Consciousness and Reflex

An analogy is drawn between the functions of consciousness and the model of a reflex. Consciousness consists of an afferent part, which is the perception of the external world; a central part, which is thought; and an efferent part, which is a decision concerning an action and the transmission of a motor command. At the basis of higher mental functions lies the unification of reflexes into complexes; and within these complexes, key structures are differentiated that synthesize qualitatively disparate information. The centers of integration for the effectuation of the afferent and efferent functions of consciousness are located in the posterior and anterior sections of the brain, respectively. Predominantly afferent and efferent stages, with localized foci of interaction, may also be distinguished in thought. The communicative function of consciousness is realized primarily by centers in the left hemisphere. A discrepancy between the afferent and efferent functions of consciousness may underlie certain forms of mental pathology.     

Modalities of GABA and Glutamate Neurotransmission in the Vertebrate Inner Ear Vestibule

GABA and glutamate have been postulated as afferent neurotransmitters at the sensory periphery inner ear vestibule in vertebrates. GABA has fulfilled the main criteria to act as afferent neurotransmitter but may also be a putative efferent neurotransmitter, mainly due to cellular localization of its synthesizing enzyme glutamate decarboxylase derived from biochemical, immunocytochemical, in situ hybridization and molecular biological techniques, whereas glutamate afferent neurotransmission role is supported mainly by pharmacological evidences. GABA and Glu could also act as afferent co-neurotransmitters based upon immunocytochemical techniques. This multiplicity was not considered earlier and postulates a peripheral modulation of afferent information being sent to higher vestibular centers. In order to make a definitive cellular assignation to these putative neurotransmitters it is necessary to have evidences derived from immunocytochemical and pharmacological experiments in which both substances are tested simultaneously. Special issue article in honor of Dr. Ricardo Tapia.     

Primary afferent fibers conduct impulses in both directions under physiological stimulus conditions

Summary In electric fish of the family Mormyridae some primary afferent fibers conduct impulses not only from electroreceptors to the brain but also from the brain to the receptors. The efferent impulses may be elicited by electrical stimulation which is within the physiological range, i.e., by stimulation which is similar in amplitude and duration to the stimulation that is caused by the fish's own electric organ discharge. Afferent and efferent impulses in the same afferent fiber were identified by: simultaneously recording from a fiber at two different points, at the receptor and at the nerve trunk (Figs. 2C-H; 3B-D); by cutting the afferent fiber between the brain and the recording site as well as between the recording site and the periphery; and by intra-axonal recording from the afferent fiber near its entry into the brain (Fig. 4). The efferent impulses result from the central integration of a corollary discharge of the electric organ motor command with excitatory and inhibitory input from several different receptors near the one from which afferent impulses originate (Fig. 4). The centrally originating impulse may be capable of modifying the effect of signals originating in the periphery.Abbreviations ELLL electrosensory lateral line lobe - EOCD electric organ corollary discharge - EOD electric organ discharge - epsp excitatory postsynaptic potential - NPLL posterior lateral line nerve     

Afferent and efferent components of joint position sense; interpretation of kinaesthetic illusion

The present model of joint angle perception is based on the following hypotheses: the perception and control of joint angle are closely interrelated processes; central motor commands are adequately expressed by shifts of an equilibrium point resulting from the interaction of antagonistic muscles and a load; two fundamental commands-reciprocal (r) and coactivative (c) provide for changes in activity of the antagonistic muscle pair. The dependence of joint angle on static muscle torque and r and c commands is derived (Eq. 5). The following principles of joint position sense are formulated: 1) the r component of the efferent copy plays the role of a reference point which shifts during voluntary regulation of muscle state, but remains unchanged during any passive alterations of joint position; 2) muscle afferent signals deliver not absolute but relative information (i.e. measured relatively to the central reference point). These signals turn out to be related to active muscle torque; 3) the nervous system evaluates muscle afferent signals on the basis of a scale determined by the level of coactivation of the antagonistic muscles. Kinaesthetic illusions appear to be due to disruptions in perception of afferent and/or efferent components of position sense. The present model is consistent with all the variety of kinaesthetic illusions observed experimentally. A qualitative neurophysiological schema for joint angle perception is proposed involving efferent copy and information concerning muscle torque delivered by the tendon organ, muscle spindle, and perhaps, articular receptors. It is known that the cerebellum incorporates both afferent and efferent information concerning movement. One may presume that it plays an essential role in position sense.     

