Basic science and clinical aspects of procaine HCl as a limbic system excitant

Modelling Anxiety Disorders Following Chemical Exposures

The effects of kindling and inverse benzodiazepine receptor agonist -carbolines on animal models of anxiety are briefly reviewed in relation to affective disorder associated with chemical exposure. Recent experimental results are described. In the present study, cats were given the inverse benzodiazepine receptor agonist, FG-7142, a powerful anxiogenic compound in humans and animals. Neural transmission in pathways involved in defensive behavior in the cat was monitored using evoked potential techniques. Change in these pathways was related to behavioral changes induced by the drug. It was found that a single dose offG-7142 lastingly increased defensive response to rodents for at least 40 days after drug administration. Behavioral change was specific to defensive response, since approach-attack behavior remained unchanged, replicating previous studies. The benzodiazepine receptor antagonist, Flumazenil, reversed the increase in defensiveness in a drug-dependent manner, replicating previous findings. Increased defensiveness was paralleled by a delayed onset potentiation of neural transmission between the amygdala and the medial hypothalamus of the left hemisphere. Potentiation in the left hemisphere was transient, decaying between 6 and 12 days after the drug. There was a longer lasting potentiation (LTP) of activity evoked in the left and right amygdalo-periacqueductal gray pathways and in the right amygdalo-medial hypothalamic pathway. Potentiation in these pathways appeared at the time of behavioral change. Potentiation of the right amygdalo-periacqueductal gray and right amygdalo-medial hypothalamic pathways persisted until the end of the experiment. In contrast, potentiation of the left amygdalo-periacqueductal gray pathway faded by 40 days after the drug. Flumazenil decreased potentiation only in the right amygdalo-periacqueductal gray pathway. These data strongly suggest that lasting affective change is mediated by lasting changes in particular efferents of the amygdala of the right hemisphere. Behavioral and physiological effects offG-7142 were blocked by the N-methyl-D-Aspartate (NMDA) receptor blocker, AP7. The data suggest that failure of neural inhibition induced by FG-7142 engages NMDA receptor processes to produce lasting potentiation of transmission in neural circuits that mediate defensive response with behavioral consequences. Since FG-7142 interferes with GABA mediated neural inhibition and is proconvulsant, its action might mimic the action of other environmental chemicals with similar properties, such as chlorinated hydrocarbon insecticides. The relationship of the present data to the literature on the neural and behavioral effects of insecticide exposure is discussed. The significance of these findings for multiple chemical sensitivity disorder is also briefly discussed.

Gender differences in limbic responsiveness, by SPECT, following a pharmacologic challenge in healthy subjects

Limbic system functioning is integral to the control and modulation of affect, motivation, reward, and memory. Neuropsychiatric disturbances involving disruptions in these cognitive and emotional dimensions exhibit different prevalence rates for men and women. Gender-specific differences in this integrated brain area may therefore be important in understanding both normal behavioral functioning and the etiologic underpinnings of neuropsychiatric disorders. To further explore such differences in limbic system function, we assessed regional cerebral blood flow, by SPECT, in men and women following the administration of procaine. Procaine is a local anesthetic that preferentially stimulates limbic structures. Psychiatrically and medically healthy, age-matched women (n = 15, 33.2 +/- 6.9 years) and men (n = 15, 32.8 +/- 6.9 years) were administered 1.38 mg/kg procaine or saline intravenously in two separate sessions. Using voxel-based analyses (P < 0.001), males significantly activated the bilateral insular cortex following procaine, whereas females more strongly activated the bilateral anterior and mesial temporal cortex. Both groups demonstrated significant anterior cingulate activation. Subjective responses to procaine did not significantly differ between the men and women. To our knowledge, this is the first report demonstrating gender-specific responses in limbic activation following a pharmacologic challenge. These findings suggest that men and women can activate different limbic structures following the same provocative pharmacologic stimulus, despite sharing a similar subjective experience. Studies assessing pharmacologic challenges of limbic system structures should consider gender as a critical variable in assessing biologic responsiveness.

