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The lateral hypothalamic area revisited: ingestive behavior.

This article discusses the role of the lateral hypothalamic area (LHA) in feeding and drinking and draws on data obtained from lesion and stimulation studies and neurochemical and electrophysiological manipulations of the area. The LHA is involved in catecholaminergic and serotonergic feeding systems and plays a role in circadian feeding, sex differences in feeding and spontaneous activity. This article discusses the LHA regarding dietary self-selection, responses to high-protein diets, amino acid imbalances, liquid and cafeteria diets, placentophagia, "stress eating," finickiness, diet texture, consistency and taste, aversion learning, olfaction and the effects of post-operative period manipulations by hormonal and other means. Glucose-sensitive neurons have been identified in the LHA and their manipulation by insulin and 2-deoxy-D-glucose is discussed. The effects on feeding of numerous transmitters, hormones and appetite depressants are described, as is the role of the LHA in salivation, lacrimation, gastric motility and secretion, and sensorimotor deficits. The LHA is also illuminated as regards temperature and feeding, circumventricular organs and thirst and electrolyte dynamics. A discussion of its role in the ischymetric hypothesis as an integrative Gestalt concept concludes the review.

Animals↗

Manipulation of duration of action of a synthetic prostaglandin analogue (TPT) assessed in the pregnant beagle bitch.

Beagle bitches were treated on days 20-22 of pregnancy with TPT as an aqueous solution administered subcutaneously via a minipump at a rate of 10 micrograms per hour for either 24 (I) or 48 hours (II). Additional animals received a single subcutaneous injection of 200 micrograms of TPT as an aqueous solution (III) or dissolved in polyethylene glycol 400 (IV) or the methyl ester of TPT dissolved in polyethylene glycol 400 (V). The duration of action was assessed by the nadir in circulating progesterone levels. By this criterion the duration of action in the different groups ranked I=III<II=IV<V, the nadir occurring at 2, 3 and 3-4 days post treatment, respectively. Duration of action correlated with the incidence of abortion. Salivation, emesis and diarrhea or hypothermia side effects, previously noted for this agent, were not affected by the manipulations of duration of action.

Abortifacient Agents↗

Ethanol-mediated taste aversions and state-dependency in preweanling (16-day-old) rats.

Requirements for conditioning of an ethanol-mediated taste aversion in 16-day-old rat pups were examined. Experiment 1 demonstrated that preweanling rats are capable of acquiring, in two trials, an aversion to a 15% sucrose solution when followed by intragastric intubation of a 1.2 g/kg dose of 17% v/v ethanol, but not when followed by a 0.4 g/kg dose. Comparison was with control animals given sucrose followed by an equivalent volume isocaloric Half and Half. When the 0.4 g/kg dose of ethanol preceded sucrose presentation by 30 min (Experiment 2), the aversion was learned, suggesting that the effective delay between the sucrose and the critical consequences of the ethanol had been too long with the former procedure. Expression of the sucrose aversion required, however, the reinstatement of the context of intoxication--state-dependent retention. Finally, the results of Experiment 3B indicated that, in addition to the association between the sucrose and the aversive consequences of alcohol intoxication, the orosensory cues resulting from alcohol's direct elimination, via such processes as respiration and salivation, became associated with the appetitive properties of the sucrose. This was evidenced by a conditioned increase in preference for ethanol odor. Possible age-related differences in the ability to associate stimuli with alcohol's unconditioned consequences, and in state dependency are discussed.

Animals↗

Petit mal seizure spikes in olfactory bulb and cortex caused by runaway inhibition after exhaustion of excitation.

