Pinch Response Research Articles

Evaluation of two protocols for chemical restraint in guinea pigs (Cavia porcellus).

Abstract: This study evaluated the cardiorespiratory parameters, analgesia, sedation depth and duration, and recovery quality in guinea pigs undergoing elective castration, using dexmedetomidine or xylazine combined with esketamine hydrochloride and morphine. In a crossover study, guinea pigs (Cavia porcellus) (n=8), 9 months and 650 g (p = 0,3831) received xylazine (1 mg/kg), esketamine (10 mg/kg), and morphine (0,5 mg/kg) (GXIL), or dexmedetomidine (5 mcg/kg), esketamine (10 mg/kg), and morphine (0,5 mg/kg) (GDEX) intramuscularly at a two-week interval. Cardiorespiratory parameters, including respiratory rate (RR), heart rate (HR), SpO2, and rectal temperature (RTºC), were recorded at baseline (M0) and every 5 minutes post-administration (M5 to M60). Sedation depth was assessed via ear/toe pinch response, jaw tone, righting reflex, posture, palpebral reflex and reaction to manipulation, based on the criteria established by D'OVÍDIO et al. (2017). Statistical analysis included the Shapiro-Wilk test, unpaired t-test, two-way repeated measures ANOVA, and non-parametric tests (Kruskal-Wallis, Wilcoxon, Mann-Whitney U). GXIL induced more profound sedation, with significant differences in ear/toe pinch response and jaw tone compared to GDEX. HR and RR significantly decreased in the GXIL group, with an average reduction of 13,6% in HR and 32,6% in RR. GDEX demonstrated less sedation depth and a milder decrease in RR. Both protocols were effective and safe for chemical restraint in guinea pigs, though GXIL provided deeper sedation and greater cardiorespiratory depression than GDEX. However, GDEX maintained a more stable cardiorespiratory profile, suggesting it. Nonetheless, both treatments provided minimal cardiorespiratory alterations, demonstrating their safety for use.

Sex differences in cholinergic signaling affect functional outcomes for theta-gamma coordination in hippocampal subcircuits following experimental febrile status epilepticus.

Sex determines cognitive outcome in animal models of early life seizure, where males exhibit impaired hippocampal-dependent learning and memory compared with females. The physiological underpinnings of this sex effect are unclear. Cholinergic signaling is essential for the generation of hippocampal oscillations, and supplementation of cholinergic precursors prior to status epilepticus in immature male rats prevents subsequent memory deficits. We hypothesized that there are sex differences in acetylcholine circuits and their response to experimental febrile status epilepticus (eFSE). eFSE was induced in male and female rat pups. We transversed the hippocampus of postnatal day >60 control (CTL) and eFSE rats with a 64-channel laminar silicon probe to assay cholinergic-dependent theta oscillations under urethane anesthesia. Local field potential properties were compared during (1) baseline sensory stimulation, (2) pharmacological stimulation via acetylcholine reuptake blockade, and (3) sensory stimulation after muscarinic acetylcholine receptor block (atropine). In all groups, a baseline tail pinch could elicit theta oscillations via corticohippocampal synaptic input. Following atropine, a tail pinch response could no longer be elicited in CTL male, CTL female, or eFSE female rats. In contrast, induced slow theta power in eFSE males after atropine was not decreased to spontaneous levels. Analysis of oscillation bandwidths revealed sex differences in acetylcholine modulation of theta frequency and slow gamma frequency and power. This study also identified significant effects of both sex and eFSE on baseline theta-gamma comodulation, indicating a loss of coupling in eFSE males and a potential gain of function in eFSE females. There are differences in cholinergic modulation of theta and gamma signal coordination between male and female rats. These differences may underlie worse cognitive outcomes in males following eFSE. Promoting the efficacy of muscarinic acetylcholine signaling prior to or following early life seizures could elucidate a mechanism for the temporal discoordination of neural signals within and between hippocampus and neocortex and provide a novel therapeutic approach for improving cognitive outcomes.

Reduced Sensitivity to Anesthetic Agents upon Lesioning the Mesopontine Tegmental Anesthesia Area in Rats Depends on Anesthetic Type.

