Biomedical subjects

G W Bennett

Publications and source records attributed to G W Bennett.

At least 37 records · Page 2Linked to original sources

PubMed1997

Barakol, a natural anxiolytic, inhibits striatal dopamine release but off uptake in vitro.

The present study investigated the effects of barakol on the in vitro release of endogenous and radiolabelled dopamine from rat striatal slices in comparison with the dopamine receptor agonists, quinelorane dihydrochloride (1 microM) and pergolide methanesulfonate (100 microM), and the dopamine receptor antagonist, S(-)-eticlopride hydrochloride (10 microM) using a semi-superfusion method and high-performance liquid chromatography with electrochemical detector measurement of endogenous dopamine. Barakol (1, 10 and 100 microM) reduced K(+)-stimulated endogenous dopamine release as did the dopamine D2 receptor agonists but had no effect on [3H]dopamine release. The inhibition of barakol (10 microM) on K(+)-stimulated endogenous dopamine release was antagonised by a dopamine D2 receptor antagonist, eticlopride. Barakol (0.1 nM-10 microM) had no effect on [3H]dopamine uptake except at the highest concentration (100 microM) when inhibition was observed. The results indicate that barakol might act as a dopamine agonist to inhibit endogenous dopamine release without a change in dopamine uptake.

Animals↗

PubMed1997

A simple method for measuring dopamine release from rat brain slices.

In many circumstances, rapid information is required about the effects of drugs on neurotransmitter release in brain, and a common method used is measurement of radiolabelled release from superfused brain slices or synaptosomes in vitro. However, the method requires expensive equipment and is not readily adapted to the measurement of endogenous release. The method described here uses readily available cheap chromatographic columns to measure both radiolabelled and endogenous dopamine (DA) release from striatal slices in repeated incubation samples. The results showed that the [3H]DA release is sensitive to temperature, K(+)-stimulation, and to both a DA agonist (pergolide) and an antagonist (eticlopride). Endogenous DA release was also stimulated by high K+ (20 mM) and sensitive to a DA agonist. Pergolide (100 microM) reduced both [3H]DA and endogenous DA release, while eticlopride (10 microM) increased [3H]DA, but not endogenous DA release. The results demonstrate an alternative cheap and quick way to study neurotransmitter release from brain in vitro.

Animals↗

PubMed1996

Barakol: a potential anxiolytic extracted from Cassia siamea.

The behavioural effects of an extract of Cassia siamea, a plant used in Thai traditional medicine, and barakol, its active chemical, were studied on an elevated plus-maze compared with diazepam. An aqueous extract of C. siamea (1, 6, and 12 g/kg body wt., orally) produced a small increase in the percentage of the open: total number of arm entries and time, time spent on the end of the open arms, total number of arm entries, and number of rears/min. Barakol [10 mg/kg, intraperitoneally (IP)] significantly increased all of these behavioural parameters in a manner similar to diazepam (1 mg/kg, IP, 30 or 60 min before testing), except that barakol and not diazepam increased both the number of rears and total arm entries. Barakol at 25 and 50 mg/kg increased the percentage of the open: total number of arm entries and time and number of rears. The results indicate that barakol has anxiolytic properties similar to diazepam but differs from diazepam in that it also increases exploratory and locomotor behaviour, as shown by the number of rears and total arm entries.

Animals↗

PubMed1996

Effect of a thyrotrophin-releasing hormone analogue, RX77368, on AMPA-induced septal-hippocampal lesioned rats in an operant delayed non-matching to position test.

