Review and update of ultrasonic vocalization in animals: Correlation with autism spectrum disorder experimental models?

Revisión y actualización de la vocalización ultrasónica en animales: ¿correlación con el modelo del trastorno del espectro autista?

Revisão teórico-integrativa na atualização sobre vocalização ultrassônica em animais: Correlação com o modelo de transtorno do espectro autista?

Juciara da C Silva

Nove de Julho University (UNJ), Brazil

Miriam O Ribeiro

Mackenzie Presbyterian University (UPM), Brazil

Déborah M. dos Santos

Nove de Julho University (UNJ), Brazil

Carlos Alberto A Penatti carlospenatti@uni9.pro.br

Nove de Julho University (UNJ), Brazil

The development and sophistication of human language are essential characteristics for our species. Although many animals have varied and elaborated communication systems, human communicability allows an array of almost infinite construction of oral sound phrases and meanings, not only to share needs and desires but also to establish an even more complex personal relationship (Werker & Hensch, 2015).

Vocal comprehension and expression comprise development in the broadest sense employing verbal and non-verbal assessments. The delays and interruptions in the acquisition of phases that are necessary for the maturation of communication may generate consequences that affect a child’s cognitive, social, behavioral, and emotional functions and impact his/her progression into adulthood (Liu, Zahrt, & Simms, 2018).

Communication disorders in children include: delay only in expressive language or errors in the production of simple sounds (articulation); multiple errors in the production of sounds with some degree of deficit in motor planning or delay in expressive language; and mixed receptive language with difficulty in complex language processing (Liu, Zahrt, & Simms, 2018).

During healthy development, a series of communicative acts emerges and matures as the structural language develops. The maintenance of the conversational topic appears in interactions with adults, and the adequacy of responses increases. In the past decade, the communicative, social, and emotional aspects of language have followed a qualitative distribution in 27 observable behaviors. These are classified into five relevant domains for children aged between 5 and 11 years. The five domains are defined by 1. introduction and responsiveness (the ability to introduce communication and to be receptive to the communication of others); 2. non-verbal communication (usage and understanding of gestures, facial expressions, body postures and proximity between speakers); 3. socio-emotional attunement (interpreting the emotional reactions of others and demonstrating appropriate responses); 4. executive function (given the interactions and flexibility in the planning of the communicative content); and 5. negotiation (cooperating and negotiating properly with communicative partners). For children with communication deficits who develop verbal language, the previously described pragmatic difficulties persist and evolve into language deficits, which include unskilled attempts to initiate communication, narrower intervals of communication acts and difficulties in the production of communication of new language (Parsons, Cordier, Munro, Joosten, & Speyer, 2017).

Among neurodevelopmental disorders that can affect communication, there are autism spectrum disorders (ASD). This neuropsychological entity, which is characterized by deficiencies in expression/understanding of verbal language and social interactions with significant seclusion, unveils a series of variations demonstrated in repetitive, stereotyped behaviors and determines restricted social interests in many cases. Although there is no clinical correlation between ASD with specific mechanisms in neurobiological development per se, the proposition for early intervention with psychological follow-up and speech therapy supports improvement. In addition to specific pedagogical criteria, they have been shown to improve cognition and adaptive behavior by altering brain responses to social stimuli (Schuetze, Rohr, Dewey, McCrimmon, & Bray, 2017).

The diagnosis of ASD is based on communicative deficits that are observed in everyday social interactions. Deficits become evident in situations in which there is a divergence between verbal communication and the understanding of the literal meaning of a sentence or a phrase (in the case of irony or sarcasm, for example) and have been considered products of a primary commitment in representing mental states. Some studies suggest that communication deficits arise from the main difficulties with motivation, social attention, or cognitive flexibility (Wadge, Brewer, Bird, Toni, & Stolk, 2019).

The most recent edition of the ‘Diagnostic and Statistical Manual of Mental Disorders’ (DSM-5) removed language difficulties as a major condition of ASD. However, a significant proportion of children with ASD have difficulties in acquiring spoken language. The severity of these difficulties varies considerably. Most children with ASD acquire language during the preschool years, usually at the age of five. However, about 25 to 30 % do not develop any functional spoken language or remain minimally verbal. Language difficulties in children with ASD can result in several adverse sequelae, which include behavioral difficulties, deficits in adaptive functional skills, and a social relationship (Brignell et al., 2018).