The brainstem mesopontine tegmental anesthesia area is a key node in circuitry responsible for anesthetic induction and maintenance. Microinjecting the γ-aminobutyric acid-mediated (GABAergic) anesthetic pentobarbital in this nucleus rapidly and reversibly induces general anesthesia, whereas lesioning it renders the animal relatively insensitive to pentobarbital administered systemically. This study investigated whether effects of lesioning the mesopontine tegmental anesthesia area generalize to other anesthetic agents. Cell-selective lesions were made using ibotenic acid, and rats were later tested for changes in the dose-response relation to etomidate, propofol, alfaxalone/alfadolone, ketamine, and medetomidine delivered intravenously using a programmable infusion pump. Anesthetic induction for each agent was tracked using five behavioral endpoints: loss of righting reflex, criterion for anesthesia (score of 11 or higher), criterion for surgical anesthesia (score of 14 or higher), antinociception (loss of pinch response), and deep surgical anesthesia (score of 16). As reported previously for pentobarbital, on-target mesopontine tegmental anesthesia area lesions reduced sensitivity to the GABAergic anesthetics etomidate and propofol. The dose to achieve a score of 16 increased to 147 ± 50% of baseline in control animals ± SD (P = 0.0007; 7 lesioned rats and 18 controls) and 136 ± 58% of baseline (P = 0.010; 6 lesioned rats and 21 controls), respectively. In contrast, responsiveness to the neurosteroids alfaxalone and alfadolone remained unchanged compared with baseline (94 ± 24%; P = 0.519; 6 lesioned rats and 18 controls) and with ketamine increased slightly (90 ± 11%; P = 0.039; 6 lesioned rats and 19 controls). The non-GABAergic anesthetic medetomidine did not induce criterion anesthesia even at the maximal dose tested. The dose to reach the maximal anesthesia score actually obtained was unaffected by the lesion (112 ± 8%; P = 0.063; 5 lesioned rats and 18 controls). Inability to induce anesthesia in lesioned animals using normally effective doses of etomidate, propofol, and pentobarbital suggests that the mesopontine tegmental anesthesia area is the effective target of these, but not necessarily all, GABAergic anesthetics upon systemic administration. Cortical and spinal functions are likely suppressed by recruitment of dedicated ascending and descending pathways rather than by direct, distributed drug action.

Acute and sub-acute toxicity study of bacterial signaling inhibitor Solanum torvum root extract in Wister rats

BackgroundSolanum torvum root extract is used to treat Asthma, Diabetes, and hypertension by Garo tribal healers of India and Bangladesh. Root tea is used to treat cough and fever by Attapadi tribal people of Kerala, India. The in vivo toxicological effects of Solanum torvum root extract was assessed by acute and sub-acute toxicity studies according to the OECD (Organisation for Economic Co-operation and Development) guidelines and per the guidance of Committee for the Purpose of Control and Supervision of Experiments on Animals (CPCSEA), Ministry of Environment and Forest, government of India.ResultsA single dose of Solanum torvum root extract (300 mg/kg, 600 mg/kg and 1200 mg/kg) was administrated daily for 14 days to estimate acute toxicity whereas subjects were treated for 28 days to assess the sub-acute toxicity. General functional behaviors, Physiological, histological, biochemical and hematological parameters were observed to understand the effect of extract upon study animal. All the study subjects were alive after the study period after acute and sub-acute toxicity assay. Functional and behavioral characteristics such as body position, respiration, clonic involuntary movement, tonic involuntary movement, palpebral closure, approach response, touch response, pinna reflex and tail pinch response; palpebral closure, lacrimation, salivation, piloerection, pupillary reflex, abdominal tone, limb tone, when held in hand were also found to be normal. Histological, biochemical and hematological parameters were also normal compared that with untreated group.ConclusionsThe acute and sub-acute toxicological analysis of Solanum torvum root extracts up on Wister rats suggested that there are no any dose response relation between extract administrated and toxicity, therefore there are no toxic effect by STRE, however more enlightenment regarding toxicity due to prolonged exposure can only be understood from chronic toxicity analysis.

Myxoma virus derived immune modulating proteins, M-T7 and Serp-1, reduce early inflammation after spinal cord injury in the rat model.

