Depression of the vestibulo-ocular and optokinetic responses by intrafloccular microinjection of GABA-A and GABA-B agonists in the rabbit

The functional implication of the cerebellar flocculus in regulation of the VOR and OKR gain has mostly been studied by lesion experiments, and the hypotheses derived from these experiments are not always in line with one another. In the present study, a reversible method was used to inhibit floccular Purkinje cells. The GABA-A agonist muscimol or the GABA-B agonist baclofen were bilaterally injected into the flocculus of rabbits, and the effects of these injections on the gain of the VOR and OKR were studied. Both drugs induced a reduction by at least 50% of the gain of the VOR in light and darkness, and of the OKR. Although GABA-A and GABA-B receptors are known to have different cerebellar localizations, muscimol and baclofen injections resulted in quantitatively similar effects. It is suggested that these GABA-agonists cause either direct or indirect inhibition of floccular Purkinje cells, thus reducing modulation of the firing rate of these neurons by afferent mossy and climbing fibers. Because the flocular Purkinje cells act out of phase with the vestibular neurons which drive the oculomotor neurons, a reduced output of floccular Purkinje cells would result in a reduction of the VOR and OKR gain. These experiments provide strong evidence that the cerebellar flocculus has a positive influence on the basic VOR and OKR gain.     

Is the adaptation model a valid description of the vestibulo-ocular reflex?

The pendulum model of the vestibulo-ocular reflex, including the effects of adaptation, has been evaluated using the responses of 36 normal subjects to impulsive stimuli of 128 and 256°/s. Estimates of the model parameters such as the time constants, the slow velocity threshold, and the minimum stimulus required to produce an after-nystagmus have been obtained using a new analytical technique. Although some of the data support the validity of the adaptation model, evidence is presented to demonstrate that the overall applicability of the model is limited.     

Neural network models of velocity storage in the horizontal vestibulo-ocular reflex

The vestibulo-ocular reflex (VOR) produces compensatory eye movements by utilizing head rotational velocity signals from the semicircular canals to control contractions of the extraocular muscles. In mammals, the time course of horizontal VOR is longer than that of the canal signals driving it, revealing the presence of a central integrator known as velocity storage. Although the neurons mediating VOR have been described neurophysiologically, their properties, and the mechanism of velocity storage itself, remain unexplained. Recent models of integration in VOR are based on systems of linear elements, interconnected in arbitrary ways. The present study extends this work by modeling horizontal VOR as a learning network composed of nonlinear model neurons. Network architectures are based on the VOR arc (canal afferents, vestibular nucleus (VN) neurons and extraocular motoneurons) and have both forward and lateral connections. The networks learn to produce velocity storage integration by forming lateral (commissural) inhibitory feedback loops between VN neurons. These loops overlap and interact in a complex way, forming both fast and slow VN pathways. The networks exhibit some of the nonlinear properties of the actual VOR, such as dependency of decay rate and phase lag upon input magnitude, and skewing of the response to higher magnitude sinusoidal inputs. Model VN neurons resemble their real counterparts. Both have increased time constant and gain, and decreased spontaneous rate as compared to canal afferents. Also, both model and real VN neurons exhibit rectification and skew. The results suggest that lateral inhibitory interactions produce velocity storage and also determine the properties of neurons mediating VOR. The neural network models demonstrate how commissural inhibition may be organized along the VOR pathway.     

Gravity-dependent and gravity-independent gain changes during vertical vestibulo-ocular reflex (VOR) adaptation

The gain of the vertical angular vestibulo-ocular reflex (aVOR) was adaptively increased or decreased with monkeys in a side down position, and the gains were tested with the axis of rotation tilted in 10 degrees increments from left- to right-side-down. Gain changes, expressed as a percentage of the preadapted values, were plotted as a function of head tilt, and fit with a cosine function. The amplitude of the cosine was half of the gravity-dependent component of the gain change and the bias, the gravity independent component. The largest changes in the gain of both components occurred in the first 30 min and continued at a slower rate throughout adaptation. The gravity-dependent and -independent gain changes were larger for gain decreases than for gain increases, but both components had similar dynamics. We conclude that the alteration in gain of the aVOR always occurs in the context of gravity.     

