Electrophysiologic changes associated with potassium depletion of frog skin

Summary Skins from the frogRana pipiens pipiens were studied under short-circuited conditions during the course of removing and replacing potassium in the inner bathing media in 14 experiments. The intracellular potential (V _SC), fractional resistance (FR), short-circuit current (I _SC) and total tissue conductance (g _T) were constantly monitored during impalements of the epithelial cells. The mean value (±se) forV _SC was –79 (±3) mV under baseline conditions. Removal of potassium from the inner bathing solution transiently stimulated the short-circuit current and hyperpolarized the basolateral membrane; with sufficiently long incubations, the basolateral membrane was eventually depolarized. Restoration of potassium to the inner solution within 43 min after initiating the perfusion with K⁺-free solution depolarized the basolateral membrane. However, restoration of potassium after at least 11/2 hr of incubation hyperpolarized the membrane. Ouabain consistently depolarized the basolateral membrane, even after extended periods of potassium depletion as long as 320 min. In the presence of ouabain, restoration of potassium depolarized the basolateral membrane. The data provide further evidence for the concept that the Na–K exchange pump of frog skin is rheogenic. Furthermore, the results suggest that the pump continues to be active even during prolonged periods of potassium depletion, reaccumulating potassium which has leaked out of the epithelial cells.     

Synaptic changes in cortical and subcortical brain formations in old rats

Electron microscopy was used to study structural changes of synapses in sensorimotor, parietal, limbic cortical areas, hippocamp, blue spot and hypothalamus of old Wistar rats, aged 28-30 months. Polymorphism of ultrastructural changes in neuronal and synapse processes and individual variability of these shifts in the brain of old rats have been revealed. The predominant damage of post-synaptic synapse components with ageing is demonstrated. Along with dystrophic and destructive changes in pre- and post-synaptic parts of the contact, signs of compensatory adaptive resettings in inter-neuronal links have been detected.     

Synaptic changes in the rabbit amygdala after unilateral lobectomy

Synapse morphology on neurons of the rabbit amygdala was investigated in intact animals and after unilateral lobectomy. The pattern of distribution of synapses normally observed on the neuron surface is altered after disturbance of cortico-amygdalar connections. These changes cannot be entirely explained by degeneration of some afferents. The results support the view that one morphological form of synapse can change into another in the process of function.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 8, No. 2, pp. 134–138, March–April, 1976.     

Synaptic proteome changes in mouse brain regions upon auditory discrimination learning

Changes in synaptic efficacy underlying learning and memory processes are assumed to be associated with alterations of the protein composition of synapses. Here, we performed a quantitative proteomic screen to monitor changes in the synaptic proteome of four brain areas (auditory cortex, frontal cortex, hippocampus striatum) during auditory learning. Mice were trained in a shuttle box GO/NO-GO paradigm to discriminate between rising and falling frequency modulated tones to avoid mild electric foot shock. Control-treated mice received corresponding numbers of either the tones or the foot shocks. Six hours and 24 h later, the composition of a fraction enriched in synaptic cytomatrix-associated proteins was compared to that obtained from na?ve mice by quantitative mass spectrometry. In the synaptic protein fraction obtained from trained mice, the average percentage (±SEM) of downregulated proteins (59.9 ± 0.5%) exceeded that of upregulated proteins (23.5 ± 0.8%) in the brain regions studied. This effect was significantly smaller in foot shock (42.7 ± 0.6% down, 40.7 ± 1.0% up) and tone controls (43.9 ± 1.0% down, 39.7 ± 0.9% up). These data suggest that learning processes initially induce removal and/or degradation of proteins from presynaptic and postsynaptic cytoskeletal matrices before these structures can acquire a new, postlearning organisation. In silico analysis points to a general role of insulin-like signalling in this process.     