Spinal cord injury (SCI)-initiated inflammation was treated with anti-inflammatory reagents. We compared local spinal cord or intraperitoneal infusion of two Myxoma virus derived immune modulating proteins, Serp-1 and M-T7, with dexamethasone (DEX). Hemorrhage and necrosis after SCI initiate acomplex pathogenesis dominated by early, severe and highly destructive inflammatory macrophage infiltration. We examined sustained, 7-day, subdural infusion of either M-T7, achemokine modulator or Serp-1, aplasminogen activator and factor inhibitor. Mature male rats had epidural balloon crush SCI and sustained subdural infusion of Serp-1, M-T7, DEX or saline for 7 days via the osmotic pump. Aseparate group of rats with SCI had intra-peritoneal infusion. Clinical evaluation included endpoint monitoring with body weight, hemorrhagic cystitis and bilateral toe pinch response. Sections of the spinal cord were analyzed histologically and macrophage numbers counted by standardized protocol in the cavity of injury (COI). While the rats administered DEX demonstrated substantial body weight loss, dehydration and dermal atrophy consistent with steroid toxicity, rats infused with Serp-1 and M-T7 had no toxicity. Serp-1 improved withdrawal responses. Subdural infusion of Serp-1, M-T7 and DEX significantly reduced numbers of phagocytic, CD68-positive macrophages. With intraperitoneal infusion only M-T7 reduced macrophage counts, Serp-1 showed only atrend. Local infusion of highly active immune modulating proteins; Serp-1 and M-T7, targeting serine protease and chemokine pathways demonstrated excellent potential for neuroprotection after severe SCI in arat model, without adverse side effects. Sustained subdural infusion offers an alternative route of administration for treatment of SCI.

Efeitos da associação de tiletamina/zolazepam ou cetamina S(+)/midazolam/tramadol para contenção química em bugios-ruivos (Allouatta guariba clamitans)

Avaliaram-se dois protocolos para contenção química em bugios-ruivos. Para tal, foram utilizados 12 macacos bugios, hígidos, com peso médio de 6,4±0,4 kg, os quais foram submetidos a jejum alimentar e hídrico de seis e duas horas, respectivamente. Os animais foram alocados em dois grupos que receberam injeção via intramuscular: TZ (n=6), os quais receberam uma associação de tiletamina e zolazepam (Zoletil®) na dose de 3,6mg/kg e CEMTRA (n=6), que receberam cetamina S(+), midazolam e tramadol (Cemtra ®, lote piloto 001/10, Ouro Fino Saúde Animal Ltda., Cravinhos, SP-Brasil, constituído por 100mg/ml de cetamina S+, 20mg/ml de tramadol e 10mg/ml de midazolam) na dose de 1ml da associação para cada 10kg de peso corporal, correspondendo às doses de 10mg/kg, 1mg/kg e 2mg/kg, respectivamente. Anteriormente a administração dos fármacos (M0) foram avaliadas: frequência cardíaca (FC) e respiratória (f), temperatura retal (TR), tempo de preenchimento capilar (TPC), pressão arterial sistólica (PAS), saturação de oxigênio na hemoglobina (SpO2), presença de salivação, grau de miorrelaxamento e sedação, índice Bispectral (BIS) e Sinal de Qualidade do BIS (SQI), resposta ao pinçamento interdigital e tempos de latência, deambulação e de recuperação total (TRT). Os parâmetros foram reavaliados em M5, M10, M20, M30, M40 e M50 (5, 10, 20, 30, 40 e 50 minutos após a administração dos fármacos). No TZ os animais foram mais responsivos ao pinçamento interdigital ao longo dos tempos. Os animais do CEMTRA apresentaram maior grau de miorrelaxamento e de sedação. A f do CEMTRA foi menor após a administração do tratamento em todos os momentos em relação ao M0. Entre grupos a f do CEMTRA foi menor em relação ao TZ em M2 e M4. Os tempos totais de sedação e de recuperação foram de 48±4 e 150,1±42,1 min para o CEMTRA e de 38±7 e 73,1±20,6 para o TZ. Conclui-se que ambas as formulações são seguras para contenção química de bugios, sendo que o CEMTRA apresentou melhor sedação e miorrelaxamento.

