Changes In Unit Activity Research Articles

Unilateral, intranigral infusions of amphetamine produce differential, bilateral changes in unit activity and extracellular levels of ascorbate in the neostriatum of the rat

Simultaneous recordings of single-unit activity and oxidation current were obtained bilaterally from the neostriatum of rats in response to unilateral infusion of d-amphetamine (2.0 μl of 10 μg/μl) into the substantia nigra. Whereas neuronal activity increases ipsilaterally and decreases contralaterally, the electrochemical signals, which reflect extracellular ascorbate, increase bilaterally. In each case, changes in unit activity precede the change in ascorbate release. Systemic administration of haloperidol (0.2 mg/kg) blocks the increase in oxidation current bilaterally, but reverses the neuronal activity response only on the ipsilateral side. These results lend further support to the view that intranigral amphetamine facilitates neostriatal ascorbate release, but this effect is not correlated with changes in single-unit activity.

Prefrontal unit activity during delayed conditional Go/No-go discrimination in the monkey. II. Relation to Go and No-go responses

Three monkeys were trained to perform a Go/No-go discrimination task where the animals were required to perform a muscular movement (Go) or to withhold it (No-go) depending on the previously presented signal. Single unit activity was recorded from the prefrontal cortex during the performance of the task. Among 512 task-related prefrontal units, 253 units showed differential activity in relation to the type of the trial (Go or No-go) either at the time of the response or both during the preparatory period for the response and at the time of the response. These units were classified into 3 types depending on whether the changes in unit activity were observed selectively on Go trials (Go units, n= 47), or selectively on No-go trials (No-go units, n= 28) or on both Go and No-go trials (Go/No-go units, n= 178). A small number of units from the premotor cortex ( n= 31) were examined inadvertently and the 3 types of units were present in this area as well. The existence of the 3 types of prefrontal units (Go, No-go and Go/No-go) indicates that the prefrontal cortex is involved in the behavioral inhibitory mechanism besides participating in the behavioral excitatory mechanism.

Unit activity of motor cortex during acoustically signalled reaching in rats

Changes of unit activity, accompanying a discriminated instrumental reaction were studied in the motor cortex of rats (n = 15) trained to reach into a narrow tubular feeder for food pellets. A shutter opened the feeder for 1280 ms while the presence of food was signalled by 600 Hz (CS +) tone and its absence by a 3000 Hz (CS −) tone. The electrophysiological experiments were performed after the rats had developed a preference for reaching with the left or right forepaw and when their discriminations were 75% correct. Unit activity was recorded in the motor cortex contralateral to the preferred forepaw using capillary microelectrodes and a head-mounted microdrive. Post-stimulus histograms (PSHs) to CS + (n = 71) showed an increase of firing rate in the first 120 ms after CS onset (40% units) and a tonic excitation (55% units) starting some 200 ms later. The second component was related to movement as revealed by simultaneously plotted peri-reach histograms. The first component was related to preparatory activity and was also present in the PSHs obtained during correct reactions to CS − (n = 29). Then, absence of reaching was manifested by inhibition replacing the second excitatory component. The first but not the second excitatory components were seen in the PSHs plotted during negative reactions to CS + (n = 18). It is concluded that the conditioned stimuli elicit in the motor cortex preparatory activity preceding actual movement by 200–250 ms. The neuronal populations engaged in the preparatory activity and movement execution overlap.

The bed nucleus of the stria terminalis and immobilization-stress: Unit activity, escape behaviour, and gastric pathology in rats

Multiple unit-activity in the bed nucleus of the stria terminalis was increased or decreased, relative to baselines, during physical restraint in rats. Changes in unit-activity were also obtained by presenting an auditory stimulus that had been paired with the immobilization treatment. The animals escaped from that stimulus in behavioural tests, and bilateral lesions in the bed nucleus reduced the latencies of escape responses. The lesion also increased the severity of restraint-induced mucosal erosions. The latter effect was most pronounced when the damage was in the lateral portion of the bed nucleus. It was concluded that the bed nucleus of the stria terminalis is part of a coping system which responds when the organism is placed in a stressful situation.

