A case of instantaneous rigor?

The question of whether instantaneous rigor mortis (IR), the hypothetic sudden occurrence of stiffening of the muscles upon death, actually exists has been controversially debated over the last 150 years. While modern German forensic literature rejects this concept, the contemporary British literature is more willing to embrace it. We present the case of a young woman who suffered from diabetes and who was found dead in an upright standing position with back and shoulders leaned against a punchbag and a cupboard. Rigor mortis was fully established, livor mortis was strong and according to the position the body was found in. After autopsy and toxicological analysis, it was stated that death most probably occurred due to a ketoacidotic coma with markedly increased values of glucose and lactate in the cerebrospinal fluid as well as acetone in blood and urine. Whereas the position of the body is most unusual, a detailed analysis revealed that it is a stable position even without rigor mortis. Therefore, this case does not further support the controversial concept of IR.

Adenosine induces initial hypoxic-ischemic depression of synaptic transmission in the rat hippocampus in vivo.

The present study was designed to investigate the role of adenosine in the hypoxic depression of synaptic transmission in rat hippocampus. An in vivo model of hypoxic synaptic depression was developed in which the common carotid artery was occluded on one side in the urethane-anesthetized rat. Inspired oxygen levels were controlled through a tracheal cannula. Rats were placed in a stereotaxic apparatus for stimulation and recording of bilateral hippocampal field excitatory postsynaptic potentials. The percent inspired oxygen could be reduced to levels that produced a reversible and repeatable depression of evoked synaptic transmission restricted to the hippocampus ipsilateral to the occlusion. Further reduction in the level of inspired oxygen depressed synaptic transmission recorded from both hippocampi. The adenosine nonselective antagonist caffeine and the A(1) selective antagonist 8-cyclopentyltheophylline prevented the initial depression in synaptic transmission. We conclude that the initial depression of synaptic transmission observed in the rat hippocampus in vivo is due to endogenous adenosine acting at neuronal adenosine A(1) receptors.

Basal forebrain and frontal cortex neuron responses during visual discrimination in the rat.

Using a classical conditioning procedure in urethane-anesthetized rats, a light applied to one eye (CS+) was paired with medial forebrain bundle (MFB) stimulation, whereas a light applied to the other eye (CS-) was not paired. Basal forebrain neurons in the substantia innominata, medial globus pallidus, and nucleus basalis magnocellularis responded differentially to CS+ and CS-, with larger responses to CS+. Some neurons were excited by CS+, and others were inhibited. Fifty percent of these neurons responded in the same direction to CS+ and MFB stimulation, and 38% responded in opposite directions. Frontal cortex neurons exhibited similar differential responses; 47% of the differential responses to CS+ were in the same direction as the response to MFB stimulation, and 29% were in the opposite direction. When light to either eye was paired with MFB stimulation, conditioning-related basal forebrain neuron responses of comparable magnitude to left and right eye illumination were observed, providing evidence that association of CS and UCS rather than the eye to which light was applied determined the differential response to CS+. Also, two different intensities of light induced comparable basal forebrain responses when both were paired with the UCS. These experiments provide support for a role of the basal forebrain in conditioning-related neural activity. Furthermore, this preparation can be utilized to investigate transmitter systems that mediate conditioning-related responses of basal forebrain neurons.

A role for acetylcholine in conditioning-related responses of rat frontal cortex neurons: microiontophoretic evidence.