Three combinations of clonidine in association with tiletamine-zolazepam for anaesthesia induction in rats: evaluation of reflexes and pain sensibility

The aim of this study was to assess the combination of tiletamine-zolazepam (Zoletil 20<sup>®</sup>) with three different doses of clonidine for general anaesthesia induction in rats submitted to vascular microsurgery. The evaluation of anaesthetic and analgesic effects was performed in 30 Wistar rats randomly divided into three groups and induced with Zoletil 20 [90 mg/kg Intraperitoneal (IP)] associated with three different doses of clonidine (60–90–120 μg/kg IP). Four clinical parameters were evaluated after induction: loss of righting reflex, voluntary movement, the pedal withdrawal response, and pain sensitivity tested by pinching the tail. The combination of Zoletil with 90 and 120 μg/kg of clonidine provided a surgical anaesthesia; however, 90 μg/kg of clonidine provided the most rapid anaesthesia induction, as confirmed by data obtained by clinical evaluation of the loss of the pedal withdrawal response and the absence of the tail pinch response. The increase in dose of clonidine did not lead to a more rapid action of the α2 agonist, probably due to achievement of a dose-dependent plateau.

The Effect of Repetitive Intraperitoneal Anesthesia by Application of Fentanyl-Medetomidine and Midazolam in Laboratory Rats

ABSTRACTBackground: Literature reviews show numerous options for anesthesia in the small laboratory animals. Many methods are associated with complications, such as high technical effort, difficult monitoring, respiratory and cardiovascular depression, and prolonged sedation. In the present study, we report first time results after repeated use of an intraperitoneal combined anesthesia with a high tolerability. Methods: Three hundred and seventy-four anesthesias were performed on 38 adult male lewis rats (280–460g). Each animal was anesthetized repeatedly over a period of three months, using an intraperitoneal combination of Fentanyl-Medetomidine and Midazolam (FMM). The time required for the animals to lose ear pinch response and the ability to perform a righting and pedal withdrawal reflex was measured. For evaluation of the clinical state, a four-point vitality scale was developed. The anesthesia was antagonized with Naloxone, Flumazenil, and Atipamezole (s.c.). Results: The animals lost all three reflex responses within 5 (± 2.4) min of injection. Without antagonism of anesthesia, the ear pinch response returned on average within 125 (± 21.5) min. After antagonism of anesthesia, the rats needed 5 (± 2.9) min to regain all three reflex responses. No significant differences of vitality-index were measured after repeated use of FMM during the investigation period. Conclusions: A repeatable and secure anesthesia is indispensable for any experimental studies that require multiple anesthesia of a single animal. Intraperitoneal combination of FMM provides an adequate procedure to induce a well tolerable, repeatable state of anesthesia, which conforms to all the necessary requirements for laboratory rats.

