Cynthia A. Kelm-Nelson

Early identification and treatment of communication and swallowing deficits in Parkinson disease.

Parkinson disease (PD) is a complex, progressive, neurodegenerative disorder that leads to a wide range of deficits including fine and gross sensorimotor impairment, autonomic dysfunction, mood disorders, and cognitive decline. Traditionally, the focus for diagnosis and treatment has been on sensorimotor impairment related to dopamine depletion. It is now widely recognized, however, that PD-related pathology affects multiple central nervous system neurotransmitters and pathways. Communication and swallowing functions can be impaired even in the early stages, significantly affecting health and quality of life. The purpose of this article is to review the literature on early intervention for communication and swallowing impairment in PD. Overarching themes were that (1) studies and interpretation of data from studies in early PD are limited; (2) best therapy practices have not been established, in part due to the heterogeneous nature of PD; and (3) as communication and swallowing problems are pervasive in PD, further treatment research is essential.

Evidence for early and progressive ultrasonic vocalization and oromotor deficits in a PINK1 gene knockout rat model of Parkinson's disease

Parkinsons disease (PD) is a progressive neurodegenerative disease that leads to a wide range of motor and nonmotor deficits. Specifically, voice and swallow deficits manifest early, are devastating to quality of life, and are difficult to treat with standard medical therapies. The pathological hallmarks of PD include accumulation of the presynaptic protein α‐synuclein (αSyn) as well as degeneration of substantia nigra dopaminergic neurons. However, there is no clear understanding of how or when this pathology contributes to voice and swallow dysfunction in PD. The present study evaluates the effect of loss of function of the phosphatase and tensin homolog‐induced putative kinase 1 gene in rats (PINK1–/–), a model of autosomal recessive PD in humans, on vocalization, oromotor and limb function, and neurodegenerative pathologies. Behavioral measures include ultrasonic vocalizations, tongue force, biting, and gross motor performance that are assayed at 2, 4, 6, and 8 months of age. Aggregated αSyn and tyrosine hydroxylase immunoreactivity (TH‐ir) were measured at 8 months. We show that, compared with wild‐type controls, PINK1–/– rats develop 1) early and progressive vocalization and oromotor deficits, 2) reduced TH‐ir in the locus coeruleus that correlates with vocal loudness and tongue force, and 3) αSyn neuropathology in brain regions important for cranial sensorimotor control. This novel approach of characterizing a PINK1–/– genetic model of PD provides the foundational work required to define behavioral biomarkers for the development of disease‐modifying therapeutics for PD patients.

Curvilinear relationships between mu-opioid receptor labeling and undirected song in male European starlings (Sturnus vulgaris)

Female-directed communication in male songbirds has been reasonably well studied; yet, relatively little is known about communication in other social contexts. Songbirds also produce song that is not clearly directed towards another individual (undirected song) when alone or in flocks. Although the precise functions of undirected song may differ across species, this type of song is considered important for flock maintenance, song learning or practice. Past studies show that undirected song is tightly coupled to analgesia and positive affective state, which are both mediated by opioid activity. Furthermore, labeling for the opioid met-enkephalin in the medial preoptic nucleus (POM) correlates positively with undirected song production. We propose that undirected song is facilitated and maintained by opioid receptor activity in the POM and other brain regions involved in affective state, analgesia, and social behavior. To provide insight into this hypothesis, we used immunohistochemistry to examine relationships between undirected song and mu-opioid receptors in male starlings. Polynomial regression analyses revealed significant inverted-U shaped relationships between measures of undirected song and mu-opioid receptor labeling in the POM, medial bed nucleus of the stria terminalis (BSTm), and periaqueductal gray (PAG). These results suggest that low rates of undirected song may stimulate and/or be maintained by mu-opioid receptor activity; however, it may be that sustained levels of mu-opioid receptor activity associated with high rates of undirected song cause mu-opioid receptor down-regulation. The results indicate that mu-opioid receptor activity in POM, BSTm, and PAG may underlie previous links identified between undirected song, analgesia, and affective state.

Behavioral indices of breeding readiness in female European starlings correlate with immunolabeling for catecholamine markers in brain areas involved in sexual motivation

In seasonally-breeding songbirds, lengthening photoperiod, increases in estradiol and exposure to male courtship facilitate breeding behavior in females in spring. However, there is extreme variability in the extent to which spring-condition females are attracted by male courtship or engage in nesting behavior. Here we explore possible links between catecholamines and individual differences in behaviors indicative of breeding readiness. Female European starlings were placed in conditions typical of the breeding season (spring-like) or the non-breeding season (fall-like). Although many females examined nesting locations, only a subset of spring-like females occupied nest sites. Labeling for dopamine-beta-hydroxylase (DBH; the enzyme involved in norepinephrine synthesis) in the ventromedial nucleus of the hypothalamus (VMH) was densest in females that acquired nest sites compared to spring-like females without nest sites or fall-like females. Within the group of spring-like females, nesting behaviors correlated positively with DBH labeling in VMH. Females with nest sites had the lowest density of DBH labeling in the ventral tegmental area, and labeling correlated negatively with spring-like female nesting behaviors. Labeling for tyrosine hydroxylase (TH; the rate limiting enzyme for catecholamine synthesis) in putative nucleus accumbens was lowest in spring-like females without nest sites, and labeling correlated positively with nesting behavior in spring-like females. TH labeling density in the medial preoptic nucleus was highest in fall-like females, but a trend was observed for a positive correlation between TH labeling and spring-like female nesting behaviors. These results link distinct patterns of catecholamine activity in brain regions implicated in sexual motivation to female breeding readiness.