Progressive postnatal increases in Fos immunoreactivity in the forebrain and brain stem of rats after viscerosensory stimulation with lithium chloride

Interoceptive signals have a powerful impact on the motivation and emotional learning of animals during stressful experiences. However, current insights into the organization of interoceptive pathways stem mainly from observation and manipulation of adults, and little is known regarding the functional development of viscerosensory signaling pathways. To address this, we have examined central neural activation patterns in rat pups after treatment with lithium chloride (LiCl), a malaise-inducing agent. Rat pups were injected intraperitoneally with 0.15 M LiCl or 0.15 M NaCl (2% body wt) on postnatal day (P)0, 7, 14, 21, or 28, perfused 60 to 90 min postinjection, and their brains assayed for Fos protein immunolabeling. Compared with saline treatment, LiCl increased Fos only slightly in the area postrema, nucleus of the solitary tract, and lateral parabrachial nucleus on P0. LiCl did not increase Fos above control levels in the central nucleus of the amygdala, bed nucleus of the stria terminalis (BNST), or paraventricular nucleus of the hypothalamus on P0 but did on P7 and later. Maximal Fos responses to LiCl were observed on P14 in all areas except the BNST, in which LiCl-induced Fos activation continued to increase through P28. These results indicate that central LiCl-sensitive interoceptive circuits in rats are not fully functional at birth, and show age-dependent increases in neural Fos responses to viscerosensory stimulation with LiCl.     

Chromatin changes in frog neurons after eighth nerve transection

Fourteen days after unilateral eighth nerve transection in the frog, Purkinje neurons of the lobus vestibulolateralis and corpus of the cerebellum and medium-sized neurons of the vestibular nuclear complex showed changes in metabolic activity. In the ipsilateral parts, and to a lesser extent in the contralateral parts, of operated frogs, the Feulgen-DNA values were higher and the nuclear areas larger, associated with decondensation of chromatin. The cytoplasmic basophilia was also less. These changes could be due to anabolic responses of the neuronal populations during regeneration. The anabolic reaction of the corpus cerebelli and contralateral vestibular nuclear complex is only partially non-specific and ascribable to the surgical trauma (comparison between sham-operated and unoperated frogs). The results indicate clear patterns of connection between the ipsilateral and contralateral parts and between the cerebellar and vestibular nuclear complex neurons.     

Synaptic secretion of BDNF after high-frequency stimulation of glutamatergic synapses.

The protein brain-derived neurotrophic factor (BDNF) has been postulated to be a retrograde or paracrine synaptic messenger in long-term potentiation and other forms of activity-dependent synaptic plasticity. Although crucial for this concept, direct evidence for the activity-dependent synaptic release of BDNF is lacking. Here we investigate secretion of BDNF labelled with green fluorescent protein (BDNF-GFP) by monitoring the changes in fluorescence intensity of dendritic BDNF-GFP vesicles at glutamatergic synaptic junctions of living hippocampal neurons. We show that high-frequency activation of glutamatergic synapses triggers the release of BDNF-GFP from synaptically localized secretory granules. This release depends on activation of postsynaptic ionotropic glutamate receptors and on postsynaptic Ca(2+) influx. Release of BDNF-GFP is also observed from extrasynaptic dendritic vesicle clusters, suggesting that a possible spatial restriction of BDNF release to specific synaptic sites can only occur if the postsynaptic depolarization remains local. These results support the concept of BDNF being a synaptic messenger of activity-dependent synaptic plasticity, which is released from postsynaptic neurons.     

Synaptic reactions of sensomotor cortex neurons to stimulation of emotionally significant brain structures

The study deals with synaptic and spike responses of neurones in the rat sensorimotor cortex to stimulation of the lateral and medial hypothalamus, locus coeruleus and raphe nuclei. The activity of 57 neurones was recorded, 41 of them intracellularly and quasi-intracellularly, in response to the stimulation of sites in these structures, which were previously identified as "emotionally/ significant. No considerable differences in the effects of the stimulation of different "emotiogenic" zones were found. The stimulation parameters, differing from the "behavioural" ones by a greater strength, elicited in the majority of neurones clear post-synaptic responses, often in the form of EPSP-IPSP. Latencies of the responses varied from 3 to 80 msec. The most stable and pronounced responses were obtained to the stimulation of the lateral hypothalamus. No significant correlations of the latencies of the responses to the stimulation of different "emotiogenic" structures were found.