183: Maternal obesity and evidence of fetal programming of lipid metabolism

programming of lipid metabolism Beth Plunkett, Gina Morgan, Richard Silver, Susan Crawford NorthShore University HealthSystem, Department of Obstetrics and Gynecology, Evanston, IL, NorthShore University HealthSystem, Surgery, Evanston, IL OBJECTIVE: To determine if pregestational maternal obesity alters fetal lipid metabolism in a leptin-deficient mouse model. STUDY DESIGN: Leptin-deficient mice (ob/ob) lack appetite control and become obese through overeating. Fetuses of LEAN ob/ob dams were compared to fetuses of OBESE ob/ob dams. LEAN ob/ob dams were treated with exogenous leptin after weaning to maintain normal body weight and fertility. The OBESE ob/ob dams were treated only with periconceptional leptin. Leptin treatments were stopped in both groups after post-conception D6.5. Dams were mated to C57Bl6 wildtype (WT) studs and sacrificed on D18. Fetal livers were harvested and RNA extracted for Affymetrix gene array analysis and Ingenuity Pathway Assessment. RESULTS: Preconceptional weight was significantly lower in the LEAN (n 4) than OBESE (n 5; 20.7 2.9 vs. 28.5 2.3g, P 0.05) as was D18 glucose (196.0 36.9 vs. 172.3 41.2 mg/dL, respectively, P 0.05) and D18 insulin (1.00 0.5 and1.14 1.0 ng/ml, respectively, P 0.05). Fetal livers (n 3) demonstrated significant changes in the expressions of 15 genes related to lipid metabolism in the fetuses of LEAN versus OBESE. CONCLUSION: In a leptin-deficient mouse model, maternal preconceptional obesity independently changes expression of multiple genes involved in fetal lipid metabolism. The identified genes modulate physiological processes associated with glucose intolerance and triglyceride metabolism. These findings suggest that significant metabolic disturbance related to maternal obesity may begin in fetal life. 184 Neonatal neurologic evaluation in a retinoic acid induced rat myelomeningocele model Brendan Grubbs, Shelley Hough, Samer Assaf, Lisa Korst, Martin Pera, Ramen Chmait University of Southern California, Obstetrics & Gynecology, Los Angeles, CA, University of Southern California, Eli & Edythe Broad CIRM Center for Regenerative Medicine and Stem Cell Research at USC, Los Angeles, CA, USC Keck School of Medicine, Obstetrics & Gynecology, Los Angeles, CA, University of Melbourne, Florey Neuroscience Institute, and the Walter and Eliza Hall Institute of Medical Research, Melbourne, Australia OBJECTIVE: To evaluate the response to limb pinch in newborn rats with retinoic acid induced myelomeningocele. STUDY DESIGN: Pregnant (Day 10) Sprague-Dawley dams were gavage fed retinoic acid (60 mg/kg), as described by Danzer (Danzer E, et al. Experimental Neurology 2005; 194: 467-475), in order to generate open neural tube defects. Cesarean sections were performed on day 21.5, under isoflurane anesthesia, and forceps were used to lightly pinch a fore limb and a hind limb 3 times each. Withdrawal of the pinched limb each time, and full body squirm were considered positive reactions. To control for anesthesia and death prior to evaluation, only pups exhibiting a positive forelimb response were included in analysis. A 2-tailed Fisher’s exact test was used for analysis of the results. RESULTS: Of 44 rat fetuses exposed to retinoic acid, 40 (91%) developed a myelomeningocele. Ten of these pups were excluded for a negative forelimb pinch response. 26 of the 30 (86.7%) remaining pups with myelomeningoceles vs. 1 of 12 (8.3%) control pups exhibited a negative response to hind limb pinch, yielding an odds ratio of 71.5 (95% CI 6.1-1981.1, p 0.0001). CONCLUSION: Our findings verify the efficacy of the retinoic acid model, and demonstrate that rat pups affected by myelomeningocele were substantially more likely to exhibit a negative pinch response compared with control pups. Observation of the response to limb pinch in this model may be useful for evaluation following attempts at repair or regeneration of damaged neural tissue.

Transcranial focused ultrasound to the thalamus alters anesthesia time in rats

A pulsed application of focused ultrasound (FUS) to the regional brain tissue alters the state of tissue excitability and thus provides the means for noninvasive functional neuromodulation. We report that the application of transcranial FUS to the thalamus of anesthetized rats reduced the time to emergence of voluntary movement from intraperitoneal ketamine/xylazine anesthesia. Low-intensity FUS was applied to the thalamus of anesthetized animals. The times required for the animals to show distinct physiological/behavioral changes were measured and compared with those times required in a control session without sonication. The sonication significantly reduced the time to show pinch response and voluntary movement. The modulatory effects of FUS on anesthesia suggest potential therapeutic applications for disorders of consciousness such as minimally consciousness states.

Analgesic and motor-blocking action of epidurally administered levobupivacaine or bupivacaine in the conscious dog

