Avian tuberculosis in naturally infected captive water birds of the Ardeideae and Threskiornithidae families studied by serotyping, IS901 RFLP typing, and virulence for poultry.

Avian tuberculosis was detected in one flock of 38 water birds of the families Ardeideae (n = 20) and Threskiornithidae (n = 18). Mycobacterium avium subsp. avium (MAA, serotype 1, genotype IS901+ and IS1245+) was more often (p = 0.01) detected in tissue and/or faecal samples in 18 (90.0%) birds form the Ardeideae family: little egret (Egretta garzetta), buff-backed heron (Bubulcus ibis), great white egret (Egretta alba), and bittern (Botaurus stellaris) in comparison to two (11.1%) birds from the Threskiornithidae family: sacred ibis (Threskiornis aethiopicus). Avian tuberculosis was not diagnosed in spoonbills (Platalea leucorodia). Tuberculous lesions were found in nine birds. MAA isolates of IS901 RFLP type F-C3 were present in all of the 20 infected birds and in all environmental isolates. A mixed infection with the MAA isolates of three RFLP types F-C3 (tissue isolate), G-C3, and T-C3 (faecal isolates) was found in one sacred ibis. All 20 tissue isolates of IS901 RFLP type F-C3 from 20 birds and 8 environmental MAA isolates were fully virulent in pullets, whilst the isolates of RFLP types G-C3 and T-C3 were non-virulent in pullets. All of the tested MAA isolates had the same IS1245 RFLP "bird profile". In 12 of 20 infected birds with MAA M.a. hominissuis isolates of serotypes 4, 8, 9 and genotype IS901- and IS1245+ were detected and in 8 other birds mycobacteria not belonging to the M. avium complex were found. The presence of MAA in the environment may be a source for further spread of the causal agent of avian tuberculosis among other groups of animals in zoological gardens, farm animals, and also among their keepers.

Ketamine blockade of spreading depression: rapid development of tolerance.

Persistence of the ketamine-induced blockade of spreading depression (SD) was studied in 15 rats, anesthetized with 200 mg/kg ketamine followed at 50- to 60-min intervals by 3-5 injections of 100 mg/kg of the drug. Cortical or caudate SDs evoked 10 min after the first ketamine injection were blocked but the amplitude of SD waves elicited at regular 10-min intervals gradually increased while the blockade induced by subsequent ketamine injections weakened and became unrecognizable after the fifth injection. The result was not due to prolonged action of ketamine alone but rather to combined effect of ketamine and SD repetition. The development of tolerance is probably due to use-dependence of NMDA-gated channels which must be taken into account when assessing the therapeutic value of NMDA antagonists in treatment of brain ischemia.

Brain transplants enhance rather than reduce the impairment of spatial memory and olfaction in bulbectomized rats.

The possibility to compensate the loss of olfactory and non-olfactory functions due to removal of the olfactory bulb by embryonal brain grafts was investigated in adult rats. Spatial working memory was examined in an 8-arm radial water maze task 6 weeks after bulbectomy. During 15 daily trials, performance gradually improved in bulbectomized controls (n = 10) and in rats with olfactory bulb transplants (n = 9), but did not attain that of intact controls (n = 10). No improvement was observed in the rats with substantia nigra grafts (n = 8). Eleven weeks after bulbectomy, the same rats were tested in the water tank navigation task. The performance improved during ten 12-trial sessions in bulbectomized rats less than in intact controls, but more than in the transplanted rats. The olfactory food retrieval test performed 14 weeks after bulbectomy revealed almost full recovery of smell in bulbectomized rats, but not in the transplanted animals. It is concluded that the spatial memory deficit is probably due to bulbectomy-induced interference with septohippocampal function which is not alleviated, but rather enhanced by transplantation. The results suggest that the effect of brain grafting is not always beneficial.

Functional ablation of the olfactory bulb by spreading depression: unit activity changes and transient anosmia.