The Ulrastructure of the Gill of the Lugworm Arenicola marina (L.) (Annelida,Polychaeta)

Arenicola marina gills are hollow, branched, body outgrowths with a central coelomic cavity and afferent and efferent vessels. The gill surface area per unit body weight is about 4 cm²/g wet weight. The blood vascular system anatomy differs from the tip to the base of the gill. In the distal branches of the gill the superficial afferent and efferent vessels are joined by connecting vessels. All vessels arise as spacings between the basal laminae of the thin epidermis and of the coelomic myoepithelium. The contractile part of this epithelium mainly borders the afferent and efferent vessels, whereas pedicel-like cytoplasmic processes extend from the cell bodies and mainly line the connecting vessels. In the proximal branches of the gill the afferent and efferent vessels located in the coelomic cavity are surrounded by the coelomic myoepithelium, and a peripheral blood plexus is present below the epidermis. The gill epidermis is everywhere thin and does not exhibit the characters of a transporting epithelium. The gill coelomic myoepithelium has several functions: (i) periodic contractions of the gill, propelling blood and coelomic fluid toward the central vascular and coelomic compartments; (ii) blood ultrafilration toward the coelomic cavity; (iii) probably transport, suggested by the specialized structures of the lateral membranes of the cells.     

Outlines of a new theory of photoreception

A critical examination of the “classical” theories of photoreception in view of more recent experimental findings yields the result that these theories do not possess the property to describe all the more significant phenomena of photoreception correctly, and to some extent suffer the lack of more general applicability. The basis for a new and presumably more general theory of photoreception based on dynamical aspects is laid out. Emphasis is put on the time course of afferent and efferent excitation in the photoreception model, consisting of a receptor element, an afferent and an efferent neuron of the one-factor Rashevsky-type, and an effector organ.     

Synaptic organization of a multifunctional interneuron in the central nervous system of Helix pomatia L.

Summary The morphology, axonal arborization and ultrastructure of synaptic connections of the V21 giant neuron in the visceral ganglion of the snail Helix pomatia has been investigated following intracellular labelling with horseradish peroxidase. The V21 neuron establishes several afferent and efferent axo-axonic connections, mainly along the first half of the primary axon. Collaterals of 200–300 m length originate from the primary axon, which shows further arborization, and both afferent and efferent synaptic contacts are formed on these fine axon profiles. Afferent and efferent contacts of the cell occur within very short distances of a few micrometers. On the basis of ultrastructure and vesicle and granule content, several afferent terminals can be distinguished on V21 labelled axon profiles. The majority of these afferent terminals resembles peptidergic-(neurosecretory)-like terminals. This finding supports the possible transmitter role of neuropeptides in the central nervous system of gastropods. Our results are consistent with and provide morphological evidence for recent electrophysiological observations suggesting that, in addition to integrating input, the V21 neuron functions as an interneuron in Helix central nervous system.     

Modulation of the population density of identifiable epidermal Langerhans cells associated with enhancement or suppression of cutaneous immune reactivity