Enhancement of both long-term depression induction and optokinetic response adaptation in mice lacking delphilin

In the cerebellum, Delphilin is expressed selectively in Purkinje cells (PCs) and is localized exclusively at parallel fiber (PF) synapses, where it interacts with glutamate receptor (GluR) delta2 that is essential for long-term depression (LTD), motor learning and cerebellar wiring. Delphilin ablation exerted little effect on the synaptic localization of GluRdelta2. There were no detectable abnormalities in cerebellar histology, PC cytology and PC synapse formation in contrast to GluRdelta2 mutant mice. However, LTD induction was facilitated at PF-PC synapses in Delphilin mutant mice. Intracellular Ca(2+) required for the induction of LTD appeared to be reduced in the mutant mice, while Ca(2+) influx through voltage-gated Ca(2+) channels and metabotropic GluR1-mediated slow synaptic response were similar between wild-type and mutant mice. We further showed that the gain-increase adaptation of the optokinetic response (OKR) was enhanced in the mutant mice. These findings are compatible with the idea that LTD induction at PF-PC synapses is a crucial rate-limiting step in OKR gain-increase adaptation, a simple form of motor learning. As exemplified in this study, enhancing synaptic plasticity at a specific synaptic site of a neural network is a useful approach to understanding the roles of multiple plasticity mechanisms at various cerebellar synapses in motor control and learning.     

Parameters adaptation in the populations models

Ecology-evolutionary models of low dimensions were developed on the basis of competitive selection criteria. Dynamics of variables (number of individuals) and the search of evolutionary-stable values of parameters (biological characterictics of populations) were monitored in the suggested models. If the environmental temperature is changing periodically, the average (a) and width (d) of temperature tolerance range appears to be the important parameters. By model experiments it was established that stable values of temperature (a), favorable for development of highly specialized algae (d is low) were close to minimum and maximum of temperature curve. And for the low specialized algae (d is high) this values were close to the average temperature of environment. In a similar manner, a set of evolutionally stable parameters (a, d) was established for either of the two interacted populations (competitors and "predator-prey"). The hypotheses concerning it's geometric structure and the process of coevolution is formulated.     

Physical models of biological information and adaptation

The bio-informational equivalence asserts that biological processes reduce to processes of information transfer. In this paper, that equivalence is treated as a metaphor with deeply anthropomorphic content of a sort that resists constitutive-analytical definition, including formulation within mathematical theories of information. It is argued that continuance of the metaphor, as a quasi-theoretical perspective in biology, must entail a methodological dislocation between biological and physical science. It is proposed that a general class of functions, drawn from classical physics, can serve to eliminate the anthropomorphism. Further considerations indicate that the concept of biological adaptation is central to the general applicability of the informational idea in biology; a non-anthropomorphic treatment of adaptive phenomena is suggested in terms of variational principles.     

Cold adaptation in insects of Central Yakutia

The mode of cold hardening was for the first time assessed for 20 insect species living in the extremely cold climate of Yakutia. All insects tested were found to adapt through freeze tolerance, producing ice-nucleating agents that cause the hemolymph to freeze at high subzero temperatures. For the first time ice-nucleating agents were demonstrated in Lepidoptera. Pieris rapae exemplified the possibility of switchover in the survival strategy depending on the climatic conditions.     

Central adaptation to inspiratory-inhibiting expiratory-prolonging vagal input

We reported earlier on the changes in excitability of central respiratory switching mechanisms in the course of a brief inspiratory-inhibiting vagal stimulus (J. Appl. Physiol. 50: 1183-1192, 1981). To further define the dynamics of central processing of such input we studied the changes in the excitability of timing mechanisms in the immediate (less than 1.0 s) and late (1-20 s) periods after stimulus removal. We also examined the changes in respiratory timing in the course of protracted (greater than 20 s) stimulation. Studies were done using pentobarbital-anesthetized cats. For studies involving long-term stimulation or late off responses, cats were paralyzed, vagotomized, carotid denervated, and artificially ventilated. We found that the inspiratory inhibitory influence of a brief stimulus continues, in a declining fashion, for 0.3-10 s after removal of the stimulus. This was followed by a paradoxical response, inspirations were prolonged and expirations were shortened, which was maximal 1-2 s after stimulus removal and which declined gradually over a period of 6-16 s. There was progressive decline in inspiratory-shortening expiratory-prolonging influence in the course of sustained stimuli. These results indicate substantial adaptation in the course of even brief stimuli and provide an explanation for inspiratory-expiratory duration and expiratory-inspiratory duration linkages.     