In an associative conditioning paradigm, an auditory stimulus (CS+) was paired with rewarding medial forebrain bundle stimulation or a tone of different frequency (CS-) was presented without pairing. After training, slow potential (SP) and single neuron responses were recorded from rat frontal cortex. When cortical SP responses indicated the development of discrimination between CS+ and CS- tones, single neurons could be isolated that exhibited a discriminative response to CS+. Seventy-three percent of the 56 neurons which discriminated between CS+ and CS- were excited by the paired tone while the remainder were inhibited. Iontophoretically applied acetylcholine increased spontaneous firing rate in 90% of the excited cells and 87% of the inhibited cells. Iontophoretic administration of a muscarinic receptor antagonist, either atropine or tropicamide, during trial presentation attenuated the conditioning-related response to CS+ as well as the response to acetylcholine in the majority of neurons. The largest group of discriminating neurons were excited by both CS+ and acetylcholine, and both responses were suppressed by the antagonists. The results provide evidence that conditioning-related responses of a major population of frontal cortex neurons are modulated by cholinergic input, a portion of which may originate in the basal forebrain area. There also may be a significant non-cholinergic influence on these neuronal responses.

Nucleus basalis involvement in conditioned neuronal responses in the rat frontal cortex.

Rat frontal cortex neurons exhibit alterations in firing in response to a 2 sec tone cue followed by rewarding medial forebrain bundle (MFB) stimulation. Nucleus basalis neurons supply up to 75% of the cortical cholinergic innervation. The nucleus basalis and ACh have been implicated as playing a role in cognitive function. Three experiments were designed to test the hypothesis that the nucleus basalis cholinergic system is involved in the generation of conditioned neuronal responses in the rat frontal cortex. Local microinjection of the cholinergic antagonist, atropine, into the frontal cortex suppressed the conditioned responses of 22 of 25 cortical single units. Unilateral kainic acid lesioning of the nucleus basalis resulted in a significant decrease in the proportion of units exhibiting conditioned responses in the cortex ipsilateral to the lesion (25%) compared to the proportion of responding units from the cortex of untreated animals (70%). When the firing rates of units encountered in the region of the nucleus basalis were monitored during presentation of the cue-MFB paradigm, 28 of 38 unit recordings exhibited significant increases or decreases in firing rate. Therefore, the results of the experiments indicate that the nucleus basalis cholinergic neurons are involved in the generation of conditioned neuronal responses in the rat frontal cortex.

Discriminative conditioning-related slow potential and single-unit responses in the frontal cortex of urethane-anesthetized rats.

A model is described for obtaining long-term and stable discriminative conditioning-related slow-potential and single-unit responses from the frontal cortex of urethane-anesthetized rats. Responses were recorded and analyzed to reinforced (rewarding medial forebrain bundle stimulation) and non-reinforced tone cues. In the present study, cortical event-related slow potentials provided an adequate index of the level of discriminative conditioning. Single-unit response patterns are described for 57 neurons which demonstrated a discriminative response to either the reinforced or non-reinforced tone cue.

Generation of cortical event-related slow potentials in the rat involves nucleus basalis cholinergic innervation.

These experiments were conducted to gather information regarding the role of cholinergic innervation to the cortex in the generation of event-related slow potentials. The effects of unilateral drug treatments or lesions on ipsilateral and contralateral frontal cortex slow potential (SP) responses were examined in rats. The SP responses were recorded with silver-silver chloride electrodes and were generated by a 2 sec light cue which preceded rewarding medial forebrain bundle stimulation. The following approaches were used: microinjection of GABA, procaine or saline into the nucleus basalis magnocellularis; microinjection of atropine or saline subdurally in the SP recording area; electrolytic lesion of the nucleus basalis area; and kainic acid lesion of the nucleus basalis area. The following bilateral measurements were obtained lesion studies: choline acetyltransferase (ChAT) in cortex and hippocampus; serotonin in cortex, hippocampus, striatum and nucleus accumbens; norepinephrine in cortex and hippocampus; dopamine in striatum and nucleus accumbens; and metabolites of serotonin, norepinephrine and dopamine in these areas. The cortical SP responses were reduced on the side ipsilateral to the injections of GABA and procaine into the nucleus basalis, and on the side of the subdural atropine injection. With either type of lesion, the SP responses on the lesioned side were significantly reduced as compared to the non-lesioned side. Reductions in cortical ChAT and other measures were observed ipsilateral to the electrolytic lesion, but only cortical ChAT activity was reduced in the kainic acid-lesioned animals. Thus, pharmacological depression of nucleus basalis neurons, blockade of cholinergic muscarinic receptors in the cortex, and nucleus basalis lesions that reduce cortical choline acetyltransferase activity depress event-related slow potentials in the rat frontal cortex. These results provide evidence that cortical slow potential responses in the rat are dependent upon cholinergic innervation from the nucleus basalis.

