Hippocampal mediation of shaking behavior induced by electrical stimulation of the perforant path in the rat

Perforant path stimulation in awake, unrestrained rats caused frequency-dependent shaking behavior in the absence of detectable epileptiform activity. Granule cell discharge, monitored by evoked field potentials, was necessary for the induction of shaking behavior. Direct stimulation of the granule cell layer also caused shakes. Intracebroventricular injections of kaininc acid destroyed hippocampal CA3 pyramidal cells and blocked the shake response. These results indicate that hippocampal granule cell discharge mediates stimulation-induced shaking behavior, and, that epileptiform activity is not required for the induction of shaking behavior by electrical stimulation.     

Eye movements evoked by electrical stimualtion of the brain in anesthetized fishes.

Several eye movements were evoked by electrical stimulation of the brain in anesthetized sunfish and goldfish. Conjugate lateral rolling movements, similar to eye movements observed when an unoperated fish is rotated about its long axis, were evoked from the acoustico-lateral area of the medulla and the eminentia granularis and an adjacent medial portion of the cerebellum. Bilateral and unilateral backward rotations, similar to the eye movements observed when unoperated fish are rotated forward about the interpupillary axis, were evoked from the medial longitudinal fasciculus and areas related to the oculomotor nerve. Bilateral forward rotations, comparable to the eye movements resulting when unoperated fish are rotated backward about the interpupillary axis, were elicited by stimulation near the trochlear nerve roots in the valvula of the cerebellum; unilateral responses resulted from stimulation near the exiting trochlear nerves. Convergence was elicited by stimulation in the midline near the oculomotor complex and the medial longitudinal fasciculus while unilateral vergence responses were triggered by stimulation in the medial longitudinal fasciculus and areas lateral to the oculomotor nucleus. Conjugate eye movements in the horizontal plane were frequently evoked but were not studied in detail.     

Influences of hypothalamic stimulation upon septal and hippocampal electrical activity in the cat.

Spontaneous patterns of hippocampal EEG and septal cell activity were studied in immobilized cats, and the influences of high frequency stimulation of medial hypothalamus (MH) and lateral hypothalamus (LH) were determined. Septal cells were divided into 3 classes on the basis of their discharge patterns: (1), rhythmic bursting (2), non-rhythmic bursting and (3), non-bursting, and the relationship of these discharge patterns to hippocampal theta rhythm was analyzed. Rhythmic bursting cells displayed close frequency and phase relations to hippocampal theta rhythm and were located chiefly in the diagonal band of Broca. Cells of the other two categories were found both within and outside of the diagonal band region.     

Phase-switching of respiration induced by central gray and hippocampal stimulation in the cat

Summary In vagotomized adult cats with the spinal cord transected at T₂, short trains of electrical pulses delivered to the central gray substance of the midbrain and the ventral hippocampus initiated a phase reversal in respiration from expiration to inspiration. A transition from inspiration to expiration, however, was not observed. It is suggested that this phase-switch may be mediated via a reticular formation input into the medulla rather than via the pontine synchronizing mechanisms.With 5 FiguresThis investigation was supported by grants from the Addiction Research Foundation of Ontario, and the Medical Research Council of Canada. — A preliminary report of portions of this work was presented at the 7th Annual Winter Conference on Brain Research at Steamboat Springs, Colorado in January, 1974.     

Developmental aspects of hippocampal electrical activity and motor behavior in the rat.

The developmental aspects of hippocampal electrical activity and motor behavior were studied in freely moving infant rats implanted with microelectrodes in the CA1 and dentate regions. The pup's motor abilities developed concomitantly with hippocampal electroencephalographic (EEG) activity. The uncoordinated and limited locomotion of 6- to 9-day-old pups was associated with very low-amplitude, low-frequency, irregular activity, similar to that accompanying immobility. Starting at 10 days, the EEG-behavior correlation described by Vanderwolf and his colleagues became evident: Voluntary movements were associated with hippocampal theta rhythm whereas immobility was associated with irregular activity. A second, lower-frequency type of theta, not correlated with movement, also appeared at 10 days. It was induced by anticholnesterase drugs and abolished by anticholinergics. Administration of anticholinergics caused minor disruption of movement-related theta, especially in younger animals. Observations of tonic and phasic REM sleep also demonstrated that the two types of theta activity appeared at 10 days of age. Despite the difference in the time course of morphogenesis, the prenatally formed CA1 pyramidal region and the postnatally formed dentate granule region developed in parallel with respect to the appearance of both types of theta activity at about 10 days. Theta frequency and amplitude developed to adult values during the next 2 weeks, but the activity in CA1 remained smaller than in the dentate region. The study thus supported the hypothesis that there are two main generators of theta activity, the CA1 pyramidal region and the dentate region.     

Behavioral and hippocampal electrical changes during operant learning in cats and effects of stimulating two hypothalamic--hippocampal systems.

