Effects Of Procaine Research Articles

Effects of intrathecal morphine and spinal anaesthesia on sympathetic nerve activity in humans

Microneurography with direct registration of efferent sympathetic nerve activity to muscle or skin was used to study the effect of morphine and procaine given intrathecally to patients scheduled for transurethral resection of the prostate. A lumbar spinal catheter was inserted and multiunit postganglionic sympathetic activity was recorded in a muscle or skin fascicle of the peroneal nerve. After injection of 0.4 mg morphine, sympathetic nerve activity to muscle (n = 6) or skin (n = 2) was recorded for 30 min. Compared with a 10-min control period prior to the injection no change in activity could be observed. In contrast, spinal anaesthesia (procaine 75-100 mg) with an upper level of sensory blockade at T3-T11 completely eliminated intraneurally recorded sympathetic activity within 5 min (n = 8). Skin vasodilation and loss of sudomotor responses in the foot accompanied the neural blockade.

An epifluorescent microscopy study of the effects of procaine on model membrane systems

An epifluorescent microscopy study of the effects of procaine on model membrane systems

Detecting localized proton currents in photophosphorylation by procaine inhibition of the transthylakoid pH-gradient

The relationship between the transthylakoid pH-gradient, ΔpH, and the velocity of photophosphorylation, V p, in thylakoid membranes from spinach was investigated using the local anesthetic amine procaine as inhibitor of ΔpH. When ΔpH was driven by Photosystem (PS) II + I-dependent electron flow, passing through the cytochrome b 6 f complex, inhibition by procaine was accompanied by an increase of ATP formation. It appeared that procaine allowed for values of V p similar to those in controls (without procaine) at a significantly lower ΔpH than in the controls. In contrast, when ΔpH was driven by cyclic electron flow around PS I or by PS-II + I-dependent electron flow via a bypass around the cytochrome b 6 f complex, or by PS II alone, procaine simultaneously caused an inhibition of ΔpH and a decrease of ATP formation. Inhibition of ΔpH by procaine did not induce an electrical membrane potential gradient that otherwise may have energetically compensated for the observed decline of ΔpH. The electron flow capacity was unaffected by procaine. However, inhibition of ΔpH did not significantly relax pH-dependent control of electron flux. Procaine accelerated ATP hydrolysis by pre-activated thylakoid ATPase to rates which were observed in the presence of uncouplers and had no direct effect on the activation state of the ATPase. The shift in the relationship between ΔpH and V p towards lower ΔpH persisted in thermodynamic equilibrium between the phosphorylation potential and ΔpH. The data indicated that the unconventional effect of procaine on photophosphorylation may be related to effects on proton translocation at the cytochrome b 6 f complex and that a localized protonic coupling may occur between cytochrome b 6 f and thylakoid-ATP-synthase complexes.

Kinetics of Ca2+ release and contraction induced by photolysis of caged D-myo-inositol 1,4,5-trisphosphate in smooth muscle. The effects of heparin, procaine, and adenine nucleotides.

The kinetics of Ca2+ release and contraction induced by photolytic release of inositol 1,4,5-trisphosphate (InsP3) were determined in permeabilized smooth muscle. The rate of Ca2+ release was half-maximal at 1 microM InsP3. The concentration-dependent delay of Ca2+ release at saturating InsP3 concentration was approximately 10 ms and within the uncertainty of the measurements. The relationship between the delay and InsP3 concentration showed no evidence of a high level (n = 4 or higher) of cooperativity but could not distinguish between no cooperativity (n = 1) or a low level (n = 2) of cooperativity. Submaximal [InsP3] caused only partial Ca2+ release from the InsP3-sensitive stores. InsP3-induced Ca2+ release was markedly potentiated by ATP or by adenosine 5'-(beta,gamma-methylene-triphosphate), but neither the rate nor the amplitude of release was significantly affected by procaine (2-5 mM). Heparin increased the delay between photolysis and Ca2+ release, indicating that the off rate of inert ligand(s) bound to InsP3 receptors may contribute to the physiological delay in Ca2+ release. There was a much longer (370 ms +/- 45 S.E.) delay between the rise of Ca2+ and force development, presumably reflecting events preceding and associated with myosin light chain phosphorylation.

A patch-clamp study of the Ca2+ mobilization from internal stores in bovine aortic endothelial cells. I. Effects of caffeine on intracellular Ca2+ stores.