The olfactory bulb (OB), anterior olfactory nucleus (AON) and prepyriform cortex (PC) maintain 3 kinds of feedback among their populations of excitatory and inhibitory neurons: negative feedback, mutual excitation, and mutual inhibition. At normal levels of synaptic input these are balanced and give rise to chaotic and near-sinusoidal oscillatory EEG activity. Under intense repetitive electrical stimulation of the lateral olfactory tract (LOT), there is failure of the afferent excitatory terminals, perhaps due to transmitter depletion. In this circumstance there is deficient excitatory input under the condition of a high level of sustained activity among mutually inhibitory neurons. An instability develops in which some inhibitory neurons become more disinhibited (excited) and others more inhibited (less active) to the point of a paroxysmal discharge that is manifested in a massive compound IPSP of the excitatory neurons. The paroxysm terminates abruptly, but by mechanisms still unclear repeats at a rate of about 3/s for 10-70 s. It is accompanied by simultaneous ipsilateral twitching of the eyelids and muzzle, salivation, tearing, arrest, and lack of responding to sensory stimuli but without loss of posture, resembling absence in humans. It does not result from runaway mutual excitation, and it rarely culminates in full-blown convulsions. Similar spikes usually also occur in the OB and AON; the sequences of spikes appear to entrain. These normal and seizure EEGs are simulated with a network of non-linear differential equations, that is designed in conformance with the anatomy and physiology of the olfactory system. The seizure appears as an emergent property of the OB, AON and PC interactive system, that is due to an induced asymmetry in the feedback network that controls normal background activity.

Animals↗

Salivary secretion induced by L-DOPA in haloperidol-treated rats.

The effect of chronic haloperidol treatment on salivary secretion induced by L-dopa, was studied in male Sprague-Dawley rats. Dose-response relationships for L-dopa, obtained 24 h after haloperidol treatment, showed that salivary secretion was greater in rats that had been injected with haloperidol (2 mg/kg/day, i.p.) for 7 days than in controls. The threshold doses requirements were significantly reduced in that group. Pretreatment with carbidopa suppressed the salivary secretion produced by L-dopa in haloperidol-treated and control rats whose glands had been denervated. The secretory response in innervated glands was higher in haloperidol-treated animals than in controls. Haloperidol treatment also increased salivation induced by L-noradrenaline as determined by dose-response relationships. This was associated with a decrease in the threshold doses requirement. In controls and in rats chronically treated with haloperidol, the salivary responses to L-noradrenaline were temporarily depressed by 80-90% by a prior acute injection of haloperidol (2 mg/kg, i.v.) presumably acting as an alpha blocker. A similar reduction was observed after acute treatment with phentolamine (3 mg/kg, i.v.). The data obtained in this study, i.e. that chronic administration of haloperidol increases the salivary response to L-dopa and L-noradrenaline, suggests that such an affect could be due to the development of supersensitivity of striatal dopamine receptors as well as of peripheral alpha-adrenergic receptors.

Animals↗

Salivary changes associated with seasickness.

Salivary composition and flow rate were measured in 13 healthy male volunteers exposed to a real seasickness situation. The flow rates of whole unstimulated and stimulated saliva were significantly reduced at sea in about 80% of the subjects. Salivary flow rate was negatively correlated with seasickness severity. These results contrast with the classic concept of increased salivation during seasickness. At sea, the potassium concentration of both unstimulated and stimulated saliva was significantly reduced, while sodium concentration was consistently elevated. The sodium and protein concentrations were positively correlated with seasickness severity. Thus, objective measurements of salivary flow rate and composition may be recommended for evaluation of the seasickness syndrome.

Adolescent↗

High-dose clonidine motor syndrome: relationship to serotonin syndrome.

