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Synchronized calling in a treefrog (Smilisca sila). Short behavioral latencies and implications for neural pathways involved in call perception and production.

A neotropical treefrog, Smilisca sila, exhibits an unusual ability to synchronize its calling with that of neighbors such that calls often overlap temporally. Call playback experiments measured the latency to evoked calling in response to one-note and two-note mating calls. Approximately one-half of the responses overlapped the one-note stimulus call, while 20% overlapped the two-note stimulus call. Minimum response latencies were 55 ms and 78 ms in response to the one-note and two-note calls, respectively. These data were used to evaluate the efficacy of proposed neural pathways involved in call recognition and production. Based on neural and behavioral latencies presented in those studies, it is suggested that the proposed pathways for call recognition and production might not accommodate the short behavioral latencies in S. sila. One possible explanation for this discrepancy is that call detection is decoupled from call recognition, the former requiring a shorter neural pathway thus permitting a shorter behavioral latency.

Animals↗

An electrophysiological study of neural pathways for corticofugally inhibited neurons in the central nucleus of the inferior colliculus of the big brown bat, Eptesicus fuscus.

This electrophysiological study tests the hypothesis that one possible neural pathway for corticofugally inhibited neurons in the central nucleus of the inferior colliculus (ICc) of the big brown bat, Eptesicus fuscus, is mediated through excitatory projections from the auditory cortex (AC) to the external nucleus of the IC (ICx), which then sends inhibitory inputs to the ICc. This study shows that all neurons in the ICx are broadly tuned to stimulus frequency. Electrical stimulation in the AC typically increases the number of impulses, expands the auditory spatial response areas, and broadens the frequency tuning curves (FTCs) of neurons in the ICx. This corticofugal facilitation is mediated at least in part through NMDA receptors, since application of DL-2-amino-5-phosphonovaleric acid (APV), an antagonist for NMDA, decreases these response properties of neurons in the ICx. Electrical stimulation in the ICx typically decreases the number of impulses, reduces the auditory spatial response areas, and narrows the FTCs of neurons in the ICc. This inhibition is mediated at least in part through GABAA receptors, since application of bicuculline, an antagonist for GABA, increases these response properties of neurons in the ICc. These data suggest that corticofugal facilitation of the ICx and the inhibition of the ICx to the ICc may be one of the polysynaptic pathways for corticofugal inhibition of neurons in the ICc. Possible functions of this polysynaptic pathway in acoustic orientation and signal processing are discussed.

Animals↗

Are different affordances subserved by different neural pathways?

This paper questions whether affordances are allied exclusively to dorsal stream processing within the visual system, or whether in fact different affordances are subserved by functionally independent neural pathways. Using case study evidence from patients with various visual pathologies, I argue that affordances can be categorised into type based upon their respective neurological underpinning. Such categorisation has implications for the extent to which affordances are consciously perceived or non-consciously 'picked up' within the optic array, as well as whether they indicate merely potentials for action or provide necessary information in the actualisation of behaviour.

Agnosia↗

Pyloric relaxation regulated via intramural neural pathway of the antrum.

Current information about pyloric relaxation is not sufficient. For this reason, our study aimed at measuring pyloric relaxation correctly and determining the role of the intrinsic and extrinsic neural pathway in pyloric relaxation. Five groups of dogs were used: five dogs had an intact gastrointestinal tract (control group); five dogs had transection and reanastomosis of the antrum 3 cm proximal to the pylorus (antral transection group); five dogs had extrinsic pyloric denervation (denervation group); five dogs had transection and reanastomosis of the antrum with extrinsic pyloric ring denervation (transection with denervation group); and five dogs had truncal vagotomy (vagotomy group). Gastropyloroduodenal motility was recorded by a strain-gauge force transducer in conscious dogs. In the control and denervation groups, pyloric relaxation was observed only during phase III of the interdigestive migrating motor complex. In the antral transection, transection with denervation, and vagotomy groups, pyloric relaxation was not observed in either the interdigestive or the postprandial state. The frequency of pyloric contractions increased in these groups in comparison with the control group. In conclusion, the results suggest that pyloric relaxation occurred during phase III to expel undigested particles from the stomach and that descending antral intramural pathways play an important role in the control of pyloric relaxation.

