High Levels Of Spontaneous Activity Research Articles

The programming of circadian flight‐activity in relation to mating and the gonotrophic cycle in the mosquito, Aedes aegypti

ABSTRACT. The circadian flight activity of female Aedes aegypti (L.) changes after insemination and during the course of the gonotrophic cycle. Virgin females attain a high level of spontaneous activity within 3–4 days of adult emergence; in LD 12:12 there are peaks of activity at the beginning and end of the light phase. Inseminated females are less than 20% as active as virgins, but exhibit a similar daily pattern. After blood‐feeding, inseminated females become almost totally inactive for about 48h and then show a unimodal pattern of activity which is consistent with oviposition behaviour; after oviposition they revert to the basic inseminated pattern and level of activity. Blood‐fed virgin females continue to show a high level of spontaneous activity. It is suggested that insemination has the general effect of raising the threshold for activity and that it is necessary before blood‐fed females can switch to the gravid behaviour programme. Blood‐fed uninseminated females thus continue with behaviour which will maximize the probability of insemination.

Ipsilateral inhibitory responses in the cat lateral superior olive

Ipsilateral inhibitory responses in the cat lateral superior olive

Effect of prolonged isolation on learning, biogenic amine turnover and aggressive behaviour in three strains of mice

Two albino strains (MF-1 and CF-1) and one non-albino inbred strain (DBA/2J) of mice were compared for shuttle-box avoidance acquisition and fighting behaviour following a 5-week isolation period. Brain levels and turnover rates of norepinephrine and serotonin were also measured in groups of isolated mice. Mice housed in groups of five (aggregated) served as control subjects. Only the albino strains became aggressive after isolation; DBA/2J mice did not fight when paired. Results obtained in order of increasing facility of avoidance acquisition and a higher level of spontaneous activity were: DBA/2J mice > CF-1 mice > MF-1 mice. These results were correlated with whole-brain steady-state levels of norepinephrine among the strains. No differences in avoidance acquisition or serotonin levels and turnover rates were observed between isolated and aggregated mice within the same strain. CF-1 mice had lower levels and a faster turnover rate of serotonin compared with the other strains. Norepinephrine turnover rates were unchanged in CF-1 and DBA/2J mice following isolation, but were significantly slowed in MF-1 isolated mice compared with their controls. It is concluded that no clear-cut relationship exists among learning ability, aggressive behaviour and biogenic amine turnover rates in isolated or aggregated mice.

Responses of interpositus neurones to nerve stimulation in chloralose anaesthetized cats

Eccles et al. 6 have recently described the responses of neurones of the nucleus interpositus to stimulation of forelimb and hindlimb cutaneous afferents in decerebrate cats. The responses included two phases of excitation associated with cell discharges with latencies of about 6 and 19 msec. These were separated and succeeded by phases of inhibition. The first excitation was attributed to the action of collaterals of cuneo-cerebellar or direct spino-cerebellar axons and the second to collaterals of reticulo-cerebellar and olivo-cerebellar axons. The inhibitions were attributed to the action on the nuclear cells of the impulses from Purkinje cells 5 discharged by the afferent volleys. The present paper describes firing patterns of interpositus neurones following nerve stimulation in cats anaesthetised with a-chloralose. A somewhat surprising finding was that the cells did not always display the high level of spontaneous activity which previous authors have reported for intracerebellar nuclear neurones in unanaesthetised 15, decerebrate 6 or barbiturate anaesthetised s preparations. In addition the responses to nerve stimulation included a hitherto undescribed component consisting of a high-frequency burst of action potentials. The experiments were performed on 17 cats initially anaesthetised with ether or halothane followed by 60 mg/kg of recrystallised a-chloralose dissolved in propane1,2-diol. Some animals were paralysed with gallamine triethiodide and artificially respired. Recordings were usually begun about 7 h after the initial dose of chloralose. The left deep radial (DR), sural (SUR), femoral (FEM), gastrocnemius-soleus (GS) nerves and both superficial radial (SR) nerves were dissected and stimulated with single shocks at a repetition rate of 1/2 sec. Stimulus strengths were usually in the range 1-4 times the threshold of the most excitable fibres in the nerve, though stronger stimuli were occasionally used. Interpositus axons were stimulated in the region of the right red nucleus using a concentric stainless steel electrode. In 7 experiments a similar electrode was placed in the rostral part of the right inferior olivary nucleus.