ObjectiveTo compare the analgesic and motor-blocking effects of epidurally administered levobupivacaine and bupivacaine in the conscious dog. Study designProspective, randomized, cross-over study. AnimalsSix adult female Beagle dogs. MethodsEach animal received three doses of levobupivacaine or bupivacaine (0.5, 1.0 and 1.5 mg kg−1; concentrations 0.25%, 0.50%, and 0.75%, respectively) in a total volume of 0.2 mL kg−1 by means of a chronically implanted epidural catheter. Onset, duration (through pinch response in the sacral, lumbar and toe areas) and degree of analgesia and motor-blocking status was determined with a scoring system and at regular intervals over 8.5 hours before (baseline) and after drug administration. ResultsEpidurally administered levobupivacaine and bupivacaine had a similar dose-dependent analgesic action with no significant differences in onset (range: 5–8 minutes), duration (bupivacaine: 42 ± 28, 135 ± 68 and 265 ± 68 minutes, and levobupivacaine: 28 ± 33, 79 ± 55 and 292 ± 133 minutes; 0.25%, 0.50%, and 0.75%, respectively) or maximum degree of analgesia. However, levobupivacaine tended to produce a shorter duration of motor block than bupivacaine and the difference in the motor to nociceptive blockade times was significant at the highest dose. ConclusionEpidural levobupivacaine produced an analgesic action similar to that of bupivacaine. Clinical relevanceEpidural levobupivacaine is suitable for clinical use in dogs, mostly at the highest dose if a high degree of analgesia is required.

Behavioral depression induced by an amygdala seizure and the opioid fentanyl was mediated through the nucleus accumbens

To study the behavioral depression induced by a generalized limbic seizure and by an opioid. The hypothesis that an opioid fentanyl and an amygdala-evoked seizure induced behavioral depression through the nucleus accumbens was tested. The behavioral depression induced by an amygdala-kindled seizure was studied in fully kindled rats, with or without prior injection of fentanyl (0.05 mg/kg, s.c.). Local infusion of a nonspecific opioid antagonist, naloxone, or saline, was made bilaterally in the nucleus accumbens. The durations of loss of righting reflex (LORR), loss of tail-pinch response, and catalepsy were assessed. Fentanyl induced an LORR following a generalized kindled seizure. The combination of fentanyl and a generalized seizure, as compared to fentanyl alone or a generalized seizure alone, resulted in a prolonged duration of LORR, catalepsy, and loss of tail pinch response. Infusion of naloxone as compared to saline in the nucleus accumbens reduced the duration of catalepsy and LORR induced by fentanyl, with or without a generalized seizure. Postictal depression that follows a generalized kindled seizure enhanced the behavioral effects of the opioid fentanyl. Network synaptic depression induced by the seizure acted synergistically with fentanyl to produce analgesia, catalepsy, and LORR, in part through the nucleus accumbens.

Anaesthesia with ketamine/medetomidine in the rabbit: influence of route of administration and the effect of combination with butorphanol

ObjectiveTo compare the characteristics of anaesthesia induced with ketamine/medetomidine administered by the subcutaneous and intramuscular routes and to assess the effects of the addition of butorphanol to this combination. Study designProspective randomised study. AnimalsSix female New Zealand White rabbits. MethodsRabbits were given one of four combinations of ketamine and medetomidine (K/M) either subcutaneously (SC) or intramuscularly (IM) on four successive occasions with a 7–day interval between treatments. The dose combinations were; 15/0.25 mg kg−1 SC; 15/0.25 mg kg−1 IM; 15/0.5 mg kg−1 SC, and 15/0.25 mg kg−1 together with 0.4 mg kg−1 butorphanol (K/M/B) SC. The effects of anaesthesia on arterial blood gas values and cardiovascular variables were recorded at predetermined time points. Toe and ear pinch reflexes were judged to determine the duration of surgical anaesthesia. Loss of the righting reflex was used to measure the duration of sleep time. Analyses used repeated measures analysis of variance. ResultsAll groups lost the righting reflex and ear pinch response. Three animals in the groups that received K/M alone lost their toe pinch reflex, whereas four lost this reflex when given K/M/B. Time of onset of loss of the righting, toe and ear pinch reflexes did not differ significantly among the groups. The higher dose combination of medetomidine with ketamine and the combination of K/M/B produced a greater duration of loss of the ear pinch response than the lower dose of K/M administered by either route. No significant differences were found among the groups in the duration of loss of the toe pinch reflex. All animals developed a moderate bradycardia (mean heart rate <166 beats minute−1) and moderate hypoxaemia (mean PaO2 < 6.0 kPa). Animals given butorphanol showed the greatest reduction in respiratory rate (31 ± 13 breaths minute−1, p < 0.05) but this was not reflected in any significant differences in arterial PCO2, PO2 or pH among the groups. ConclusionsAdministration of K/M by the SC route produced equivalent effects in comparison to intramuscular administration. The addition of butorphanol increased the duration of anaesthesia, but produced a slight increase in the degree of respiratory depression. All dose rates resulted in hypoxaemia so oxygen should be administered when these combinations are used in rabbits. Clinical relevanceSubcutaneous administration is both technically simpler and may cause less discomfort to the animal than IM injection, and so is preferred. The combination of K/M with butorphanol has relatively minor effects on the depth and duration of anaesthesia, so offers little advantage to the use of K/M alone.