Animals↗

Polysynaptic neural pathways between the hypothalamus, including the suprachiasmatic nucleus, and the liver.

The suprachiasmatic nucleus of the hypothalamus is responsible for a 24-h rhythm in basal glucose levels in the rat. The neural pathways used by the suprachiasmatic nucleus to mediate this rhythm in plasma glucose have not yet been identified. In the present study we examined whether there are any connections between hypothalamic centers, including the suprachiasmatic nucleus, and the liver, which is the main site for glucose production and storage. Transneuronal virus tracing from the liver showed that after injection of pseudorabies virus, specific neuronal cell populations in the central nervous system were labeled retrogradely, suggesting that specific sites in the central nervous system may control liver metabolism. First-order neurons belonged to the sympathetic and parasympathetic system, while second-order and third-order neurons were present in both the brainstem and hypothalamus. The presence of third-order neurons in the suprachiasmatic nucleus suggests an involvement of the biological clock in the neural control of the liver.

Animals↗

Differences in aging in two neural pathways: proposed explanations from the nervous system of Aplysia.

A basic question in studies of the neurobiology of aging is to what extent age-related changes are genetically preprogrammed or epigenetically mediated. Our approach to this question is to compare the effect of age on two neural pathways in the marine mollusc, Aplysia. The advantage of Aplysia as a model of neural aging is that age-sensitive properties in the pathways can be studied at the behavioral, physiological, and morphological levels. The two pathways we are investigating respond differently to aging; a comparison of the pathways' properties provides a means of distinguishing the effect of age from other variables in the same animal. Age effects are expressed in the gill withdrawal reflex pathway at the three levels but are minimal in the gill respiratory pathway. The behavioral and physiological expressions of the reflex pathway are weakened in old animals (250 days of age and older) when compared to those in mature ones (ca. 160 days of age). The major differences between the two pathways are: (1) the reflex pathway appears to exhibit more plasticity than the respiratory pathway, and (2) the level of use of the respiratory pathway is more regular and frequent than that of the reflex pathway. The greater plasticity intrinsic to the reflex pathway and its level of use may well be the characteristics upon which age-related changes depend. An interplay between genetic and epigenetic factors is suggested to help explain the differential aging in the two pathways.

Aging↗

Selective lesions of neural pathways following viral inoculation of the olfactory bulb.

In the present study, herpes simplex virus type 1 (HSV1) was injected into the olfactory bulb of the rat in order to determine the impact of viral infection on neural pathways, neurotransmitters, and behavior. In many animals, these injections caused considerable neuronal loss in regions that project to the bulb including the primary olfactory cortex and locus coeruleus (LC). Short-term (2-5 days postinjection) studies using immunocytochemical colocalization of virus and transmitter markers showed that cholinergic (ACh) neurons in the horizontal nucleus of the diagonal band, serotonergic (5-HT) neurons in the dorsal and median raphe nuclei, and noradrenergic (NE) neurons in the LC became infected with virus. Almost all NE neurons in the ipsilateral LC were infected while a smaller proportion of 5-HT and ACh neurons in their respective nuclei contained virus. In order to determine long-term effects of viral infection, virus injection into the olfactory bulb was followed by antiviral treatment and sacrifice 17 days to 7 months postinjection. Quantitative analysis of selected cortical regions (olfactory bulb, cingulate cortex, parietal cortex) revealed decreased NE-immunoreactive fibers while 5-HT axons from the dorsal and median raphe nuclei were not significantly affected. No changes in acetylcholinesterase staining in these cortical regions were observed, indicating that cholinergic axons were not significantly changed. Ten of the 36 animals that survived long-term after HSV1 inoculation were also tested in a water maze task before sacrifice to determine if the viral infection was associated with spatial learning deficits. Spatial learning deficits correlated with the degree of primary olfactory cortex damage but not with 5-HT, NE, or ACh axon losses.

Animals↗

A pontine call site in the domestic cat: behavior and neural pathways.

