Alberto Meli

Is the forced swimming test a suitable model for revealing antidepressant activity

The forced swimming test is reviewed. This test appears to be suitable for detecting antidepressant activity in rats but not in mice. Difference in experimental procedure may account for the different sensitivity to drugs of the two animal species.

Competitive antagonists discriminate between NK2 tachykinin receptor subtypes

1 We have compared the ability of various tachykinins and selective tachykinin receptor agonists to induce contraction of the endothelium‐denuded rabbit pulmonary artery (RPA) and hamster trachea (HT) and have estimated the affinity of some newly developed NK2 selective antagonists in the same tissues. 2 In confirmation of previous findings, experiments with the agonists indicated that NK2 receptors are the main if not the sole mediators of the response to tachykinins in both RPA and HT. No evidence for significant degradation of neurokinin A (NKA) was found in either tissue when experiments were repeated in the presence of a mixture of peptidase inhibitors (thiorphan, captopril and bestatin, 1 μm each). 3 The peptide antagonists tested were: Peptide I = [Tyr5, d‐Trp6,8,9, Arg10]‐NKA(4–10); Peptide II = [Tyr5, d‐Trp6,8,9, Arg10]‐NKA(3–10); Peptide III = Ac‐Leu‐Asp‐Gln‐Trp‐Phe‐Gly‐NH2. The three peptides produced a concentration‐dependent rightward shift of the concentration‐response curve to NKA in both RPA and HT with no significant depression of the maximal response attainable. The slopes of the Schild plots were not significantly different from unity, indicating a competitive antagonism. Peptides I and II were about 100 times more potent in the RPA than in the HT, while Peptide III was about 100 times more potent in the HT than RPA. 4 The pA2 values obtained in these two tissues with the three antagonists were not significantly different when tested in the absence or presence of peptidase inhibitors, or when a selective NK2 receptor agonist, [βAla8]‐NKA(4–10) was used instead of NKA. Similar pA2 values were obtained after 15 or 90 min of incubation with the antagonists. Peptides I, II and III had no inhibitory effect on contractions produced by noradrenaline in the RPA or by carbachol in the HT. 5 Peptides I, II and III showed weak or no antagonistic activity toward the vasodilatator effect of substance P in the dog carotid artery (NK1 receptor‐mediated) or toward the contractile effect of neurokinin B in the rat portal vein (NK3 receptor‐mediated). 6 These results provide pharmacological evidence for heterogeneity of NK2 receptors in the RPA and HT. The NK2 receptors present in these tissues are not discriminated by natural tachykinins or selective agonists, but are recognized with very different affinity by NK2 receptor antagonists.

The nonstop transvesical cystometrogram in urethane-anesthetized rats: A simple procedure for quantitative studies on the various phases of urinary bladder voiding cycle

A new cystometric procedure that involves a nonstop transvesical (through a needle inserted into the bladder dome) infusion of saline in urethane-anesthetized rats is described. This permits the obtainment of a series of repetitive voiding cycles in both male and female rats. Recording at high-chart speed permits quantitative measurements of the various phases of the voiding cycle. Micturition was almost invariably associated with appearance, during a sustained increase of intravesical pressure, of a series of high-frequency oscillations, which were paralleled by a stream-like emission of the infused fluid. Micturition was not observed after topical tetrodotoxin, after bilateral transection of pelvic nerves, or in acute spinal rats. Intravenous hexamethonium produced a dose-related impairment of the voiding cycle, and, at high doses, suppressed micturition, and overflow incontinence ensued. The experimental procedure described herein appears to be suitable for physiopharmacological studies dealing with regulation of voiding cycle.

A model to measure anticipatory anxiety in mice

Among animals from the same cage, mice removed last had a higher temperature compared to those removed first. This phenomenon a) persisted 2 and 24 h later; b) was present regardless of the number of the animals (5, 10, 15 and 20) in each cage, c) was independent of whether the number of animals was reduced or maintained constant in the cage and d) could even be observed by reversing the order of removal of the animals from the cage. In addition, the fewer the animals allocated to a cage the greater the percentage of those which became hyperthermic. This rise in rectal temperature of mice removed last was prevented by diazepam (2.5 and 5 mg/kg PO, 30 min), nitrazepam (2 and 4 mg/kg PO, 30 min) but not by imipramine (15 and 30 mg/kg PO, 30 min) or haloperidol (0.5 and 1 mg/kg PO, 60 min) and was observed in a greater opercentage of mice following subcutaneous yohimbine treatment (2 mg/kg, 60 min). This phenomenon does not seem to depend on physical exercise due to an attempt to escape, since no correlation appears to exist between motor activity (open-field) and rise in rectal temperature. These data would seem to indicate that hyperthermia in the last animals may represent a new tool for studying the neurobiology of anticipatory(?) anxiety.