Development of optokinetic neuronal responses in the pretectum and horizontal optokinetic nystagmus in unilaterally enucleated rats

Responses of single units to constant-velocity rotations of the visual surround (0.25-10 degrees/s) were studied in the pretectum of unilateral enucleated rats at different ages. Enucleation was performed either in the first postnatal week ("early" enucleated rats) or in the adult stage ("late" enucleated rats). Pretectal unitary responses were recorded in early enucleated animals at postnatal day 20-21, 36-49 and, in both experimental groups, in the adult stage. Optokinetic ocular nystagmus was studied in early and late enucleated rats in the adult stage. Gain of optokinetic nystagmus in temporo-nasal stimulus direction was not changed for visual surround rotations of up to 20 degrees/s compared to controls in monocular viewing conditions. At higher stimulus velocities, however, the gain dropped. In naso-temporal stimulus direction, optokinetic nystagmus was improved in gain for optokinetic pattern motions of up to 5-10 degrees/s. There were only minor differences in the gain behaviour of optokinetic nystagmus obtained from early or late enucleated rats. The optokinetic responses of pretectal neurons obtained from early and late enucleated rats were reduced in sensitivity by more than 50%. The response patterns of neurons recorded in the contralateral pretectum relative to the intact eye were shifted by a large amount from directional selective to directional nonselective response types. No such changes were obtained in the ipsilateral pretectum. In contrast to normal rats, there were very few directional selective units responding to temporo-nasal pattern motion. On the other hand, a large proportion of directional selective units responded to naso-temporal pattern motion. These latter units were found in both early and late enucleated rats. A similar response type has previously been described for intact young rats but not for adult rats. The velocity tuning curve of pretectal units studied in the adult stage was similar in shape in early and late enucleated rats and resembled that obtained from enucleated or intact young animals. Our results show that response sensitivity, direction and velocity tuning of pretectal units depend crucially on retinal afferent input originating from both eyes. The data suggest that the response characteristics of many of the pretectal units that are considered to be important for mediating optokinetic reflexes depend on interpretectal signal processing using commissural connections. There is very little evidence for an adaptative structural plasticity of the optokinetic system following loss of one eye. The reduced asymmetry observed in gain of optokinetic responses correlated in both early and late enucleated rats with the shifts observed in the distribution of pretectal unitary response patterns.     

Traditional occupations and nutritional adaptation among Central Indian caste populations

The socioeconomic milieu has benefits and drawbacks for determining level of nutrition. The Indian population provides an excellent example of nutrition-driven adaptation. The present paper deals with the relationship between BMI (body mass index) and traditional occupation and process of adaptation among adult males of Central India. Anthropometric data collected by the Anthropological Survey of India on stature, sitting height and weight of 6663 adult males belonging to 22 castes were used for computation of BMI and Cormic index. The caste groups earning their living as labourers are found to be shortest (157.4+/-6.5 cm), and the caste group practising priesthood are tallest (168.6+/-6.6 cm). The prevalence of chronic energy deficiency is found to be highest (72%) among castes earning their living as daily wage labourers. The ANOVA on Cormic index and BMI suggests that people within the same occupational group are more homogeneous than those from different occupational groups. The t test also supports the homogeneity of the same occupational group.     

Interactions between enzyme-forming systems during adaptation

Experiments on enzymatic adaptations in yeast to galactose and maltose under various conditions are examined. The pertinent facts established may be summarized as follows:- 1. The presence of exogenous nitrogen stimulates the rate of adaptation and raises considerably the attainable level of enzyme activity. 2. This stimulation is absent if the cells are unable to assimilate the added nitrogen. 3. Competitive interactions can be exhibited between two adaptive enzyme systems induced either serially or simultaneously in the same cell. 4. A similar kind of interaction was observed between an adaptive and a so called "constitutive" enzyme. 5. The presence of exogenous nitrogen modifies greatly the nature and extent of the interaction between the enzyme-forming systems. The significance of these results to our understanding of the mechanism of the modification and maintenance of cellular enzymatic constitution is discussed. The validity of the distinction between "constitutive" and "adaptive" enzymes is reexamined in the light of the data presented.     

Central GABA-ergic systems and feeding behavior

Central GABA-ergic systems appear to be involved in the regulation of food intake and body weight in animals. Studies performed with systemic or intracerebral administration of GABA, GABA-agonists and GABA-antagonists support this view.     

Mediators of communication and adaptation in the neuroendocrine and immune systems.

Bidirectional interactions between the immune and neuroendocrine systems influence specifically physiological activities as diverse as tissue localization of lymphocytes, antibody responses, hypothalamic-pituitary hormone secretion, and neural signal transmission. Our understanding of intersystem communications has been increased by the delineation of the innervation of immune organs, effects of neuromediators on immune cells, and neuroendocrine responses to individual immune cytokines. Two patterns of responses to neuroimmune mediators have been defined to distinguish between direct alterations in cellular function and the more complex states of differentiation and adaptation that condition the threshold and nature of reactions to subsequent stimuli. Recent identification of the molecular mechanisms of action of neuroimmune mediators is exemplified by elucidation of the requirement for prolactin in T lymphocyte proliferation and of the effects of vasoactive intestinal peptide on B lymphocyte expression of adherence proteins. Further knowledge of the advantages of multisystem integration of functions in host defense may reveal other novel mechanisms of cellular communication and biological adaptation.