Quantitative study of plasticity in the auditory nuclei of chick under conditions of prenatal sound attenuation and overstimulation with species specific and music sound stimuli

Abstract

Morphological effects of prenatal sound attenuation and sound overstimulation by species specific and music sounds on the brainstem auditory nuclei of chick have been evaluated quantitatively. Changes in length, volume, neuron number, size of neuronal nuclei and glial numbers of second and third order auditory nuclei, n. magnocellularis (NM) and n. laminaris (NL), were determined from thionine-stained serial sections of control and experimental groups on posthatch day 1 using stereological methods. Significant increase in volume of both auditory nuclei attributable to increase in length of nucleus, number and size of neurons, number of glia as well as neuropil was observed in response to both species specific and music overstimulation given during the critical period of development. The enhanced development of auditory nuclei in response to enriched environment prenatally indicates a positive effect of activity on neurons which may have clinical implications in addition to providing explanation for preference to auditory cues in the postnatal life. Reduction in neuron number with a small increase in proportion of cell nuclei of large size as well as an increase in glial numbers was seen in both NM and NL of the prenatally sound attenuated chicks. The increase in size of some neuronal nuclei may probably be evidence of enhanced synthesis of proteins involved in cell death or an attempt at recovery. The dissociated response of neurons and glia under sound attenuated and auditory stimulated conditions suggests that they are independently regulated by activity-dependent signals with glia also being under influence of other signals for a role in removal of dead cell debris.

Expression of Synaptic Proteins in the Hippocampus and Spatial Learning in Chicks following Prenatal Auditory Stimulation

“…A double-walled insulated incubator under controlled temperature of 37 ° C (36-38 ° C) and humidity 70% (68-72%) was used for incubating the eggs [39] . Tilting of eggs was automatically controlled for 4 times a day and a photoperiodicity of 12:12 h day and night cycle was maintained throughout the incubation period (21 days).…”

“…The incubating eggs were given auditory stimuli through 2 built-in speakers at 65 dB connected to a Philips double-deck sound system with auto-reverse facility. The sound was given for a 15-min stretch, once every hour, 24 h per day from embryonic day (E) 10 until hatching [39] . The protocol and number of animals used in the experiment was approved by the institution ethics committee [grant No.INV.324/05-IAEC (PRF)].…”

Bigger Brains or Bigger Nuclei? Regulating the Size of Auditory Structures in Birds

“…Factors such as afferent input and auditory experience could regulate the differences in the extent of cell death in NM seen between barn owls and chickens. For example, the number of apoptotic profiles in the developing auditory nuclei of chickens is reduced when the embryos are exposed to species-specific vocalizations [Wadhwa et al, 1999]. Otocyst removal in the embryonic chicken results in a reduction of NM cells by cell death [Parks, 1979].…”

Developmentally regulated expression of c‐Fos and c‐Jun in the brainstem auditory nuclei of Gallus domesticus is modified by prenatal auditory enrichment

“…In our previous studies, developing embryos of the domestic chick were provided with prenatal auditory enrichment of speciesspecific sounds and music (sitar) in a frequencygraded manner from embryonic day 10 (E10) to hatching. The brainstem auditory nuclei NM and NL of the auditory stimulated embryos exhibited significant increase in number and size of neurons (Wadhwa et al, 1999). An enhancement in expression of synaptic proteins-synaptophysin and syntaxin1-as well as the presence of more than one axosomatic contact on NM neurons at E16 was found (Alladi et al, 2002).…”