The epidermis on the backs or ears of DBA/2 mice treated for 7 days with a 20% concentration of monobenzyl ether of hydroquinone (MBEH) had a significantly greater population density of ATPase- and Ia-positive cells compared with control mice treated with diluent. There was no decrease or increase in ATPase- or Ia-positive cells at sites distal from the treated tissue. This increase in population density of Langerhans cells was associated with a significant increase in functional afferent immune reactivity measured by allergic contact hypersensitivity. We also found evidence for enhanced efferent immune reactivity. Animals treated on the ears for 7 days with MBEH were sensitized to DNFB on untreated back. MBEH treated ears with more Ia-positive Langerhans cells demonstrated a threefold greater increase in swelling after the DNFB challenge than the control mice. Results of other studies suggest that the afferent and efferent enhanced immune reactivity produced by MBEH are local effects. We postulated that MBEH produced its effects by activating the oxidation of arachidonic acid (AA) to prostaglandins. To test this, we applied AA to mouse skin. AA has a biphasic effect on epidermal Langerhans cells: in low doses it increases their number; in high amounts it decreases the number of identifiable cells with either the Ia or the ATPase technique. An increased population density of identifiable epidermal Langerhans cells induced with AA was correlated with an increase in afferent and efferent immune reactivity. In contrast, reduction of Langerhans cells with larger amounts of AA suppress the afferent and efferent limb of the immune response. DNFB applied to skin with decreased Langerhans cell density from AA induced a state that mimics immune tolerance. The findings are significant because we report the only method to either increase or decrease the population density of Langerhans cells: and to modulate up or down the afferent or efferent limbs of the cutaneous immune response. Our results also suggest that the Langerhans cell may be involved in the efferent limb of the immune efferent response. These effects may be modulated in part by products of AA metabolism.     

Are there efferent synapses in fish taste buds?

In fish, nerve fibers of taste buds are organized within the bud's nerve fiber plexus. It is located between the sensory epithelium consisting of light and dark elongated cells and the basal cells. It comprises the basal parts and processes of light and dark cells that intermingle with nerve fibers, which are the dendritic endings of the taste sensory neurons belonging to the cranial nerves VII, IX or X. Most of the synapses at the plexus are afferent; they have synaptic vesicles on the light (or dark) cells side, which is presynaptic. In contrast, the presumed efferent synapses may be rich in synaptic vesicles on the nerve fibers (presynaptic) side, whereas the cells (postsynaptic) side may contain a subsynaptic cistern; a flat compartment of the smooth endoplasmic reticulum. This structure is regarded as a prerequisite of a typical efferent synapse, as occurring in cochlear and vestibular hair cells. In fish taste buds, efferent synapses are rare and were found only in a few species that belong to different taxa. The significance of efferent synapses in fish taste buds is not well understood, because efferent connections between the gustatory nuclei of the medulla with taste buds are not yet proved.     

Adrenergic innervation of the gills of brown and rainbow trout,Salmo trutta and S. gairdneri

The adrenergic innervation of structures in the gills of brown and rainbow trout was studied with catecholamine fluorescence histochemistry. In the arterio-arterial vascular pathway, there was an innervation of the afferent and efferent lamellar arterioles, but the afferent and efferent filamental arteries and the secondary lamellae were devoid of any fluorescent nerve fibres. In S. trutta only, there was an additional innervation of the afferent and efferent branchial arteries and the base of the efferent filamental artery. The innervation of the arterio-venous vascular pathway was similar in both trout species. Many fluorescent nerve fibres were found on nutritive arterioles in the gill arch and interbranchial septum, and in the core of each filament between the surface epithelium and the wall of the filament venous sinus. No fluorescent nerve fibres were observed at the origins of the capillaries arising from the efferent filamental artery. The sympathetic nerve supply is provided to the gills mainly through the posttrematic nerve, with an occasional small contribution through the pretrematic nerve. The presence of adrenergic nerves in the gills is discussed in relation to the regulation of blood flow through the arterio-arterial and arterio-venous pathways.     

A matrix calculus for neural nets: II

In a previous paper a method was given by which the efferent activity of an idealized neural net could be calculated from a given afferent pattern. Those results are extended in the present paper. Conditions are given under which nets may be considered equivalent. Rules are given for the reduction or extension of a net to an equivalent net. A procedure is given for constructing a net which has the property of converting each of a given set of afferent activity patterns into its corresponding prescribed efferent activity pattern.     

