Relationships among rat ultrasonic vocalizations, behavioral measures of striatal dopamine loss, and striatal tyrosine hydroxylase immunoreactivity at acute and chronic time points following unilateral 6-hydroxydopamine-induced dopamine depletion

Rats chirp with their mouth full: During an experimental meal, adult male Wistar rats emitted flat ultrasonic vocalisations upon feeding

Rats produce ultrasonic vocalisation (USVs) that are classified into different types, based on their average frequency. In pups 40 kHz USVs are produced upon social isolation, and in adults USVs can be associated with affective states and specific behavioural patterns (i.e., appetitive 50 kHz vocalisations of frequency range 30-100 kHz, or aversive 20 kHz vocalisations of frequency range 18-30 kHz). Generally, USVs of frequency around 50 kHz are linked to activation of brain reward pathways, during anticipation or experience of rewarding stimuli. Previous studies have described several subtypes of 50 kHz USVs, according to their acoustic properties. We asked whether USV production might be relevant to feeding behaviour. We recorded USVs from 14-week old adult rats during the satisfaction of a physiological need: refeeding following mild food deprivation (17 h overnight fast). We analysed a 10 min consummatory phase, preceded by a 10 min anticipatory phase, as a control for the experimental meal. Following identification of USV subtypes, we applied frequentist and Bayesian (Monte Carlo shuffling) statistical analyses to investigate the relationship between USV emission and rat behaviour. We found that it was not total USV quantity that varied in response to food consumption, but the subtype of USV produced. Most importantly we found that rats who feed tend to produce flat USVs of a frequency around 40 kHz. Beyond the previous reports of circumstantial association feeding-flat USVs, our observation directly correlate vocalisation and ingestive behaviour. Our study highlights that, in addition to quantification of the production rate, study of USV subtypes might inform us further on rat consummatory behaviour. Since this vocalisation behaviour can have a communicative purpose, those findings also illustrate nutrition studies might benefit from considering the possible social dimension of feeding behaviour.

Gestational hypoxia in late pregnancy differentially programs subcortical brain maturation in male and female rat offspring

Background

Hypoxia is associated with pregnancy complications, such as preeclampsia, placental abruption, and gestational sleep apnea. Hypoxic insults during gestation can impact the brain maturation of cortical and subcortical pathways, such as the nigrostriatal pathway. However, the long-term effects of in utero hypoxic stress exposure on brain maturation in offspring are unclear, especially exposure during late gestation. The purpose of this study was to determine the impact of gestational hypoxia in late pregnancy on developmental programming of subcortical brain maturation by focusing on the nigrostriatal pathway.

Methods

Timed pregnant Long–Evans rats were exposed to chronic intermittent hypoxia or room air normoxia from gestational day (GD) 15–19 (term 22–23 days). Male and female offspring were assessed during two critical periods: puberty from postnatal day (PND) 40–45 or young adulthood (PND 60–65). Brain maturation was quantified by examining (1) the structural development of the nigrostriatal pathway via analysis of locomotor behaviors and the substantia nigra dopaminergic neuronal cell bodies and (2) the refinement of the nigrostriatal pathway by quantifying ultrasonic vocalizations (USVs).

Results

The major findings of this study are gestational hypoxia has age- and sex-dependent effects on subcortical brain maturation in offspring by adversely impacting the refinement of the nigrostriatal pathway in the absence of any effects on the structural development of the pathway. During puberty, female offspring were impacted more than male offspring, as evidenced by decreased USV call frequency, chirp USV call duration, and simple call frequency. In contrast, male offspring were impacted more than female offspring during young adulthood, as evidenced by increased latency to first USV, decreased simple USV call intensity, and increased harmonic USV call bandwidth. No effects of gestational hypoxia on the structural development of the nigrostriatal pathway were observed.

Conclusions

These novel findings demonstrate hypoxic insults during pregnancy mediate developmental programming of the cortical and subcortical pathways, in which male offspring exhibit long-term adverse effects compared to female offspring. Impairment of cortical and subcortical pathways maturation, such as the nigrostriatal pathway, may increase risk for neuropsychiatric disorders (e.g., mood disorders, cognitive dysfunction, brain connectivity dysfunction).

Supplementary Information

The online version contains supplementary material available at 10.1186/s13293-022-00463-x.

Brain maturation of the nigrostriatal pathway is sex- and age- dependent. Exposure to hypoxia in late pregnancy impacts brain maturation of the nigrostriatal pathway that can be observed during puberty and young adulthood.

Gestational hypoxia impacted female offspring during puberty more than males, whereas it impacted male offspring during young adulthood more than females.

These novel findings demonstrate that hypoxic insults during pregnancy mediate developmental programming of the cortical and subcortical pathways, in which male offspring exhibit long-term adverse effects compared to female offspring.