Electrical stimulation of the brain of the domestic cat elicited vocalizations from a site in the ventrolateral pons in the region of the medial lemniscus. The evoked vocalizations were analysed by means of sound spectrographs and classified as meows, growls, hisses and meow-growls. The neural pathways associated with these call sites were traced by following the pattern of fiber degeneration resulting from lesions placed at these sites. A descending fiber pathway was traced to the magnocellular tegmental field, the facial nucleus and the retrofacial nucleus, while an ascending system terminated in the zona incerta, the red nucleus, contralateral oculomotor nucleus, the ventroposterior lateral nucleus of the thalamus and inferior colliculus. It is concluded from these findings and the nature of the behavior evoked that the ventrolateral pontine call site lies on common pathway for a majority of vocalizations in the cat.

Anesthesia↗

Estrous odors and sexually conditioned neutral odors activate separate neural pathways in the male rat.

Olfactory stimuli play important roles in sexual behavior. Previous studies have demonstrated that both estrous odors and initially neutral odors paired with copulation influence the sexual behavior of male rats. The present study examines the pattern of neural activation as revealed by Fos immunoreactivity (Fos-IR) following exposure to bedding scented with either a neutral odor (almond) paired previously with copulation, estrous odors or no odor. Following exposure to estrous odors Fos-IR increased in the accessory olfactory bulb, medial amygdala, medial bed nucleus of the stria terminalis, medial preoptic area, ventromedial hypothalamus, ventral tegmental area, and both the nucleus accumbens core and shell. Conversely, following exposure to the sexually conditioned odor Fos-IR increased in the piriform cortex, basolateral amygdala, nucleus accumbens core, and the anterior portion of the lateral hypothalamic area. In addition, following exposure to almond odor Fos-IR increased in the main olfactory bulb independent of its pairing with copulation. These patterns of Fos-IR following exposure to estrous or sexually conditioned odors were not influenced by either the addition or omission of the other type of odor. These findings demonstrate that estrous and sexually conditioned odors are processed by distinct neural pathways and converge in the nucleus accumbens core, suggesting that this structure has a unique role in processing sexual stimuli of both pheromonal and olfactory natures.

Animals↗

Meal-induced jejunal absorption requires intact neural pathways.

A signal for meal-induced absorption originates from the small intestine and is transmitted to a luminally excluded segment of the proximal jejunum (Thiry-Vella [TV] fistula). Using intraluminal topical anesthesia with oxethazaine, this study assessed the role of intestinal neural pathways in basal and postprandial jejunal water and electrolyte absorption. Studies (n = 45) were performed on dogs with 25-cm proximal jejunal TV fistulae and feeding jejunostomies, using luminal perfusion with 14C-polyethylene glycol. The animals were randomized into five study groups: (1) jejunostomy oxethazaine alone, (2) jejunostomy water and jejunal meal, (3) jejunostomy oxethazaine and jejunal meal, (4) TV fistula water and jejunal meal, and (5) TV fistula oxethazaine and jejunal meal. The jejunal meal significantly increased TV fistula absorption, whereas oxethazaine significantly reduced basal absorption when administered via the TV fistula and postprandial absorption when administered via the jejunostomy (p less than 0.05). TV fistula oxethazaine did not diminish the magnitude of postprandial absorption. We conclude that intact intestinal neurotransmission is necessary for maintenance of the normal basal absorptive state of the proximal jejunum and for the generation of a normal meal-stimulated proabsorptive signal from the small intestine. A nonneural mechanism appears to be of predominant importance in transmitting the proabsorptive signal from the intact gastrointestinal tract to the TV fistula.

Anesthetics, Local↗

Duplication of the escape-response neural pathway by mutation of the bithorax-complex.

Each Drosophila segment exhibits specific patterns of epidermal cells, muscles, and neurons. Mutations in the homeotic genes of the bithorax-complex cause transformations of these patterns. Whereas abundant information exists concerning homeotic transformation of epidermis, transformations of muscles and motor neurons have been largely unexplored. An important indication of neuromuscular transformation in a segment is the expression of novel behavioral and physiological functions within that segment. We have resolved some of the segmental identities of neuromuscular elements in the transformed metathorax of the bithorax-complex mutant, abx bx3 pbx/Df(3R) P2, and have established the presence of a duplicated neural pathway for the escape-jump response within that segment. Although we observed frequent homeotic transformation of neural elements and the tergotrochanteral ("jump") muscle in mutants, corresponding transformation of flight muscles was infrequent, indicating that the presence of a motor neuron was not always sufficient to induce or determine the development of its target muscle.