The effects of agents known to interfere with Ca2+ release processes of endoplasmic reticulum were investigated in bradykinin (BK)-stimulated bovine aortic endothelial cells (BAE cells), via the activation of Ca(2+)-activated potassium channels [K(Ca2+) channels]. In cell-attached patch experiments, the external application of caffeine (1 mM) caused a brief activation of K(Ca2+) channels in Ca(2+)-free and Ca(2+)-containing external solutions. The application of BK (10 nM) during cell stimulation by caffeine (1-20 mM) invariably led to a drastic channel activation which was maintained during a recording period longer than that observed in caffeine-free conditions. In addition, the cell exposure to caffeine (20 mM) during the BK stimulation enhanced systematically the channel activation process. Since a rapid inhibition of BK-evoked channel activity was also produced by removing caffeine from the bath medium, it is proposed that the sustained single-channel response recorded in the concomitant presence of both agents was due to their synergic action on internal stores and/or the external Ca2+ entry pathway resulting in an increased [Ca2+]i. In addition, the local anesthetic, procaine, depressed the initial BK-induced K(Ca2+) channel activity and completely blocked the secondary phase of the channel activation process related to the external Ca2+ influx into stimulated cells. In contrast, this blocking effect of procaine was not observed on the initial caffeine-elicited channel activity and could not suppress the external Ca(2+)-dependent phase of this channel activation process. Our results confirm the existence of at least two pharmacologically distinct types of Ca(2+)-release from internal stores in BAE cells: an inositol 1,4,5-triphosphate (InsP3)-dependent and a caffeine-induced Ca(2+)-release process.

Effects of procaine and caffeine on calcium release from the sarcoplasmic reticulum in frog skeletal muscle.

1. Resting myoplasmic free [Ca2+] and [Ca2+] transients (delta [Ca2+]) were measured in single voltage-clamped frog skeletal muscle fibres in the presence and absence of procaine, caffeine or procaine plus caffeine using Fura-2 fluorescence and antipyrylazo III (Ap III) absorbance signals. The rate of release (Rrel) of calcium from the sarcoplasmic reticulum (SR) was calculated from the calcium transients and corrected for the relatively small decline due to depletion of calcium from the SR. 2. Procaine (1 mM) reversibly suppressed delta [Ca2+] and the corresponding Rrel by about 40% for 60-100 ms depolarizing steps to -40 to +20 mV. Procaine had little effect on either the waveform or voltage dependence of the Rrel records. 3. [Ca2+] transients calculated from Fura-2 fluorescence changes in the presence or absence of procaine had similar time courses and amplitudes as those calculated from the Ap III absorbance changes suggesting that 1 mM-procaine did not interfere with the ability of Ap III or Fura-2 to monitor delta [Ca2+]. 4. Although 1 mM-procaine depressed Rrel it had no effect on intramembrane charge movements (IQ) calculated from membrane currents recorded simultaneously with delta [Ca2+]. 5. Procaine (1 mM) reversibly inhibited the potentiating effect of 0.5 mM-caffeine on delta [Ca2+]. The amplitude and waveform of the Rrel records were similar in control fibres and in the presence of 1 mM-procaine plus 0.5 mM-caffeine. 6. In the presence of 0.5 mM-caffeine delta [Ca2+] after 10-20 ms voltage steps exhibited an increase in the time to peak and a slower decay time course compared with caffeine-free controls, suggestive of significant calcium-induced calcium release in the presence of caffeine. These effects of caffeine were completely and reversibly blocked by 1 mM-procaine. 7. In the absence of caffeine, 1 mM-procaine caused a small decrease in time to peak of delta [Ca2+] after 10-30 ms duration voltage steps compared to the bracketing control and wash runs without procaine. Rrel turned off faster after 10 ms pulses in procaine than in the absence of procaine, but the turn-off of release was about equally fast with or without procaine after pulses of 20 ms or longer. The effect of procaine after 10 ms pulses in the absence of caffeine may indicate suppression of a component of calcium-induced calcium release in control that inactivates during the pulse.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of local anesthetics on the Chara plasmalemma

The effects of lidocaine, tetracaine, procaine and bupivacaine (< 1000 μM) on the Chara corallina internodal cell were studied. These local anesthetic depolarized the membrane at rest, while they affected the rising phase and the peak level of action potential not appreciably. Instead, they prolonged the time course of the falling phase of action potential as slowly as the repolarization was imperfect, even after enough lapse beyond the refractory period. Consequently, an action potential appeared to enhance the degree of depolarization at rest. Such a depolarization with stimulus/excitation was named use-dependent depolarization, while the depolarization without excitation, the resting one. The order of the potency of the use-dependent depolarization almost coincided with that of the nerve-blocking potency. During depolarization the change in membrane conductance was not simple. However, the conductance-voltage ( G m− V m) relationship curve in the presence of local anesthetic suggested that depolarization was due to, not only the decrease in the electrogenic H +-pump, but also the increase in the diffusion conductance.