The aim of the present study was to determine the effect of a thyrotrophin-releasing hormone (TRH) analogue, RX77368, on performance of a working memory test, using a delayed non-matching to position (DNMTP) procedure, in (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-induced septal-hippocampal lesioned rats. Following a post-surgery recovery period, pretrained rats were tested once daily on DNMTP, 30 min post-administration of RX77368 (1.0 mg kg-1, i.p.) or saline. AMPA-induced lesions significantly reduced percent correct responses during the second week of testing. Comparison of percent correct responses between days 1 and 13 of testing showed that sham rats significantly improved DNMTP performance, whereas lesioned rats did not. RX77368 significantly reduced general locomotor activity in sham rats in activity boxes, but did not disrupt non-mnemonic measures, such as locomotion and motivation, in the DNMTP test. RX77368 increased percent correct responses in AMPA-lesioned rats on days 8-10 and 11-13. There was also a significant improvement in percent correct responses achieved between day 1 and 13 in RX77368-treated lesioned and sham rats. These results showed that: (i) septal-hippocampal lesioned rats did not improve over the testing period; and (ii) on test days when a significant impairment was present, RX77368 partially improved DNMTP performance.

Animals↗

PubMed1995

Adult German cockroach (Dictyoptera: Blattellidae) movement patterns and resource consumption in a laboratory arena.

Computerized moving-image analysis was used to determine movement behavior of adult German cockroaches among food, water, and harborage resource sites. Adults at different stages in the female reproductive cycle (nonmated females, mated nongravid females, and gravid females) and males were examined continually for 5 d under a photoperiod of 12:12 (L:D) h. Corresponding food and water consumption rates for these adult classes were also determined. Differences were evident among the female reproductive classes and males. Mated nongravid females were the most active overall, and consumed the most resources. Nonmated females were second to the mated nongravid females in consumption and were less active. Gravid females were the most inactive, spending the greatest time in the harborage and consuming the fewest resources. Males were second to females in the mated nongravid class regarding activity, but consumed significantly fewer resources than females in both the mated nongravid and nongravid females. Implications of these findings relating to the biology of these adult classes are discussed.

Animals↗

PubMed1994

Effects of (R)-alpha-methylhistamine and scopolamine on spatial learning in the rat assessed using a water maze.

The effects of (R)-alpha-methylhistamine ((R)-alpha-MeHA, a selective H3-receptor agonist) and scopolamine (SCOP, a muscarinic antagonist) were investigated on spatial learning and memory in the rat (Hooded Lister) using a water maze (WM). (R)-alpha-MeHA treatment (6.3 and 10 mg/kg IP) had no apparent effect on spatial learning but did result in enhanced spatial recall at the higher dose, assessed by a transfer (probe) test after training. In contrast, SCOP (0.5 mg/kg IP) induced a learning and memory deficit measured both during and after training. In animals treated with (R)-alpha-MeHA and SCOP, (R)-alpha-MeHA partially (6.3 mg/kg) and completely (10 mg/kg) reversed the SCOP-induced deficit during the training phase, while in the post-training transfer test, (R)-alpha-MeHA (10 mg/kg) significantly reduced the SCOP-induced memory deficit. None of the treatments described resulted in impaired visual acuity as demonstrated by a raised platform test. These results are consistent with a role for histamine in cognitive processes and suggest a possible interaction between central histamine and cholinergic mechanisms associated with rodent spatial learning and memory.

Animals↗

PubMed1994

Novel methods for the preparation of antibody microprobes.

Antibody microprobes are devices which have been used to determine the release sites of several neuropeptides. The production of microprobes using the previous methodology is a time-consuming procedure requiring a high level of skill. The aim of the study was to investigate alternative methods for the production of microprobes which would simplify this procedure. Specific antibodies to thyrotrophin-releasing hormone (TRH) were bound to the outside of glass and tungsten wire microprobes using (a) an aminosilane coating, (b) a polycarbonate plastic coating and (c) an epoxylite resin-activated charcoal coating. Microprobes were assessed in vitro and in vivo for their ability to measure the neuropeptide TRH. All methods considerably reduced the time required to manufacture microprobes (more than 5-fold) and the aminosilane and epoxylite resin/charcoal-coated probes were suitable for use in vivo. The preferred binding coat was epoxylite/charcoal which has now been used to determine sites of TRH release in rat brain.

