Experience-dependent regulation of functional maps & protein expression in visual cortex

Despite great progress in understanding of how experience modifies cortical circuitry in primary visual cortex (VI), the underlying physiological and molecular mechanisms still remain to be understood fully. Although some of the molecules associated with the critical period for ocular dominance plasticity in cats have been examined, the role of downstream signalling molecules that form pathways with receptor subunits has received scant attention. The present study demonstrates using optical imaging of intrinsic signals that sensory experience is not required for initial establishment of ocular dominance column layout and iso-orientation domains but is required for maintenance of these properties its absence leads to their eventual breakdown. Animals were sacrificed and VI was removed and homogenised, followed by immunoblotting for quantification of protein expression. The immunoblotting findings point to a set of proteins (including NR2A, PSD-95, aCaMKQ, NR2B and GABAAala) that are regulated developmentally and the effects of dark-rearing indicate that sensory activity regulates mechanisms associated with both excitatory (NR2A and NR2B) and inhibitory (GABAAala) transmission and synaptogenesis (synaptogenesis) so as to maintain a homeostatic balance. Pattern or form information is necessary in both eyes to maintain normal maps in both eyes while differences in illumination between two eyes did not affect ocular dominance and orientation maps in normally reared or in dark-reared cats subsequently exposed to light. Monocular deprivation (MD) for 2 days and 7 days resulted in similar depression of deprived eye responses. In contrast, potentiation of non-deprived eye responses was almost double in magnitude after 7 days compared to 2 days of MD. The immunoblotting findings demonstrate that MD regulates signalling molecules (PSD-95, aCaMKH and synGAP) downstream of NMD A receptors and GluRl subunit it appears that different mechanisms are activated depending on the nature of sensory experience

Effects of different forms of monocular deprivation on primary visual cortex maps

Monocular deprivation (MD) by lid suture is one of the classic paradigms for the study of developmental plasticity in the cerebral cortex, and we have detailed knowledge of its anatomical and physiological consequences as well as underlying molecular and cellular mechanisms. However, the effects of other forms of manipulating visual input through one eye on the functional architecture of the primary visual cortex (V1) have not yet been examined directly. We compared MD by lid suture with the effects of daily monocular lens wear using either a frosted lens or a neutral density (ND) filter. We used optical imaging of intrinsic signals and visually evoked potentials (VEPs) to assess responses in V1 to monocular stimulation. We found that loss of stimulus contrast through monocular frosted lens wear resulted in marked takeover of cortical territory by the nondeprived eye (NDE) similar to that caused by classic MD, and in virtual absence of orientation-selective responses following stimulation of the deprived eye (DE). Furthermore, amplitudes of VEPs in response to gratings of a range of spatial frequencies were significantly reduced in the DE compared to the NDE. In contrast, differences in luminance between two eyes caused by an ND filter in front of one eye did not affect ocular dominance and orientation maps, and there was no significant difference in the amplitude of VEPs elicited through the two eyes. Our results are consistent with previous electrophysiological studies in demonstrating that binocular pattern information is necessary to maintain normal functional maps in both eyes, while reduced luminance in one eye has little effect on the overall functional architecture and visual responses in V1

Characterisation of development and electrophysiological mechanisms underlying rhythmicity of the avian lymph heart

Despite significant advances in tissue engineering such as the use of scaffolds, bioreactors and pluripotent stem cells, effective cardiac tissue engineering for therapeutic purposes has remained a largely intractable challenge. For this area to capitalise on such advances, a novel approach may be to unravel the physiological mechanisms underlying the development of tissues that exhibit rhythmic contraction yet do not originate from the cardiac lineage. Considerable attention has been focused on the physiology of the avian lymph heart, a discrete organ with skeletal muscle origins yet which displays pacemaker properties normally only found in the heart. A functional lymph heart is essential for avian survival and growth in ovo. The histological nature of the lymph heart is similar to skeletal muscle although molecular and bioelectrical characterisation during development to assess mechanisms that contribute towards lymph heart contractile rhythmicity have not been undertaken. A better understanding of these processes may provide exploitable insights for therapeutic rhythmically contractile tissue engineering approaches in this area of significant unmet clinical need. Here, using molecular and electrophysiological approaches, we describe the molecular development of the lymph heart to understand how this skeletal muscle becomes fully functional during discrete in ovo stages of development. Our results show that the lymph heart does not follow the normal transitional programme of myogenesis as documented in most skeletal muscle, but instead develops through a concurrent programme of precursor expansion, commitment to myogenesis and functional differentiation which offers a mechanistic explanation for its rapid development. Extracellular electrophysiological field potential recordings revealed that the peak-to-peak amplitude of electrically evoked local field potentials elicited from isolated lymph heart were significantly reduced by treatment with carbachol; an effect that could be fully reversed by atropine. Moreover, nifedipine and cyclopiazonic acid both significantly reduced peak-to-peak local field potential amplitude. Optical recordings of lymph heart showed that the organ’s rhythmicity can be blocked by the HCN channel blocker, ZD7288; an effect also associated with a significant reduction in peak-to-peak local field potential amplitude. Additionally, we also show that isoforms of HCN channels are expressed in avian lymph heart. These results demonstrate that cholinergic signalling and L-type Ca2+ channels are important in excitation and contraction coupling, while HCN channels contribute to maintenance of lymph heart rhythmicity