Conditioned cortical slow potential responses in urethane anesthetized rats.

Cortical slow potential (SP) responses to tone or light stimuli preceding medial forebrain bundle (MFB) stimulation were recorded in urethane anesthetized rats. In the first study, rats were implanted with Ag-AgCl electrodes for recording frontal cortex SPs as well as monopolar electrodes for MFB stimulation. Following recovery, optimum stimulation parameters for SP conditioning were determined for each rat during self-stimulation sessions. These animals were then subjected to extensive associative conditioning in the unanesthetized state. Trials were presented at variable intervals and a 2-sec tone preceded a single 0.5 sec train of MFB stimulation. Negative SP responses developed with training and responses of similar waveform and amplitude were observed in the same animals under urethane anesthesia. Other rats were implanted with MFB stimulating electrodes and, after recovery, stimulation parameters were determined as above but the animals were not subjected to the conditioning procedure prior to urethane administration. Under urethane anesthesia, Ag-AgCl electrodes were placed on the dura over frontal cortex for recording SP responses during pseudoconditioning, conditioning, extinction and retraining trials, using either light or tone stimuli. Negative bilateral SP responses to the tone or light were minimal or nonexistent during pseudoconditioning, developed gradually with pairing, diminished markedly during extinction and returned to maximum amplitude with retraining. The SP responses also reflected discrimination between reinforced and nonreinforced tone and light stimuli as well as reversal conditioning. Furthermore, turning off a light could also serve as the conditioned stimulus for SP response generation. Cortical slow potential responses can be conditioned in urethane anesthetized rats. Therefore, it may be possible to apply additional neurophysiological techniques in these animals to investigate event-related slow potential mechanisms.

Conditioning-related single unit activity in the frontal cortex of urethane anesthetized rats.

Responses of frontal cortex single units to a tone preceding medial forebrain bundle (MFB) stimulation were recorded in urethane anesthetized rats. The animals were implanted with monopolar electrodes for MFB stimulation and, following recovery, stimulation parameters which supported self-stimulation were determined for each rat. Prior to the unit recording experiment, the animals were trained to associate a 2-sec tone with MFB stimulation. Trials were presented at variable intervals. Under urethane anesthesia, single units were isolated and the responses of units to paired and unpaired tones were determined. The results indicate that conditioning-related responses of frontal cortex single units can be recorded in urethane anesthetized rats.

Microinjection of procaine or GABA into the nucleus basalis magnocellularis affects cue-elicited unit responses in the rat frontal cortex.

Male rats were chronically implanted for recording of single units in the frontal cortex during a cue-event paradigm. The rats were sedated and restrained during the experiments. Units were selected which had large-amplitude, clearly isolated action potentials. The animals were first trained to associated a 2-s tone cue with rewarding medial forebrain bundle stimulation. After training, units responded to the cue by an increase or decrease in discharge rate. Cumulative histograms of the unit response to the cue were obtained and then either procaine hydrochloride or GABA was microinjected into the nucleus basalis magnocellularis (nBM). Immediately after drug administration another histogram was obtained to ascertain the drug effect. Procaine microinjections to the nBM suppressed the frontal cortex unit responses in 9 of 10 units that had previously responded with an increase in firing rate and 10 of 12 units that had decreased their firing rate before drug administration. GABA microinjections antagonized the response in 15 of 19 excited units and 2 of 2 inhibited units. Recovery was obtained in 23 units. Other units did not remain isolated long enough to obtain complete recovery. The nBM supplies the frontal cortex with as much as 70% of its cholinergic innervation. Lesions of the region do not significantly alter the amounts of neurotransmitters other than acetylcholine in the frontal cortex. These results indicate that neurons in the nucleus basalis magnocellularis are involved in the cue-elicited changes in the rate of discharge of units in the rat frontal cortex.