Animals↗

Identification of neural pathways activated in dehydrated rats by means of Fos-immunohistochemistry and neural tracing.

The distribution of Fos-immunoreactivity (Fos-IR) was studied in the brains of rats deprived of water for 24 or 48 h and compared with that in brains of water-replete rats. Intense Fos-IR was observed in many neurons of the median preoptic nucleus (MnPO), organum vasculosum of the lamina terminalis (OVLT), supraoptic nucleus and hypothalamic paraventricular nucleus. There was less intense and sparse Fos-IR in the subfornical organ. In water-replete rats, Fos-IR was absent or very low in these regions. In other rats, cholera toxin B-gold conjugate was microinjected bilaterally into the supraoptic nucleus to identify retrogradely labelled neurons in the lamina terminalis projecting to the supraoptic nucleus. Approximately 30% of these retrogradely labelled neurons in the OVLT and MnPO also exhibited Fos-IR after 48 h of water deprivation. These data show that neurons in the MnPO, OVLT and, to a lesser extent, the subfornical organ probably play an important role in homeostatic responses to dehydration, such as vasopressin secretion.

Animals↗

A genetic approach to visualization of multisynaptic neural pathways using plant lectin transgene.

The wiring patterns among various types of neurons via specific synaptic connections are the basis of functional logic employed by the brain for information processing. This study introduces a powerful method of analyzing the neuronal connectivity patterns by delivering a tracer selectively to specific types of neurons while simultaneously transsynaptically labeling their target neurons. We developed a novel genetic approach introducing cDNA for a plant lectin, wheat germ agglutinin (WGA), as a transgene under the control of specific promoter elements. Using this method, we demonstrate three examples of visualization of specific transsynaptic neural pathways: the mouse cerebellar efferent pathways, the mouse olfactory pathways, and the Drosophila visual pathways. This strategy should greatly facilitate studies on the anatomical and functional organization of the developing and mature nervous system.

Animals↗

Conduction properties of identified neural pathways in the central nervous system of mice in vivo.

Various lines of transgenic or knockout mice are now available that have abnormalities in neuron, glial cells or neuron-glial interaction. However, the techniques for quantitative analysis of their pathophysiological functions are still limited. We established an experimental model system to measure the properties of nerve conduction of identified neural pathways in the CNS using anesthetized and immobilized mice. Dorsal column (DC), vestibulospinal/reticulospinal tracts (VRST) and pyramidal tract (PT) were stimulated by inserting stimulating electrodes into the dorsal column nuclei, medial longitudinal fasciculus, and the medullary pyramid, respectively. Volleys were recorded at various segments in the cervical spinal cord with surface electrodes, and their conduction velocities (CVs) and relative refractory periods (RRPs) were measured. The CVs of the DC, VRST and PT were 26.25 +/- 4.96 m/s (n = 7), 51.55 +/- 4.65 m/s (n = 7), 8.89 +/- 1.81 m/s (n = 7), respectively. Data from paired stimulation indicated that the median values of RRPs of the DC, VRST and PT were 10, 2 and 4 ms, respectively, which suggested marked difference among individual tracts. This is the first attempt to measure the conduction properties of the central tracts in mice in vivo. This experimental procedure will give us a physiological measure of CNS functions in normal and genetically manipulated mice and contribute to clarifying the molecular mechanisms and pathophysiology of neurodegenerative diseases such as multiple sclerosis (MS) and amyotrophic lateral sclerosis (ALS).

Animals↗

Firing rate relationship in the saccade system neural pathway.

This paper describes the relationship among the structures of the brain involved in the control of the saccadic system. The eye position information is pre-processed by the cerebral cortex and then projected to the cerebellum where this signal is propagated to several structures that are in charge of the control and correction of the eye movement signal. Once this processing is completed, the output is propagated to the final neural stage (the motor neurons), and then to the Rectus and Oblique group of muscles of the eye. In our simulated model, the interaction of the different areas in this neural pathway and its feedback loops is shown through the correlation of the different firing rates of each structure, including background or spontaneous activity components. In order to improve portability the model is implemented with the Matrix Laboratory Language (MATLAB) and the Simulink toolbox.