Effects of different forms of monocular deprivation on primary visual cortex maps

Monocular deprivation (MD) by lid suture is one of the classic paradigms for the study of developmental plasticity in the cerebral cortex, and we have detailed knowledge of its anatomical and physiological consequences as well as underlying molecular and cellular mechanisms. However, the effects of other forms of manipulating visual input through one eye on the functional architecture of the primary visual cortex (V1) have not yet been examined directly. We compared MD by lid suture with the effects of daily monocular lens wear using either a frosted lens or a neutral density (ND) filter. We used optical imaging of intrinsic signals and visually evoked potentials (VEPs) to assess responses in V1 to monocular stimulation. We found that loss of stimulus contrast through monocular frosted lens wear resulted in marked takeover of cortical territory by the nondeprived eye (NDE) similar to that caused by classic MD, and in virtual absence of orientation-selective responses following stimulation of the deprived eye (DE). Furthermore, amplitudes of VEPs in response to gratings of a range of spatial frequencies were significantly reduced in the DE compared to the NDE. In contrast, differences in luminance between two eyes caused by an ND filter in front of one eye did not affect ocular dominance and orientation maps, and there was no significant difference in the amplitude of VEPs elicited through the two eyes. Our results are consistent with previous electrophysiological studies in demonstrating that binocular pattern information is necessary to maintain normal functional maps in both eyes, while reduced luminance in one eye has little effect on the overall functional architecture and visual responses in V1

Experience-dependent regulation of functional maps and synaptic protein expression in the cat visual cortex

Although the basis of our knowledge of experience-dependent plasticity comes from studies on carnivores and primates, studies examining the physiological and molecular mechanisms that underlie development and plasticity have increasingly employed mice. We have used several common rearing paradigms, such as dark-rearing and monocular deprivation (MD), to examine the timing of the physiological and molecular changes to altered experience in the cat primary visual cortex. Dark-rearing from birth or for 1 week starting at 4 weeks of age produced a similar reduction in the amplitude of responses measured through intrinsic signal imaging and a reduction in orientation selectivity. One week of visual experience following dark-rearing until 4 weeks of age yielded normal responses in both amplitude and orientation selectivity. The depression of deprived-eye responses was similar in magnitude after 2 and 7 days of MD. In contrast, non-deprived-eye responses almost doubled in magnitude after 7 days compared with 2 days of MD. These changes in the functional properties of primary visual cortex neurons were mirrored by specific changes in synaptic protein expression. Changes in proteins such as the NR2A and NR2B subunits of the N-methyl-D-aspartate receptor, postsynaptic density protein 95, alpha-CA2+/calmodulin-dependent protein kinase II (αCaMKII), and GABAAα1a indicated that the levels of sensory activity regulated mechanisms associated with both excitatory (NR2A and NR2B) and inhibitory (GABAAα1a) transmission so as to maintain response homeostasis. Additionally, we found that MD regulated the AMPA receptor glutamate (GluR1) subunit as well as signalling molecules (αCaMKII and synaptic Ras GTPase activating protein, SynGAP) downstream of N-methyl-D-aspartate receptors. Proteins in a common signalling pathway appeared to have similar developmental expression profiles that were broadly similar between cats and rodents

Changes in the odor quality of androstadienone during exposure-induced sensitization

Androstadienone is a steroid found in human sweat and other secretions. It has been widely proposed as a candidate for a human pheromone. As an odorant it possesses some unique properties. Here we demonstrate that, firstly, there is a very wide range of thresholds in the human population, and they are not normally distributed. Secondly, repetitive exposure causes a decrease in detection threshold of more than four orders of magnitude, and thirdly, accompanying this sensitization process is a change in the perceived odor quality. Those with low to intermediate sensitivities ascribe to it a wide range of odor descriptors across the hedonic scale, but as these individuals become sensitized, their description changes to predominantly putrid. We propose that this change in odor quality reflects the presence of at least two receptor populations for androstadienone; a low-affinity receptor conveying pleasant odor qualities and a high-affinity receptor mediating unpleasant odor qualities. We further propose that repetitive exposure results in the increased expression of the high-affinity receptor thereby shifting the balance of perception to the negative end of the hedonic scale

Evoked local field potential recorded from lymph heart before and after addition of carbachol followed by atropine in the presence of carbachol.

<p>A) Representative trace of evoked local field potential (LFP) obtained from control, in the presence of carbachol (10μM) B) and after adding atropine (5μM) in the presence of carbachol C). D) Bar charts show average peak to peak of evoked LFP amplitude calculated from control, in the presence of carbachol and after adding atropine in the presence of carbachol (n = 9). The data for evoked LFP in the presence of carbachol and the data for evoked LFP of atropine in the presence of carbachol was normalised to data obtained from control. After adding carbachol the average peak to peak of evoked <b>LFP</b> amplitude was significantly reduced (*** p<0.001) compared to the control. On addition of atropine in the presence of carbachol the effects were significantly reversed (*** p<0.001). Error bars represent mean ± SEM (n = 9). E) Bar chart shows average peak to peak of evoked LFP amplitude calculated from control, in the presence of TTX (n = 3). The data for evoked LFP in the presence of TTX was normalised to data obtained from control. After adding TTX the average peak to peak of evoked LFP was reduced compared to control however it was not statistically significant (p>0.05). Error bars represent mean ± SEM.</p