Protection effects of procaine on oxidative stress and toxicities of renal cortical slices from rats caused by cisplatin in vitro.

Incubation of rat renal cortical slices with 2 mM cisplatin (CDDP) at 37 degrees C for different periods of time (15-180 min) increased malondialdehyde (MDA) formation, decreased intracellular glutathione (GSH), and inhibited gluconeogenesis in the slices. CDDP-induced MDA formation increased by 53% after 180 min of incubation and GSH decreased by 35% after 60 min of incubation. Both depletion of GSH and inhibition of gluconeogenesis preceded MDA formation. Procaine (2 mM) completely inhibited CDDP-induced lipid peroxidation without affecting depletion of GSH, but even potentiated gluconeogenesis inhibition, while 2 mM dithiothreitol (DTT) largely reversed all of these biochemical indices. After 240 min of incubation, 2 mM CDDP produced marked cytotoxicities, characterized by an increase in leakage of alkaline phosphatase (ALP) (132%), lactate dehydrogenase (LDH) (115%) and N-acetyl-beta-glucosaminidase (NAG) (157%), decrease in intracellular K+ (64%), and change in total water contents in the slices. Procaine (2 mM) showed protection against CDDP-induced cytotoxicities to a certain extent. These results suggest that depletion of GSH might be a determinant step in the oxidative stress and subsequent cytotoxicity, and that procaine is a powerful antioxidant and would be a promising drug for ameliorating some of the adverse effects of CDDP.

Minimal model analyzing response of glycine receptors expressed in Xenopus oocyte: inhibition by a lipid hydroperoxide.

Glycine receptor (GlyR) was expressed in Xenopus oocytes by injecting rat brain mRNA. Glycine (Gly)-elicited responses in the oocyte were measured by the voltage-clamping method. The following measurements were made to establish the relationship between Gly concentration and the current: 1) Gly-induced membrane current before desensitization, 2) Gly-induced membrane current after desensitization equilibrium, 3) fraction of the active form of the receptor after desensitization equilibrium, 4) rate of recovery of the desensitized receptors upon removal of Gly. These results were analyzed on the basis of the minimal model proposed for nicotinic acetylcholine and gamma-aminobutyric acid A receptor. The equilibrium and rate constants of the model were evaluated for GlyR. The effects of procaine and 13-L-hydroperoxylinoleic acid (LOOH) on GlyR were examined electrophysiologically. LOOH noncompetitively inhibited the receptor with the inhibition constant of 27 microM, while 1 mM procaine, a local anesthetic, did not inhibit GlyR at all.

Ruthenium red selectively prevents Ins(1,4,5)P3-but not caffeine-gated calcium release in avian atrium.

We previously reported that inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] and caffeine evoked contractures in saponin-permeabilized chick atria. The magnitude of contractures evoked by maximally effective concentrations of Ins(1,4,5)P3 were half those evoked by maximally effective concentrations of caffeine. In the present report, we tested the hypothesis that these two agents may act on distinct calcium-release mechanisms by comparing the effects of ryanodine, ruthenium red, and procaine on the responses to Ins(1,4,5)P3 and caffeine. We find that procaine inhibits both responses with similar mean inhibitory concentrations in the millimolar range. Nanomolar concentrations of ryanodine selectively potentiate the contractures induced by Ins(1,4,5)P3 but have no effect on those induced by caffeine. Micromolar concentrations of ryanodine inhibit responses to both Ins(1,4,5)P3 and caffeine in a use-dependent way. Ruthenium red prevents the response to Ins(1,4,5)P3 and potentiates that to caffeine, as if ruthenium red had enhanced calcium accumulation in the caffeine-sensitive pool(s). Because we found that caffeine prevented the subsequent response to Ins(1,4,5)P3, but Ins(1,4,5)P3 had no detectable effect on the caffeine-induced contracture, we conclude that Ins(1,4,5)P3 and caffeine act on pharmacologically distinct calcium-release mechanisms that may reside in the same sarcoplasmic reticulum compartment.

Variation in heat sensitivity through the cell cycle of M10 and Burkitt P3HR-1 cells.

