Spike reactions of neurons of the cat thalamic reticular nucleus during elaboration of an instrumental conditioned reflex

Spike reactions of 156 neurons of the thalamic reticular nucleus (R) have been studied during performance of instrumental alimentary conditioned reflex. These reactions consist of initial and late phases. The latencies of initial reaction phase are 10-100 ms and duration--50-250 ms. The minimum data of late phase latencies are 100-300 ms. Initial responses to the conditional sound click are found in 27 neurons: 26 of them show excitation and one neuron--inhibitory-excitatory responses. The late reaction phase has been observed in 134 neurons only during performance of conditioned placing reactions: 115 of them show excitation, 19 neurons--inhibition and 22 neurons--were not reactive. Responses of 30 neurons forestalled the performance of conditioned forelimb movement. 118 neurons responded during the ballistic phase of the movement. It is concluded that the thalamic reticular nucleus takes part in the conditional signal perception and in the preparation and control of conditioned movement performance.     

Responses of the reticular nucleus neurons and dorsal thalamic nuclei neurons in the cat during extinction of a conditioned instrumental reflex

Activity of 66 neurons of the reticular nucleus (R), 31 neurons of the ventroposterolateral nucleus and 14 neurons of the posterolateral nucleus-pulvinar complex of the thalamus was investigated during extinction of the conditioned instrumental alimentary reflex. The quantity of R neurons that show initial excitation in response to the conditional stimulus in the first 300 ms decreased during extinction. Conditioned placing reactions and late excitatory and inhibitory neuronal responses in the R and dorsal thalamic nuclei with latency above 300 ms disappeared during extinction simultaneously. The background unit activity decreased during extinction in the 2/3 of investigated neurons of R and dorsal thalamic nuclei. It is suggested that the efferent influence from the R decreased during extinction.     

The effect of midbrain reticular stimulation upon perigeniculate neurons activity during different states of the sleep-waking cycle in the cat

Electrical stimulation of the mesencephalic reticular formation in chronic cats induced state-dependent effects on spontaneous firing of perigeniculate neurons. Perigeniculate neurons fired at lower rates during slow wave sleep than during wakefulness of paradoxical sleep. The stimulation caused a firing decrease in slow wave sleep; an effect which faded during wakefulness and paradoxical sleep and was superseded by a firing increase during periods of eye movements in 30% of the neurons. The responsiveness of perigeniculate neurons to optic tract and visual cortex stimulation either remained unchanged or was enhanced during the reticular induced firing changes.     

Slow rhythmic rate fluctuations of cat midbrain reticular neurons in synchronized sleep and waking

Neuronal rate fluctuations in midbrain reticular formation (MRF) in chronically implanted, behaving cat were analyzed for occurrences of slow rhythmic activity (periods 6–24 s) in quiet waking and synchronized sleep (S). Appreciable rhythmicity, when compared to that resulting from randomly ordered intervals, was found in both vigilance states with rhythmic periods usually between 8 and 12 s.Fifteen MRF neurons having epochs exceeding 2 min in S, and analyzed as a group, suggest the existence of common rhythms related to the onset of S, show a significant rate decrease about 1 min before the end of S, and suggest a possible return of common rhythms relative to the end of the state.     

Control of the tonic vibration reflex by the brain stem reticular formation in the cat

The tonic vibration reflex (TVR) has been used to investigate the areas in the brain stem which influence tone in flexor and extensor muscles in the hind limb of the cat.Tonic contraction of triceps surae and tibialis anterior was inhibited by stimulation of the medial medullary reticular formation and facilitated by lateral medullary stimulation. Between the inhibitory and facilitatory areas, a mixed area was found which produced facilitation on direct stimulation which was altered to inhibition when the contralateral motor cortex or internal capsule was stimulated simultaneously.A small area in the caudal medulla reciprocally enhanced and suppressed the TVR in flexors and extensors respectively.     

