No description available.

No description available.

No description available.

No description available.

The pigeon's colour vision was examined, using behavioural and physiological techniques Avian colour vision has aroused interest because of the suggestion that chromatic discrimination in birds is mediated by a single cone pigment, combined with several types of retinal oil-droplets which act as differential colour filters. Using an operant conditioning method, difference thresholds were measured throughout the spectrum (400 - 680 nm) to generate a wavelength discrimination function, which yields information about the type of visual system an animal possesses. Earlier work had suggested that birds are trichromatic, but the finding of three clearly defined regions of optimum discrimination at 595, 530 and 460 nm indicates instead that the pigeon's colour vision is at least tetrachromatic. The pigeon's saturation discrimination abilities were also studied using a similar technique Saturation increased towards the spectral extremes while a point of least saturation occurred at 597 nm. Additional subsidiary saturation minima were found at 443, 496, 536 and 662 nm. These results largely corroborated those of the wave length discrimination experiment but indicated that the pigeon's visual system may be more complex than a tetrachromatic one Preliminary to an extension of the wavelength discrimination study, the pigeon's spectral sensitivity was measured electroretinographically The resulting spectral sensitivity curve peaked at 560 - 580 nm, in agreement with previously reported data. Furthermore, spectral sensitivity extended well into the ultraviolet region (<400 nm), where sensitivity was quite high In a second study of wavelength discrimination, results of the first experiment showing three threshold minima were confirmed and, additionally, pigeons maintained good discrimination between wavelengths within the ultraviolet range. Experimental findings were discussed in terms of the physiological mechanisms underlying visual performance, in particular, the present results, together with other evidence, suggest that the retinal oil-droplets are not basic to avian colour vision The functional significance of the pigeon's colour vision was also considered

An anatomical and morphological study of the red nucleus of the pigeon showed that as in the mammal the nucleus is relatively highly vascularised and contains both large and small cells. The only relevant previous source indicated the existence of large cells only. Lesions of the pigeon red nucleus (r. n.) effected a variety of symptoms including torticollis, abnormalities of leg muscle tone and movement, hyporeactivity, aphagia and asymmetry of pupil dilation although the latter was probably due to third nerve damage. Electrical stimulation of the r. n. produced contralateral circling and indications of staxia. Extensive investigation using electrical stimulation and evoked potential recording revealed telencephalic inputs to the r. n. from the archiastriatum medialis, hyperstriatum ventrale, parolfactory lobe, olfactory bulb and neostriatum intermedium, diencephalic projections from the lateral hypothalamus and nucleus rotundus and a cerebellar link with the nucleus lateralis. Comparison tdth mammalian connections disclosed some similarities and in addition suggested that links with amygdala and septum may exist in the mammal. Evoked potential and single unit recordings following visual, somaesthetic and auditory stimulation demonstrated that the avian r. n. and individual cells respond in a very similar manner to that of the mammal. An olfactory projection was also demonstrated by nerve stimulation. Investigation of the effects of r. n. lesions on previously established avoidance behaviour disclosed complete disruption of learning. Similar effects were shown on a pattern discrimination acquired under positive reinforcement, although brightness aid colour discriminations were not affected. Possible mechanisms involving the r. n. in behaviour control are discussed.

A detailed quantitative study of the morphological variations of extrafusal motor end-plates of normal cat hindlimb muscles as seen in teased silver impregnated preparations was undertaken. The principal aim was to examine the hypothesis that end-plates undergo growth and degeneration in a process of cyclic degeneration and renewal ('replacement'). A new classification of the morphological complexity of end-plates was devised and the three muscles studied (peroneus brevis, peroneus digiti quinti and soleus) show characteristic variations in the proportions of complex endings, and in the size relationships of end-plates and muscle fibres. These variations are not related to differences in the proportions of muscle fibres of the three principal histochemical types. The existence of growth and degeneration of end-plates was confirmed, but no new end-plates are formed. Hence the 'replacement' hypothesis is regarded as untenable. Instead, it is suggested that growth leads to the formation of end-plates of greater complexity ('elaboration'), and degeneration to the loss of muscle fibres commonly observed in ageing mammals. The examination of muscles from cats aged 6 - l8 years supports this concept because there is a striking increase in the proportions of complex end-plates and the number of muscle fibres is reduced. By analogy with the formation of end-plates, it is suggested that 'elaboration' during ageing is a response to the increasing functional demands indicated by the increased body weights and muscle fibre diameters. An attempt to test the effects of use and disuse in kittens was unsuccessful. However, surgically-induced hypertrophy of soleus in a young adult cat resulted in an increased proportion of larger, more complex end-plates with more numerous, longer axon terminals. This strongly suggests that 'elaboration' is indeed a response to functional demand. The observations are discussed in relation to current views of the neuromuscular system.