Action of estrogen and mechanical vaginocervical stimulation on the membrane excitability of hypothalamic and midbrain neurons

The effect of vaginocervical stimulation (VCS) and estrogen iontophoresis on the electrical activity recorded in urethane-anesthetized female rats from medial preoptic-septal (MPO-S) and midbrain central gray (MCG) neurons was studied during two phases of the estrous cycle, namely metestrus (M) and late proestrus-estrus (LP-E). The spontaneous discharge rate of both MPO-S and MCG neurons varied over the two stages of the estrous cycle. The spontaneous electrical activity of the MPO-S neurons was higher during M than during LP-E whereas MCG unit activity was low during M and higher during LP-E. The VCS-evoked changes in unit activity were specific, in that they were observed in response to mechanical genital stimulation and not in response to painful stimuli and/or nonspecific arousal. These responses were not dependent on the stage of estrous cycle. Finally, the iontophoresis of 17β-estradiol hemisuccinate evoked electrophysiological responses from MPO-S and MCG neurons. More MPO-S neurons were responsive to estrogen in LP-E than in M, while fewer MCG neurons were responsive to estrogen in LP-E than in M. The results clearly show that ongoing electrical activity of hypothalamic and midbrain nerve cells can fluctuate between M and LP-E phases of the estrous cycle and change with vaginocervical probing as well as iontophoretically applied estrogen. Furthermore, the results suggest the existence of a reciprocal relationship between the membrane activity of MPO-S and MCG neurons which may be related to CNS control of reproductive activities.

Dose effects of morphine on the spontaneous unit activity recorded from the thalamus, hypothalamus, septum, hippocampus, reticular formation, central gray, and caudate nucleus.

Spontaneous activity was recorded from 652 units in 8 subcortical structures of unanesthetized rats. Recordings were obtained in central gray, mesencephalic reticular formation, parafasciculus thalami, caudate nucleus, anterior and ventromedial hypothalamus, lateral septum, and dorsal hippocampus. Eighty recordings were obtained from untreated animals and 80 from saline-injected controls, none of which showed any significant changes of unit activity during the 4- 5-hr observation period. The effect of morphine, given in 5 incremental doses from 0.5 to 30.0 mg/kg ip, was followed in 492 units. Morphine enhanced or depressed spontaneous discharge rates, or caused biphasic effects, ie enhancement alternating with depression and vice versa. Naloxone induced increase in firing after either effect of morphine, or reduced spontaneous activity after morphine-induced increases. However, when morphine reduced neuronal discharges, naloxone never caused further depression. In 86 units, morphine at any dosage failed to alter neuronal activity, but in 54 of these units naloxone nevertheless induced alterations in firing rates. The pattern of responses to morphine differed between all 8 brain regions examined and was characteristic for each individual structure. This is the first systematic study describing the dose-response characteristics of morphine in 8 brain sites recorded simultaneously. Furthermore, it utilized freely behaving animals without the interference of anesthetics, which are themselves known to interact with opiates. The variety of response patterns seen supports the neuropharmacological evidence for multiple opiate receptors or multiple sites of opiate action.

Associative and non-associative changes in unit activity of the rat hippocampus

Two main types of neurons of the dorsal hippocampus were recorded in chronic rats during the classical conditioning of an arousal phenomenon (neocortical EEG desynchrony). The relative importance of the associative and non-associative factors was assessed by a differentiation procedure. In naive rats, during the “acquisition” session most type-I neurons rapidly acquired an “inhibitory” response closely parallel to the EEG response. Neither of these responses showed differentiation. Some type-II neurons acquired an “excitatory” response which was independent of the EEG response and which had a significant tendency to differentiation. These data were confirmed in rats submitted to several “retention” sessions. All the type-I neurons were undifferentiated while 11 out of 41 type-II neurons were differentiated. Type-I neurons were characterized by a bursting mode of discharge. Their activity was higher during slow wave sleep (SWS) than during wakefulness (W) or paradoxical sleep (PS). Most of the differentiated type-II neurons were more active during W and/or PS than during SWS.

Nonsynaptic effect of the electrocorticogram of the intact hemisphere on unit activity of the neuronally isolated cortex.

The nonsynaptic influence of the electrocorticogram (ECoG) of the visual area of the intact hemisphere on unit activity in the visual area and Clare-Bishop area of the isolated cortex in darkness and during diffuse illumination of the retina was investigated in acute experiments on cats immobilized with diplacin, and with the cortex of one hemisphere neuronally isolated. Changes in unit activity of tonic character were found in darkness and both tonic and phasic responses of isolated cortical units in the visual area and Clare-Bishop area were found during diffuse photic stimulation. The possibility of using the nonsynaptic influence of the ECoG of the intact brain to stimulate different regions of the neuronally isolated cortex is examined.