Neuronal activity in the midbrain reticular formation related to behavioral habituation and sensitization

KOOTZ, J. P. AND H. M. SINNAMON. Neuronal activity in the midbrain reticular formation related to behavioralhabituation and sensitization. BRAIN RES. BULL. 3(5) 533–539, 1978.— Single units of the midbrain reticular formation (MRF) were recorded in the active rat (N = 10) during the presentation of repetitive trains of clicks or flashes. The movement and orienting behavior elicited by the stimuli, measured by direct observation and in terms of electrical disturbances in the recording cable, showed habituation in 14 cases, sensitization in six cases, and no decrement in nine cases. Of the 18 MRF units recorded during at least one of these behavioral conditions, seven were classed as congruent, i.e., they showed activity that paralleled the behavioral response. The majority of MRF units were behaviorally incongruent; in the most frequently observed case, their activity failed to change reliably when behavior habituated. Although the activity of congruent units generally showed moderate correlations with behavior that followed stimulation, disassociations between the two responses were commonly found. While the data are consistent with a role for the MRF in behavioral habituation and sensitization, they provide little evidence that the region is closely linked to the systems in direct control of behavior.     

Direct projection of pause neurons to nystagmus-related excitatory burst neurons in the cat pontine reticular formation

Brain-stem pause neurons (PNs) are inhibitory neurons which cease their tonic firing about 20 ms prior to the quick phase of horizontal vestibular nystagmus in either direction. One group of nystagmus-related burst neurons just rostral to the abducens nucleus exhibits a burst of spikes before and during the quick phase to the ipsilateral side--excitatory burst neurons (EBNs). The present study supported the conclusion that PNs project to, and tonically inhibit EBNs during the slow phase and that the burst of activity of EBNs at the quick phase is partly caused by the abrupt release from pauser inhibition. The evidence leading to this conclusion is: simultaneous recording of PNs and EBNs showed close alternation of firing; PNs were antidromically activated from the EBN region; systematic microstimulation tracks within the EBN region showed an antidromic activation pattern of low threshold sites separated by high threshold sites consistent with PN axonal branching in the EBN region; during the nystagmus slow phase there were positive field potentials in the EBN region, followed by an abrupt negative deflection whose onset was synchronous with the last pauser spike; when single PN spikes were used to trigger averages of extracellular field potentials in the EBN region (postspike averaging), a consistent short-latency positivity was observed. This study shows an additional connection in the premotor neural network responsible for the generation of the quick phase of horizontal vestibular nystagmus.     

Responses of limbic cortex neurons in the cat during performance of an instrumental conditioned reflex

Neuronal impulse activity in areas 24 and 32 was studied in cats during conditional placing. Activity of different neurons in the limbic cortex of trained cats correlated with acoustic stimuli, movement reactions and in some cases with reinforcement. Only 16% neurons of untrained animals responded to acoustic stimulations. After training the number of neurons responding to sound increased in area 32 to 51.3%. 34.6% of neurons responded by initial excitation and 26.7% by inhibition of impulse activity. Latencies of these responses were about 50 ms, their duration--up to 200 ms. Similar, but less noticeable responses were found in neurons of area 24. Short latency activation responses to conditional and differentional stimulations did not differ essentially. It is assumed that limbic cortex after conditioning can facilitate acceptability of both conditional and differential signals irrespective of their functional role.     

Diencephalic projections from the midbrain reticular formation.

(1) Physiologically guided stereotaxic coagulation was placed so as to avoid major through pathways in the midbrain reticular formation of 7 cats. Diencephalic degeneration resulting from this was traced by the Nauta method. (2) Preterminal degeneration was found in: the intralaminar nuclei and the posterior group (PO); the ventral group of thalamic nuclei; the ventral thalamus, including the zona incerta, subthalamus and fields of Forel; and the lateral hypothalamus. (3) The results are discussed in relation to somatomotor reactions, reticular influences on the electroencephalogram and telencephalic representation of pain.     

Activity of medullary reticular formation neurons in the unrestrained cat during waking and sleep

Single units, recorded in the medial medullary reticular formation (RF) in unrestrained, behaving cats, discharged in conjunction with specific movements and postures. Most cells were also active during REM sleep. Discharge rates in active waking and REM sleep were positively correlated and discharge patterns in these states were similar. We conclude that activity in these cells is related to the motor activation occurring in both active waking and REM sleep. We found no cells whose discharge was related in a non-specific way to motor tone or to REM sleep atonia. We discuss mechanisms by which medullary units with specific motor relations may give rise when stimulated to the relatively non-specific motor effects previously reported.     