The effects of topical capsaicin on rat urinary bladder motility in vivo

The effects of topical capsaicin on urinary bladder motility were investigated following saline-induced distension of the bladder wall in urethane-anaesthetized rats and compared to the effects of topical substance P and acetylcholine. Capsaicin and substance P produced similar excitatory effects in both quiescent and rhythmically contracting bladders, i.e., a TTX resistant tonic contraction followed by a series of rhythmic, TTX sensitive, phasic contractions. Acetylcholine, in doses equieffective in producing TTX resistant contractions was less effective than capsaicin or substance P in triggering neurogenic rhythmic contractions of bladder muscle. Atropine pretreatment prevented the neurogenic component of the excitatory effect of both capsaicin and substance P. Repeated applications of capsaicin but not of substance P led to desensitization. Bladders of animals pretreated (4 days before) with a large dose of s.c. capsaicin developed insensitivity to topical capsaicin and a larger volume of saline was required to trigger neurogenic rhythmic contractions of the detrusor muscle. These results suggest that capsaicin acts by interfering with the mechanism(s) regulating the threshold for the micturition reflex to occur.

Potent contractile effect of endothelin in isolated guinea-pig airways

Endothelin produced a concentration-dependent (1 nM-0.3 microM) contraction of isolated guinea-pig airways (trachea and main bronchi). The response was unaffected by tetrodotoxin (1 microM) and slightly depressed by indomethacin (5 microM) but promptly abolished by isoprenaline (1 microM) or EDTA (3 mM). In the bronchi, the response to endothelin was enhanced by removal (rubbing) of the epithelium. The response of the trachea or bronchi to endothelin (0.3 microM) was unaffected by NiCl2 (0.1 mM) or omega conotoxin (0.1 microM) but was partially inhibited by nifedipine (1 microM).

The effect of omega conotoxin GVIA, a peptide modulator of the N-type voltage sensitive calcium channels, on motor responses produced by activation of efferent and sensory nerves in mammalian smooth muscle.

Summary1.The effect of omega-conotoxin (CTX) GVIA, a peptide which blocks neuronal calcium channels, were investigated on nerve-mediated motor responses in a variety of isolated smooth muscle preparations from rats and guinea-pigs.2.In the rat or guinea-pig isolated vas deferens CTX (1 nM − 1 μM) produced a concentration and time-related inhibition of the response to field stimulation, while the responses to KCI, noradrenaline or adenosine triphosphate were unaffected. In the presence of CTX a series of tetrodotoxin-resistant contractions could be elicited by field stimulation by increasing pulse width and/or voltage.3.In the rat or guinea-pig isolated urinary bladder, CTX produced a concentration and time-dependent inhibition of twitch responses to field stimulation without affecting the response to exogenous acetylcholine. In the rat bladder the maximal effect did not exceed 25% inhibition while a much larger fraction of the response (about 70%) was inhibited in the guinea-pig bladder. The CTX-resistant response was abolished, in both tissues, by tetrodotoxin.4.The effects of CTX in the rat bladder were also studied with a whole range of frequencies of field stimulation (0.1–50 Hz). Maximal inhibition was observed toward contractions elicited at frequencies of 2–5 Hz. At low frequencies the inhibitory effects of CTX and atropine were almost additive while at high frequencies of stimulation a large component of the atropine-sensitive response was CTX-resistant.5.In the rat isolated proximal duodenum, field stimulation in the- presence of atropine and guanethidine produced a primary relaxation followed by a rebound contraction. Both responses were abolished by tetrodotoxin, indicating the activation of intramural nonadrenergic noncholinergic nerves. The primary relaxation was totally CTX resistant while the rebound contraction was slightly inhibited.6.The motor responses produced by capsaicin (1 μM) in the rat or guinea-pig bladder (contraction) and in the rat proximal duodenum (relaxation) were unaffected by CTX. Likewise, the release of substance P-like immunoreactivity from sensory nerves of the guinea-pig bladder muscle was unaffected by CTX.7.These findings indicate that CTX-sensitive calcium channels modulate transmitter release in autonomic nerve terminals of mammals, but noticeable species and organ related variations exist in sensitivity to this peptide, possibly reflecting the existence of a heterogenous population of voltage-sensitive calcium channels. CTX-sensitive calcium channels are apparently not involved in the excitatory action of capsaicin on sensory nerve terminals.