Animals↗

PubMed1994

Diel activity cycles in nymphal stadia of the German cockroach (Dictyoptera: Blattellidae).

Computerized moving-image analysis was used to determine movement behavior of individual German cockroach, Blattella germanica (L.), nymphs (second and fifth instars) between food, water, and harborage resource sites. Both second and fifth instars (n = 10) were examined for the entire nymphal stadium, during which a 12:12 (L:D) photoperiod was maintained. In addition, corresponding resource consumption rates for these nymphal stages also were determined. Both nymphal stages exhibited a pattern of high activity for the first half of the nymphal stadium, especially during each scotophase. For the last third of the stadium, the nymphs remained continuously in the harborage, moved very little, and consumed little or no resources. We discuss implications of these findings regarding control, future research, and possible hormonal behavior regulation.

Animals↗

PubMed1994

Hydroprene effects on the dynamics of laboratory populations of the German cockroach (Dictyoptera: Blattellidae).

The influence of sterilization by hydroprene on population dynamics in the German cockroach, Blattella germanica (L.), was studied in the laboratory where more detailed and accurate assessments could be achieved than would be possible under typical field situations. The gradual accumulation of sterile adultoids (i.e., adults with twisted wings, indicating exposure to hydroprene) during treatment, or their decreasing abundance after treatment, produced distinctive patterns in the dynamics of treated populations. The percentage of gravid females (a reproductive index) was first to respond to treatments, because increases (or decreases) in the percentage of gravid females preceded reductions (or recoveries) in sample density and nymph-to-adult ratios by 4-6 wk. Trends in the percentage of adultoids were negatively correlated with the percentage of gravid females and indirectly measure the activity of hydroprene. Initial reductions in the percentage of gravid females, sample density, and nymph-to-adult ratios began at or about the time when approximately 80% of adults had twisted wings (i.e., were adultoids). As the percentage of adultoids attained (or declined below) the 80% level, we can accurately predict the subsequent decline (or recovery) in nymph-to-adult ratios and, thus, sample density. These data support a proposal to adopt the 80% level of adultoids as an action threshold for regulating juvenoid treatments to maximize population suppression. The role of this action threshold in the long-term management of chronic B. germanica infestations or insecticide resistant populations is discussed.

Animals↗

PubMed1993

Detection of thyrotrophin releasing hormone in rat brain in vivo using novel antibody microprobes: effects of amphetamine.

Antibody microprobes of novel design were used to monitor thyrotrophin releasing hormone (TRH) in rat brain before and after-parenteral administration of amphetamine. Specific antibodies to TRH were bound to the outside of glass microprobes by adsorption to a surface of activated charcoal embedded in epoxylite resin. In male Wistar rats anaesthetised with chloral hydrate a series of antibody microprobes were implanted in forebrain. Amphetamine (10 mg/kg i.p.) caused a highly significant decrease in the binding of 125I-TRH to microprobes, indicating an increase in extracellular TRH localised in the lateral septum. There was also evidence of TRH release in the septo-hypothalamic nucleus. Neither saline, nor amphetamine at 2 mg/kg were able to evoke changes in the release of TRH at any sites.

Amphetamine↗

PubMed1993

The serotoninergic bulbospinal system and brainstem-spinal cord content of serotonin-, TRH-, and substance P-like immunoreactivity in the aged rat with special reference to the spinal cord motor nucleus.