Apparent serotonergic modulation of the dose-dependent biphasic response of neostriatal neurons produced by d-amphetamine

Previous reports indicate that amphetamine produces a dose-dependent shift to the firing rate of neurons in the anterior neostriatum that parallels the shift in behavior from locomotion to focused stereotypy. To determine if para-chlorophenylalanine (PCPA), which alters the pattern of the behavioral response to amphetamine, also changes the pattern of the neuronal response to the drug, a dose-response analysis was performed on amphetamine-induced changes in unit activity in the anterior neostriatum of rats pretreated 48 h previously with 300 mg/kg PCPA or vehicle. An intraperitoneal injection of 1.0 mg/kg D-amphetamine, which inhibited neostriatal activity in vehicle controls, produced in PCPA-pretreated animals a prolonged excitation. In contrast, the pronounced increase in firing rate produced by 7.5 mg/kg D-amphetamine in control rats was significantly reduced following PCPA pretreatment. Liquid chromatography with electrochemical detection revealed that compared to controls, PCPA produced a significant reduction of serotonin, but not dopamine or norepinephrine, in the telencephalon. The differential effects of PCPA on the action of low and high doses of D-amphetamine in the anterior neostriatum may explain the differential influence of serotonergic systems on amphetamine-induced locomotion add stereotypy.

Unit activity changes elicited in amygdala and neocortex of anaesthetized rats by intraperitoneal injection of lithium chloride

Intraperitoneal injection of 0.15 M LiCl (2% body weight) to anaesthetized rats elicited, after a 6 min latency, discharge of about 50% units in basolateral amygdala (n = 27). The activation lasted for 15 min on the average. Cortical neurones were not affected by the LiCl injection. It is suggested that the amygdalar reaction to LiCl administration may account for the association of the gustatory trace with the visceral signals of poisoning which mediates acquisition of conditioned taste aversion under anaesthesia.

Electrophysiological correlates of the reversed postoptokinetic nystagmus in the rabbit: Activity of vestibular and floccular neurons

Unit activity changes accompanying the optokinetic nystagmus (OKN) and reversed postoptokinetic nystagmus (RPN) in the rabbit were examined in 180 vestibular and floccular neurons. After initial charging of the RPN generator by 60-min optokinetic stimulation, a sequence of 1-min optokinetic stimulation (OKN) followed by 1-min darkness (RPN) and 1-min illumination of the stationary optokinetic drum (L), was cycled while corresponding unit activity changes were recorded during 3–5 cycles and evaluated with a computer. About 50% of vestibular neurons (type A) increased their activity during OKN and/or decreased it during RPN with respect to the L period, whereas 24% (type B) reacted in a reciprocal manner. The remaining neurons were either unaffected or responded in an atypical way. Most floccular neurons (75%) were activated during ipsilateral optokinetic stimulation, but were not significantly affected by RPN. It is suggested that the neural trace of RPN develops in the vestibular complex and vestibulocerebellum as a part of the process compensating for the effect of continued optokinetic stimulation.

Dynamics of auditory cortical unit responses of the waking cat during defensive conditioning to acoustic stimulation

In chronic experiments on cats unit responses of the primary auditory cortex (area 50) were studied by microelectrode recording during defensive conditioning to sound. During formation of the reflex biphasic responses with relatively short-latency (50–100 msec) and longer-latency (400–500 and 800–900 msec) activation predominated. Neighboring neurons, whose activity was recorded by the same microelectrode, also were involved more intensively in activity. Application of a differential stimulus in 70% of cases produced definite changes in unit activity, among which responses of activation type predominated. Analysis of the course of spike responses of the same neuron during the period of action of a large number of combinations and its comparison with the formation of the conditioned-reflex motor response revealed no direct correlation between these events.

Effect of stimulation of the amygdala and subthalamus on unit activity of the mesencephalic central gray matter

Characteristics of unit activity of the mesencephalic central gray matter were studied during electrical stimulation of the amygdala and subthalamus (chiefly the zona incerta) in acute experiments on rats. Stimulation of the amygdala evoked chiefly inhibitory unit responses (72%), whereas stimulation of the zona incerta evoked chiefly excitatory responses (59%). The effectiveness of regular (5 Hz) stimulation of the amygdala in producing prolonged changes in unit activity was noted and points to the modulating character of the influence of this structure on the central gray matter. In 31 of 114 neurons tested convergence of impulses from the amgydala and zona incerta was observed. The two types of stimulation most frequently induced inhibition (71%).

Changes in the functional organization of the lateral geniculate body after tetanus toxin injection

Changes in unit activity in the lateral geniculate body during formation of a generator of pathologically enhanced excitation as a result of local injection of tetanus toxin into this nucleus were investigated in unanesthetized cats. To assess changes taking place a classification of geniculate neurons in normal animals obtained by analysis of interspike interval histograms of spontaneous activity and poststimulus histograms of unit activity evoked by photic stimulation was used. As a result of the action of the toxin substantial changes were observed in the quantitative distribution of the neurons by groups. A new group of neurons with a considerably increased duration of the first spike volley also was identified. The appearance of these neurons is connected with disappearance of the inhibitory pause in the overwhelming majority of relay neurons of the nucleus.