The cell-cycle age response to 44 or 45 degrees C hyperthermic treatment was studied in M10, a mutant of mouse L5178Y cells, and human Burkitt P3HR-1 cells synchronized by centrifugal elutriation. Survival response to 44 degrees C hyperthermia or radiation showed that Burkitt cells were relatively hyperthermic resistant and average in radiosensitivity, while M10 cells were relatively hyperthermic sensitive and substantially radiosensitive. A typical age-response to hyperthermia through the cell-cycle was observed in M10 cells, although no significant variation in the response to hyperthermia was demonstrated in Burkitt P3HR-1 cells. Combined effect of procaine with 44 degrees C 20-min treatment for Burkitt P3HR-1 cells showed a substantial enhancement of cytotoxicity in S phase cells. The probable implication of membrane composition, membrane changes due to heat and its modifying agents are discussed. Furthermore, when hyperthermia was combined with radiation in Burkitt P3HR-1 cells, cytotoxic enhancement was observed in G1/S boundary phase, not in S phase.

Experimental nerve ischemia and injury produced by cocaine and procaine

The effects of ethanol, glycerol, procaine, and cocaine were tested on rat sciatic nerve blood flow. Blood flow measurements were made using a laser Doppler blood perfusion monitor with a 1 mm diameter probe. The local anesthetics procaine and cocaine produced a dose-dependent and time-dependent decrease in nerve blood flow, but 80% ethanol, 80% glycerol, and 0.9% saline did not significantly alter nerve blood flow either acutely (10 min) or for up to 4 h. For histopathologic studies, the same nerves were removed at 2 days after blood flow tests. Evidence of nerve injury (edema and nerve fiber pathology) was observed for the neurolytic agents ethanol and glycerol and for both local anesthetics. No relationship between nerve blood flow and injury was seen for either ethanol or glycerol; however, both local anesthetics exhibited a highly significant negative correlation ( P < 0.01) between blood flow at 4 h and injury at 2 days. These data provide additional evidence that local anesthetics can decrease nerve blood flow; and these results are consistent with an ischemic mechanism for local anesthetic-induced nerve injury.

Effects of Procaine on the Intracellular pH of Chinese Hamster Ovary Cells Heated at 42.0 or 45.0°C

The local anesthetic procaine greatly sensitizes cells to hyperthermia. Though it is generally accepted that procaine is a membrane-active agent that increases membrane fluidity in cells, the mechanism by which it potentiates heat killing is unknown. In this paper we report changes in intracellular pH (pHi) of Chinese hamster ovary (CHO) cells heated at 42.0 or 45.0 degrees C in the presence of procaine. The pHi was measured with flow cytometry using the dye 1,4-diacetoxy-2,3-dicyanobenzene (ADB). Studies were carried out using cells grown at normal pH (7.3) or cells placed in low-pH (6.6) medium 4 h prior to and during heating (acute low-pH treatment). Low-pH-adapted cells (PHV2), which were obtained previously by continuous culture in pH 6.6 medium, were also used. Normal cells heated in the presence of procaine at pH 7.3 underwent a large decrease in pHi compared to cells heated without procaine. Procaine had little additional effect on the intracellular pH of cells in medium with a pH of 6.6 for 4 h before and during 30 min of heating. PHV2 cells exposed to chronic low-pH conditions were resistant to acidification when heated with or without procaine. The surviving fraction of cells heated with procaine was significantly lower under all pH conditions than that of cells heated without procaine. Cells heated at 42.0 degrees C with procaine also became greatly acidified and their survival was reduced. These data suggest that the reduction in pHi caused by procaine may be part of the mechanism of heat sensitization, but cannot account for it entirely. Furthermore, the degree of procaine sensitization and intracellular acidification is dependent on the extracellular pH, with a larger effect occurring at pH 7.3 than at pH 6.6.

Genetic Determinants of Suceptability to the Rewarding and Other Behavioral Actions of Cocaine

The role of genotype as a determinant of biologically based inter-individual differences in vulnerability to substance abuse has received little systematic investigation except in the case of alcohol. This report describes the use of an animal model, the inbred mouse, to identify and to characterize variants with inherently altered susceptibilities to the rewarding and other behavioral actions of cocaine. Among a battery of nine inbred strains chosen solely for their genetic diversity, genetic polymorphisms commonly occurred which altered the potency and/or efficacy of cocaine to induce conditioned place preference, oral self-administration, motor activity activation, seizures and lethality. These changes in cocaine sensitivity generally were of a behavior-specific and pharmacodynamic nature. One strain, DBA/2J, found to be markedly hyporesponsive to the rewarding action of cocaine, also was hyporesponsive to the rewarding effects of amphetamine, etonitazene, phencyclidine, caffeine and procaine. We speculate that this strain has an inherent generalized appetitive defect. The frequent occurrence and large magnitude of inherent phenotypic changes in cocaine responsiveness which we have identified among inbred mouse strains now permits an analytical genetic study of processes underlying cocaine-mediated reinforcement.

