Lennart Gisselsson

The sigma-1 receptor enhances brain plasticity and functional recovery after experimental stroke

Stroke leads to brain damage with subsequent slow and incomplete recovery of lost brain functions. Enriched housing of stroke-injured rats provides multi-modal sensorimotor stimulation, which improves recovery, although the specific mechanisms involved have not been identified. In rats housed in an enriched environment for two weeks after permanent middle cerebral artery occlusion, we found increased sigma-1 receptor expression in peri-infarct areas. Treatment of rats subjected to permanent or transient middle cerebral artery occlusion with 1-(3,4-dimethoxyphenethyl)-4-(3-phenylpropyl)piperazine dihydrochloride, an agonist of the sigma-1 receptor, starting two days after injury, enhanced the recovery of lost sensorimotor function without decreasing infarct size. The sigma-1 receptor was found in the galactocerebroside enriched membrane microdomains of reactive astrocytes and in neurons. Sigma-1 receptor activation increased the levels of the synaptic protein neurabin and neurexin in membrane rafts in the peri-infarct area, while sigma-1 receptor silencing prevented sigma-1 receptor-mediated neurite outgrowth in primary cortical neuronal cultures. In astrocytic cultures, oxygen and glucose deprivation induced sigma-1 receptor expression and actin dependent membrane raft formation, the latter blocked by sigma-1 receptor small interfering RNA silencing and pharmacological inhibition. We conclude that sigma-1 receptor activation stimulates recovery after stroke by enhancing cellular transport of biomolecules required for brain repair, thereby stimulating brain plasticity. Pharmacological targeting of the sigma-1 receptor provides new opportunities for stroke treatment beyond the therapeutic window of neuroprotection.

Electromyographic studies of the middle ear muscles of the cat.

Abstract In an investigation of the effect of sound stimulation upon the electromyographic activity of the tensor tympani and stapedius muscles of the cat, as studied with coaxial electrodes, the following observations were made. 1. 1. The action potentials recorded were usually diphasic, with a mean duration of 1.9 msec. for the tensor tympani and 1.5 msec. for the stapedius. 2. 2. The electromyographic activity increased with the frequency and intensity of the stimulating sound. The maximum found for both muscles was at about 2000 c/sec. The stapedius muscle displayed a broader frequency response spectrum and a lower threshold than the tensor tympani muscle. 3. 3. The latency of the middle ear muscle reflex, as judged by the interval between the appearance of cochlear potentials and the first action potential from the muscle, was 7 msec. for the tensor tympani and 6 msec. for the stapedius. 4. 4. On activation the tensor tympani muscle showed cyclic activity for the first second, with bursts of potentials interspersed with periods of electrical silence.

Actin redistribution underlies the sparing effect of mild hypothermia on dendritic spine morphology after in vitro ischemia.

Brain hypothermia is at present the most effective neuroprotective treatment against brain ischemia in man. Ischemia induces a redistribution of proteins involved in synaptic functions, which is markedly diminished by therapeutic hypothermia (33°C). Dendritic spines at excitatory synapses are motile and show both shape changes and rearrangement of synaptic proteins as a consequence of neuronal activity. We investigated the effect of reduced temperature (33°C and 27°C compared with 37°C), on spine motility, length and morphology by studying the distribution of GFP-actin before, during and after induction of in vitro ischemia. Because high-concentration actin filaments are located inside spines, dissociated hippocampal neurons (7-11DIV) from transgenic mice expressing GFP-actin were used in this study. The movement of the spines and the distribution of GFP-actin were recorded using time-lapse fluorescence microscopy. Under normal conditions rapid rearrangement of GFP-actin was seen in dendritic spines, indicating highly motile spines at 37°C. Decreasing the incubation temperature to 33°C or 27°C, dramatically reduces actin dynamics (spine motility) by approximately 50% and 70%, respectively. In addition, the length of the spine shaft was reduced by 20%. We propose that decreasing the temperature from 37°C to 33°C during ischemia decreases the neuronal actin polymerization rate, which reduces spine calcium kinetics, disrupts detrimental cell signaling and protects neurons against damage.

Rho kinase inhibition protects CA1 cells in organotypic hippocampal slices during in vitro ischemia.

The actin cytoskeleton is a dynamic superstructure that regulates multiple cellular functions and that has been implicated in cell death regulation. We investigated whether modulating the neuronal actin cytoskeleton polymerization by Rho-GTPase kinase (ROCK) inhibition influences cell death in hippocampal neuronal cultures and in murine organotypic hippocampal slice cultures subjected to in vitro ischemia (IVI). During IVI, spines on vehicle treated hippocampal neurons collapsed and large dendritic actin aggregates were formed. Following ROCK inhibition by Y27632, the actin aggregates were markedly smaller while large filopodia extended from the dendritic trunk. Y27632 also provided strong neuroprotection of hippocampal pyramidal CA1 neurons, which was of similar magnitude as protection by NMDA receptor blockade. Likewise, treatment with the F-actin depolymerizing agent latrunculin during IVI diminished actin aggregation and mitigated cell death following IVI. We propose that ROCK inhibition protects neurons against ischemic damage by disrupting actin polymerization thereby mitigating NMDA receptor induced toxicity and releasing ATP bound to actin for cellular energy use. We conclude that ROCK inhibitors abrogate multiple detrimental processes and could therefore be useful in stroke therapy.

Auditory Adaptation and Fatigue in Cochlear Potentials

Urethane-anaesthetized guinea pigs -were exposed to noise and pure-tone stimulation. Cochlear potentials were recorded immediately after the exposure through electrodes cemented into the third turn.Stimulation with low intensities did not show any influence on the amplitude of the cochlear potentials. Only by exposure to intensities exceeding 95 db (re human threshold) was it possible to demonstrate a decrease in amplitude.1This decrease is assumed to be due to fatigue, not to adaptation.The recovery time after high-intensity stimulation for less than 1 minute was 1 to 5 minutes. Longer stimulation resulted in a considerable increase in the recovery time.The effect on the cochlear potentials was found to be independent of the stimulus frequency on stimulation with pure tones of the frequencies 500, 1000 and 2000 cps. Stimulation with white noise affected, in particular, the low frequencies.Stimulation with noise containing the frequencies 5000-20,000 cps exerted a greater influence on the cochlear potenti...

Effect on Microphonics of Acetylcholine Injected Into the Endolymphatic Space

Martini (1940) claimed that acetylcholine can be demonstrated in the perilymph on sound stimulation of the inner ear. However, neither in the perilymph nor in the endolymph could Gisselsson (1950) show any acetylcholine during or after sound stimulation. On the other hand, he found abundant acetylcholinesterase in the endolymph and showed that intraarterial injection of acetylcholinesterase inhibitor into the cat and the guinea-pig interfered with the generation of microphonics. Injection of acetylcholine had no demonstrable effect on the microphonic potentials. Using Koelles histochemical method Churchill, Schuhknecht & Doran (1956) demonstrated the presence of acetylcholinesterase in the nerve fibres located within and near the organ of Corti.

Operations Other Than Otosclerosis for Improvement of Impaired Hearing

It is gratifying to note that since the War otologists have shown increasing interest in the treatment of impaired hearing. The successful surgical treatment of otosclerosis has intensified the search for micro-surgical methods for treatment of the middle ear. These methods have provided possibilities to try to improve hearing impaired by pathologic changes in the transmission apparatus of the ear. The methods devised are generally referred to under the common name of tympanoplasty.