Single-unit and slow potential responses from rat frontal cortex during associative conditioning.

Single-unit and slow potential responses were recorded from the frontal cortex of unanesthetized, restrained rats trained to associate an auditory cue (tone) with rewarding medial forebrain bundle stimulation. Slow potential responses to the unpaired tone were minimal whereas large negative slow potential responses developed to the paired tone. Units were selected which had large-amplitude action potentials and positive first deflections, characteristics suggesting that the recordings were derived from pyramidal neurons. Responses of excitation, inhibition, and no change were observed during tone presentation. Forty-five percent of the units responded to the unpaired tone; with pairing, 90% of the units demonstrated significant responses. Furthermore, the magnitude of the excitatory responses was enhanced by pairing and a distribution pattern developed in which the overall response of the more superficial units was activation whereas deeper units were inhibited. The results suggest that the conditioning-related negative slow potential responses recorded from the surface of the rat frontal cortex reflect excitatory processes which are associated with an enhanced firing rate of neurons in the upper layers.

Naloxone antagonizes striatally-induced suppression of globus pallidus unit activity.

This study was designed to examine the ability of naloxone to antagonize the inhibition of neurons in the globus pallidus produced by electrical stimulation of the caudate nucleus. In rats anesthetized with chloral hydrate, bipolar stimulating electrodes were placed in the head of the caudate and seven-barrel micropipettes were utilized for recording extracellular activity of globus pallidus cells as well as for microiontophoretic application of experimental drugs. In most globus pallidus cells which were inhibited by caudate stimulation, application of naloxone (at currents which antagonized morphine-elicited depression) attenuated the caudate-induced effect. Naloxone did not antagonize depression of globus pallidus neurons induced by gamma-aminobutyrate. The results indicate that caudate stimulation causes the release of endogenous enkephalins which act to suppress neuronal activity in the globus pallidus. Thus, this study supports biochemical and histochemical studies which provide evidence for an enkephalinergic component in the striatopallidal projection.

Unit responses in the caudate nucleus to cumulative doses of morphine in unanesthetized, phenobarbital-treated rats.

The effects of cumulative i.v. doses of morphine (1 to 30 mg/kg) on the spontaneous activity of single caudate nucleus neurons were evaluated in rats administered subsurgical doses of phenobarbital. At least 1 week prior to the experiment the animals were prepared with a chronic cranial implant which allowed subsequent restraint as well as the location and recording of neuronal activity with microelectrodes. The rats were pretreated with 40 or 140 mg/kg (i.p.) phenobarbital prior to each experiment. In both phenobarbital treatment groups, 50 to 61% of the neurons tested showed no specific morphine effect. The remainder of the neurons tested in each treatment group responded with morphine-specific increases or decreases in spontaneous activity. It is concluded that a lighter level of anesthesia permits a more dynamic range of caudate neuron responses to morphine.

Spontaneous unit activity in the globus pallidus following cumulative injections of morphine in phenobarbital- or chloral hydrate-anesthetized rats.

The effect of systemically administered morphine on spontaneous unit activity, recorded from the globus pallidus, was evaluated in this study. A wide range of doses of morphine was administered in order to characterize the influences of morphine on pallidal activity in a dose-related manner. Two separate studies were conducted. In the first study, a semichronic preparation, lightly anesthetized with phenobarbitol, was used. Acutely prepared, chloral hydrate-anesthetized rats were utilized in the second experiment. With phenobarbital, morphine caused a significant reduction in pallidal activity in 75% of the cells recorded, whereas only 45% of the pallidal cells responded similarly to injection of morphine in chloral hydrate-anesthetized animals. However, the dose of morphine required to decrease unit activity was substantially less with chloral hydrate than with phenobarbital anesthesia.