Inhibitory effects of local anesthetics on migration, extracellular release of lysosomal enzyme, and superoxide anion production in human polymorphonuclear leukocytes.

This study examined the effects of four typical local anesthetics, lidocaine, prilocaine, procaine and tetracaine, on the functioning of human polymorphonuclear leukocytes (PMN). PMN were stimulated by fMet-Leu-Phe (FMLP) or phorbol myristate acetate (PMA) to elicit chemotaxis, extracellular release of beta-glucuronidase (BGL) and superoxide anion (SOA) production. The four agents inhibited chemotaxis efficiently and in a concentration-dependent manner but had only weak effects on the release of BGL. The effect of tetracaine was strongest, followed by lidocaine, then prilocaine, whereas the effect of procaine was blunt. The 50% inhibitory concentrations (IC50 in molarity) of the four local anesthetics for chemotaxis were as follows: tetracaine = 4.1 x 10(-4), lidocaine = 3.2 x 10(-3), prilocaine = 3.6 x 10(-3), procaine = 4.9 x 10(-3), those for SOA production induced by FMLP were: tetracaine = 3.1 x 10(-4), lidocaine = 5.9 x 10(-3), prilocaine = 1.9 x 10(-2), procaine = 1.2 x 10(-2), those for SOA production induced by PMA were: tetracaine = 1.1 x 10(-3), lidocaine = 1.2 x 10(-2), prilocaine = 1.5 x 10(-2), procaine = 2.5 x 10(-2), and those for release of BGL were: tetracaine = 1.6 x 10(-3), lidocaine = 5.3 x 10(-3), prilocaine = 2.8 x 10(-2), procaine = 1.2 x 10(-1). The IC50 seemed to relate to the anesthetic's chemical structures and their inhibitory properties on PMN functions, as lidocaine and prilocaine, which are aminoamide type anesthetics, preferentially inhibited chemotaxis, whereas tetracaine and procaine, aminoester type anesthetics, inhibited SOA production induced by FMLP. The results suggest that the inhibitory effects of local anesthetics on human PMN functions are also correlated with local anesthetic potency and vary according to differences in their chemical structures.

Evaluation of the stimulatory capacity of procaine on Na transport through frog skin

Procaine has different effects on various ionic conductive pathways through the frog skin. We investigated the season and temperature dependence of the stimulation by mucosal procaine, of the Na-conductive pathway. For this stimulation, we found higher half-maximal saturation constants (KNa) in winter animals (6.38 +/- 0.8 mmol/l), than in summer ones (4.03 +/- 0.7 mmol/l). Summer frogs kept for 2 weeks at 4 degrees C, reacted like winter frogs (6.24 +/- 0.8 mmol/l). However, the maximal sodium currents (INa max) did not depend on temperature adaptation. Procaine-induced increased of KNa is associated with an increase of INa. The effects of procaine associated with BIG (benzoylimidazole-2-guanidine) were non-additive, while with vasopressin they were additive. A biphasic, dose-dependent response was recorded after procaine application to the inner surface. Vasopressin counteracted the serosal procaine-induced inhibition of the Na-transport.

Vegetalization Induced by Procaine and Tetracaine in Sea Urchin Embryos: (sea urchin/development/vegetalization/procaine/tetracaine).

Vegetalization of sea urchin embryos was induced by the treatment with procaine and tetracaine, inhibitors of Ca2+ mobilization, for 3 hr starting 3-5 hr after insemination at 20°C. The treatment starting 7 hr after insemination sometimes produced similar type of vegetalized embryos. The pulse treatment starting at the other stages hardly yielded vegetalized embryos. The stages at which these compounds were effective to produce vegetalized embryos were almost the same to those for Li+ to make embryos vegetalized. On the basis of known inhibitory effects of tetracaine, procaine and Li+ on Ca2+ mobilization, we postulate that Ca2+ dependent reactions participate in the process of cell determination at these stages. Inhibitory effects of procaine, tetracaine and Li+ on Ca2+ dependent induction of fertilization membrane formation, found in the present study, indicate that these compounds block Ca2+ mobilization in sea urchin eggs.

