with 5,7-dihydroxytryptamine nor was substance P in other parts of the brain. Substance P in the spinal cord was unaffected by 6-hydroxydopamine, a drug known to destroy catecholamine-containing neurones. These results are consistent with coexistence of substance P and TRH together with 5-hydroxytryptamine in the descending axons and terminals of bulbospinal neurones.

Localization and release of 5-hydroxytryptamine thyrotrophin releasing hormone and substance P in rat ventral spinal cord

1. The highest spinal cord levels of 5-hydroxytryptamine (5-HT) and thyrotrophin releasing hormone (TRH) were found in the ventral lumbar cord, in contrast to substance P which was found predominantly in the dorsal cord. 2. 5,6- and 5,7-dihydroxytryptamine, administered into the lateral ventricles reduced 5-HT in the dorsal and ventral spinal cord by up to 90%. 3. There was a parallel reduction in substance P and TRH in ventral spinal cord while methionine-enkephalin and somatostatin in ventral and dorsal cord increased. 4. Reserpine and tetrabenazine depleted 5-HT and partially depleted substance P and TRH in the ventral cord, but had no effect on either methionine-enkephalin or somatostatin. 5. The rates of loss and recovery, after reserpine and tetrabenazine, of 5-HT were different from those of the two peptides. 6. Endogenous 5-HT and TRH release from slices of lumbar cord was enhanced by high potassium. 7. p-Chloroamphetamine and fenfluramine increased 5-HT release but reduced or had no effect on TRH release. The effect of p-chloroamphetamine on TRH release was not dependent on either the presence of 5-HT or 5-HT receptor activity. 8. The results are discussed in terms of the possible co-existence, co-storage and release of 5-HT, substance P and TRH in descending bulbospinal neurones.

Co-existence of thyrotrophin releasing hormone and 5-hydroxytryptamine in the skin of Xenopus laevis

1. The location, release and re-synthesis of thyrotrophin releasing hormone (TRH) and 5-hydroxytryptamine (5-HT) in the skin of Xenopus laevis (the South African clawed toad) have been determined using both morphological and analytical procedures. 2. High levels of TRH and 5-HT are located specifically within the dermal granular glands of X. laevis and discharged from these glands following alpha-adrenergic stimulation. 4. The common occurrence and separate production of high levels of TRH and 5-HT in amphibian skin may provide a model for studying the mechanisms of biosynthesis, interaction and release of these substances in mammalian tissues such as ventral spinal cord, where TRH and 5-HT are found in the same neurones.

The effects of 5-hydroxytryptamine-depleting drugs on peptides in the ventral spinal cord

The ventral spinal cord content of several neuronally localised peptides was measured after treatment with a number of drugs which deplete spinal cord monoamines. Reserpine and tetrabenazine, but not p-chlorophenylalanine caused a partial depletion of ventral spinal cord substance P (SP) and thyrotropin-releasing hormone (TRH). Two other peptides, methionine-enkephalin and somatostatin were not depleted by any of the drugs. The rates of loss and recovery of SP and TRH after reserpine and tetrabenazine were different from that of 5-hydroxytryptamine (5-HT), though in the ventral spinal cord these two peptides probably coexist with 5-HT in the terminals of bulbospinal neurones. The results are discussed in relation to the possible costorage of SP and TRH with 5-HT in the same vesicles in nerve terminals in the ventral spinal cord.

Location and release of TRH and 5-HT from amphibian skin

The occurrence and release of thyrotrophin-releasing hormone (TRH) and 5-hydroxytryptamine (5-HT) from amphibian skin have been described by previous investigators. In the present study, the precise location and site of release of TRH and 5-HT from the skin of Rana pipiens and Xenopus laevis have been examined using a combination of procedures including immunohistochemistry, HPLC, and radioimmunoassay. The results indicate that TRH is located specifically within the dermal glands of these species, and that both TRH and 5-HT are discharged from these glands following adrenergic stimulation. The origin and functional significance of these substances in amphibian skin granular glands are discussed.

