The nuclei of the lateral lemniscus: unexpected players in the descending auditory pathway

Introduction

In the mammalian auditory pathway, the nuclei of the lateral lemniscus (NLL) are thought to be exclusively involved in the bottom-up transmission of auditory information. However, our repeated observation of numerous NLL neurons labeled after injection of retrograde tracers into the superior olivary complex (SOC) led us to systematically investigate with retrograde tracers the descending projections from the NLL to the SOC of the rat.

Methods

We performed large injections of FluoroGold into the SOC to determine NLL contributions to descending projections, and focal injections of biotinylated dextran amine (BDA) to pinpoint the specific nuclei of the SOC innervated by each NLL.

Results

The SOC is innervated by thousands of neurons distributed across four nuclei or regions associated with the lateral lemniscus: the ipsilateral ventral and intermediate nuclei of the lateral lemniscus (VNLL and INLL); the medial paralemniscal region (PL) of both sides; and the ipsilateral semilunar nucleus (SLN), a previously unrecognized nucleus that wraps around the INLL dorsally, medially, and caudally and consists of small, flat neurons. In some experiments, at least 30% of neurons in the VNLL and INLL were retrogradely labeled. All nuclei of the SOC, except the medial and lateral superior olives, are innervated by abundant lemniscal neurons, and each SOC nucleus receives a unique combination of lemniscal inputs. The primary target of the projections from the VNLL is the ventral nucleus of the trapezoid body (VNTB), followed by the superior paraolivary nucleus (SPON), and the medial nucleus of the trapezoid body (MNTB). The INLL selectively innervates the VNTB. The PL innervates dorsal periolivary regions bilaterally. The SLN preferentially innervates the MNTB and may provide the first identified non-calyceal excitatory input to MNTB neurons.

Discussion

Our novel findings have strong implications for understanding acoustic information processing in the initial stages of the auditory pathway. Based on the proportion of lemniscal neurons involved in all the projections described, the NLL should be considered major players in the descending auditory pathway.

Psychosocial impact at the time of a rare disease diagnosis

Over half of all persons with rare diseases (RDs) in Spain experience diagnostic delay (DD) but little is known about its consequences. This study therefore aimed to analyze the psychological impact of obtaining a diagnosis of an RD, and to ascertain what social determinants are influenced and what the personal consequences are, according to whether or not patients experienced DD. Data were obtained from a purpose-designed form completed by persons registered at the Spanish Rare Diseases Patient Registry. The following were performed: a descriptive analysis; a principal component analysis (PCA); and logistic regressions. Results revealed that while searching for a diagnosis, people who experienced DD were more in need of psychological care than those diagnosed in less than one year (36.2% vs 23.2%; p = 0.002; n = 524). The PCA identified three principal components, i.e., psychological effects, social implications, and functional impact. Reducing DD would improve psychological effects, such as irritability (OR 3.6; 95%CI 1.5-8.5), frustration (OR 3.4; 95%CI 1.7-7.1) and concentration on everyday life (OR 3.3; 95%CI 1.4-7.7). The influence of the social implications and functional repercussions of the disease was greater in persons with DD (scores of 22.4 vs 20 and 10.6 vs 9.4, respectively) in terms of the difficulty in explaining symptoms to close friends and family (3.3 vs 2.9), and loss of independence (3.3 vs 2.9). In conclusion, this is the first study to analyze the psychosocial impact of diagnosis of RDs in Spain and one of few to assess it in the patients themselves, based on data drawn from a purpose-designed form from a national registry open to any RD. People affected by RDs who underwent DD experienced greater psychosocial impact than did those who were diagnosed within the space of one year.

Diagnostic Process in Rare Diseases: Determinants Associated with Diagnostic Delay

Many people living with rare disease (RD) report a difficult diagnostic process from the symptom onset until they obtain the definitive diagnosis. The aim of this study was thus to ascertain the diagnostic process in RDs, and explore the determinants related with having to wait for more than one year in this process (defined as “diagnostic delay”). We conducted a case–control study, using a purpose-designed form from the Spanish Rare Diseases Patient Registry for data-collection purposes. A descriptive analysis was performed and multivariate backward logistic regression models fitted. Based on data on 1216 patients living with RDs, we identified a series of determinants associated with experiencing diagnostic delay. These included: having to travel to see a specialist other than that usually consulted in the patient’s home province (OR 2.1; 95%CI 1.6–2.9); visiting more than 10 specialists (OR 2.6; 95%CI 1.7–4.0); being diagnosed in a region other than that of the patient’s residence at the date of symptom onset (OR 2.3; 95%CI 1.5–3.6); suffering from a RD of the nervous system (OR 1.4; 95%CI 1.0–1.8). In terms of time taken to see a specialist, waiting more than 6 months to be referred from the first medical visit was the period of time which most contributed to diagnostic delay (PAR 30.2%). In conclusion, this is the first paper to use a collaborative study based on a nationwide registry to address the diagnostic process of patients living with RDs. While the evidence shows that the diagnostic process experienced by these persons is complex, more studies are needed to determine the implications that this has for their lives and those of their families at a social, educational, occupational, psychological, and financial level.