Many children with ASD continue to demonstrate language skills below their peers. A great proportion of those youngsters do not obtain useful speech, which is defined as expressive language that can be used frequently, communicatively, referentially and semantically in a different way. Expressive language deficits are particularly important in light of the strong predictive relationship among the expressive language skills and social and adaptive outcomes for children with this type of disorder (McDaniel, D’Ambrose Slaboch, & Yoder, 2018).

Since the publication of the DSM-5, there has been a greater focus on social communication, particularly on how this skill should be assessed, and how it should be addressed. The assessment is challenging, because of the nature of how social communication must occur in a natural context where this ability can be observed directly and constantly in real-time (Hyter et al., 2017).

Animal experimentation research models counterbalance clinical research to tackle communication deficits in possible complementary approaches. Although they do not characterize a total exclusive or faithful state of human order, research with animal models is fundamental for the advances and better understanding in ASD clinical settings. They foster research settings that are experimentally controlled, rigorous in variables, treatable, and exploited mechanically for that type of disorder. Currently, some of the relevant experimental animal models show that rodents produce surprisingly complex ultrasonic vocalizations (USV) during their social and sexual interactions in an ecological/social adapted environment (Arriaga & Jarvis, 2013; Hanson & Hurley, 2012).

Among the species studied, mice have great potential in the study of ultrasound sounds (USVs), emulating the equivalent of a voice skill. Therefore, this form of vocal expression serves to provide a basic research system in animal communication, behavioral biology, and neuroscience and, additionally, collaborates to comprehend issues involved in biomedical sciences. Rodents produce both sound vocalizations in the human audible and ultrasonic ranges. They emit sounds in fundamental frequencies ranging from 100 up to 120,000 Hz. (Riede, Borgard, & Pasch, 2017). Mouse USVs appear to provide a variety of functions, including social recognition (individual, kinship, sex, and species recognition), rival bullying (intrasexual selection), and partner attraction (inter-sexual selection) (Zala, Reitschmidt, Noll, Balazs, & Penn, 2017).

Intricate language patterns are unlikely to be instinctive for rodents. The complexity of ultrasonic vocalization patterns contains important communicative information. Quantitative assessment of the value of the media reward is not yet available for rodents or individuals with ASD (Mony, Hong, & Lee, 2018). Although there are some established models to assess or to work with ASD symptoms, newer and improved models are needed. Designing a behavioral model specifically relevant to human mental disorders presents a great challenge, as there is a discontinuity between human social interactions and those exhibited by non-primate mammals, such as rodents. Besides, ASD-related symptoms are unique, but inherently variable in humans.

Regarding the genetic approach, rodent research models that incorporate a growing list of changes in possible genes involved in language have been used to detail and deepen the understanding of the effects of genetic mutations on cellular/tissue formation, connectivity, physiology and neuronal behavior (Lazaro & Golshani, 2015).

The importance of the communicability of individuals considered as ASD prompts us to organize and highlight the main studies within basic research that use animal models focusing on ultrasonic vocalization. Specifically, we aim to assess the importance of these studies and future perspectives for the neurobehavioral canvas in developmental communication deficits.

We searched for articles that used and analyzed the theme of ultrasonic vocalization in animal experimentation models correlated to basic ASD research.

Communication deficits are characteristic of ASD. Depending on the individual’s intellectual capacity, communication disarrangements can manifest as lack of speech, language delay, use of odd prosody and intonation, stereotyped speech, persevering phrases, and difficulties with language pragmatics, such as those involved in initiation and maintenance of appropriate language and meaningful conversations. Rodents emit complex ultrasonic vocalizations (USVs) during social meetings with their peers. Leading researchers assume that the USV emission features as a sign of potential complex communication. It is believed that USVs function as a means of social recognition and courtship behavior, which may indicate to provoke an approaching behavior and to communicate aggression. USVs vary between spectrotemporal parameters, such as frequency, duration, and intensity. These resources are used to analyze USVs in different categories by the researchers. USVs have become a model commonly used to emulate and, thus, to add to the understanding of human communication (Screven & Dent, 2019).

Currently, different types of USVs are recognized in rodents: emitted by isolated pups; produced by youngsters in interaction; vocalized by adult males exposed to females. The emission of USVs is used to study the characteristics related to ASD. For example, the puppies emit USVs causing a search behavior during the separation of the mother (Scattoni, Crawley, & Ricceri, 2009).