The 5-hydroxytryptamine (5HT) containing bulbospinal pathway was studied with immunohistochemical (IF) and chemical techniques in 2-3 and 30 months old male Sprague-Dawley rats. The coexisting neuropeptides substance P (SP), thyrotropin-releasing hormone (TRH) and galanin were also analysed. Furthermore, the expression of mRNA encoding aromatic L-amino acid decarboxylase (AADC), prepro-TRH, and preprotachykinin (prepro-SP) was analysed with in situ hybridization (ISH) in the midline raphé nuclei inthe lower brainstem. The results showed a decreased number of axonal 5HT fibers with a normal morphology in the ventral horn of the aged rat lumbosacral spinal cord, and several 5HT immunoreactive (IR) fibers with an aberrant morphology, suggestive of axonal degeneration, were intermingled. This was evident in both the dorsal and ventral horn of the spinal cord. The 5HT-IR fibers with an aberrant morphology usually also contained TRH-and/or SP- and/or galanin-like immunoreactivity (LI) in the ventral horn. These signs of degeneration were clearly less evident in the thoracic and cervical spinal cord segments. Moreover, these changes varied between aged litter-mates. This was in agreement with behavioural signs of motor disturbances, present in about 40% of the aged rats and which in all cases were confined to the hindlimbs. Chemical analyses disclosed significantly lower levels of TRH-LI and, in particular, SP-LI in both the ventral and dorsal quandrants of the spinal cord in the aged rat compared to young adults. The differences were largest in the lumbar regions of the spinal cord. Corresponding analysis of 5HT and 5-hydroxyindoleacetic acid (5HIAA) in the same tissue specimens revealed largely unaltered levels of 5HT and a slight increase in 5HIAA, indicating the possibility of an increased 5HT turnover in the aged rat spinal cord. Neurons in nucleus raphé obscurus and nucleus raphé pallidus were immunoreactive to 5HT, and after pretreatment with colchicine to TRH-, SP-, and galanin-LI as well. There was no obvious difference in number of labeled cells, or labeling intensity, between colchicine-treated young adult and aged rats, although, in the corresponding region of medulla oblongata, chemical analysis disclosed significantly lower levels of 5HT, TRH, and, in particular, SP in untreated aged rats. In contrast, in situ hybridization analysis revealed increased mRNA levels encoding prepro-TRH and prepro-SP in old rats, while mRNA content encoding AADC mRNA was similar in young adult and aged rats.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗

PubMed1992

Thyrotropin-releasing hormone (TRH)-like immunoreactivity in the grey monkey (Macaca fascicularis) spinal cord and medulla oblongata with special emphasis on the bulbospinal tract.

The distribution of thyrotropin-releasing hormone (TRH)-like immunoreactivity (LI) has been studied in the grey monkey (Macaca fascicularis) spinal cord and medulla oblongata by the use of indirect immunofluorescence and the peroxidase-antiperoxidase (PAP) technique. Furthermore, double-labeling experiments were performed in order to study colocalization of 5-hydroxytryptamine (5-HT)- and substance P-LI. A dense innervation of TRH-immunoreactive (IR) varicose fibers was found in the ventral horn motor nuclei, in the region surrounding the central canal, in the intermediolateral cell column, and in the dorsal horn laminae II and III. In addition, cell bodies harboring TRH-LI were found in the dorsal horn laminae II-IV. In the ventral horn, many of the large cell bodies and their proximal dendrites were totally encapsulated by TRH-IR fibers. From double-labeled sections a high degree of coexistence could be established between TRH-/5-HT-LI, TRH-/substance P-LI, and 5-HT-/substance P-LI in fibers in the motor nuclei; as a consequence, a large proportion of these fibers should harbor TRH-/5-HT-/substance P-LI. A coexistence between TRH-/5-HT-LI could also be demonstrated in the intermediolateral cell column. However, no unequivocal coexistence could be found between TRH-/substance P-LI and 5-HT-/substance P-LI in this region. In the dorsal horn, no clear coexistence could be encountered for any of the above indicated combinations. Electron microscopic analysis of material from the lumbar lateral motor nucleus demonstrated TRH-IR terminals making synapses with large cell bodies and dendrites. In addition, contacts lacking synaptic specializations could also be verified. In the medulla oblongata, with the use of the PAP technique, a large number of cell bodies containing TRH-LI were encountered in the midline raphe nuclei and in nucleus reticularis lateralis. A similar distribution pattern could be found for 5-HT-LI, but no cell bodies containing substance P-LI could be seen in these regions. Chemical analysis of specimens from cervical, thoracic, and lumbar spinal cord revealed higher concentrations of TRH- and 5-HT-LI in the ventral quadrants, whereas substance P-LI dominated in the dorsal quadrants. Thus, the concentrations of TRH-, 5-HT-, and substance P-LI was in accordance with the observed regional variation in density of IR-fibers and varicosities found in the spinal cord. We have shown that TRH-LI has a distribution in the monkey spinal cord and medulla oblongata similar to that previously demonstrated in other species.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1992