Cortical spreading depression (SD) is widely used to induce functional decortication. Development of a reliable technique for eliciting SD in the olfactory bulb (OB) of rats makes it possible to achieve functional elimination of the first relay of the olfactory pathway. In order to assess the unit activity changes accompanying OBSD, adult male hooded rats (n = 31) were anesthetized with pentobarbital and activity of OB units was recorded with carbon fiber microelectrodes. The predepression activity (12.7 +/- 0.8 Hz) increased up to 35.1 +/- 4.1 Hz during the burst which attained maximum 44 +/- 6 sec after K+ acetate injection and corresponded to the steep depolarization phase of SD slow potential. The burst lasted 20.4 +/- 2.9 sec on the average and was followed by 187 +/- 20 sec of complete silence. Gradual recovery to the predepression level lasted 229 +/- 27 sec. Activity of most units (63%) in the contralateral OB was not changed. Significant reactions of OB neurons to ipsilateral cortical SD found in 57% units were mostly inhibitory (49%). OBSD-induced anosmia was examined in a group of rats (n = 8) with unilateral bulbectomy and a guiding tube implanted into the remaining OB for microinjection of K+ acetate. One week after surgery, the animals were examined in the food-retrieval olfactory test. The microinjection of K+ acetate severely disrupted the food finding behavior in 60% rats during 3-min test. Both electrophysiological and behavioral results indicate that OBSD is a convenient tool for inducing short-lasting anosmia.

Atypical glomerulization in the remnants of the olfactory bulb after bulbectomy. A light microscopic study.

Regeneration of olfactory axons after bilateral bulbectomy in adult rats leads to atypical localization of the newly formed glomeruli. These structures are localized in the remnants of the olfactory bulb either in the previously deafferented glomerular layer or between external plexiform and granule cell layers in the close vicinity of mitral cells.

Functional recovery after olfactory bulbectomy in rats: effect of embryonal brain grafts.

Regeneration of olfactory receptor neurones after bulbectomy can lead to formation of extrabulbar synapses, the functional significance of which remains controversial. Adult hooded rats (n = 27) were bilaterally bulbectomized under pentobarbital anaesthesia. Small pieces of brain tissues (1-2 mm3; OB: olfactory bulb; St: corpus striatum) were obtained from embryos of the same strain and placed into the bulbectomy-produced cavity in contact with the exposed brain surface. Smell was tested at 2- to 3-week intervals from 7 weeks to 7 months after the operation. The latency to find hidden food gradually improved and attained the intact control level in bulbectomized rats without grafts, but remained poor in the OB and St transplanted groups. Seven to ten months after transplantation, spontaneous unit activity and unit reactions to amyl acetate vapours were examined with a carbon fibre microelectrode. Unit responses in the transplants resembled those in the normal OB, but were less pronounced. Morphological examination of the transplant and of its connections with the olfactory receptor neurones and with the host brain suggested that functional recovery was mediated by the connections of the olfactory axons with the remnants of the OB, with the anterior olfactory nucleus and/or with the frontal cortex. The adverse effect of OB and St transplants was probably due to their poor connectivity with the host brain which prevented the regenerating olfactory axons from reaching higher olfactory centres.

Spreading depression in the olfactory bulb of rats: reliable initiation and boundaries of propagation.

Spreading depression in the olfactory bulb of rats is an elusive phenomenon, the demonstration of which requires specific conditioning procedures. The present paper describes a simple technique for reliable initiation of bulbar spreading depression with microinjections of potassium acetate. Adult hooded rats were anesthetized with pentobarbital (50 mg/kg) and slow potential changes accompanying spreading depression were recorded with capillary microelectrodes stereotaxically inserted into the olfactory bulb and adjacent forebrain structures. KCl microinjection (0.5-1.0 microliter, 0.134-0.670 mol/l) into the olfactory bulb elicited local depolarization which only exceptionally developed into a propagating spreading depression. Potassium acetate (0.5-1.0 microliter, 0.15 mol/l) injected into the rostral olfactory bulb evoked a negative slow potential wave (amplitude of around 25 mV and duration 30-50 s) propagating at a rate of 3-4 mm/min through all the olfactory bulb layers. Low positive (5 mV) instead of negative waves were recorded in the superficial olfactory nerve layer with reversal in the glomerular layer (200-300 micron). The slow potential decreased in the rostrocaudal direction and expired at the caudal boundary of the olfactory bulb. Bulbar spreading depression never spread to neocortex, and cortical spreading depression never entered into the olfactory bulb but stopped in the anterior olfactory nucleus 7 mm rostral to bregma. Repeated potassium acetate injections into the olfactory bulb occasionally elicited a series of spreading depression waves recurring at regular intervals, probably reflecting reverberation of scroll-shaped waves around the rostrocaudal axis of the olfactory bulb.(ABSTRACT TRUNCATED AT 250 WORDS)