The data suggest that there are several models for a better understanding of ASD (e.g., Fmr1 for Fragile X syndrome, Mecp2 for Rett syndrome, and Tsc1/2 for tuberous sclerosis, synaptic molecule genes like neurexin, neuroligin, and Shank) and other risk genes. Most models of ASD were based on symptoms similar to human behavior (Takumi et al., 2019).

The research design (Figure 3.1) found 119 articles, 25 of which were selected for the preparation of this manuscript (Table 3.1). The described species are murine animal models, highlighting Mus musculus, Wistar rat, and one species of the genus Microtus.

Figure 3.1
Quantification of the articles gathered in the review relating the impact of USV on animal research models and their possible interaction for a better understanding of ASD.

Table 3.1
List of studies included in the review.

The data show 23 experimental studies and two bibliographic reviews. Studies with mice represent the majority of research, adding up to 19 studies and five studies conducted with rats, whereas one work taking advantage of the genus Microtus.

The findings in our search review corroborate the literature. In basic research, the main model used in the study of ultrasonic vocalization is the transgenic mice. The used researched literature shows that animal experimental models exist for almost all known human gene disruption. The coding regions of the genome are especially well preserved and easier to model in mice, while non-coding DNA, including regulatory elements, shows reduced conservation among various species (St. Clair & Johnstone, 2018).

Genetically modified mice (Figure 3.2) as knockouts/knock-ins were generated and carry mutations with human correlation. Genetic associations include allelic variants such as fragile X, MET tyrosine kinase, Mecp2, neurexine, and tuberosclerosis susceptibility complexes (Bishop & Lahvis, 2011).

Figure 3.2
Genes and pathological correlations.

The reduction in communication was associated with the most diverse models, and, within them, we highlight some studies such as Binder and Lugo (2017), Berg et al. (2018), Missig et al. (2019), and some genes such as the SHANK family. In recent years, deletions and coding mutations in the SHANK1 SHANK2 and SHANK3 genes have been identified in individuals with ASD. The three SHANK genes encode many variants of mRNA splicing and generate multiple protein isoforms grouped into a large molecular cluster related to the postsynaptic density at excitatory glutamatergic terminals. As precursor proteins, they bind glutamatergic receptors in the molecular assembly pathway of the actin cytoskeleton and postsynaptic signaling. Therefore, SHANK genes are strongly involved in several synaptic functions, including terminal morphogenesis, synapse formation, transport of glutamate receptors, and neuronal activation by neurotransmission (Sungur et al., 2017).

Another gene of interest to improve the understanding of ASD molecular physiopathology is Foxp1. Individuals with Foxp1 mutations are diagnosed with ASD or intellectual disability and have global developmental delay, motor deficit, and severe speech impairment. However, detailed studies of loss of gene function that investigate the contributions of Foxp1 to phenotypes relevant to neurogenesis in the developing brain have yet to be performed. Some rodent models of Foxp1 have begun to elucidate their function mainly in the adult brain (Usui et al., 2017). In contrast, some studies report an increase in USV (Tesdahl, King, McDaniel, & Pieper, 2017; Winkler et al., 2018; Nolan et al., 2019; Toledo, Wen, Binder, Ethell, & Razak, 2019).

The acquisition of language is marked by maturation in fine aspects of brain development throughout infanthood and adolescence. This process involves different language dimensions for the development and expression of sounds, words, grammar, diction, elocution, narratives, and conversation.

It is evident, from the findings reported here, the crucial role of certain genes in modulating aspects of communication, the vast majority being markers of communication deficits. Most of the rodents of transgenic origin belong to three major groups: postsynaptic protein, synaptic cell adhesion molecules (neurexin, neuroligin, and contactin-associated protein), and genes associated with the regulation of oxytocin release.

Therefore, gene therapy based on the use of recombinant DNA can be used to repair, replace, increase, or silence essentially any gene of interest in a target cell. The advancement of techniques in proteomic research will contribute to the development of new classes and the segmentation of drugs aiming at a specific action. Other advantages of gene therapy versus small molecules include obtaining long-term clinical benefits from a single treatment.

Finally, it should be noticed that all the advances and attempts to determine more individualized and complete cellular and molecular routes in the knowledge of the pathophysiology of ASD should not mitigate the enormous success of social inclusion and pedagogical and psychotherapeutic support for individuals (in special children and adolescents) with some form of ASD. The recognition of integrative resources in several areas of health and education already defines an era of humane and social inclusion for people with neurodevelopmental communication deficits.