Pharmacological validation of a novel animal model of anticipatory anxiety in mice

The current study investigates the action of anxiolytics, antidepressants, neuroleptics, antipyretics, muscle relaxants, antihypertensives and naloxone in a novel animal model of anxiety, based on the evidence that mice removed last from their cage develop hyperthermia (stress-induced hyperthermia, SIH) when compared to those removed first. Alprazolam (0.15–0.6 mg/kg), chlordiazepoxide (25 mg/kg), estazolam (1 mg/kg), phenobarbital (20 mg/kg), ethanol (2 and 4 g/kg), buspirone (5 and 10 mg/kg) and prazosin (1 and 2 mg/kg), as well as repeatedly administered diazepam (5 mg/kg), inhibited SIH. In contrast, tofisopam (12.5–200 mg/kg), desipramine (15 and 30 mg/kg), amitriptyline (10 mg/kg), fluoxetine (10 and 20 mg/kg), tranylcypromine (5 and 10 mg/kg), chlorpromazine (1 and 2 mg/kg), clozapine (2 and 4 mg/kg), pimozide (0.5 and 1 mg/kg),l-sulpiride (15 and 30 mg/kg),l-propranolol (5 and 10 mg/kg), acetyl salicylic acid (200 and 400 mg/kg), indomethacin (2.5 and 5 mg/kg), verapamil (2.5 and 5 mg/kg), captopril (25 and 50 mg/kg), dantrolene (10 and 20 mg/kg), mephenesin (300 and 600 mg/kg),d-amphetamine (1 and 4 mg/kg) and naloxone (2.5 and 15 mg/kg) were inactive, as were 10 mg/kg imipramine, amitriptyline and fluoxetine injected every day for 21 days. Reserpine at high doses (1.25 and 2.5 mg/kg) but not at a lower dose (0.62 mg/kg) prevented SIH, but in this case animals showed a behavioural syndrome which could have interfered with the occurrence of the hyperthermia.

The antagonism induced by ruthenium red of the actions of capsaicin on the peripheral terminals of sensory neurons: further studies

Ruthenium Red, an inorganic dye which blocks transmembrane calcium (Ca) fluxes in neural tissues, reduced the capsaicin-induced release of substance P-like immunoreactivity from muscle strips of the guinea-pig urinary bladder in a concentration-dependent (30 nM - 3 microM) manner, and protected the sensory fibers from capsaicin-induced densensitization. A similar antagonism of the actions of capsaicin was observed in functional experiments (capsaicin-induced contraction of the isolated guinea-pig bladder or inhibition of twitches of the isolated rat vas deferens). In view of its established action on the depolarization-coupled entry of Ca into synaptosomes and the secretion of transmitter, we propose that Ruthenium Red could antagonize the action of capsaicin on the peripheral terminals of sensory nerves by a similar mechanism, thereby suppressing transmitter secretion and preventing the establishment of desensitization.

Discovery of antidepressant activity by forced swimming test may depend on pre-exposure of rats to a stressful situation

Antidepressant-induced anti-immobility effects have been assessed in animals exposed or not to a pretest session using the forced swimming test. Desipramine, maprotiline, mianserine (15 and 30 mg/kg), nomifensine (2.5 and 5 mg/kg), d-amphetamine (1 and 2 mg/kg) and muscimol (1 and 2 mg/kg), unlike imipramine (15 and 30 mg/kg), LY-171555 (0.1 and 0.2 mg/kg) and scopolamine (0.5 and 0.1 mg/kg), did not reduce immobility time in rats which had not received the pretest session. On the other hand, all of the drugs tested reduced immobility time in rats exposed to a pretest session. In addition, the degree of anti-immobility effects of desipramine (20 mg/kg) and nomifensine (5 mg/kg) increased proportionally with the level of water (0, 4, 15 and 30 cm) to which animals were exposed at the time of pretest. Furthermore, desipramine reduced immobility time in rats pre-exposed to types of stress different from forced swimming, cold, restraint or foot-shock. All drugs were injected intraperitoneally three times, 24, 5 and 1 h before testing. The present findings suggest that a stressful pretest session may reveal pharmacological properties of antidepressants in the forced swimming test. This is also substantiated by the fact that diazepam (2.5 and 5 mg/kg) administered 30 min before the swimming pretest antagonized the anti-immobility effect of 15 mg/kg desipramine.