Extrinsic embryonic sensory stimulation alters multimodal behavior and cellular activation

Abstract

Embryonic vision is generated and maintained by spontaneous neuronal activation patterns, yet extrinsic stimulation also sculpts sensory development. Because the sensory and motor systems are interconnected in embryogenesis, how extrinsic sensory activation guides multimodal differentiation is an important topic. Further, it is unknown whether extrinsic stimulation experienced near sensory sensitivity onset contributes to persistent brain changes, ultimately affecting postnatal behavior. To determine the effects of extrinsic stimulation on multimodal development, we delivered auditory stimulation to bobwhite quail groups during early, middle, or late embryogenesis, and then tested postnatal behavioral responsiveness to auditory or visual cues. Auditory preference tendencies were more consistently toward the conspecific stimulus for animals stimulated during late embryogenesis. Groups stimulated during middle or late embryogenesis showed altered postnatal species-typical visual responsiveness, demonstrating a persistent multimodal effect. We also examined whether auditory-related brain regions are receptive to extrinsic input during middle embryogenesis by measuring postnatal cellular activation. Stimulated birds showed a greater number of ZENK-immunopositive cells per unit volume of brain tissue in deep optic tectum, a midbrain region strongly implicated in multimodal function. We observed similar results in the medial and caudomedial nidopallia in the telencephalon. There were no ZENK differences between groups in inferior colliculus or in caudolateral nidopallium, avian analog to prefrontal cortex. To our knowledge, these are the first results linking extrinsic stimulation delivered so early in embryogenesis to changes in postnatal multimodal behavior and cellular activation. The potential role of competitive interactions between the sensory and motor systems is discussed.

Figure 1

Spectrogram of the species-specific embryonic contentment call played to bobwhite quail embryos. Vocalizations contained no harmonics and ranged from 2 to 6 kHz. The dominant frequency ranged from ∼2 to 3.8 kHz.

Figure 2

Spectrograms of the conspecific and heterospecific calls used in auditory choice tests. Although the two calls are similar in frequency range and harmonic structure, the heterospecific call has a more stereotyped prosody, a sharp broad-spectrum bark at the beginning of each call, and a notable lack of intrasyllabic inflection compared with the conspecific call. Both calls contain harmonics in the same frequency range as the embryonic contentment call in Figure 1.

Figure 3

Schematic parasagittal sections depicting locations of the counting frames (to scale) for neural regions of interest, including stratum griseum centrale (SGC) subregions in the optic tectum: mesencephalis lateralis pars dorsalis (MLd); ventrolateral SGC (vlSGC), dorsolateral SGC (dlSGC), and dorsomedial SGC (dmSGC); medial nidopallium (MN); caudomedial nidopallium (NCM); and caudolateral nidopallium (NCL). The laminae pallio-subpallialis (LPS) and mesopallialis (LaM) served as morphological landmarks for frame placement.

Figure 4

Effects of differently timed embryonic auditory stimulation on animals’ choice for filial auditory or visual stimuli. Control groups are shaded to aid visual comparison of within-group measures. A: For auditory latency, hatchlings in all four groups showed a faster response to the conspecific stimulus, and this effect was particularly robust for the E22–E23 group. In contrast, only animals from the control and E8–E9 groups showed a faster response to the conspecific stimulus in the visual choice tests. The E15–E16 group showed a faster response to the heterospecific stimulus. B: Duration scores are closely in line with latency data in response direction and strength, with the exception that the E15–E16 group showed no statistically significant difference for either stimulus in visual tests. Data signify median with interquartile range. Significance values represent those obtained from Wilcoxon signed-ranks tests, *p < 0.05; **p < 0.01; ^‡p < 0.0001; ns, not significantly different.

Figure 5

ZENK-IP cell number per unit tissue volume for each brain region of interest, for birds receiving prenatal stimulation during E15–E16, or no prenatal stimulation (controls). ZENK-IP cell number was significantly greater for dlSGC, dmSGC, MN, and NCM. Significance reflects values from paired-samples t-tests, *p < 0.05; **p < 0.01. Inset: coefficient of error for number of cells counted per brain, per region; dots are mean CEs per brain region, lines are means and SEMs per group.