Binocular units in the lateral geniculate nucleus of chronic cats

Summary The effect of monocular and binocular stimulation on cells in the lateral geniculate nucleus was investigated in awake cats with painless head fixation. The cells were stimulated by moving visual patterns presented on a tangent screen. The features of the behavior of the cells were a relatively high level of spontaneous activity and a vigorous response to the moving patterns without any evidence of directional selectivity. Typically, the cells showed either on-, off- or on-off-responses to stimulation with diffuse light. When both eyes were stimulated by the moving patterns, the response varied from cell to cell. According to the form of the response, the cells were classified into 8 types. Depending on receptive field organization and balance of the center-surround influences, responses were either purely excitatory or inhibitory, or combinations of excitation and inhibition. Binocular response was compared with each of two monocular responses in 406 cells. The response was obtained exclusively by stimulation of one eye in 222 cells (54.7%). Binocular interaction occurred in the remaining 184 cells (45.3%). Of these, 85 cells (20.9%) were excited binocularly and various types of binocular interaction, either facilitation, summation or occlusion , occurred. In 70 cells (17.2%), excitation occurred upon stimulation of one eye and inhibition occurred upon stimulation of the other eye, and the response from the dominant eye was markedly suppressed when both eyes were stimulated simultaneously. In 16 cells (3.9%) no response occurred with monocular stimulation of each of the two eyes, but a clear response occurred upon binocular stimulation. Nine cells (2.3%) were activated monocularl, but the input from the non-dominant eye gave a facilitatory influence upon the response and the binocular response was markedly larger than the monocular response. The non-dominant eye gave an inhibitory influence in 4 cells (0.9%). The binocular response was smaller than the dominant eye response. Binocularly activated cells tended to be located in two areas. One area is in the dorsal part of layer A and the other area is below layer A 1 . On the other hand, the cells that were excited by stimulation of one eye and inhibited by stimulation of the other were located predominantly in the two main dorsal layers, A and A 1 .

Reciprocal control of spontaneous activity and reflex effects in static and dynamic flexor gamma-motoneurones revealed by an injection of DOPA.

AbstractSingle γ‐efferents to flexors have been studied in the spinal unanesthetized cat before and after an intravenous injection of DOPA. The γ‐efferents could be classified in two groups, one with a high level of spontaneous activity that was decreased after an injection of DOPA, and another with a low level of activity that was enhanced after DOPA. These data together with differences in reflex behaviour between the two types of γ‐motoneurones provided a basis for a comparison with the deduced properties of dynamic and static γ‐motoneurones obtained from studies of spindle afferents with primary and secondary endings. It could be concluded that the former type is identical with dynamic and the latter with static γ‐motoneurones. Both dynamic and static neurones could be reflexly activated in the long‐latency flexor reflex occurring after DOPA. Likewise both types of γ‐motoneurones were activated in the short‐latency flexor reflex, the dynamic more effectively before and the static more effectively after DOPA. The results suggest that descending noradrenergic fibres control reflex activation and the spontaneous activity of γ‐motoneurones to flexors in a reciprocal fashion.

Central mechanisms controlling the activity of locust flight muscles

Abstract The activity of single neurons of a metathoracic ganglion in Locusta migratoria migratorioides was recorded extracellularly in the output region of the first and second segmental nerves by means of microelectrodes. A high level of spontaneous activity has been revealed. This activity proved to be endogenous. Among spontaneously discharging neurons there occurred units with exclusively rhythmical and stable discharges which responded to afferent stimulation chiefly by inhibition. Among silent neurons there were units which needed afferent stimulation largely for initiating and maintaining a required (threshold) activity level. These neurons are compared with generatory neurons (pacemakers) in the centre of the cicada tymbal muscles. The conclusion is drawn about similar functional mechanisms of both types of neurons. In the paper is given a preliminary scheme of the functional organization of the flight control system of the locust by considering the role of pacemaker (generatory) and spontaneously discharging neurons.