The electrical activity of the dorsal and ventral hippocampus and of the anterior and posterior neocortex is described and illustrated during the development of trained operant behavior in water-deprived cats learning to bar-press for water reward under three operant conditioning schedules: (a) continuous reinforcement; (b) alternating 10 sec periods of reinforcement and non-reinforcement; and (c) mixed reinforcement and non-reinforcement with special auditory and visual cues. In addition, the contrasting effects of 100 c/sec electrical stimulation of the medial and lateral hypothalamic systems upon hippocampal electrical activity and operantly trained behavior are reported. During the early stages of learning to bar-press for water reward, when close attention to the bar and water-well are required, hippocampal electrical activity manifests synchrony (theta rhythm) and neocortical electrical activity is desynchronized. Subsequently, as bar-pressing performance improves and requires little attention to the manipulanda, the pattern of hippocampal and neocortical electrical activity is one of irregular slow waves mixed with low voltage high frequency activity, characteristic of relative inattention and automatic performance. During alternating or mixed reinforcement and non-reinforcement schedules of operant training differential effects are observed during reinforcement and non-reinforcement periods, the latter being characterized generally by lower voltage, mixed low and high frequency activity, except when orienting and shifting of attention occurred with associated theta rhythm bursts. Stimulation of the medial hypothalamic system has a striking inhibitory effect upon bar-pressing for water reward. Bar-pressing ceases for many minutes but its eventually resumed at the pre-stimulation rate. In contrast, stimulation of the lateral hypothalamic system only interrupts bar-pressing for a matter of seconds. Possible causes of these differential effects, and especially the prolonged inhibition of bar-pressing induced by medial hypothalamic stimulation, are discussed.     

Rotational behavior in the cat induced by electrical stimulation of the pulvinar-lateralis posterior nucleus complex: role of the cholinergic system

We studied the involvement of the cholinergic system in the contralateral head-eye-body turning induced in the cat through stimulation of the pulvinar-lateralis posterior nucleus complex (P-LP). In 17 cats through a cannula aimed at the P-LP, agonists and antagonists of the cholinergic system were injected. The electrical activity of the P-LP could be recorded through the same cannula or through electrodes attached to it. In addition, electrodes were implanted ipsilaterally in the dorsal hippocampus, caudate nucleus, amygdala, and superior colliculus to record through them and through one screw placed on the skull the electrical activity of those structures and of the cortical P-LP projection. Seven days after surgery, carbachol, an agonist of the cholinergic system was injected in the P-LP, and the behavior and electrical activity of the unrestrained cat (previously accustomed to a plastic cage) were recorded. A control volume of 0.9% NaCl was always injected previously. The usual drug volume injected was 1 microliter; occasionally, 2 microliter were injected. Weekly or biweekly sessions were conducted to determine (a) the threshold for cholinergic activation, (b) the threshold for turning behavior, (c) the blocking effect of local atropine sulfate injected previously, (d) the effect of haloperidol previously injected (locally or systemically), and (e) the effect of dioxolane, an exclusive muscarinic agonist. In 14 of 17 cats, contralateral turning behavior was evoked by carbachol. In two of the three cats that did not respond to carbachol, dioxolane induced turning. The effect of dioxolane was similar to that of carbachol when tried in five cats. Besides turning behavior, carbachol produced numerous symptoms due to cholinergic activation. Atropine blocked the rotational effect of carbachol in all cats, and haloperidol blocked it in 68% of them. Electrolytic coagulation of the dorsal hippocampus surrounding the P-LP did not disturb the effects induced by carbachol. These experiments show that both systems of the P-LP, cholinergic and catecholaminergic, are involved in the contralateral turning. We conclude that the effect induced by carbachol is due to activation of muscarinic receptors because it is totally blocked by local atropine sulfate and is reproduced by dioxolane, an exclusive muscarinic agonist.     

Turning behavior induced by electrical stimulation of the nigro-neostriatal system of the rat.

Rats were prepared with electrodes chronically implanted in the posterolateral hypothalamus close to the ascending axons of the nigrostriatal dopamine neurons. During continuous electrical stimulation through these electrodes the rats circled rapidly towards the unstimulated side. The circling behavior was inhibited by drugs which deplete brain dopamine and by drugs thought to block dopamine receptors, while low doses of amphetamine potentiated it. The method was developed with the hope of obtaining an in vivo model for studies on nerve impulse related dopamine release in the brain.     

Hippocampal electrical activity and behavior in the presence of novel environmental stimuli in rabbits

Male rabbits have been used in a simultaneous study of their behavioral and neural activity in different experimental situations related to attention and emotionality. The electrical activity of the dorsal hippocampus and frontal cortex was recorded in the following experimental situations: Neutral Environment (response to a novel environment); Object (response to a novel stimulus); Stuffed sparrow hawk; and live cat. Results show that behavioral and electrical responses depend upon: (a) the nature of the stimulus; and (b) whether or not the stimulus is moving. As for the immobile stimuli, the stuffed animal presentation significantly reduced both behavioral activity and percentage and frequency of rhythmic slow activity (RSA); prolonged periods of ECoG synchronization were also recorded. The introduction of the live cat greatly increased the percentage and frequency of RSA, especially when the cat was looking at the rabbit. The experimental situations caused differences in the distribution of RSA frequencies as well. The percentage of high RSA frequencies (>6.5 Hz during immobility; >7.2 Hz during movement) recorded in response to the immobile stimuli was negatively correlated to the amount of RSA. Results are discussed in the light of attentional and emotional theories.     