Dose-response measures of rCBF and subjective changes following procaine in healthy female volunteers

The intravenous administration of procaine shows relatively specific activation of limbic structures. Several investigators have utilized this property of procaine to probe limbic system dysfunction in neuropsychiatric disorders. The dose of procaine utilized in human studies varies significantly, however, and the optimal dose of procaine as a limbic probe has not been demonstrated. In two 10-individual groups of healthy female volunteers, we assessed the regional cerebral blood flow (rCBF) response, by single-photon emission computed tomography (SPECT), to saline and 1.38 mg/kg procaine (Group I), and saline, 0.5 mg/kg and 1.0 mg/kg procaine (Group II). Compared to saline, 0.5 mg/kg procaine produced minimal rCBF changes, 1.0 mg/kg procaine induced both limbic and non-limbic activation, and 1.38 mg/kg procaine showed relatively specific rCBF limbic activation. Subjective responses increased in a dose-response manner. We conclude that a dose of 1.38 mg/kg procaine provides a more limited and specific activation of limbic structures than 1.00 mg/kg procaine and thus may be more useful as a specific probe of limbic function.

Kainic acid induces distinct types of epileptiform discharge with differential involvement of hippocampus and neocortex

Systemic administration of kainic acid (KA), an excitatory amino acid agonist, provides a model of epilepsy due to increased neural excitation. We examined discharges using multi-channel EEG recording and spectral analysis in rats implanted with neocortical and hippocampal electrodes after intravenous infusion of KA (10 mg/kg), until and including the first convulsive seizure. Gamma activity (30-80 Hz) increased in hippocampus from 3-9 min after KA administration. Two types of preconvulsive bilateral rhythmic discharges were observed, both consisting of generalised high voltage sharp waves at low frequencies (<10 Hz) mixed with fast oscillations (<20 Hz): (1) generalised non-convulsive discharges (GNCD) occurred in all animals and (2) spike-wave discharges (SW), predominantly localised in neocortex, occurred in 45% of animals. Convulsive seizure evolved out of a GNCD. Spectral profiles of epileptiform discharges were characterised by an increase in power of low (<10 Hz) and high (beta and gamma range, 20-80 Hz) frequencies which were differently expressed in neocortex and hippocampus. Thus, in this model of convulsive epilepsy caused by increased excitation, there is an early increase in gamma activity, a process that might contribute to synchronisation, and two distinct types of bilateral discharges, hippocampal-neocortical (GNCD) and preferentially neocortical (SW). Neocortical, not hippocampal, changes in EEG power correlated with development of convulsive behaviours.

Psychopharmacologic violence associated with cocaine abuse: kindling of a limbic dyscontrol syndrome?

1. An association of cocaine abuse with aggressive or violent behavior arising from direct pharmacologic effects of cocaine is demonstrable in the forensic and clinical literature. 2. The neurobehavioral basis for this association is considered form among known CNS actions of cocaine. A hypothesis is developed concerning the role of pharmacological kindling by cocaine that may sensitize for release of limbic-hypothalamic mechanisms of aggressive behavior, and for a drug-induced dyscontrol syndrome. 3. Parallels are drawn to kindling by electrical stimuli, and to neurophysiological research on mechanisms of aggression. 4. A role of concurrent hyperthermic effects of cocaine is suggested. 5. Potential contributions of cocaine actions on CNS serotonergic, catecholaminergic and/or adenosinergic systems are considered. 6. A likely role of concurrent ethanol ingestion to enhance the manifestation of cocaine-associated violence is recognized. 7. Pharmacological challenges, lidocaine or caffeine, are suggested as a means of detecting lowered thresholds of limbic excitability as a consequence of repeated cocaine exposures.

Procaine-induced increases in limbic rCBF correlate positively with increases in occipital and temporal EEG fast activity

Previous independent EEG and PET studies suggest that administration of intravenous procaine hydrochloride selectively activates limbic brain structures. To further elucidate procaine's effects and explore the relationship between quantitative EEG (qEEG) and regional cerebral blood flow (rCBF), we simultaneously recorded qEEG and sampled rCBF using O-15 water PET in 20 healthy volunteers during single-blind injections of saline (baseline condition) followed by intravenous procaine (1.84 mg/kg). After thorough screening of EEG records, a subgroup of 7 subjects with EEG data relatively free of both muscle and movement artifacts was selected for analysis. Quantitative spectral EEG data from right occipital and temporal leads were then correlated with each subject's PET rCBF values on a pixel by pixel basis, both at baseline and after procaine. The most striking finding was that the increases in occipital and temporal omega activity from baseline to procaine positively correlated with rCBF increases in the amygdala and its efferents (p < .05), in a pattern very similar to the rCBF increases seen after procaine administration. This suggests that omega activity may reflect activation of deeper brain limbic structures. Also, the convergence of EEG and PET data further supports procaine's selective limbic activation.