Action Potentials↗

Involvement of the L-arginine/nitric oxide neural pathway in non-adrenergic, non-cholinergic relaxation of the bovine oesophageal groove.

1. The distribution and localization of nitric oxide synthase (NOS) immunoreactivity and nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) activity in the bovine oesophageal groove were investigated by immnunohistochemical and histochemical staining techniques. Functional in vitro studies were performed to correlate the presence of NOS-immunoreactivity (IR) and NADPH-d staining with smooth muscle relaxations involving the L-arginine/nitric oxide neural pathway in the bovine oesophageal groove activity. 2. NOS-IR and NADPH-d were expressed in nerve cell bodies of the myenteric, submucosal and intramuscular ganglia, and in nerve fibres distributed around blood vessels and throughout the different muscular layers of the bovine oesophageal groove. 3. In oesophageal groove strips treated with guanethidine (10(-5) M) and atropine (10(-7) M) to block noradrenergic neurotransmission and muscarinic receptors, respectively, electrical field stimulation (EFS, 0.5-32 Hz, 1 ms duration, 20-s trains) induced relaxations which were practically abolished by tetrodotoxin (TTX, 10(-6) M). 4. Incubation with an inhibitor of nitric oxide synthesis, NG-nitro-L-arginine (L-NOARG, 3 x 10(-5) M), significantly inhibited relaxations induced by EFS. This inhibition was partially reversed by L-arginine (L-arg, 5 x 10(-3) M). D-NOARG (3 x 10(-5) M) had no effect on EFS-induced relaxations. 5. NO added as an acidified solution of NaNO2 (10(-6) - 10(-3) M) and S-nitroso-L-cysteine (10(-7) - 10(-4) M) caused concentration-dependent relaxations of the bovine oesophageal groove. These relaxations were unaffected by L-NOARG (3 x 10(-5) M). 6. The presence of NO-synthesizing enzyme in nerves and ganglia, and the pharmacological evidence for NO-mediated smooth muscle relaxation suggested that the L-arg/NO neuronal pathway is involved in the inhibitory neurotransmission of the bovine oesophageal groove.

Animals↗

The rise of plasma ACTH induced by ether is mediated through neural pathways entering the medial basal hypothalamus.

The effect of ether stress on the release of immunoreactive ACTH was studied in rats with an antero-lateral cut around the medial basal hypothalamus. Ether failed to raise the plasma ACTH level of rats in which an antero-lateral hypothalamic cut and adrenalectomy had been performed 7 to 8 days previously. Plasma ACTH was also unchanged in rats exposed to ether 2 h after an antero-lateral cut. These data suggest that intact neural pathways entering the medial basal hypothalamus from the antero-lateral direction are necessary for the ACTH releasing action of ether stress.

Adrenal Glands↗

Ruthenium red as a tool to study calcium channels, neuronal death and the function of neural pathways.

The inorganic polycationic dye ruthenium red (RuR) exerts several effects on the nervous system when added in physiological solutions, both in vivo and in vitro. Part of these effects, including the paralysis observed in mammals after the systemic administration of RuR, can be accounted for by the binding of RuR to nerve ending membranes, which results in inhibition of Ca2+ influx through voltage-sensitive calcium channels and the consequent inhibition of neurotransmitter release. On the other hand, the administration of RuR into the cerebrospinal fluid induces intense convulsive activity, and its microinjection into the substantia nigra reticulata or the hippocampus leads to various motor behavior alterations that can be related to hyperexcitability of the neurons of the injected region. In addition, RuR penetrates the neuronal somata present in the area injected and induces cell destruction, which has been interpreted as an excitotoxic action of the dye. The penetration and the toxicity of RuR were also observed in primary neuronal cultures but did not occur in pure glial cultures, suggesting a selective action on neurons. In the present article the in vitro and in vivo effects of RuR are reviewed and discussed in terms of the usefulness of the dye as an interesting tool to study calcium channels linked to transmitter release, neuronal death mechanisms and the function of neural pathways.

Animals↗