Neurotensin and bombesin: differential effects on body temperature of mice after intracisternal administration

Intracisternal administration of neurotensin or bombesin produces a significant hypothermic response in rodents in an ambient temperature of 23°C or below; bombesin has been reported to produce a significant hyperthermic response in rats at 36°C, but no change in colonic temperature at ambient temperatures between 31 and 33°C. In this study we compared the effects of the two neuropeptides on colonic temperature of mice exposed to different ambient temperatures to determine whether neurotensin also produces a poikilothermic state. From a series of experiments conducted at ambient temperatures of 4, 23, 26, 30, 34 and 38°C, in which mice received an intracisternal injection of an equimolar dose (0.6 nmol) of neurotensin or bombesin (or vehicle), we noted that the two neuropeptides produce different effects on colonic temperature. At ambient temperatures of 26°C and below, both neurotensin and bombesin produce a significant hypothermic response; however, at higher temperatures bombesin has no effect (30°C) or produces hyperthermia (34°C). In contrast, neurotensin produces hypothermia at 30°C and no significant effect at 34 and 38°C. In addition, a wide range of doses of neurotensin failed to produce the poikilothermic effects characteristic of centrally administered bombesin.     

Inhibition of spontaneous and methaphetamine-induced locomotor activity with centrally active drugs in mice

In an effort to discover if various classes of drugs could be differentiated on the basis of their ability to inhibit spontaneous and methamphetamine-induced locomotor activity, a series of drugs with a variety of pharmacological effects was tested for activity as inhibitors of spontaneous and methamphetamine-induced locomotor activity in mice. When ED₅₀ values for the inhibition of spontaneous locomotor activity are compared to those for inhibition of locomotor activity in the presence of methamphetamine, it is found that approximately the same doses produce 50% inhibition of locomotor activity in both cases. It appears that effects on locomotor activity in the presence and absence of methamphetamine, as described in this paper, cannot be used to differentiate among the various classes of drugs tested. This finding implies that interpretation of anti-methamphetamine activity in drugs must be done with caution.     

Regulatory effects of bifidobacteria on the growth of other colonic bacteria

In the human large intestine bifidobacteria are a numerically important group of micro-organisms which are considered to exert a range of biological activities related to host health. One aspect is the inhibitory effect of these bacteria on other species, possibly excluding long term colonization by invasive pathogens. It has been suggested that the mechanism of inhibition carried out by bifidobacteria is related to the fermentative production of acids such as acetate and lactate. Experiments reported in this paper attemptedto address this theory. Co-culture experiments whereby Bifidobacterium infantis was incubated with Escherichia coli and Clostridium perfringens, in a varietyof fermentation systems, indicated that the bifidobacterium was able to exert an inhibitory effect not necessarily related to acid production. Further studies showed that eight species of bifidobacteria could variously excrete an anti-microbial substance with a broadspectrum of activity. Species belonging to the genera Salmonella, Listeria, Campylobacter and Shigella, as well as Vibrio cholerae, were all affected. These results show that bifidobacteria are able to exert more than one mechanism of inhibition, which may be of some importance with regard to protection against gastroenteritis.     

Interactive effects of nicotine and MPTP on striatal tetrahydrobiopterin in mice

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a neurotoxin known to cause dopamine (DA) neuron degeneration, while the psychoactive compound nicotine is known to excite DA neurons. Tetrahydrobiopterin is the cofactor for tyrosine hydroxylase (TOH) in the regulation of DA biosynthesis. The present study investigated the interactions between nicotine and MPTP on striatal biopterin, DA and TOH activity in BALB/c mice. The results indicated that both acute and chronic nicotine administrations at various concentrations significantly increased biopterin and DA levels in the striatum, while MPTP markedly decreased these measures. Pretreatment with nicotine at a dose having no significant effect alone, partially protected against MPTP's toxicity on biopterin and DA. Increasing the dose of nicotine did not have a further protective action. The toxicity of MPTP on TOH was also prevented by nicotine. Further, the above effects of nicotine were probably mediated through the cholinergic nicotinic receptors since mecamylamine reversed the effects of nicotine. These results suggest that nicotine interacts with the dopaminergic system probably at the level of DA biosynthesis through activating TOH and its coenzyme tetrahydrobiopterin.     

Amastatin potentiates the behavioral effects of vasopressin and oxytocin in mice

Vasopressin and oxytocin cause behavioral excitation after intracerebroventricular injection in mice. This effect is short-lasting, suggesting that the peptides are rapidly inactivated in the brain. Co-injection of microgram amounts of amastatin, an aminopeptidase inhibitor, prolonged the effect of both vasopressin and oxytocin. Amastatin did not induce large vasopressin-like behavioral effects by itself, nor did it significantly potentiate the action of 1-deamino[1,6-dicarba, 8-arginine] vasopressin (Asu-AVP), an analog that lacks the N-terminal amino group. The effect of Asu-AVP, but not that of vasopressin, was potentiated by phosphoramidon, an inhibitor of neutral metalloendopeptidase ("enkephalinase A"). These results support previous suggestions that vasopressin and oxytocin are inactivated mainly by aminopeptidase action following intracerebroventricular injection.     