Long-term adverse effects of gestational hypoxia in offspring can occur in the absence of pregnancy complications, especially if they occur within critical embryological developmental periods.

Vocal changes in a zebra finch model of Parkinson's disease characterized by alpha-synuclein overexpression in the song-dedicated anterior forebrain pathway

Deterioration in the quality of a person's voice and speech is an early marker of Parkinson's disease (PD). In humans, the neural circuit that supports vocal motor control consists of a cortico-basal ganglia-thalamo-cortico loop. The basal ganglia regions, striatum and globus pallidus, in this loop play a role in modulating the acoustic features of vocal behavior such as loudness, pitch, and articulatory rate. In PD, this area is implicated in pathogenesis. In animal models of PD, the accumulation of toxic aggregates containing the neuronal protein alpha-synuclein (αsyn) in the midbrain and striatum result in limb and vocal motor impairments. It has been challenging to study vocal impairments given the lack of well-defined cortico-basal ganglia circuitry for vocalization in rodent models. Furthermore, whether deterioration of voice quality early in PD is a direct result of αsyn-induced neuropathology is not yet known. Here, we take advantage of the well-characterized vocal circuits of the adult male zebra finch songbird to experimentally target a song-dedicated pathway, the anterior forebrain pathway, using an adeno-associated virus expressing the human wild-type αsyn gene, SNCA. We found that overexpression of αsyn in this pathway coincides with higher levels of insoluble, monomeric αsyn compared to control finches. Impairments in song production were also detected along with shorter and poorer quality syllables, which are the most basic unit of song. These vocal changes are similar to the vocal abnormalities observed in individuals with PD.

Rat Models of Vocal Deficits in Parkinson's Disease

Parkinson's disease (PD) is a progressive, degenerative disorder that affects 10 million people worldwide. More than 90% of individuals with PD develop hypokinetic dysarthria, a motor speech disorder that impairs vocal communication and quality of life. Despite the prevalence of vocal deficits in this population, very little is known about the pathological mechanisms underlying this aspect of disease. As such, effective treatment options are limited. Rat models have provided unique insights into the disease-specific mechanisms of vocal deficits in PD. This review summarizes recent studies investigating vocal deficits in 6-hydroxydopamine (6-OHDA), alpha-synuclein overexpression, DJ1-/-, and Pink1-/- rat models of PD. Model-specific changes to rat ultrasonic vocalization (USV), and the effects of exercise and pharmacologic interventions on USV production in these models are discussed.

Increased emissions of 50-kHz ultrasonic vocalizations in hemiparkinsonian rats repeatedly treated with dopaminomimetic drugs: A potential preclinical model for studying the affective properties of dopamine replacement therapy in Parkinson's disease

Dopamine replacement therapy used in Parkinson's disease (PD) may induce alterations in the emotional state that can underlie the manifestation of iatrogenic psychiatric-like disturbances. The preclinical investigation of these disturbances is limited, also because few reliable paradigms are available to study the affective properties of dopaminomimetic drugs in parkinsonian animals. To provide a relevant experimental tool in this respect, we evaluated whether dopaminomimetic drugs modified the emission of 50-kHz ultrasonic vocalizations (USVs), a behavioral marker of positive affect, in rats bearing a unilateral lesion with 6-hydroxydopamine in the medial forebrain bundle. Apomorphine (2 or 4 mg/kg, i.p.), L-3,4-dihydroxyphenilalanine (L-DOPA, 6 or 12 mg/kg, i.p.), or pramipexole (2 or 4 mg/kg, i.p.) were administered in a test cage (× 5 administrations) on alternate days. Seven days after treatment discontinuation, rats were re-exposed to the test cage to measure conditioned calling behavior and thereafter received a drug challenge. Hemiparkinsonian rats treated with either apomorphine or L-DOPA, but not pramipexole, markedly vocalized during repeated treatment and after challenge, and showed conditioned calling behavior. Moreover, apomorphine, L-DOPA and pramipexole elicited different patterns of 50-kHz USV emissions and rotational behavior, indicating that calling behavior in hemiparkinsonian rats treated with dopaminomimetic drugs is not a byproduct of motor activation. Taken together, these results suggest that measuring 50-kHz USV emissions may be a relevant experimental tool for studying how dopaminomimetic drugs modify the affective state in parkinsonian rats, with possible implications for the preclinical investigation of iatrogenic psychiatric-like disturbances in PD.