Changes in synapse and neuronal morphology have been reported in the rat hippocampal formation after the induction of long-term potentiation (LTP) of the perforant path, although few studies have investigated such parameters in the maintenance phase of L-LTP. Moreover, the results of investigations of synaptic and neuronal morphometry changes after LTP have varied and this could be due to the methods of analysis employed, the choice of stimulation protocol and or whether an <i>in vitro</i> or <i>in vivo</i> study. This <i>in vivo</i> investigation applied unbiased stereological methods to examine the morphology and morphometry of perforant path-granule cell synapses, in the dentate gyrus, after the induction of LTP. Two controls were employed, the contralateral hemisphere of each animal and the inner molecular layer, where the medial perforant path has little synaptic input. Many previous studies of the first 6Omin post tetanisation have used high frequency stimulation (HFS) to induce LTP however, in this study – to determine whether changes in morphology were due to LTP per se - potentiation was induced by theta burst stimulation (TBS). 45min after the induction of LTP there were no significant differences, between hemispheres, in the mean numerical density (Nv) of axodendritic or axospinous asymmetric synapses, or the mean number of synapses per neuron in the middle molecular layer (MML) of the dentate gyrus. There were no significant differences, between potentiated and non-potentiated tissue, in the Nvs of those asymmetric synapses with perforated or concave profiles. Neither were significant differences following LTP demonstrated in the size of the postsynaptic densities of these synaptic subtypes or the volume density of apposition zone (AZ) area (Sv) of individual, or all, asymmetric axospinous synapses. However, there was a trend towards larger perforated synapses in the potentiated hemisphere and, in both hemispheres, concave and perforated synapses were larger than average. In the inner molecular layer (IML), there were no differences except for a significant decrease in the total AZ volume density in the potentiated hemisphere. This would suggest that any morphological modifications taking place in the induction phase of L-LTP may be restricted to a fraction of synapses in the MML, although perforated synapses appear to be involved. The second part of this study examined morphological correlates 24h after the induction of LTP with TBS and HFS. In the MML after induction of LTP with TBS there were significant increases in the Nv of asymmetric axodendritic synapses and the mean number of axodendritic synapses per neuron. There was an increase in the Nv of axospinous synapses and in the mean number of axospinous synapses per neuron that was not significant. This was reflected in significant increases in the total AZ Sv and in the frequency of macular synapses in the potentiated hemisphere. 24h post tetanisation with HFS, there was a significant difference in the Nv of axospinous synapses in the MML of the potentiated compared to the contralateral hemisphere. There were also significant differences in the frequency of synapses with perforated and concave profiles. There were no significant differences in synaptic morphometric parameters, between hemispheres, in the IML after either of the stimulating regimes. Results from the three animals in each group showing the greatest degree of potentiation, were pooled and demonstrated significant differences in the Nv and mean number of axospinous synapses per neuron. There was also a significant difference in the number of synapses with concave profiles but this was replicated in the IML. The effects of these morphological changes, after LTP induction, on the cellular mechanisms involved and on synaptic efficacy are discussed, and possible reasons for the variable pattern of morphology after different stimulating protocols is considered.

No description available.

An in vitro conditioning paradigm was developed to investigate the different phases of memory leading to associative long-term memory formation in the feeding system of the pond snail, Lymnaea stagnails. Using a one-trial chemical conditioning paradigm, a paired application of the CS (amyl acetate) and US (sucrose) to the lips/oesophagus in a semi-intact preparation was carried out. The conditioned response was measured as an increase in the frequency of fictive feeding cycles in feeding motoneurons following application of the CS to the lips. The time course of expression of the memory trace from 10 min to 4 hr after conditioning was followed. Importantly, the expression of the in vitro memory trace was shown to be intermittent unlike the one observed in behavioural experiments that was continuous. The in vitro memory trace was detected at 10 min, 1 hr and up to 4hr but not at 30 min and 2 hr. Protein synthesis was required for the expression of a memory trace from 1 hr after raining and for later time points, but not at 10 min. This result suggests a correspondence between the inability to detect an in vitro memory trace at 30 min and the transition from a protein independent mechanism for memory expression to a protein-dependent one. Experiments using RNA-synthesis blockers have shown a requirement for de novo synthesis of RNA from 4 hr after training and onward. Based on in vitro and in vivo data, a model for associative conditioning is presented, suggesting the presence of a short-term memory trace at 10 min after conditioning (protein synthesis and RNA synthesis-independent), an intermediate-term memory trace at 1-3 hr after conditioning (protein synthesis-dependent, RNA synthesis-independent) and a long-term memory trace (protein synthesis-dependent, RNA synthesis-dependent) at 4 hr and up to 24 hr after conditioning.