Reciprocal forepaw treading, hindlimb abduction, and Straub tail are some of the abnormal motor behaviors of the classical 'serotonin syndrome,' which results from activation of serotonin (5-HT) receptors. However, we also observed them in the syndrome evoked by the alpha-adrenergic agonist clonidine, at high doses (5-40 mg/kg). Other features of the clonidine syndrome (scored from videotapes) were body and head tremor, forelimb hyperextension, ataxia, vertical jumping, tactile hyperreactivity, and autonomic signs (piloerection, pupillary dilatation, salivation, proptosis). The clonidine syndrome persisted for several hours and was not lethal. Clonidine suppressed locomotor activity (photocell recording) and induced episodes of catalepsy and 5-HT-independent impairment of motor habituation. Single high doses of drugs active at several different neurotransmitter receptors significantly reduced total behavioral score through effects primarily on tremor and autonomic signs, but none prevented the clonidine syndrome. Lesions of monoaminergic neurons [intracisternal 5,7-dihydroxytryptamine (DHT) or 6-hydroxydopamine] or monoamine depletion by intraperitoneal reserpine all failed to prevent this motor syndrome. Co-administration of 5-HTP and clonidine did not exacerbate the clonidine syndrome in naive rats and did not prevent the onset of the serotonergic syndrome in rats with DHT lesions. These data suggest that neither catecholamines nor 5-HT have a major role in the serotonin-like behavioral responses to high doses of clonidine.

Adrenergic alpha-Antagonists↗

Effects of VIP, PHM and substance P on blood vessels and secretory elements of the human submandibular gland.

The effects of the neuropeptides VIP, PHM and substance P (SP) on vascular smooth muscle tone, K+ secretion from exocrine elements and tissue content of cyclic AMP (cAMP) in the human submandibular gland were studied in vitro. All three peptides caused relaxation of noradrenaline contracted human submandibular arteries at nM concentrations. SP was slightly more active than VIP and PHM which had a similar potency as vasodilators. Only carbachol but not VIP, PHM or SP stimulated K+ secretion from exocrine elements of the human submandibular gland. Principally similar in vitro effects on K+ secretion were obtained on the cat submandibular gland, but in the rat not only carbachol but also SP stimulated K+ secretion. VIP and PHM increased cAMP production of exocrine elements in the human submandibular gland in nM concentrations. VIP was about 5-fold more potent than PHM with regards to cAMP production. In conclusion, VIP, PHM and SP relaxed human submandibular arteries in vitro. Both VIP and PHM stimulated cAMP production in glandular tissue but none of the three peptides induced K+ secretion from human submandibular gland tissue. This suggests that, in contrast to the situation in the rat, SP does not cause watery salivation in man, while VIP and PHM may modulate protein e.g. amylase content of the saliva.

Adult↗

Vasoactive intestinal polypeptide and acetylcholine stimulate exocrine secretion of epidermal growth factor from the rat submandibular gland.

The effect of vasoactive intestinal polypeptide (VIP) and acetylcholine on secretion of epidermal growth factor (EGF) from the rat salivary glands was investigated. VIP in doses of 3 X 10(-10) to 3 X 10(-8) mol/kg per h stimulated secretion of saliva and total output of EGF dose-dependently. Acetylcholine also stimulated salivation and output of EGF. VIP in a dose of 3 X 10(-11) to 3 X 10(-10) mol/kg per h enhanced the stimulatory effect of acetylcholine, but this effect disappeared when the dose of VIP was increased. Adrenalectomy decreased acetylcholine stimulated total output of EGF by approximately 50%, but only by 20% when acetylcholine plus VIP was administered. EGF was localized to the convoluted granular tubules in the submandibular gland, whereas EGF could not be detected in the remaining salivary glands. The results suggest that VIP and acetylcholine cooperate in the control of exocrine secretion from the rat salivary glands. The effect of acetylcholine, however, seems to be partly dependent on circulating catecholamines.

Acetylcholine↗

Inhibition of substance P-induced vascular leakage in rat by N-acetyl-neurotensin-(8-13).

Substance P (SP) administered 40 micrograms/kg s.c. to pentobarbital-anesthetized rats induced salivation and leakage of plasma constituents into the skin, muscle, trachea, esophagus and bladder, as measured by Monastral blue B labeling of small blood vessels or by extravasation of Evans blue dye into tissues. These SP effects were inhibited by N-acetyl-neurotensin-(8-13) (Ac-NT-(8-13)) and by CP-96,345, a nonpeptide SP receptor antagonist. Intralumenal injection of Ac-NT-(8-13) or CP-96,345 into the bladder reduced SP-induced leakage of Evans blue dye but not dye leakage into the pawskin, indicating a localised drug action. Ac-NT-(8-13) appears to act directly on discrete sites in skin and in mucous membranes to functionally antagonize the inflammatory effects of SP.