Oral toxicity, formulation effects, and field performance of flufenoxuron against the German cockroach (Dictyoptera: Blattellidae).

Laboratory and field studies on the benzoylphenyl urea (BPU) chitin synthetase inhibitor flufenoxuron (DPX EY-059) showed great potential for its use in suppressing infestations of German cockroach, Blattella germanica (L.). When fed continuously to fifth (last) instars, the LC50 of flufenoxuron was estimated at 0.82 ppm (95% FL, 0.76-0.87 ppm). A rating scale specific for BPU effects was developed and shown to be positively correlated with the insect's exposure to concentration of flufenoxuron. Manipulating the particle size of wettable powder formulations of flufenoxuron significantly altered their activity in contact bioassays. Larger particles (volume mean diameter, 12.2 mu; range, 10-20 mu) were more active. Field trials in multifamily housing with this wettable powder formulation at 0.033 and 0.066% (AI) achieved high level (greater than 80%) population suppression within 8 wk of treatment. The potential for the use of flufenoxuron in B. germanica management programs is discussed.

Animals↗

PubMed1991

Development of a radioimmunoassay for RX77368 (pGlu-His-3,3-dimethyl proline amide)--a stable analogue of thyrotrophin releasing hormone (TRH).

The recent interest in RX77368 for the treatment of Motor Neurone Disease (MND) has led to the requirement for an assay (RIA) capable of detecting the peptide at low levels in plasma. Several drug conjugates were prepared in which RX77368 was covalently linked to larger proteins, e.g. bovine serum albumin, keyhole limpet haemocyanin or bovine thyroglobulin, the best yield being obtained with the bis-diazotized benzidine reaction (BDB) linking RX77368 to KLH. The latter conjugate was injected into sheep and ultimately produced an antibody of sufficiently high titre to be used. This combined with an iodinated radiolabel formed the basis of the radioimmunoassay. Cross-reactivity studies using similar analogues and RX77368 metabolites showed that the antibody was specific for RX77368. The greatest cross-reactivity was exhibited by the pGlu-His-monomethylProNH2 peptide (RX74355), but, not being a natural metabolite, this did not interfere with the assay. The RIA was used to measure RX77368 in MND patients in a recent clinical study, where RX77368 was administered both by the intravenous and oral routes. High plasma concentrations of RX77368 were found in the patients given intravenous drug by infusion. The oral route exhibited much lower levels, but had a sustained duration of action of up to 12 h.

Animals↗

PubMed1991

Influence of starvation and lighting on the movement behavior of the German cockroach (Blattodea: Blattellidae).

Computerized moving-image analysis measured the influence of starvation and lighting conditions on the locomotor activity of the German cockroach, Blattella germanica (L.). Starvation increased the distance traveled, velocity, and the proportion of time in motion of adult males and last instars but did not increase adult female movement. For females, males, and nymphs, starvation increased cockroach residence time around the source of water and harborage and decreased the distance traveled by females and nymphs around the observation arena's edge. Fluorescent light reduced the proportion of time in motion for males, but the velocity of males was greater in fluorescent light relative to infrared light. Adult males and females stopped more frequently in infrared light. Overall, males and nymphs were more mobile than females and they explored larger areas. The moving-image analysis technique is an efficient and accurate tool for observing movement of individual cockroaches and has applications in repellency, attractancy, and basic movement behavior studies.