Potentiation of the halothane-cooling contractures of mammalian muscles by denervation

Denervation potentiated the cooling-induced contractures and the halothane-cooling contractures of isolated extensor digitorum longus and soleus muscles of the mouse. These effects were more striking in extensor digitorum longus than in soleus muscles. Significant increases in the peak amplitudes of the halothane-cooling contractures of both muscles and of the cooling contractures of soleus muscle were observed within 2 and 7 days of denervation. The potentiation of the contractures persisted for 90 days, the period of this study. Denervation (greater than 2 days) endowed extensor digitorum longus with the ability to generate cooling contractures in the absence of halothane. The rate of tension development of cooling-induced contractures in the absence or presence of halothane was significantly greater in denervated (2-90 days) than in innervated muscles. Denervation also reduced the effectiveness of procaine in inhibiting the halothane-cooling contractures. It is proposed that the potentiation of cooling-induced contractures in denervated muscles results primarily from an increase in the rate of efflux and in the quantity of Ca2+ released from the sarcoplasmic reticulum, upon cooling and (or) when challenged with halothane.

A comparative study of the effects of procaine, lidocaine, tetracaine and dibucaine on the functions and ultrastructure of isolated rat liver mitochondria

The effects of procaine, lidocaine, tetracaine and dibucaine (10 −5–10 −2 M) were tested on isolated rat liver mitochondria by measurements of the respiratory rates and of the membrane potential and by electron microscopy. A general concentration-dependent stimulation of the basal state (respiration before ADP addition) was observed for all local anesthetics studied. Up to the concentration of 10 −3 M, the order of stimulation was: procaine < lidocaine < dibucaine < tetracaine. However, with the exception of dibucaine, which inhibited state-3 respiration (ADP present) in a strictly concentration-dependent manner, the other drugs had a biphasic effect: slight stimulation of state 3 at low and moderate concentrations (⩽ 10 −3 M) and inhibition at higher concentrations. Nevertheless, due to a stronger stimulation of the basal state, the acceptor control ratio decreases progressively (uncoupling effect) as the concentration of the drugs increases. The only exception to this observation is procaine in the range of 10 −5–10 −4 M, where the stimulation of the two respiration states (although small) is approximately equal and thus the uncoupling effect is absent or negligible. Membrane ptoential recordings suggested that membrane integrity and phosphorylation capacity were negatively affected at high drug concentrations (> 10 −3 M), especially in the case of tetracaine and dibucaine, when 5 · 10 −3 M even produced the collapse of the membrane potential and complete loss of the phosphorylation ability. Electron microscopy confirmed these effects, showing an abundance of either swollen or supercondensed mitochondria, with many membrane ruptures. The action mechanisms of the tertiary amines studied are discussed in terms of interaction of drug with the lipid bilayer and with the membrane proteins. It is concluded that both the inhibitory and the uncoupling effects are dependent, in the first place, on the degree of hydrophobicity of each local anesthetic.

Differential effects of atropine, procaine and dopamine in the rat ventral tegmentum on lateral hypothalamic rewarding brain stimulation

Microinjections of the muscarinic antagonist, atropine, of dopamine, or of the local anesthetic, procaine, in the ventral tegmentum elevated frequency thresholds for lateral hypothalamic self-stimulation. The largest and most robust effects were observed following atropine (30 or 60 μg) microinjections. The most sensitive sites for the atropine effect were near dopamine cells. In order to determine if the effects of atropine can be reversed by pretreatment with a cholinergic agonist, carbachol (1–3 μg) was microinjected 15 min prior to atropine. Carbachol pretreatment attenuated the frequency threshold elevation of atropine by 47–95%. Since atropine is a local anesthetic, the effects of procaine on self-stimulation thresholds were tested as well. Procaine (100 or 250 μg) in ventral tegmentum elevated frequency thresholds by much less than atropine. Therefore, while atropine attenuates reward primarily through blockade of muscarinic receptors, the local anesthetic effect of atropine may enhance the threshold elevation. Dopamine (1–10 μg) also elevated frequency thresholds, but when dopamine injections were repeated daily, the threshold elevations were attenuated. This attenuation contrasted with the robust effects of atropine, and may reflect the development of autoreceptor subsensitivity. Hence, both dopaminergic and muscarinic receptors in ventral tegmentum are involved in lateral hypothalamic brain stimulation reward.