Animals↗

The role of vector saliva in transmission of arthropod-borne disease.

Blood-sucking arthropod disease vectors all share one important feature: while probing for blood in the vertebrate host's skin they salivate into the wound they create. Recent studies on the pharmacological properties of vector saliva have revealed an array of activities that are potentially beneficial to both the vector and to the pathogen. These observations may help explain why certain vectors and pathogens have co-evolved. In this article, Richard Titus and Jose Ribeiro discuss the role vector saliva may play in disease transmission, and the prospects for its use in the control of arthropod-borne pathogens.

Journal Article↗

VIP and noncholinergic vasodilatation in rabbit submandibular gland.

The effect of parasympathetic nerve activation on rabbit submandibular gland (SMG) blood flow and saliva secretion were studied before and after systemic administration of atropine or hexamethonium. The parasympathetic fibers were stimulated electrically (2 and 15 Hz, 10 V, 1 msec) at the plexus around the submandibular salivary duct or at the chorda lingual nerve. In untreated animals, stimulation of parasympathetic fibers caused a frequency-dependent increase of salivary secretion and blood flow in the SMG. Atropine treatment completely abolished saliva secretion at 2 Hz and 15 Hz and the increase in SMG blood flow during stimulation at 2 Hz. Although atropine significantly reduced the vasodilatory response at 15 Hz, the highest blood flow measured under such circumstances was still about 2.5 times the prestimulation value. After hexamethonium administration no blood flow increase or saliva secretion was seen upon chorda lingual stimulation. The concentration of vasoactive intestinal polypeptide (VIP)-like immunoreactivity in the venous effluent of the SMG increased during nerve stimulation. Atropine significantly reduced, and hexamethonium abolished this VIP-output elicited by parasympathetic nerve stimulation. Local infusion of VIP, peptide histidine isoleucine (PHI) and substance P all caused atropine-resistant vasodilation but no salivation. The present data suggest that VIP and possibly PHI play a role in the atropine-resistant vasodilatation in rabbit submandibular gland elicited by parasympathetic nerve stimulation. The contribution of sensory mediators such as substance P released by stimulation of afferent nerves in the chorda lingual nerve to the salivary and vasodilatory responses seems to be of minor importance in the rabbit submandibular gland.

Animals↗

Peptidergic innervation of the major salivary glands of the ferret.

In parotid, sublingual and submandibular glands of the ferret, morphological correlates were looked for, using immunocytochemistry, to previous physiological findings showing parasympathetic "atropine-resistant" salivary secretion and neuropeptide-evoked salivation in this species. Nerve fibers storing VIP were numerous in association with acini, ducts and blood vessels, while the number of fibers storing substance P was moderate and those containing CGRP and galanin few; also the number of NPY-containing fibers was low around acini and ducts but relatively high around vessels. Sympathectomy eliminated all NPY- and almost all dopamine beta-hydroxylase-containing fibers. Parasympathectomy of the parotid gland resulted in a total loss of the VIP-containing fibers, and a profound reduction in the number of substance P- and CGRP-containing fibers.

Animals↗

Subchronic inhalation toxicity of morpholine in rats.

The inhalation toxicity of 25-, 100-, and 250-ppm morpholine was investigated by 6 hr/day, 5 day/week exposures to Sprague-Dawley rats for 13 weeks. Irritant effects of morpholine exposures were evident mostly in the high exposure group; a reddish discharge was observed around the nose and mouth in the 250-ppm group rats after the first week; salivation was also observed. Ten rats/sex/dose level were sacrificed after 7 weeks. The high-level (250-ppm) exposure resulted in focal erosion and focal squamous metaplasia of the maxilloturbinates; effects were observed in 6/10 male rats and 2/10 female rats. There was also a sporadic increase of secretions in the Harderian gland sections. Almost all high-level rats sacrificed after 13 weeks demonstrated comparable effects; the lesions, which were increased in incidence and severity, involved the nasal septum and anterior nasal cavities in addition to the nasoturbinates and maxilloturbinates. Lesions of chronic murine pneumonia were increased in severity in the 250-ppm group. The only compound-related histomorphologic alterations observed in the 100-ppm group consisted of focal necrosis and necrotic cell debris in the nasal cavity of two female rats at terminal sacrifice. No exposure related effects were observed in the 25-ppm group. No significant compound-related effects on body weight, clinical chemistry, hematology, or organ weight data were observed.