Animals↗

PubMed1991

Logistic models describing effects of temperature and humidity on residual effectiveness of chlorpyrifos and cyfluthrin formulations against German cockroaches (Dictyoptera: Blattellidae).

Multifactored logistic models were developed for chlorpyrifos and cyfluthrin formulations based on mortality data from laboratory studies with the German cockroach, Blattella germanica (L.). Insecticides were applied to stainless steel surfaces and aged at three different temperatures (23, 30, and 37 degrees C) and two levels of relative humidity (40 and 70%). After the insecticides dried, the treated panels were placed opposite plywood panels to simulate a crack and crevice application. At appropriate aging times, treated panels were removed from environmental chambers for bioassay. The combined effects of high temperature, high humidity, and aging of residues caused the greatest decline in cockroach mortality for chlorpyrifos. Increasing temperature and aging of residues resulted in decreased cockroach mortality for cyfluthrin formulations; however, mortality was greater than 87% for all formulations through 84 d. Information from this study can be incorporated into integrated pest management programs for German cockroaches.

Animals↗

PubMed1991

Sensitive developmental period of last-instar German cockroaches (Dictyoptera: Blattelidae) to fenoxycarb and hydroprene.

The sensitive developmental period of last-instar German cockroaches, Blattella germanica (L.), to topical applications (10 micrograms/microliters) of fenoxycarb and hydroprene was determined. Developmental duration of last instars treated with fenoxycarb on days 1, 3, or 6 was 9-11 d longer than the development of nymphs treated with hydroprene or acetone. In addition, fenoxycarb caused mortality in 59% of the nymphs treated on day 6. A high level of wing twisting and sterility was observed among female and male cockroaches treated with fenoxycarb or hydroprene on days 1, 3, or 6 of the last stadium. Nymphal production by adults treated with juvenoids on day 9 of the last stadium (3-4 d before eclosion) was not affected. Our findings show that the sensitive developmental period for juvenoid-induced effects in last-instar B. germanica is limited to the first half of the stadium.

Animals↗

PubMed1991

Ventral horn neuropeptides modulate the release of noradrenaline from tissue slices of rat brainstem and ventral thoracic spinal cord.

The release of endogenous noradrenaline (NA) from slices of adult rat brainstem and ventral thoracic spinal cord was investigated using a fixed-volume incubation technique and HPLC with electrochemical detection. Incubation with potassium (15-50 mM) produced a dose-related increase in basal NA release that was calcium dependent. The potassium-evoked release of NA from spinal cord or brainstem slices was potentiated according to dose by preincubation with either (a) the selective alpha 2-adrenoceptor antagonist idazoxan (10(-6)-10(-4) M) or (b) the thyrotrophin-releasing hormone (TRH) analogue RX 77368 (pGlu-His-3,3'-dimethyl ProNH2; 10(-5) and 10(-4) M). Incubation of spinal cord slices with the NA uptake inhibitor maprotiline (1 microM) enhanced the effect of idazoxan but inhibited that of RX 77368. The effects of RX 77368 and potassium alone (15 mM) on NA release from both spinal cord and brainstem slices were reduced to basal levels with tetrodotoxin (10(-7) M). Similarly, preincubation of spinal cord, but not brainstem, slices with the insect neuropeptide proctolin (10(-4) M) significantly attenuated the potassium- or RX 77368-induced release of NA, whereas substance P (3 X 10(-5) and 1 X 10(-4) M) had no effect on either tissue. These results suggest that changes in NA release in the spinal cord and brainstem may mediate some of the actions of neuropeptides in ventral spinal cord, although the peptides may not be acting directly on the noradrenergic nerve terminals in these tissues.

Adrenergic alpha-Antagonists↗