Hippocampal interictal spikes induced by kindling: relations to behavior and EEG

Hippocampal spontaneous interictal spikes (SISs) were recorded during the course of daily tetanization (kindling) of afferent fibers to the hippocampal CA1 region. SISs were detected after 3-10 tetanizations. A clear variation of SIS rate with behavior was observed. SIS rate was high during slow-wave sleep (SWS), waking immobility, face-washing and chewing and low during rapid-eye-movement sleep (REMS), walking and rearing. Scopolamine hydrochloride (2.5-5 mg/kg i.p.) increased the SIS rate during walking. Despite the negative correlation of SIS occurrence with the theta rhythm in normal rats, abolishing the theta rhythm by medial septal lesions did not affect the suppression of SISs during REMS as compared to SWS. When interictal or postictal spikes were seen together with the theta rhythm, the spikes tended to occur at a phase of about 240 degrees after the positive peak of the alvear surface rhythm.     

Hypothalamically induced emotional behavior and immunological changes in the cat

Numerous animal studies on the correlation between stress and immunity have been performed but few such studies have been made concerning the relationship between various kinds of stress-related emotional behavior and immunological changes. Electrical stimulation of the hypothalamus in cats elicits various emotional behaviors such as restlessness, defensive attack, defensive retreat and quiet biting attack. We examined changes in the lymphocyte proliferative responses and plasma cortisol level which accompanied such emotional behavior. A significant increase in plasma cortisol was observed in the restlessness, defensive attack and defensive retreat groups, but not in the quiet biting attack or non-response (control) groups. A significant increase in the lymphocyte proliferative responses to phytohemagglutinin (PHA) was observed in the restlessness and defensive attack groups but not in the defensive retreat, quiet biting attack or non-response groups. These results suggest that various kinds of emotional behavior appear to be differentially correlated with the lymphocyte proliferative responses, while also being differentially correlated with the plasma cortisol concentration. Because the changes in lymphocyte responses and plasma cortisol did not always completely correlate with one another, the changes in the lymphocyte responses are not considered to be influenced by plasma cortisol alone.     

Hippocampal EEG and behaviour in dog. I. Hippocampal EEG correlates of gross motor behaviour.

It was shown that rewarding spectral shifts (i.e. increase in amplitude or peak frequency of the hippocampal EEG) causes a solitary dog to show increased motor behaviour. Rewarded spectral shifts concurred with a variety of behavioural transitions. It was found that statistically significant modulations occur in the spectral properties of the hippocampal EEG correlated with: (1) the transition from walking to standing; (2) the transition from standing while eating to walking away from the food dish; (3) the increase in speed of a walking dog, caused by rewarding the animal; and with (4) each head movement in a learned series of head movements. Thus behavioural transitions to a more active state are accompanied by an increase of amplitude, frequency and rhythmicity in the theta band of the hippocampal EEG; behavioural transitions to a less active state show the inverse relationship with the hippocampal EEG. A close relationship between modulations of the dog's hippocampal EEG activity and elementary motor acts is stressed. The hypothesis is put forward that the spectral properties of the hippocampal EEG reflect the degree to which a number of motor and sensory structures in the limbic midbrain and brain stem are active.     

Morphine suppression of bradycardia induced by electrical stimulation of gigantocellular reticular nucleus in the cat

In chloralose-urethane-anesthetized cats, intravertebral injection of morphine (1,2 and 4 mg/kg) promoted a drastic suppression of the bradycardia elicited by stimulating the medullary gigantocelular reticular nucleus (GRN). The degree of blockadge of GRN-induced cardioinhibition was directly dependent upon the dose of morphine and inversely related to the reticular stimulus train intensity and pulse frequency. The possibility that the GRM may be a site of action for morphine in its production of hypotension and bradycardia was discussed.     

Hippocampal EEG and behaviour in dog. II. Hippocampal EEG correlates with elementary motor acts.

A positive correlation has been shown between the speed of forced stepping on a conveyor belt and the amplitude and frequency of the concomitant hippocampal EEG. Significant modulation in the spectral properties of the dog's hippocampal EEG has been found in relation to 3 elementary motor acts: stepping, respiratory movements and a reflex movement in reaction to linear acceleration of the animal. The findings support the idea that within a certain experimental situation the hippocampal EEG reflects the intensity of motor behaviour in a non-specific but predictable way. However, some experimental results indicate that sensory inputs may modulate the hippocampal EEG as well.