Effects of propofol on hippocampal synaptic transmission in behaving rats.

The action of propofol has been studied in vitro and in vivo, but the effects of intravenously administered propofol on synaptic transmission in freely behaving rats have not been studied before. Rats were implanted with recording electrodes in the dentate gyrus and with stimulation electrodes in the medial perforant path (MPP). Paired pulses at different interpulse intervals (IPIs) were delivered to the MPP, and average evoked potentials were recorded in the dentate gyrus before and after a bolus of propofol (10 or 20 mg/kg administered intravenously) or control vehicle was injected via femoral vein cannula. Because of the layered structure of the hippocampus, population excitatory postsynaptic potentials and population spikes could be distinguished and analyzed. Propofol has no significant effect on the population excitatory postsynaptic potentials or population spike evoked by a single MPP stimulus pulse. However, paired-pulse inhibition of the dentate population spikes was increased at IPI of 20 and 30 ms. Paired-pulse inhibition of the population spike was most prominent when tail pinch response was lost (deep and moderate anesthesia), but it persisted during light anesthesia. At 200 ms IPI, paired-pulse facilitation of population spikes was observed during moderate anesthesia in most rats. In freely behaving rats, intravenous propofol enhanced paired-pulse inhibition at < 50 ms IPI, likely by enhancing gamma-aminobutyric acid A receptor-mediated inhibition. Propofol also increased paired-pulse facilitation at 200 ms IPI through an unknown mechanism, which may contribute to the neuroexcitatory effect of propofol.

C-fos can be induced in the neonatal rat spinal cord by both noxious and innocuous peripheral stimulation

The development of spinal cord nociceptive pathways has been investigated in neonatal rat pups using the expression of Fos immunoreactivity in laminae I and II cells produced by high and low intensity skin stimulation. Noxious pinch of the hindpaw evoked a clear response in the newborn rat pup, which was not significantly different from that seen at postnatal day (P) 21. Low intensity touch stimulation also produced a significant fos response in laminae I and II cells at P3 which was 60% that of the pinch response. This was reduced to 27% of the pinch response by P10 and was gone by P21. Electrical stimulation through percutaneous electrodes showed that Aβ fibre stimulation also produced a fos response at P3 that was not significantly different from that produced by C fibre stimulation. By P21 and P30 the response to C fibre stimulation was much greater and the response to A fibre stimulation was not significantly above background. The results suggest that in the neonatal spinal cord, low threshold A fibres are able to activate pathways in lamina I and II of the dorsal horn that in the adult are predominantly nociceptive.

Role of catecholamines in the frontal cortex in the modulation of basal and stress-induced autonomic output in rats

Exposure of animals to noxious or stressful stimuli increases heart rate (HR) and blood pressure through activation of the autonomic nervous system (ANS) and elicits the release of the catecholamines noradrenaline (NA) and dopamine (DA) in the frontal cortex. Subregions of the frontal cortex, such as the medial frontal cortex (MFC) and agranular insular cortex (AIC) project directly to brainstem nuclei involved in autonomic control. It may be hypothesized that catecholamines in the frontal cortex could influence autonomic output through actions on these descending pathways. To evaluate this hypothesis, the effects of intracortical microinjections of drugs acting at NAergic and DAergic receptors were assessed on an autonomically mediated response, the increase in HR induced by tail pinch, in rats anesthetized with urethane. Intra-MFC or AIC injections of an antagonist of β-adrenoceptors reduced the magnitude of the HR response to pinch. Injections of an agonist of β-adrenoceptors into these regions increased basal HR but did not affect the pinch response. Injections of drugs acting at α-adrenoceptors were without effect. When injected alone, drugs acting at DAergic receptors did not effect basal HR or the response to pinch, but intra-AIC injections of a combination of a D 2 antagonist and an agonist of β-adrenoceptors increased the magnitude of the pinch response. These results suggest that catecholamines, especially NA, released in the frontal cortex are important modulators of the basal and stress-induced output of the ANS.