Antidromic responses and reflex activity of single salivatory neurons in the cat

Single salivatory neurons of the brain stem of the urethane-chloralose anesthetized cat were identified by their antidromic responses to stimulation of the chorda tympani. The antidromically identified neurons were recorded in the lateral reticular formation of the brain stem between the spinal trigeminal nucleus and the vestibular complex. As suggested by previous anatomic work, the salivatory neurons appear to be diffusely distributed within the region. The identified neurons responded synaptically to stimulation of the lingual nerve, but this reflex activity was not mediated by an input from the taste fibers.     

Effects of peripheral stimulation on the activity of neurons in the ventral tegmental area, substantia nigra and midbrain reticular formation of rats

Extracellular recordings were obtained from neurons in the ventral tegmental area (VTA), the substantia nigra, including the zona compacta (SNC) and the zona reticulata (SNR), and the midbrain reticular formation (FOR) of adult female albino rats anesthetized with urethane and chloral hydrate. Based on electrophysiological characteristics the neurons were divided into two types. Type I neurons, with relatively long spike durations and slow discharge rates, were confined to the VTA and SNC. Type II neurons, with shorter spike durations and faster discharge rates, were observed in the SNR and FOR as well as the VTA and SNC. The effects of foot pinch (FP), tail pinch (TP) and stimulation of the vaginal cervix (VC) on the activity of the two types of neurons were investigated. Previously it was demonstrated that FP was aversive, TP elicited locomotion, sniffing and gnawing responses and VC lordosis response, vocalization and immobility. For approximately two-thirds of the neurons the effects of the three peripheral stimuli were similar; either they were activated or suppressed. Approximately 8 percent of the neurons were suppressed by FP and TP and activated by VC whereas a similar number were activated by FP and TP and suppressed by VC. Type 1 and Type II neurons in the VTA and SN were activated and suppressed by the peripheral stimuli with suppression being the most common response to FP and TP. The results are consistent with the view that VTA and SN neurons integrate a number of central and peripheral inputs.     

Eye movement related neurons in the cat pontine reticular formation: projection to the flocculus

This study examines projection to the cerebellar flocculus of eye movement-related neurons in the median and paramedian part of the cat pontine tegmentum between the trochlear and the abducens nucleus. They were identified by rhythmic activity related to horizontal vestibular nystagmus induced by sinusoidal rotation. These neurons were classified into several groups by their discharge patterns during nystagmus, using criteria of earlier studies on saccadic eye movements and vestibular nystagmus in the monkey. Electrical stimulation of the ipsilateral flocculus elicited antidromic spike responses in a number of burst-tonic neurons and long-lead and medium-lead burst neurons. These neurons were located in and around the medial longitudinal fasciculus, the nucleus raphe pontis and the nucleus reticularis tegmenti pontis. A few neurons tested were also activated antidromically by stimulation of the contralateral flocculus. In contrast, no pauser neurons were activated from the ipsi-lateral flocculus. It is concluded that eye movement-related neurons in the medial pontine tegmentum, except for pauser neurons, directly project to the flocculus and may convey information about eye movements of visual and vestibular origins to the flocculus.     

Direct projection of type II vestibular neurons to eye movement-related pause neurons in the cat pontine reticular formation

Brain stem pause neurons play an important role in the regulation of rapid eye movements. However, the input sources that drive pause neurons are uncertain. In the present study, horizontal canal type II neurons in the medial vestibular nucleus were antidromically activated by electrical stimulation of the pause neuron region. Systematic microstimulation tracks within that region showed an antidromic activation pattern of low-threshold sites separated by high-threshold sites consistent with axonal branching of type II neurons in the pause neuron region. Spike-triggered averaging of single spontaneously firing type II vestibular neuronal discharges in the pause neuron region resulted in short-latency, positive field responses. These results supported the conclusion that horizontal canal type II neurons of the medial vestibular nucleus project to and inhibit pause neurons monosynaptically.     

Unit activity in the thalamic reticular nucleus during external stimulation in cats taught an instrumental conditioned reflex

Application of heteromodal extrastimuli (ES) promotes selected excitation of most of the responding neurons in the thalamic reticular nucleus (R). Twelve of 32 tested neurons responded to visual ES and 4 from 21 tested neurons responded to auditory ES. Initial responses of neurons and quantity of cells with initial responses decreased during habituation to ES. Grouped discharges disappeared after external stimulation. Initial responses to ES and to the following conditional stimulus appeared during external inhibition (EI), while late responses usually accompanying conditioning were inhibited almost in half of the studied neurons. It was suggested that R neurons participated in EI and in habituation to ES.