Lymphocyte traffic through granulomas: Differences in the recovery of indium-111-labeled lymphocytes in afferent and efferent lymph

Afferent lymphatics draining granulomas and efferent lymphatics from normal and stimulated lymph nodes were cannulated in sheep. There was a greatly increased output of cells in afferent lymph-draining chronic inflammatory sites or Freund's adjuvant-induced granulomas. Cells collected from these lymphatics were radiolabeled with ¹¹¹In and injected intravenously. The reappearance of these labeled cells in lymph at various sites was measured. Labeled afferent lymph cells migrated from blood through the granuloma back into afferent lymph in large numbers and with kinetics which were comparable to efferent lymphocytes recirculating through a lymph node. When labeled afferent lymph cells were injected the specific activity (cpm/10⁷ cells) in afferent lymph was five times higher than that in efferent lymph from a normal node. When efferent lymph cells were labeled the afferent lymph specific activity was one-half that in efferent lymph. It is suggested that the cells in afferent lymph migrate preferentially from blood through the granuloma and constitute a unique population of cells.     

Neuronal organization of the avian paraventricular nucleus: intrinsic, afferent, and efferent connections

The heterogeneous paraventricular nucleus (PVN) of birds offers favorable conditions for the analysis of intrinsic, afferent, and efferent connections of neuroendocrine systems. Paraventricular neurons are successfully impregnated with the Golgi-technique. The findings indicate a direct influence of the cerebrospinal fluid (CSF) on the magnocellular neurons that, via their axon terminals in the neural lobe of the pituitary, are also exposed to the hemal milieu. The magnocellular neurons are intermingled with parvocellular elements which may represent local interneurons. A group of parvocellular nerve cells is identified as CSF-contacting neurons. This type of cell forms a basic morphologic component of the avian neuroendocrine apparatus. Immunocytochemical and ultrastructural studies further support the concept of neuronal interactions between parvocellular and magnocellular elements. Moreover, these findings speak in favor of the existence of recurrent collaterals of the magnocellular neurons. Nerve cells giving rise to afferent connections to the PVN are located in the limbic system and autonomic areas of the upper and lower brainstem. Further afferents may originate from the subfornical organ, the organon vasculosum laminae terminalis, the ventral tegmentum, and the area postrema. Via efferent projections, the PVN is connected to the nucleus accumbens, lateral septum, several hypothalamic nuclei, the neural lobe of the pituitary, the organon vasculosum laminae terminalis, the subfornical organ, the pineal organ, the area postrema, the lateral habenular complex, and various autonomic areas of the reticular formation in the upper and lower brainstem and the spinal cord. In conclusion, the PVN may be regarded as an integral component of the neuroendocrine apparatus reciprocally coupled to the limbic system, several circumventricular organs, and various autonomic centers of the brain.     

Efferent fibers innervate gustatory and mechanosensitive afferent fibers in frog fungiform papillae

A possibility of efferent innervation of gustatory and mechanosensitive afferent fiber endings was studied in frog fungiform papillae with a suction electrode. The amplitude of antidromic impulses in a papillary afferent fiber induced by antidromically stimulating an afferent fiber of glossopharyngeal nerve (GPN) with low voltage pulses was inhibited for 40 s after the parasympathetic efferent fibers of GPN were stimulated orthodromically with high voltage pulses at 30 Hz for 10 s. This implies that electrical positivity of the outer surface of papillary afferent membrane was reduced by the efferent fiber-induced excitatory postsynaptic potential. The inhibition of afferent responses in the papillae was blocked by substance P receptor blocker, L-703,606, indicating that substance P is probably released from the efferent fiber terminals. Slow negative synaptic potential, which corresponded to a slow depolarizing synaptic potential, was extracellularly induced in papillary afferent terminals for 45 s by stimulating the parasympathetic efferent fibers of GPN with high voltage pulses at 30 Hz for 10 s. This synaptic potential was also blocked by L-703,606. These data indicate that papillary afferent fiber endings are innervated by parasympathetic efferent fibers.     

Renorenal reflexes: interaction between efferent and afferent renal nerve activity.