Decreased approach behavior and nucleus accumbens immediate early gene expression in response to Parkinsonian ultrasonic vocalizations in rats

Many individuals with Parkinson disease (PD) have difficulty producing normal speech and voice, resulting in problems with interpersonal communication and reduced quality of life. Translational animal models of communicative dysfunction have been developed to assess disease pathology. However, it is unknown whether acoustic feature changes associated with vocal production deficits in these animal models lead to compromised communication. In rodents, male ultrasonic vocalizations (USVs) have a well-established role in functional inter-sexual communication. To test whether acoustic deficits in USVs observed in a PTEN-induced putative kinase 1 (PINK1) knockout (KO) PD rat model compromise communication, we presented recordings of male PINK1 KO USVs and normal wild-type (WT) USVs to female rat listeners. We measured approached behavior and immediate early gene expression (c-Fos) in brain regions implicated in auditory processing and sexual motivation. Our results suggest that females show reduced approach in response to PINK1 KO USVs compared with WT. Moreover, females exposed to PINK1 KO USVs had lower c-Fos immunolabeling in the nucleus accumbens, a region implicated in sexual motivation. These results are the first to demonstrate that vocalization deficits in a rat PD model result in compromised communication. Thus, the PINK1 KO PD model may be valuable for assessing treatments aimed at restoring vocal communicative function.

Modulation of male song by naloxone in the medial preoptic nucleus.

Studies in songbirds implicate opioid neuropeptides in singing behavior; however, past results are contradictory. In starlings, the effect of opioid manipulations on sexually motivated courtship song differed in birds naturally singing at low compared to high rates, and mu-opioid receptors were denser in several regions, including the medial preoptic nucleus (POM) in low singing males. In the present study, we found that low singing male starlings also had significantly higher enkephalin (ENK) immunolabeling densities in the POM than high singers. We blocked opioid receptor activity in the POM with naloxone injections and found that this increased both song rate and song bout length in low singers, suggesting that high densities of mu receptors and ENK in the POM actively suppress song in these males. In contrast to its effects on low singers, naloxone in the POM of high singers dose dependently decreased song rate and tended to reduce song bout length. This suggests that at least some level of opioid activity in POM is necessary for song production. Our results are the first to demonstrate that direct administration of naloxone into the POM influences sexually motivated song, and that effects differ depending on an individuals initial rate of song and associated density of ENK. We suggest that differential effects seen in past studies of opioids and song may in part be explained by differences in the natural song rate of subjects and accompanying differences in ENK activity and neural substrate sensitivity to opioids in POM.

Context-dependent links between song production and opioid-mediated analgesia in male European starlings (Sturnus vulgaris).

Little is known about the neural mechanisms that ensure appropriate vocal behaviors within specific social contexts. Male songbirds produce spontaneous (undirected) songs as well as female-directed courtship songs. Opioid neuropeptide activity in specific brain regions is rewarding, at least in mammals, and past studies suggest that the opioid met-enkephalin in such areas is more tightly linked to undirected than female-directed song. Recent data using a song-associated place preference paradigm further suggest that production of undirected but not directed song is tightly linked to intrinsic reward. Opioids have analgesic properties. Therefore, if production of undirected song is closely linked to opioid-mediated reward, the production of undirected but not directed song should be associated with analgesia. Consistent with this prediction, in male starlings we identified a positive correlation between analgesia (decreased reactivity to a hot water bath) and undirected song (in non-breeding season condition males in affiliative flocks) but not female-directed song (in breeding season condition males presented with females). When breeding condition males were divided according to social status, a negative correlation was found in subordinate males (i.e. males that failed to acquire a nest box). These data are consistent with the hypotheses 1) that the production of undirected song is facilitated or maintained by opioids (and/or other neuromodulators that also induce analgesia) and 2) that production of female-directed song is not linked in the same way to release of the same neuromodulators. Results also demonstrate a link between analgesia and song in subordinate individuals lacking a nesting territory within the breeding season. Overall, the findings indicate that distinct neural mechanisms regulate communication in different social contexts and support the working hypothesis that undirected but not directed song is tightly linked to opioid release.

Inverted-U shaped effects of D1 dopamine receptor stimulation in the medial preoptic nucleus on sexually motivated song in male European starlings.