Control of thalamic transmission by corticofugal and ascending reticular pathways in the visual system.

Control of thalamic transmission by corticofugal and ascending reticular pathways in the visual system.

Changes in unit activity in the cat sensomotor cortex during heterosensory stimulation

Changes in unit activity in the sensomotor cortex during repetitive (once per second) photic stimulation was investigated in animals immobilized with diplacin. During the development of habituation of responses to the basic (photic) stimulus the neurons were shown to begin to respond to stimuli of a different modality (somatic) if applied during the cycle of change in functional state after the photic stimulus. In the case of continuous “reinforcement” of the photic stimulus by somatic after a delay of 100–300 msec no habituation of responses to the photic stimulus was observed. It is postulated that these effects reflect functional reorganization of afferent systems.

Somatosensory cortical unit responses during avoidance conditioning to sound

Unit responses of the primary somatosensory cortical-projection area were recorded in cats with established conditioned avoidance to sound during the conditioned response. Five types of changes in unit activity were distinguished during the conditioned reflex. The responses were 400–1000 msec in duration; their time of onset coincided with that of the expected reinforcing stimulus. As a rule the change in unit activity was preceded by changes in the electromyogram of the corresponding limb muscles. Among neurons responding to the conditioning stimulus, the proportion with a short latent period of response to electrical stimulation of the skin was less than during investigation of ordinary unit responses to the same stimulus.

Tissue culture study of unit activity of the rat cerebral cortex

Spontaneous unit activity and morphological characteristics of visual cortical neurons from young rats aged 1 and 2 days were investigated during long-term culture (up to 34 days) of explants in vitro. Three types of spontaneous unit activity were found: single spikes, volleys, and grouped discharges. The types of spontaneous activity were found to depend on the duration of cultivation of the brain tissue. The discharge of single spikes, characteristic of neurons during the first 7–15 days in culture, subsequently was replaced by grouped discharges or volleys of spikes. The changes in unit activity were shown to coincide in time with morphological maturation of the synapses. In experiments in which strychnine (10 µg/ml) was added to the culture medium, a marked increase was observed in the mean frequency of spontaneous unit activity, accompanied by the appearance of discrete series of volley-type discharges. The genesis of spontaneous cortical unit activity is discussed on the basis of these findings.

Macular input to neurons of the spinoreticulocerebellar pathway

The present report summarizes the results obtained in previous experiments in which the responses to lateral tilt of both reticulocerebellar neurons located in the lateral reticular nucleus (NRL) and ascending spinoreticular tract axons, located in the lateral funiculi of the cervical segments C2-C3, had been recorded in precollicular decerebrate cats. Steady changes in unit activity were evoked by 15-20 degrees tilts which lasted as long as the position of the cat was maintained. Most of the units responsive to tilting showed an increase in discharge rate during tilt in one direction and a decrease in discharge rate during tilt in the opposite direction. Moreover the magnitude of the unitary responses was clearly related to the degree of tilt. The responses of the NRL neurons to tilt were attributed in part to direct efferent vestibuloreticular projections from the Deiters' nucleus, in part to some indirect influence of the lateral vestibulospinal tract on neurons of the cervical ascending spinoreticular pathway. Since most of these ascending units affected by tilt were influenced by stimulation of both ipsilateral and contralateral forelimb nerves, and some of them also by stimulation of high threshold neck muscle afferents, it was postulated that these neurons projected to the forelimb and the neck region of the cerebellar cortex of the anterior lobe. This corticocerebellar region may therefore integrate from time to time not only the signal input originating from macular receptors but also the somatosensory input which originates from neck receptors as a result of the actual displacement in head position induced by the vestibulospinal reflex.

Unit activities in the hypothalamus and midbrain during stimulation of hypothalamic attack sites

Unit activity in the hypothalamus and midbrain of unanesthetized cats was studied during electrical stimulation of the hypothalamus at sites that induced attack and at other comparable sites from which attack was not induced. The changes in the firing of units at distances from 0.7 to 1.9 mm from the site of stimulation were similar to those of units at distances from 2.0 to 5.2 mm. Although stimulation in general affected a majority of units, resulting in increases rather than in decreases of firing rates, and produced similar patterns of unit activity, stimulation at sites that induced attack affected more units, produced a greater change in unit activity and markedly increased firing rates in the lateral hypothalamus and the dorsal part of the midbrain.