Control of rabbit nictitating membrane movements

The objective of this study is to understand more precisely the relationship of motoneuron activity to movements of the rabbit nictitating membrane (NM). We use a model of the oculomotor plant to investigate what NM movements are generated by a given pattern of neural input and what inputs are required to generate particular NM movements. Simulated peak NM extensions can occur well over 50 ms after the end of motoneuron activity. The neural input required for the model to generate full amplitude NM extension responses is more consistent with single accessory abducens unit recordings from awake rabbits than recordings from anesthetized rabbits. An initial high frequency burst of neural activity followed by a rapid decay is required for simulations of conditioned responses (CRs) trained at a 125 ms interstimulus interval (ISI). For CRs trained with a 250 ms ISI, a more slowly rising and decaying neural activity is required. Model simulations show that the linear correlation between the shape of histogrammed motoneuron activity and the shape of NM movements can be high for long duration responses (> 400 ms) but is low for short duration responses (< 200 ms). Simulations are also consistent with the hypothesis that NM retraction is generally passive.     

Effects of MSH/ACTH 4–10 on the classically-conditioned rabbit nictitating membrane

Subjects were conditioned/extinguished under four experimental conditions using either MSH/ACTH 4–10 (A) or diluent (D): D/D, D/A, A/D, and A/A. The major question investigated was whether or not the peptide has an effect on this classically-conditioned behavior similar to that reported for instrumental conditioning paradigms. The results indicated that it does not. An effect was seen on performance, not on learning or attentional processes. Animals treated with the peptide performed more poorly (i.e., displayed fewer conditioned responses) during both acquisition and extinction. In addition, there was an apparent residual effect of the peptide that lasted 24 but not 48 hours.     

Pavlovian conditioning: pigeon nictitating membrane

A new Pavlovian conditioning preparation was developed using the nictitating membrane of the restrained pigeon. Either visual or auditory stimuli served as conditioned stimuli (CSs) with an unconditioned stimulus (US) of a puff of air to the cornea. Movement of the nictitating membrane constituted the conditioned and unconditioned responses (CR and UR). Conditioning was studied with the Kamin blocking procedure. In agreement with findings from other conditioning preparations, responding to the redundant stimulus was attenuated relative to a stimulus that received the same number of CS-US pairings in a compound-conditioning procedure. Although response attenuation occurred, substantial individual variation was observed within the blocking procedure, a finding with some precedent in the experimental literature. Theoretical analysis and neural-network simulations indicate that inter-subject variation in response attenuation may result from differences in the extent to which contextual stimuli contribute to the functional CS.     

The refractive significance of the nictitating membrane of the bird eye

Summary Previous authors have suggested that in certain aquatic birds a transparent nictitating membrane of high refractive index could compensate for the refractive loss of the cornea in water. Measurements of refractive indices, refractive state and curvature carried out on a number of aquatic birds indicate that the nictitating membrane does not have a refractive function; the refractive indices of the cornea and nictitating membrane are very similar (approximately 1.37), the nictitating membrane does not alter the refractive state of the eye, and its curvature, when it is in place in front of the globe, is virtually the same as that of the cornea.This research was supported by grants from the National Research Council of Canada and the Canadian National Sportsmen's Fund. The assistance of Mote Marine Laboratory, The Mount Desert Island Biological Laboratory, the Niska Wildlife Foundation and the Felicadades Wildlife Foundation is gratefully acknowledged. The herring gulls and black guillemots were provided by Dr. W.B. Kinter. In addition, the authors are grateful for the assistance provided by Drs. J.L. Lincer and D. Peakall and Mr. R. Orleib.     

Histochemical studies on the adrenergic innervation of the nictitating membrane of the cat

Summary The sympathetic adrenergic innervation has been studied with the fluorescence method of Falck and Hillarp. The smooth muscle of the membrane has been found to be richly innervated which is well correlated to the high amounts of noradrenaline (NA) found in that organ with biochemical methods. The distribution of the nerves in a ground plexus and the close contacts between the nerves and the muscle cells have been discussed in relation to the physiology of this sympathetically innervated organ.     