Dissimilar responses of cortical neurons to chronic trazodone or desipramine treatment.

The effects of acute and chronic trazodone or desipramine treatment on the spontaneous firing rate of cortical neurons in chloral hydrate anesthetized rats were determined. Either trazodone (30 or 60 mg/kg, po) or desipramine (5 or 10 mg/kg, po) was administered daily for periods of up to 11 or 16 days respectively. A significant reduction in the firing rate of cortical neurons was observed after acute and chronic 10 mg/kg desipramine treatment. Chronic treatment with 5 mg/kg desipramine had no effect on activity. Neither acute nor chronic treatment with trazodone produced any significant alteration in cortical unit activity. The results suggest that the spontaneous activity of randomly encountered cortical neurons is not involved in the mechanism of the therapeutic action produced by chronic treatment with the two clinically effective antidepressants. The response of the cortical neurons to antidepressant treatment might help differentiate the relative effects of the drugs on monoaminergic receptors. Also, the depressant effect of desipramine on the spontaneous rate of cortical neurons does not appear to be a specific effect of chronic treatment since it occurred after a single dose.

Haloperidol antagonism of amphetamine-induced effects on event-related slow potentials from rat cortex.

Slow potential (SP) responses to a click followed after 2 sec by rewarding stimulation of the medial forebrain bundle were recorded from the frontal cortex of rats with permanently implanted electrodes. The SP responses were frequently enhanced by haloperidol (0.0125 to 0.1 mg/kg). Both haloperidol and alpha-methyltyrosine antagonized amphetamine-induced suppression of the SP responses. The results are consistent with the idea that dopamine (and possibly norepinephrine) exerts an inhibitory influence on the mechanisms involved in generation of event-related slow potentials.

Spontaneous and cortically-evoked unit activity in the caudate nucleus after systemic morphine.

The ability of systemically administered morphine to alter spontaneous and cortically-evoked single unit activity in rat caudate nucleus was assessed in this study. The animals were prepared with permanently implanted microelectrode guide cannulas and cortical stimulating electrodes. For recording sessions, they were pretreated with phenobarbital to allow mounting in the stereotaxic device. Morphine was administered intravenously in incremental doses from 1 to 30 mg/kg. Neither spontaneous activity nor evoked firing was altered in approximately half the units. Spontaneous activity was depressed in 12 of 33 cells and stimulated in 5 of 33 cells. Evoked activity was reduced in 7 of 36 units and enhanced in 9 of 36 cells. A large proportion of the responses to morphine were not reversed by 1 mg/kg naloxone, especially the changes in cortically-evoked firing. These results demonstrate a multiplicity of changes in spontaneous and cortically-evoked activity of caudate nucleus neurons following systemically administered morphine.

Auditory cue preceding intracranial stimulation induces event-related potential in rat frontal cortex: alterations by amphetamine.

Slow potential (SP) responses to a click followed by rewarding stimulation of the medial forebrain bundle (MFB) were recorded from the frontal cortex of rats with permanently implanted electrodes. Trials were presented at variable intervals and the final interval between the click and MFB stimulation was 2 seconds. Negative SP responses developed rapidly with training, as the interstimulus interval was gradually increased from 0.5 sec to 2 sec. No decrement of the SP response was observed during recording sessions consisting of more than 300 trials. The SP responses remained stable over several weeks of recording. Dextroamphetamine produced a dose-related depression of the SP responses. Since the effect of amphetamine in this study was similar to the effect in studies using food reinforcement, the results suggest that amphetamine-induced depression of event-related slow potentials in rat frontal cortex is not dependent on the type reinforcement. Advantages of the use of intracranial stimulation as reinforcement for event-related potential studies are discussed.