Animals↗

Acute toxicity studies with oxamyl.

The acute toxicity of oxamyl, an insecticide and nematicide, has been evaluated to establish proper handling guides. The material is highly toxic when given as a single oral dose; its LD50 is in fasted rats 2.5 to 3.1 mg/kg, 2.3 to 3.3 mg/kg in fasted mice, and 7 mg/kg in guinea pigs. A beagle dog given 30 mg/kg died, while 15 mg/kg was not lethal. In all species, clinical signs of cholinesterase inhibition (lacrimation, salivation, tremors) were observed. Cholinesterase activity was depressed in rats treated with a single oral dose. Atropine, when given immediately after oxamyl, was antidotal. When given by intraperitoneal injection, oxamyl was highly toxic to rats, mice, and guinea pigs. The material is a mild eye irritant with the reaction limited to the conjunctiva and iris, but systemic absorption via eye contact makes use of protective equipment essential. Oxamyl produces mild skin irritation and the dermal absorption toxicity in rats (LD50 is greater than 1,200 mg/kg) and rabbits (740 mg/kg) is relatively high suggesting limited absorption. No sensitization was produced when tested in guinea pigs. Oxamyl is highly toxic via inhalation with the 1-hr LC50 value in rats being 0.17 mg/liter (male) and 0.12 mg/liter (female). The corresponding 4-hr value is 0.064 mg/liter for male rats which indicates that concentration X time is a constant through the time periods tested. Repeated-dose studies, orally in rats and dermally in rabbits, showed oxamyl to be noncumulative, with the target system being the nervous system mediated through cholinesterase inhibition. No specific tissue or organ pathology was seen in either species tested.

Administration, Oral↗

Sublethal acute toxicity of carbosulfan [2,3-dihydro-2,2-dimethyl-7-benzofuranyl(d i-n-butylaminosulfenyl)(methyl)carbamate] in the rat after intravenous and oral exposures.

Sublethal toxicity of car-carbosulfan, 2,3-dihydro-2,2-dimethyl-benzofuranyl(di-n-butylaminosulfenyl++ +)(methyl)carbamate , was evaluated in female Sprague-Dawley rats. Erythrocyte acetylcholinesterase (AChE) activity was maximally inhibited 1 min after iv administration (38, 23, and 15% of pretreatment activity after 86, 250, and 690 micrograms/kg, respectively) and recovered by 4 hr. Maximum AChE inhibition (63% of pretreatment activity) was measured 45 min after oral dosing (690 micrograms/kg) and activity recovered after 5 hr. Signs included urination, defecation, facial muscle fasciculations, salivation, and tremors. Carbosulfan was less toxic when given orally. Metabolic activation of carbosulfan to carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranol methylcarbamate) was investigated by measuring plasma concentrations 4, 30, and 240 min after iv (80-120 or 620-640 micrograms/kg) and oral (540-700 or 2030-2190 micrograms/kg) dosages of [carbonyl-14C]carbosulfan. Peak plasma concentrations were measured at 4 and 30 min after iv and oral exposure, respectively. Carbosulfan was rapidly activated to carbofuran. Reduction in AChE activity was better correlated (r = 0.97) with plasma concentration of [carbosulfan + carbofuran] and plasma carbofuran (r = 0.96) than with plasma carbosulfan (r = 0.73). Signs generally occurred when AChE activity was less than 65% of pretreatment levels, corresponding to 40 pmol/ml [carbosulfan + carbofuran] in plasma. Based on regression analysis and metabolic studies, both carbosulfan and carbofuran contributed to the observed AChE inhibition; however, carbofuran, a more potent in vitro inhibitor and the usual predominant inhibitor in plasma, was responsible for most of the erythrocyte AChE inhibition.