Intervention changes acoustic peak frequency and mesolimbic neurochemistry in the Pink1-/- rat model of Parkinson disease

The neural mechanisms underlying behavioral therapy for vocal acoustic deficits in patients with Parkinson disease is unknown. A primary hypothesis is that voice therapy may modulate mesolimbic brainstem regions, including the ventral tegmental area (VTA). The VTA is implicated in ultrasonic call peak frequency, involved in rewarding behaviors, and impacted by Parkinsonism. We tested the hypothesis that chronic (daily) behavioral vocal exercise of male Pink1-/- rats would alter ultrasonic vocalization acoustics and mesolimbic neurochemistry (catecholamines, GABA, mu-opioid receptor) compared to three different controls: sham-exercised Pink1-/-, unexercised Pink1-/-, and unexercised wildtype (WT) rats. A sub-hypothesis is that sham-exercise rats may exhibit changes to VTA neurochemistry as a result of a type or rewarding intervention. Results demonstrate that average bandwidth (frequency range) of ultrasonic vocalizations did not differ between WT, Pink1-/- no exercise vs. sham and vocal-exercise rats. However, average peak frequency is significantly reduced in vocal-exercised Pink1-/- rats compared to Pink1-/- no exercise, and WT groups. Unexpectedly, there were no significant acoustic differences between the vocal- and sham-exercised groups. There were no differences in catecholamine protein concentrations or tyrosine hydroxylase mRNA expression in the VTA between any of the groups. However, there was significant upregulation of all GABA-related genes in both vocal- and sham-exercised Pink1-/- rats (Gad1, Gad2, Gls, Glul); this finding was confirmed with follow up quantitative Western blotting for GAD. Additionally, there were differential results for mu-opioid receptor quantification in the VTA: vocal-exercised Pink1-/- rats showed increased mRNA expression for mu-opioid receptors whereas Western blotting indicated decreased protein levels in all Pink1-/- rats compared to WT controls suggesting the possible onset of pathology in this model. These data demonstrate modulatory effects of a rewarding behavioral paradigm on ultrasonic vocalization peak frequency. The results suggest that neuromodulators such as GABA and opioid activity, as well as the rewarding aspects of therapy may play a key role in shaping vocal treatments.

Noradrenergic receptor modulation influences the acoustic parameters of pro-social rat ultrasonic vocalizations

Rats produce high rates of ultrasonic vocalizations (USVs) in social situations; these vocalizations are influenced by multiple neurotransmitter systems. Norepinephrine (NE) plays a significant role in vocalization biology; however, the contribution of NE to normal, prosocial vocal control has not been well established in the rat. To address this, we used NE adrenoceptor agonists (Cirazoline, Clonidine) and antagonists (Prozasin, Atipamezole, Propranolol) to quantify the contribution of specific alpha-1, alpha-2, and beta NE receptors to USV parameters in male Long Evans rats during seminaturalistic calling. We found that multiple USV acoustic variables (intensity, bandwidth, duration, peak frequency, and call profile) are modified by alterations in NE signaling. Very generally, agents that increased NE neurotransmission (Atipamezole) or activated alpha-1 receptors (Cirazoline), led to an increase in intensity and duration, respectively. Agents that decreased NE neurotransmission (Clonidine) or blocked alpha-1 receptors (Prazosin) reduced call rate, intensity, and bandwidth. However, the beta-receptor antagonist, Propranolol, was associated with increased call rate, duration, and intensity. Limb motor behaviors were largely unaffected by any drug, with the exception of Clonidine. Higher doses of Clonidine significantly reduced gross motor, grooming, and feeding behavior. These results confirm the involvement of NE transmission in vocal control in the rat, and suggest that this USV model is useful for studying the neuropharmacology of behavioral measures that may have implications for disease states, such as Parkinson's disease. (PsycINFO Database Record

Vocal training, levodopa, and environment effects on ultrasonic vocalizations in a rat neurotoxin model of Parkinson disease

Levodopa does not improve dysarthria in patients with Parkinson Disease (PD), although vocal exercise therapy, such as "LSVT/LOUD(®)", does improve vocal communication. Most patients receive vocal exercise therapy while concurrently being treated with levodopa, although the interaction between levodopa and vocal exercise therapy on communication in PD is relatively unknown. Further, carryover of vocal exercise therapy to novel situations is critical for successful outcomes, but the influence of novel situations on rehabilitated vocal communication is not well understood. To address the influence of exercise, medications, and environment on vocal communication with precise experimental control, we employed the widely used 6-OHDA rat neurotoxin model of PD (infusion to the medial forebrain bundle), and assessed ultrasonic vocalizations after: vocal exercise, vocal exercise with levodopa, levodopa alone, and control conditions. We tested USVs in the familiar training environment of the home cage and a novel cage. We hypothesized that parkinsonian rats that undergo vocal exercise would demonstrate significant improvement of ultrasonic vocalization (USV) acoustic parameters as compared to the control exercise and levodopa-only treatment groups. We further hypothesized that vocal exercise in combination with levodopa administration, similar to what is common in humans, would lead to improvement in USV outcomes, particularly when tested in a familiar versus a novel environment. We found that the combination of exercise and levodopa lead to some improvement in USV acoustic parameters and these effects were stronger in a familiar vs. a novel environment. Our results suggest that although treatment can improve aspects of communication, environment can influence the benefits of these effects.