Studies on new,centrally active and reversible acetylcholinesterase inhibitors

We have synthesized the tertiary amines of pyridostigmine and neostigmine, 3-pyridinol dimethylcarbamate (norpyridostigmine) and 3-dimethylaminophenol dimethylcarbamate (norneostigmine) respectively, and we have tested their abilities to cross the blood-brain barrier and inhibit mouse brainAChE activity. The in vivo inhibition of AChE activity by norpyridostigmine reaches 72% at 10 minutes which is comparable to that seen with physostigmine (73% at 10 minutes). Inhibition by norneostigmine is less effective (50% at 10 minutes) and approaches that obtained with tetrahydroaminoacridine (57% at 10 minutes). These data show that both norpyridostigmine and norneostigmine cross the blood-brain barrier and that they are effective inhibitors of mouse brain AChE activity. These drugs could be useful in the treatment of memory, impairment associated with Alzheimer's disease, and other memory disorders.     

Interactive effects of rutin and constant versus alternating temperatures on performance ofManduca sexta caterpillars

The effects of different concentrations of rutin and constant temperature (20 °C) versus alternating temperatures (23∶15 °C) on growth, molting and food utilization efficiencies of third instar tobacco hornworms (Manduca sexta) were determined. Relative consumption rate (RCR) and relative growth rate (RGR) were significantly higher for larvae at the alternating thermal regime compared to those at the constant (representing the average) temperature. With increasing concentrations of rutin, the negative effect of rutin on RCR and RGR increased for the larvae in the alternating thermal regime; however, at the constant temperature, rutin had little effect. The alternating thermal regime promoted synchrony in the timing of spiracle apolysis (the earliest morphological marker of molt). Rutin disrupted that synchrony. I discuss how patterns of host plant resistance may be altered with a decrease, in amplitude of diurnal temperatures (as has been documented recently for temperate regions) through the uncoupling of herbivore performance and allelochemical concentration. I conclude that simultaneous consideration of fluctuating temperatures and allelochemicals is advisable when assessing the effects of temperature and allelochemicals on performance of insect herbivores because interactive effects between temperature and dietary components occur and perhaps are common.     

Interactive effects of rising temperatures and urbanisation on birds across different climate zones: A mechanistic perspective

Climate change and urbanisation are among the most pervasive and rapidly growing threats to biodiversity worldwide. However, their impacts are usually considered in isolation, and interactions are rarely examined. Predicting species' responses to the combined effects of climate change and urbanisation, therefore, represents a pressing challenge in global change biology. Birds are important model taxa for exploring the impacts of both climate change and urbanisation, and their behaviour and physiology have been well studied in urban and non-urban systems. This understanding should allow interactive effects of rising temperatures and urbanisation to be inferred, yet considerations of these interactions are almost entirely lacking from empirical research. Here, we synthesise our current understanding of the potential mechanisms that could affect how species respond to the combined effects of rising temperatures and urbanisation, with a focus on avian taxa. We discuss potential interactive effects to motivate future in-depth research on this critically important, yet overlooked, aspect of global change biology. Increased temperatures are a pronounced consequence of both urbanisation (through the urban heat island effect) and climate change. The biological impact of this warming in urban and non-urban systems will likely differ in magnitude and direction when interacting with other factors that typically vary between these habitats, such as resource availability (e.g. water, food and microsites) and pollution levels. Furthermore, the nature of such interactions may differ for cities situated in different climate types, for example, tropical, arid, temperate, continental and polar. Within this article, we highlight the potential for interactive effects of climate and urban drivers on the mechanistic responses of birds, identify knowledge gaps and propose promising future research avenues. A deeper understanding of the behavioural and physiological mechanisms mediating species' responses to urbanisation and rising temperatures will provide novel insights into ecology and evolution under global change and may help better predict future population responses.     

Exogenous oxytocin reverses the decrease of colonic smooth muscle contraction in antenatal maternal hypoxia mice via ganglia

Oxytocin (OT) has been reported to have a potential protective effect on stress-induced functional gastrointestinal disorders. This study determined whether colonic contraction in adults was affected by antenatal maternal hypoxia, and whether OT is involved in antenatal maternal hypoxia induced colonic contraction disorder. Isometric spontaneous contractions were recorded in colonic longitudinal muscle strips in order to investigate colonic contractions and the effects of exogenous OT on the contraction in antenatal maternal hypoxia and control mice. Both high potassium and carbachol-induced contractions of proximal colon but not distal colon were reduced in antenatal maternal hypoxia mice. Exogenous OT decreased the contractions of proximal colonic smooth muscle strips in control mice, while it increased contractions in antenatal maternal hypoxia mice. OT increased the contractions of distal colonic smooth muscle strips in both antenatal maternal hypoxia and control mice. Hexamethonium blocked the OT-induced potentiation of proximal colon but not distal colon in antenatal maternal hypoxia mice. These results suggest that exogenous oxytocin reverses the decrease of proximal colonic smooth muscle contraction in antenatal maternal hypoxia mice via ganglia.