In rats, stimulation of renal mechanoreceptors by increasing ureteral pressure results in a contralateral inhibitory renorenal reflex response consisting of increases in ipsilateral afferent renal nerve activity, decreases in contralateral efferent renal nerve activity, and increases in contralateral urine flow rate and urinary sodium excretion. Mean arterial pressure is unchanged. To study possible functional central interaction among the afferent renal nerves and the aortic and carotid sinus nerves, the responses to renal mechanoreceptor stimulation were compared in sinoaortic denervated rats and sham-denervated rats before and after vagotomy. In contrast to sham-denervated rats, there was an increase in mean arterial pressure in response to renal mechanoreceptor stimulation in sinoaortic-denervated rats. However, there were no differences in the renorenal reflex responses among the groups. Thus, our data failed to support a functional central interaction among the renal, carotid sinus, and aortic afferent nerves in the renorenal reflex response to renal mechanoreceptor stimulation. Studies to examine peripheral interaction between efferent and afferent renal nerves showed that marked reduction in efferent renal nerve activity produced by spinal cord section at T6, ganglionic blockade, volume expansion, or stretch of the junction of superior vena cava and right atrium abolished the responses in afferent renal nerve activity and contralateral renal function to renal mechanoreceptor stimulation. Conversely, increases in efferent renal nerve activity caused by thermal cutaneous stimulation increased basal afferent renal nerve activity and its responses to renal mechanoreceptor stimulation. These data suggest a facilitatory role of efferent renal nerves on renal sensory receptors.     

Suppression of antigraft immunity by preimmunization. III. Characterization of suppressor T cells involved in suppression of the efferent phase of DTH against alloantigens

Suppressor T (Ts) cells that can suppress delayed type hypersensitivity (DTH) against histocompatibility (H) antigens can be isolated from spleen and lymph nodes a few days after i.v. immunization of mice with irradiated allogeneic spleen cells. In this paper we investigated the suppression of the efferent phase of DTH to characterize the Ts cells involved, and to compare them with the afferent phase Ts cells that have been characterized in a previous paper of this series. The DTH against third party alloantigens that were not used for the i.v. suppressive immunization could be suppressed by presenting the third party alloantigens together with the original alloantigens in the challenge inoculum for eliciting the DTH reaction. Thus the ultimate suppressive effect by the Ts cells that are active during the efferent phase of DTH is nonspecific. This non-specific suppression of DTH to alloantigens has previously been found for the afferent phase Ts cells as well. For suppression of the efferent phase of DTH to alloantigens, a population of Lyt-1+2+ Ts cells appeared to be essential, just like in the suppression of the afferent phase of DTH to alloantigens. We did not find evidence for the involvement of cyclophosphamide-sensitive auxiliary Ts cells in suppression of the efferent phase of DTH. Also no evidence was found for H-2 or Igh-restricted activation and function of the Ts cells that were active during afferent and efferent phases of the DTH response to H antigens. In view of these similarities between afferent phase and efferent phase Ts cells we conclude that there are no arguments as yet to suppose that there is more than one type of T cells involved in the suppression of the afferent and efferent limb of DTH against H antigens.     

A neural network model for selective attention in visual pattern recognition

A neural network model of the mechanism of selective attention in visual pattern recognition is proposed and simulated on a digital computer.When a complex figure consisting of two patterns or more is presented to the model, it is segmented into individual patterns, and each pattern is recognized separately. Even if one of the patterns to which the model is paying selective attention is affected by noise or defects, the model can recall the complete pattern from which the noise has been eliminated and the defects corrected. It is not necessary for perfect recall that the stimulus pattern should be identical in shape to the training pattern. Even though the pattern is distorted in shape or changed in size, it can be correctly recognized and the missing portions restored.The model consists of a hierarchical neural network which has efferent as well as afferent connections between cells. The afferent and the efferent signals interact with each other in the network: the efferent signals, that is, the signals for selective attention, have a facilitating effect on the afferent ones, and, at the same time, the afferent signals gate efferent signal flow. When some feature in the stimulus is not extracted in the afferent paths, the threshold for detection of that feature is automatically lowered by decreasing the efficiency of inhibition, and the model tries to extract even vague traces of the undetected feature.     