Animal behavioral assessments in current research of Parkinson's disease

Parkinson's disease (PD), a neurodegenerative disorder, is traditionally classified as a movement disorder. Patients typically suffer from many motor dysfunctions. Presently, clinicians and scientists recognize that many non-motor symptoms are associated with PD. There is an increasing interest in both motor and non-motor symptoms in clinical studies on PD patients and laboratory research on animal models that imitate the pathophysiologic features and symptoms of PD patients. Therefore, appropriate behavioral assessments are extremely crucial for correctly understanding the mechanisms of PD and accurately evaluating the efficacy and safety of novel therapies. This article systematically reviews the behavioral assessments, for both motor and non-motor symptoms, in various animal models involved in current PD research. We addressed the strengths and weaknesses of these behavioral tests and their appropriate applications. Moreover, we discussed potential mechanisms behind these behavioral tests and cautioned readers against potential experimental bias. Since most of the behavioral assessments currently used for non-motor symptoms are not particularly designed for animals with PD, it is of the utmost importance to greatly improve experimental design and evaluation in PD research with animal models. Indeed, it is essential to develop specific assessments for non-motor symptoms in PD animals based on their characteristics. We concluded with a prospective view for behavioral assessments with real-time assessment with mobile internet and wearable device in future PD research.

Noise trauma induced plastic changes in brain regions outside the classical auditory pathway

The effects of intense noise exposure on the classical auditory pathway have been extensively investigated; however, little is known about the effects of noise-induced hearing loss on non-classical auditory areas in the brain such as the lateral amygdala (LA) and striatum (Str). To address this issue, we compared the noise-induced changes in spontaneous and tone-evoked responses from multiunit clusters (MUC) in the LA and Str with those seen in auditory cortex (AC) in rats. High-frequency octave band noise (10-20 kHz) and narrow band noise (16-20 kHz) induced permanent threshold shifts at high-frequencies within and above the noise band but not at low frequencies. While the noise trauma significantly elevated spontaneous discharge rate (SR) in the AC, SRs in the LA and Str were only slightly increased across all frequencies. The high-frequency noise trauma affected tone-evoked firing rates in frequency and time-dependent manner and the changes appeared to be related to the severity of noise trauma. In the LA, tone-evoked firing rates were reduced at the high-frequencies (trauma area) whereas firing rates were enhanced at the low-frequencies or at the edge-frequency dependent on severity of hearing loss at the high frequencies. The firing rate temporal profile changed from a broad plateau to one sharp, delayed peak. In the AC, tone-evoked firing rates were depressed at high frequencies and enhanced at the low frequencies while the firing rate temporal profiles became substantially broader. In contrast, firing rates in the Str were generally decreased and firing rate temporal profiles become more phasic and less prolonged. The altered firing rate and pattern at low frequencies induced by high-frequency hearing loss could have perceptual consequences. The tone-evoked hyperactivity in low-frequency MUC could manifest as hyperacusis whereas the discharge pattern changes could affect temporal resolution and integration.

Reduced vocal variability in a zebra finch model of dopamine depletion: implications for Parkinson disease

Midbrain dopamine (DA) modulates the activity of basal ganglia circuitry important for motor control in a variety of species. In songbirds, DA underlies motivational behavior including reproductive drive and is implicated as a gatekeeper for neural activity governing vocal variability. In the zebra finch, Taeniopygia guttata, DA levels increase in Area X, a song-dedicated subregion of the basal ganglia, when a male bird sings his courtship song to a female (female-directed; FD). Levels remain stable when he sings a less stereotyped version that is not directed toward a conspecific (undirected; UD). Here, we used a mild dose of the neurotoxin 6-hydroxydopamine (6-OHDA) to reduce presynaptic DA input to Area X and characterized the effects on FD and UD behaviors. Immunoblots were used to quantify levels of tyrosine hydroxylase (TH) as a biomarker for DA afferent loss in vehicle- and 6-OHDA-injected birds. Following 6-OHDA administration, TH signals were lower in Area X but not in an adjacent subregion, ventral striatal-pallidum (VSP). A postsynaptic marker of DA signaling was unchanged in both regions. These observations suggest that effects were specific to presynaptic afferents of vocal basal ganglia. Concurrently, vocal variability was reduced during UD but not FD song. Similar decreases in vocal variability are observed in patients with Parkinson disease (PD), but the link to DA loss is not well-understood. The 6-OHDA songbird model offers a unique opportunity to further examine how DA loss in cortico-basal ganglia pathways affects vocal control.