Olfactory neuroepithelium transplanted onto the parietal cortex of rats: electroolfactogram in absence of connections with the host brain.

A technique, allowing continuous electrophysiological monitoring of the functional properties of transplanted olfactory neuroepithelium is described. Viability of isolated parts of nasal mucosa obtained from adult rats was tested in vitro. Pieces of olfactory neuroepithelium (2 X 2 mm) were transplanted onto the exposed parietal cortex of adult rats and protected by plastic wells covered with a transparent lid. At one-week intervals the lid was removed and the transplanted epithelium was tested for electrical responses to amyl acetate vapours. Reliable electroolfactograms appeared 3 weeks after transplantation and could be elicited in 60% of transplants (n = 15) during the subsequent 6 weeks but disappeared later. Morphological control at the conclusion of the experiment showed that the transplant consisted of pieces of epithelium forming vesicular or semivesicular structures but not containing olfactory sensory neurons and not connected with the host brain. It is concluded that the method allows recording responses of the transplanted neuroepithelium to olfactory stimuli but does not yield a sufficiently stable preparation for establishing ectopic olfactory input to the brain.

Ketamine blockade of cortical spreading depression in rats.

The failure to elicit cortical spreading depression (SD) under ketamine anesthesia has been examined in 25 rats. SD was elicited by microinjection of K+ acetate (1 microliter, 0.15 mol/l) into the cerebral cortex and monitored by recording the accompanying slow-potential waves. I.p. injection of ketamine HCl (50 mg/kg) elicited after 5-10 min blockade of SD propagation lasting 30-40 min. SD penetration into a cortical area superfused with 10(-4) and 10(-3) mol/l ketamine was partly or completely blocked, respectively. Systemic ketamine doses eliciting SD blockade only slightly reduced spontaneous activity of cortical units recorded with carbon fiber microelectrodes and did not increase but rather decreased the rate of K+ removal from a KCl pool (30 microliters, 40 mmol/l) contacting a 12.5 mm2 area of exposed cortical surface. The results indicate that the ketamine-induced SD blockade is due neither to epileptic activity nor to enhanced active transport of ions but rather to interference with chemically gated ionic channels and/or to stabilization of postsynaptic membranes.

Terminal anoxic depolarization proceeds more slowly in the olfactory bulb than in the cerebral cortex of rats.

The time course of terminal anoxic depolarization and of the concomitant [K+]e increase was compared in the cerebral cortex and olfactory bulb of rats anesthetized with pentobarbital. Respiration arrest elicited by (+)-tubocurarine induced a negative slow potential shift which reached 50% of maximum after 90 s in the cortex and after 180 s in the olfactory bulb (n = 10). Bulbar [K+]e increased slowly to 16 mmol/l, then more rapidly to 40 60 mmol/l and reached 90 mmol/l after 10 min asphyxia (n = 10). While the resting and maximal [K+]e levels were the same in the cortex and olfactory bulb, the fast [K+]e rise started in the olfactory bulb at a higher level (16 mmol/l) and proceeded at a slower rate (doubling time 14 s) than in the cortex, where the same values were 11 mmol/l and 5 s, respectively. It is argued that the olfactory bulb resistance to asphyxia is due to a powerful GABAergic inhibition which counteracts the autoregenerative ionic shift and accounts for the absence of spreading depression in this structure.