Past studies in songbirds have highlighted a central role for the medial preoptic nucleus (mPOA) in context‐appropriate vocal communication. During the breeding season, male songbirds sing primarily to attract females (sexually motivated song) and to repel competitors (agonistically motivated song). Past data have linked dopamine and D1 dopamine receptors in the mPOA to sexually motivated but not agonistically motivated song; however, direct effects of dopamine receptor manipulations in the mPOA on song have not been experimentally tested. Here, we tested the hypothesis that D1 receptor stimulation in the mPOA selectively influences sexually motivated male song, and the possibility that the effects of D1 receptor agonism differ at low and high doses. In a first study, breeding‐condition male European starlings received infusions of saline or a single dose of the D1 receptor agonist SKF 38393 on separate test days into the mPOA or hypothalamic control areas. Stimulation of D1 receptors in the mPOA triggered sexually motivated but not agonistically motivated song. A second study showed inverted‐U shaped dose–response effects of the agonist, such that low levels of sexually motivated song were observed at low and high levels of D1 receptor activation. A third study showed that the effects of the D1 receptor agonist were blocked by the D1 receptor antagonist SCH 23390. These findings suggest that an optimal level of D1 receptor stimulation in the mPOA is needed to facilitate sexually motivated vocal production. The results support a central, context‐specific role for the mPOA in vocal communication, and more broadly demonstrate a complex, modulatory influence of D1 receptors in the mPOA on sexually motivated behavior.

Atp13a2 expression in the periaqueductal gray is decreased in the Pink1 -/- rat model of Parkinson disease.

Vocal communication deficits are common in Parkinson disease (PD). Widespread alpha-synuclein pathology is a common link between familial and sporadic PD, and recent genetic rat models based on familial genetic links increase the opportunity to explore vocalization deficits and their associated neuropathologies. Specifically, the Pink1 knockout (-/-) rat presents with early, progressive motor deficits, including significant vocal deficits, at 8 months of age. Moreover, this rat model exhibits alpha-synuclein pathology compared to age-matched non-affected wildtype (WT) controls. Aggregations are specifically dense within the periaqueductal gray (PAG), a brainstem region involved in the coordination of emotional and volitional control of vocalizations. Here, we investigated changes in gene expression within the PAG at 8 months of age in Pink1 -/- rats compared to WT. Our data demonstrate that Pink1 -/- rat mRNA expression levels of alpha-synuclein are comparable to WT. However, Pink1 -/- rats show significantly decreased levels of Atp13a2, a transmembrane lysosomal P5-type ATPase suggesting a potential mechanism for the observed abnormal aggregation. We found no difference in the expression of glucocerebrosidase (Gba) or the CASP8 and FADD-like apoptosis regulator (Cflar). Further, we show that mRNA expression levels of dopaminergic markers including Th, D1 and D2 receptor as well as GABA signaling markers including Gaba-A and glutamate decarboxylase 2 (Gad2) do not differ between genotypes. However, we found that glutamate decarboxylase 1 (Gad1) is significantly reduced in this PD model suggesting possible disruption of neurotransmission within the PAG. These results are the first to suggest the hypothesis that alpha-synuclein aggregation in this model is not a result of increased transcription, but rather a deficit in the breakdown and clearance, and that the observed vocal deficits may be related to impaired neural transmission. Altogether, these findings are consistent with the hypothesis that differences in neural substrate sensitivity contribute to the early pathogenesis of vocalizations and motivation to communicate in the Pink1 -/- rat model of PD. Our results suggest novel therapeutic pathways, including the lysosomal degradation pathway, which can be used in to further study the pathogenesis and treatment of vocal dysfunction PD.

Exercise Effects on Early Vocal Ultrasonic Communication Dysfunction in a PINK1 Knockout Model of Parkinson’s Disease

BACKGROUND Parkinsons disease (PD) is a complex neurodegenerative disease with vocal communication deficits that manifest early, progress, and are largely resistant to medical interventions; however, they do respond to exercise-based speech and voice therapies. OBJECTIVE AND METHODS To study how exercise-based vocal treatment can affect the progression of communication deficits related to PD, we studied ultrasonic vocalizations (USVs) in rats with homozygous knockout (-/-) of PINK1, a gene mutation known to cause PD, under the manipulation of a behavioral vocal exercise paradigm that allows us to precisely control dose and timing of exercise in the prodromal (prior to diagnosis) stages. RESULTS We show that intensive vocal-training rescues frequency range and intensity deficits as well as leads to an increase in call complexity and duration of calls compared to sham-training; however, over time this training regime loses significant effect as the disease progresses. We also show effects of frequent handling and conspecific (male-female) interaction in the sham-training group as they demonstrated significantly higher call rate, intensity, frequency range, and call complexity compared to rats without any form of training and consequently less handling/interaction. Further, we confirm that this model exhibits progressive gross motor deficits that indicate neurodegeneration. DISCUSSION This study suggests that the evolving nature of vocal communication deficits requires an adjustment of therapy targets and more intensive training over the course of this progressive disease and demonstrates the importance of frequent social experiences.