Intrathecal Somatostatin in Rats

Effects of intrathecal (i.t.) somatostatin (SST) (10, 30, and 100 micrograms) on nociception, and autonomic and motor function were evaluated in rats with chronically implanted lumbar i.t. catheters. Doses of 10 and 30 micrograms SST i.t. had no effect on thermal cutaneous nociception, (hot plate and tail flick response). Thirty micrograms SST i.t. did not effect the visceral chemical evoked nociception (acetic acid writhing test) as compared to saline control groups. Rats treated with 100 micrograms SST i.t. invariably showed temporary or permanent hindlimb motor dysfunction, with flaccid paralysis in the most severe cases (motor function tests, electromyographic response). Blockade of the tail flick and foot pinch response was observed to a variable degree, and only in the presence of detectable motor impairment. Out of 40 animals injected with 100 micrograms SST i.t., 25% died within 10 min following injection. Effects of SST on the volume evoked micturition reflex were assessed in rats with chronically implanted bladder catheters. Three of the nine surviving animals receiving 30 micrograms SST i.t. and all animals receiving an additional dose of 60 micrograms SST i.t. showed a complete block of the micturition reflex and subsequent development of an overflow bladder. Histological examination of spinal cords revealed a mild inflammatory response in four out of five animals treated with 30 micrograms SST i.t. In spinal cords of animals, which had received 100 micrograms SST i.t. (n = 4), mild or severe nucleolysis of ventral and dorsal horns in the presence of inflammatory reaction was observed. Present experiments clearly demonstrate highly toxic effects of SST in rats with no margin of safety between antinociception and motor dysfunction.

Pharmacological activity of the basic fraction of marihuana whole smoke condensate alone and in combination with delta-9-tetrahydrocannabinol in mice

The basic fraction (BF) of marihuana whole smoke condensate was subjected to pharmacological testing in male, Swiss-Webster mice. In a general pharmacological activity screen looking at behavioral, neurologic, and autonomic parameters, BF, at iv doses of 5, 10, and 20 mg/kg, caused impairment of visual placing, increase in tail pinch response, decrease in tail elevation, and induction of piloerection. These effects, although statistically significant, were slight and not consistently dose dependent. In a second study with doses ranging from 10 to 29 mg/kg, BF caused a decrease in spatial locomotion, rearing behavior, and urination incidence. In a third study, body temperatures of mice were measured periodically for 2 hr following administration of BF (1.2, 2.4, and 4.8 mg/kg) alone or in combination with 1.0 mg/kg delta-9-tetrahydrocannabinol (THC). BF did not alter body temperature, nor did it affect THC-induced hypothermia. These results, although suggesting that the basic fraction of marihuana whole smoke condensate has pharmacological activity in mice, offers little evidence for the presence of highly active compounds.

Systematic examination in the rat of brain sites sensitive to the direct application of morphine: Observation of differential effects within the periaqueductal gray

An extensive mapping of the rat brain (403 sites) ranging from AP +8 to AP −3 revealed that the region showing maximum sensitivity to the intracerebral administration of morphine in the elevation of the nociceptive threshold lay within the periaqueductal gray. Analysis of the distribution of responsive sites indicated that the most active sites, those having the shortest latency of effect, were located within the ventrolateral aspect of the caudal periaqueductal gray. These antinociceptive actions of morphine were observed to be both dose-dependent and reversible by the administration of naloxone. We observed that microinjections of morphine could produce changes in the pinch withdrawal response which were distributed in a crude somatotopic fashion. Injections into the rostral aspect of the periaqueductal gray yielded a block of the pinch response in the rostral portions of the body, whereas such injections into the caudal periaqueductal gray always yielded a whole body analgesia. In the rostral sites, transient ipsilateral blocks of the pinch response were occasionally seen. A pinch block limited to the hind paws alone was never observed. It is suggested that morphine acting through the periaqueductal gray may actuate a potent supraspinal modulatory system related to the transmission of information derived from behaviorally aversive stimuli.