The role of procaine in adverse reactions to procaine penicillin in horses

Procaine penicillin is a commonly used antibiotic in equine medicine but its use is associated with a substantial incidence of adverse reactions. Soluble procaine concentrations were determined by HPLC in several commercially available procaine penicillin preparations, including some that were involved in adverse reactions. The mean (+/- SEM) soluble procaine concentrations in the veterinary preparations was 20.18 +/- 5.07 mg/ml, which was higher than the concentration in the only procaine penicillin preparation for use in humans in Australia of 7.3 mg/ml. Heating the veterinary procaine penicillin preparations to 50 degrees C for 1 day led to a significant (P less than 0.01) increase in the amount of soluble procaine. Heating to 50 degrees C for 7 days also produced a significant (P less than 0.02) increase. Soluble procaine tended to return to baseline concentrations when veterinary procaine penicillin preparations were heated to 50 degrees C for 2 days then stored for 7 days at room temperature. Administration of procaine HCl intravenously (IV) at 2, 5, and 10 mg/kg produced behavioural, locomotor and vascular reactions, which were clinically similar to those reported in adverse reactions to procaine penicillin. The more severe reactions occurred at higher doses, although different horses responded variably at the same dose. Some adverse reactions lead to recumbency but none were fatal. The blood procaine concentrations 1 min after IV administration averaged 19.0 +/- 12.6 and 25.3 +/- 16 micrograms/ml at 2.5 mg/kg and 5 mg/kg, respectively. Ten min after administration, blood procaine concentrations were significantly higher (P less than 0.001) in the 5 mg/kg group than in the 2.5 mg/kg group. Intramuscular (IM) procaine HCl at 5 mg/kg produced significantly lower (P less than 0.001) blood concentrations than similar IV doses, and, in contrast to the IV doses, the amount of procaine in the blood was significantly higher 5 and 10 min after administration than it was after 1 min. Mild excitatory reactions in 4/5 horses were noted 5 to 10 min after IM administration. Administration of diazepam 20 s before procaine HCl prevented the excitatory adverse reaction in 2/2 horses, but administration after the procaine did not influence the outcome.

A strategy for the pharmacotherapy of personality disorders

Current research reveals that biological factors play an important role in shaping normal and disordered personality features. Judicious use of medications can facilitate the treatment of individuals with personality disorders.

Cocaine-induced coronary artery disease: recognition and treatment

Recreational use of cocaine has reached epidemic proportions. Recent reports have linked cocaine use to various acute and chronic cardiovascular disorders. The pharmacology of cocaine is discussed in this article, and the experiences with cocaine-induced coronary artery disease reviewed.

Local anaesthetic actions of cocaine: effects on excitatory and inhibitory synaptic responses in the hippocampus in vitro

1. The basis for the proconvulsant action of cocaine was investigated in the CA1 region of the rat hippocampal slice in vitro. 2. Superfusion with 100 microM cocaine depressed inhibitory and excitatory postsynaptic potentials recorded intracellularly from CA1 pyramidal neurones; both types of potentials were inhibited to an equal extent. When inhibition was assessed using extracellular recording of population spike responses before and after conditioning impulses, there did not appear to be any selective effect upon either recurrent or feed-forward gamma-aminobutyric acid (GABA)ergic inhibition. 3. Not all responses showed equivalent sensitivity to the local anaesthetic actions of cocaine. In particular, the antidromic population spike evoked by stimulation of the alveus was significantly more sensitive than the presynaptic fibre spike elicited by stimulation of stratum radiatum. 4. The rate of interictal spiking in hippocampus, induced by penicillin and increased potassium in the perfusion medium, was depressed by superfusion with cocaine in the range 5-100 microM. 5. These results suggest that cocaine does not have a selective depressant effect upon inhibitory pathways in the CA1 region of the hippocampus. Although the hippocampus shows epileptiform activity following systemic administration of local anaesthetics such as cocaine in the intact rat, this effect may not reflect a direct hippocampal site of drug action.