Response linearity determined by recruitment strategy in detailed model of nictitating membrane control

Many models of eyeblink conditioning assume that there is a simple linear relationship between the firing patterns of neurons in the interpositus nucleus and the time course of the conditioned response (CR). However, the complexities of muscle behaviour and plant dynamics call this assumption into question. We investigated the issue by implementing the most detailed model available of the rabbit nictitating membrane response (Bartha and Thompson in Biol Cybern 68:135-143, 1992a and in Biol Cybern 68:145-154, 1992b), in which each motor unit of the retractor bulbi muscle is represented by a Hill-type model, driven by a non-linear activation mechanism designed to reproduce the isometric force measurements of Lennerstrand (J Physiol 236:43-55, 1974). Globe retraction and NM extension are modelled as linked second order systems. We derived versions of the model that used a consistent set of SI units, were based on a physically realisable version of calcium kinetics, and used simulated muscle cross-bridges to produce force. All versions showed similar non-linear responses to two basic control strategies. (1) Rate-coding with no recruitment gave a sigmoidal relation between control signal and amplitude of CR, reflecting the measured relation between isometric muscle force and stimulation frequency. (2) Recruitment of similar strength motor units with no rate coding gave a sublinear relation between control signal and amplitude of CR, reflecting the increase in muscle stiffness produced by recruitment. However, the system response could be linearised by either a suitable combination of rate-coding and recruitment, or by simple recruitment of motor units in order of (exponentially) increasing strength. These plausible control strategies, either alone or in combination, would in effect present the cerebellum with the simplified virtual plant that is assumed in many models of eyeblink conditioning. Future work is therefore needed to determine the extent to which motor neuron firing is in fact linearly related to the nictitating membrane response.     

Regulation of postsynaptic alpha-1 adrenoceptors in smooth muscle of the cat nictitating membrane

Findings from radioligand research into smooth muscle in the cat nictitating membrane revealed the presence of specific [³H]prazosin binding sites corresponding to alpha-1 adrenoceptors. After smooth muscle sympathectomy, numbers of alpha-1 adrenoceptors rose without any significant change in their affinity. Incubating previously sympathectomized smooth muscle with noradrenaline led to a decline in the number of alpha-1 adrenoceptors — again without alteration in binding affinity. It was deduced that numbers of alpha-1 adrenoceptors are controlled by the sympathetic nervous system.S. V. Kurashov Medical Institute, Kazan'. Translated from Neirofiziologiya, Vol. 21, No. 6, pp. 735–741, November–December, 1989.     

家兔钙调节蛋自-红细胞膜的制备

 本文介绍用等渗咪唑缓冲液溶血,并用低温高速或常速离心机制备出一种带钙调节蛋白(简称CaM)的红细胞膜。它具有与膜稳定结合的CaM,在钙离子存在下可以激活膜上的靶酶——Ca~(2+)+Mg~(2+)-ATP酶活性,为研究CaM功能及有关药物机制提供一种简便而理想的材料。     

Extension of the CS past the US can facilitate conditioning of the rabbit's nictitating membrane response

Five experiments were conducted in which the onset of a tone conditioned stimulus (CS) preceded the unconditioned stimulus (US) by 500 ms. Across experiments, the offset of the CS was extended past the offset of the US by values ranging from 0 ms to 40000 ms. Extensions of the CS of 2000 ms or greater produced acquisition of a conditioned response (CR) that was as fast or faster than in the no-extension condition (0 ms). While extension of a forward tone CS after the US enhanced excitatory conditioning, insertion of another CS (light) in a purely backward relationship with the US passed only a retardation test, indicative of latent inhibition, and not a summation test needed for conditioned inhibition. The results add to the evidence that excitatory and inhibitory processes are both engaged following US offset. Alternative theories of CS processing are discussed.