Dopamine stimulates the degradation of gonadotropin releasing hormone by rat synaptosomes

Immunohistochemical studies have shown the existence of synapses between nerve endings containing dopamine and gonadotropin releasing hormone (LH-RH) respectively in the hypothalamic median eminence. It is generally accepted that this transmitter is involved in the regulation of gonadotropin secretion as a modulator of LH-RH release, although the evidence is conflicting and both inhibitory and excitatory actions of dopamine have been reported. In vitro studies support the excitatory effect and low doses of dopamine have been shown to release LH-RH from incubated hypothalamic fragments and synaptosomes. This report describes studies with nerve endings isolated from the rat hypothalamus in which dopamine at higher concentrations than those used previously has been found to stimulate the degradation of LH-RH but not thyrotropin releasing hormone (TRH). This mechanism seems to be physiological in that it is calcium-dependent, requires the structural integrity of the nerve endings and fluctuates with the reproductive state of the animal.

Prostaglandins and the release of LHRH from hypothalamic synaptosomes. Effects of indomethacin pretreatment

The possible role of prostaglandins (PGs) in the hypothalamic control of ovulation has been investigated by studying the effects of indomethacin (ID) and PGs on the release of luteinizing hormone-releasing hormone (LHRH) from hypothalamic synaptosomes. Female rats were chronically pretreated with ID on diestrus 2 (D2) and proestrus (P), or on diestrus 1 (D1) and D2. Basal LHRH release from hypothalamic synaptosomes prepared from rats pretreated on D2/P was reduced to 48% after a 20-min incubation period, compared with sham-treated animals. ID pretreatment on D1/D2 caused a similar but less marked reduction in LHRH release (to 66% of controls at 20 min). Extraction of the LHRH remaining within the synaptosomal pellet showed that ID pretreatment also reduced the synaptosome content of LHRH. (15S)-15-methyl PGE2 (15-E2) (10(-4) and 10(-6) M) added to the incubating medium stimulated the release of LHRH BY APPROXIMATELY 40%, but this effect was only observed in synaptosomes prepared from ID-treated rats. PGE2 (10(-4) and 10(-6) M) had no significant effect in either sham-treated or ID-treated groups.

Metabolic and secretory processes in nerve-endings isolated from post-mortem brain

Isolated nerve ending particles (synaptosomes) prepared from rat and human cerebral cortex, after varying conditions of post-mortem storage were shown to possess good structural and morphological integrity and metabolic activity. Respiration, potassium retention, lactate dehydrogenase content, and stimulus-induced release of transmitter candidate amino acids, as well as the neuropeptide somatostatin, were measured. These preparations from post-mortem material showed properties which were closely comparable with similar preparations from fresh material. The relevance of these findings to studies on human post-mortem material is discussed.

Proton penetration and control in nonhomogeneous phantoms

Accurate bolus is needed for extension of Bragg-peak therapy. Proton beam-stopping profiles in a lucite-styrofoam-tissue phantom and in a Rando phantom were recorded photographically. Air volumes caused the largest distortions. Lucite bolus was cut to achieve desired beam-stopping profiles. Verification of bolus effect in situ will be important to control beam penetration within 5 mm.

Experimental tests of proton beam localization

The depth of penetration of heavy charged-particle therapy beams is sensitive to the density of tissues traversed. Maximum depth of dose contours will vary appreciably as the beam passes through bone, muscle, lung, and air or gas. Calculations suggest that beam activation of the short-lived positron-emitting isotope 15O in vivo will permit localization of proton therapy beams with resonable detected-event density and dose. Preliminary tests of this method indicate that the beam can be located at depth with a typical dose of 15 rad, using a large field-of-view positron camera on-ling. This technique is also applicable to other heavy charged-particle beams, negative pions, and heavy ions.