Intravenous procaine as a probe of limbic system activity in psychiatric patients and normal controls

Evidence from animal and human studies suggests that procaine hydrochloride may selectively activate limbic system structures and suppress neocortical structures. We administered a series of intravenous bolus doses of procaine hydrochloride to 31 subjects (7 with affective disorders, 17 with borderline personality disorder, and 7 healthy normal volunteers). Dose-related cognitive and sensory distortions and illusions were observed; affective experiences ranged widely from euphoric to dysphoric. Topographic electroencephalogram (EEG) analysis indicated selective increases in fast activity (26-45 Hz) over the temporal lobes; the degree of increase in this activity correlated with degree of dysphoria experienced. Procaine was associated with increases in secretion of cortisol, adrenocorticotrophic hormone (ACTH), and prolactin, but not with growth hormone. These preliminary data are consistent with the possibility that procaine might serve as a clinically useful probe of psychosensory, affective, electrophysiological, and endocrine effects referable to the limbic system.

NMR investigation of the influence of procaine and its metabolites on the water exchange through human erythrocyte membranes

The effect of procaine hydrochloride and its metabolites on the diffusional water exchange through erythrocyte membranes was investigated at 37 degrees C and at concentrations ranging between 5 X 10(-5) M and 5 X 10(-1) M by using the NMR manganese doping method. Procaine hydrochloride and 2-diethylaminoethanol have a moderate stimulating effect on the water exchange, of up to 20% at concentrations ranging between 10(-3) and 10(-2) M, while an increasing inhibitory effect was found at higher concentrations. The p-aminobenzoic acid has no effect on the water exchange up to 10(-2) M and, at higher concentrations, and apparent decreasing inhibition was noticed which is thought to be an artefact due to the uptake of Mn2+ by the cells. The temperature dependence studies suggest that procaine HCl enhances the uptake of Mn2+ by the cells. An opposite effect was found for rigid erythrocytes. The p-aminobenzoic acid and 2-diethylaminoethanol appeared to be more effective than procaine hydrochloride in increasing the uptake of Mn2+.

The effects of procaine HCl on population cellular and evoked response activity within the limbic system of the cat. Evidence for differential excitatory action of procaine in a variety of limbic circuits

1. The effects of intravenous injections of procaine HCl on population cellular activity in limbic tissue and overlying cortex, and on transmission of evoked activity between limbic structures was investigated in awake cats. Clear dose-related increases in cellular activity were seen in amygdala and ventral hippocampus. Changes in cellular activity in the nucleus accumbens and temporal neocortex were also dose-related, but in a complex time-dependent manner. Changes in ventromedial hypothalamus only appeared at the second highest dose of procaine. 2. Procaine facilitated transmission of evoked excitatory activity from the amygdala to the ventromedial hypothalamus, but only after a considerable delay from the time of injection. On the other hand, procaine had no effect on activity evoked in the ventral hippocampus, nucleus accumbens or temporal cortex by amygdala stimulation. 3. It was concluded that intravenous procaine functions as an excitant of limbic system cells, and that procaine alters synaptic transmission in some, but not all, output pathways from the amygdala. The neuroexcitant effects of procaine appear to be idiosyncratic, however, varying over dose with limbic and cortical area examined.

Neuroendocrine effects of limbic activation by electrical, spontaneous, and pharmacological modes: relevance to the pathophysiology of affective dysregulation in psychiatric disorders

1. Literature is reviewed that implicates various limbic structures (particularly amygdala and hippocampus) in the modulation of stress-associated neuroendocrine systems. 2. Procaine and related local anesthetics may show a selective proclivity for activating limbic structures. 3. Procaine stimulates ACTH-cortisol and prolactin, but not growth hormone secretion. This pattern is most comparable to that elicited by stimuli which act bilaterally on temporal lobe and limbic areas. 4. Procaine may be a useful agent for helping to elucidate the anatomic and physiologic basis for mood, endocrine, and cognitive dysregulation associated with stress and affective disorders. 5. The endocrine concomitants of limbic activation may have relevance to the course and symptom complex of affective disorders and related psychiatric conditions.

Limbic system dysfunction as a factor in some schizophreniform psychoses: case report and overview

A case is presented of a young woman whose schizophreniform psychosis was unresponsive to neuroleptic treatment, but who subsequently responded well to Carbamazepine. Several converging lines of investigation, suggesting an underlying Limbic System dysfunction, are discussed. Background to the Limbic System concept is provided.