Acetylcholinesterase↗

Atropine and/or diazepam therapy protects against soman-induced neural and cardiac pathology.

Toxic doses of the organophosphonate anticholinesterase agent soman can produce neural and cardiac lesions in animals that survive the acute poisoning. The ability of two standard antidote drugs, atropine and diazepam, along with the oxime pralidoxime (2-PAM) Cl, were evaluated for their ability to block these pathological effects. Rats were challenged with a fixed dose (85 micrograms/kg, sc) of soman and treated im 5 min later with 25 mg/kg 2-PAM Cl and one of the following combinations of atropine (0.0, 1.0, 3.2, 10.0, or 32.0 mg/kg) and diazepam (0.0, 0.1, 0.32, 1.0, or 3.2 mg/kg) in a balanced design. The severity of acute anticholinesterase intoxication signs was rated 1 hr after exposure; Body weights and behavioral reactivity ratings were obtained daily for 16 days after exposure; brains and hearts of all surviving subjects were then evaluated for pathological changes. Soman challenge resulted in 33% lethality in animals that received only 2-PAM therapy; both atropine and diazepam reduced lethality in a dose-dependent fashion. Across all treatment conditions greater than 50% of the deaths occurred later than 24 hr after intoxication and treatment. Acute intoxication signs were differentially moderated by the two drugs: atropine reduced all six signs in a dose-dependent fashion; diazepam had no effect on lacrimation and eye bulb protrusion, antagonized signs of salivation and motor abnormalities in a dose-dependent manner, and antagonized the effects of soman on signs of physical activity and coordination only at low doses. All doses of diazepam and the highest dose of atropine moderated body weight loss and a syndrome of behavioral hyperreactivity observed after exposure. Brain pathology was significantly reduced by all doses of diazepam and/or the highest dose of atropine, but no single drug or drug combination was effective in protecting all animals in a group from some brain pathology. Both drugs blocked the development of cardiac lesions in a dose-dependent fashion. The results demonstrate that diazepam or high doses of atropine can antagonize the development of brain lesions that result from soman exposure. Pharmacological management of epileptiform motor abnormalities during the acute intoxication is critical for this effect. In contrast, soman-induced cardiac pathology may occur secondarily as a consequence of the severe brain lesions or develop independently of brain lesion formation due possibly to sympathetic overstimulation.

Animals↗

Subchronic inhalation toxicity of ethylbenzene in mice, rats, and rabbits.

Mice, rats, and rabbits (five/sex/group) were exposed by inhalation to ethylbenzene (EB) vapors for 6 hr/day, 5 days/week for 4 weeks (20 exposures). Rats and mice received 0, 99, 382, or 782 ppm EB while rabbits received 0, 382, 782, or 1610 ppm. No changes were evident in mortality patterns, clinical chemistries, urinalyses, or treatment-related gross/microscopic (including ophthalmologic) lesions. Rats exhibited sporadic lacrimation and salivation, as well as significantly increased liver weights at 382 and 782 ppm, and small increases in leukocyte counts at 782 ppm. Males at this exposure level also showed marginal elevations in platelet counts. In mice, females showed statistically increased absolute and relative liver weights at 382 and 782 ppm, while males had statistically increased relative liver-to-brain weight ratios only at 782 ppm. Female rabbits at the high exposure level of 1610 ppm gained weight more slowly than controls (not statistically significant); males showed a similar transient downward trend after 1 week, but showed no differences from controls at study's end. A no observed adverse effect level (NOAEL) of 382 ppm appears appropriate for rats and mice with a lowest observed adverse effect level (LOAEL) of 782 ppm. A NOAEL of 782 ppm and LOAEL of 1610 ppm are appropriate for rabbits.

Administration, Inhalation↗