Comparison of afferent and efferent lung lymph in the sheep

Efferent lymph collected from the caudal mediastinal lymph node (CMN) in the sheep lung lymph fistula model has been reported to represent free pulmonary interstitial fluid. Studies that utilize this model assume that nodal transit does not alter the composition of lymph. We collected afferent lymph from the tracheobronchial node (TBN) while simultaneously collecting CMN efferent lymph in acutely prepared sheep. We compared afferent and efferent lymph protein concentrations (CA and CE) and changes in flow rates (QLA and QLE) during base line and periods of elevated left atrial pressure (Pla). As a result of elevated Pla, QLA and QLE increased and the afferent lymph-to-plasma protein concentration ratio (CA/Cp) and the efferent lymph-to-plasma protein concentration ratio (CE/Cp) fell. The CA/Cp was significantly lower than the CE/Cp during base line (0.67 vs. 0.80) and periods of elevated Pla (0.41 vs. 0.61). Although we cannot exclude regional permeability differences, the difference between CA/Cp and CE/Cp is most likely due to the concentration of lymph within the CMN. Our data suggest nodal modification of CA is correlated with the afferent lymph-to-plasma colloid osmotic pressure ratio (pi A/pi p) and further suggest that nodal alteration of lymph during elevated Pla is due to the influence of decreased pi A/pi p at the blood-to-lymph barrier. We conclude that afferent lymph is a more accurate representation of lung free interstitial fluid because collection of pulmonary afferent lymph obviates the complications introduced by the CMN. Studies utilizing efferent lymph may have overestimated lung microvascular permeability in the acute sheep preparation.     

Functional Organization of the Teleost Gill

The circulation of the gills has been studied in the perch, trout and eel combining the conventional histological methods and casting techniques. The existence of two blood pathways in each gill arch was confirmed. 1 — An arterio-arterial pathway assuming the respiratory function. It includes the afferent branchial artery and in each primary lamella the afferent primary artery, the secondary lamellae capillaries and the primary and branchial efferent arteries. 2 — An arterio-venous pathway arising from both the branchial artery, in the gill arch, and the primary arteries in each primary lamella. This pathway includes the central venous sinus of the primary lamella, several small veins and is finally connected with the branchial veins. 3 — The lack of connections between afferent primary arteries and cvs in the trout and the perch makes impossible a direct blood flow from the afferent to the efferent artery (shunt). In the eel connections between cvs and both afferent and efferent arteries do not mean that a shunt is operating according to the pressure gradient.     

Observations of valve-like structures and evidence for rectification of flow within the gill lamellae of the crab Carcinus maenas (Crustacea,Decapoda)

Summary The isolated gills of Carcinus maenas, perfused at pressure drops of 1–10 cm of water, exhibited flow rectification, the resistance to perfusion via the afferent vessel being many times lower than that for efferent perfusion. The asymmetry was greater at the lower end of this pressure range.The overall afferent branchial resistance for Carcinus of weight 65 g, and with no ventilatory component in the transmural pressure difference, was estimated to be 0.05 cm of water. l^–1 · sec. The corresponding overall reverse (efferent) branchial resistance was 0.36 cm of water · l^–1 · sec.LM, TEM and SEM examination of the gills indicated that haemolymph leaves each gill lamella via several discrete parallel efferent channels which drain different regions of the lamella, and that each efferent channel is nearly closed, at its junction with the efferent branchial vessel, by a diaphragm of loosely interwoven and very elongated cells. It is concluded that these cells may constitute efferent valves and that narrow apertures between them may contribute a major component to the branchial resistance and be primarily responsible for the rectification of flow. Relatively wide apertures lead directly from the afferent vessel into the lamellae and are not asociated with valves of any kind.The valves may be important in enabling changes in transmural pressure associated with ventilatory reversals to pump haemolymph unidirectionally through the lamellae. Similarly valves may allow the oscillating venous pressures associated with locomotor activity to improve gill perfusion during exercise.The elongated tails of the cells of the efferent valve contain numerous microtubules. The wider cell bodies contain the nucleus and many mitochondria. Unusual organelles composed of many short (about 0.25 m long) microtubules and often lying close to the nuclear membrane may be microtubule organising centres. It is speculated that, in addition to their simple mechanical function, the valve cells may play a more dynamic role in regulating flow of haemolymph through different lamellar routes, or that they may monitor composition, pressure or flow of the efferent lamellar circulation.